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Browse subject: rain forests
Number of records: 134

Disturbance and long-term patterns of rainfall and throughfall nutrient fluxes in a subtropical wet forest in Puerto Rico
About this Resource: Nutrient fluxes in rainfall and throughfall were measured weekly in a mature subtropical wet forest in NE Puerto Rico over a 15-year period that included the effects of 10 named tropical storms, several prolonged dry periods, and volcanic activity in the region. Mean annual rainfall and throughfall were 3482 and 2131 mm yr-1, respectively. Average annual rainfall and throughfall fluxes of K, Ca, Mg, Cl, Na, and SO4(-)S were similar but somewhat larger than those reported for most tropical forests. Rainfall inputs of nitrogen were comparatively low and reflect the relative isolation of the airshed. More constituents had seasonal differences in rainfall fluxes (6 out of 12) than throughfall fluxes (4 out of 12) and all volume weighted throughfall enrichment ratios calculated for the 15-year period were greater than one. However, median weekly enrichment ratios were less than 1 for sea salts and dissolved organic carbon, between 1 and 2 for Mg, Ca, SiO2 and SO4(-)S, and greater than 10 for NH4(-)N, PO4(-)P, and K. Droughts tended to reduce enrichment ratios of cations and sea-salts, but increased enrichment ratios of NH4(-)N, PO4(-)P, and K. In the weeks following hurricanes and tropical storms, relative throughfall tended to be higher and enrichment ratios tended to be lower. Saharan dust and the activity of Caribbean volcanoes can also be detected in the time series. Nevertheless, the impacts of particular events are variable and modified by the magnitude of the event, the pre- and post-event rainfall, and the time since the previous event. Rainfall, throughfall, rainfall pH, and rainfall fluxes of seven constituents had decreasing trends over the 15-year period. However, these decreases were small, less than inter-annual and annual variations, and not considered to be ecologically significant. These long-term observations indicate that physical and biological processes associated with water passing through the canopy act to buffer internal nutrient cycles from inter-annual and seasonal variations in rainfall inputs.

Changes in Vegetation Condition and Surface Fluxes during NAME 2004
About this Resource: The vegetation in the core region of the North American monsoon (NAM) system changes dramatically after the onset of the summer rains so that large changes may be expected in the surface fluxes of radiation, heat, and moisture. Most of this region lies in the rugged terrain of western Mexico and very few measurements of these fluxes have been made in the past. Surface energy balance measurements were made at seven sites in Sonora, Mexico, and Arizona during the intensive observation period (IOP) of the North American Monsoon Experiment (NAME) in summer 2004 to better understand how land surface vegetation change alters energy flux partitioning. Satellite data were used to obtain time series for vegetation indices and land surface temperature for these sites. The results were analyzed to contrast conditions before the onset of the monsoon with those afterward. As expected, precipitation during the 2004 monsoon was highly variable from site to site, but it fell in greater quantities at the more southern sites. Likewise, large changes in the vegetation index were observed, especially for the subtropical sites in Sonora. However, the changes in the broadband albedo were very small, which was rather surprising. The surface net radiation was consistent with the previous observations, being largest for surfaces that are transpiring and cool, and smallest for surfaces that are dry and hot. The largest evaporation rates were observed for the subtropical forest and riparian vegetation sites. The evaporative fraction for the forest site was highly correlated with its vegetation index, except during the dry spell in August. This period was clearly detected in the land surface temperature data, which rose steadily in this period to a maximum at its end.

The importance of canopy structure in controlling the interception loss of rainfall: examples from a young and an old-growth Douglas-fir forest
About this Resource: The canopy water storage capacity (S), direct throughfall fraction (p), the ratio of evaporation to rainfall intensity (E/R) and interception loss (I(n)), of a Douglas-fir forest are influenced by short (seasonal) and long-term (decades to centuries) changes in the forest canopy. Gross precipitation (P(G)) and net precipitation (P(n)) were measured in a young (25-year-old) Douglas-fir forest and the results compared with measurements previously made in a nearby old-growth (>450-year-old) Douglas-fir forest [Link, T.E., Unsworth, M.H., Marks, D., 2004. The dynamics of rainfall interception by a seasonal temperate rainforest. Agric. Forest Meteorol. 124, 171-191.]. Canopy rainfall variables were estimated using a regression-based method that estimates S, p and E/R for individual storms using the relationship between P(G) and P(n). The individual storm estimates of S, p and E/R for the young forest were applied to a rainfall interception model (Gash model [Gash, J.H.C., 1979. An analytical model of rainfall interception by forest. Q. J. R. Meteorol. Soc. 105, 43-55.]) to determine the effect of seasonal changes in canopy hydrologic variables have on estimates of I(n) (young forest only). The Gash model was previously applied to the old-growth forest [Link, T.E., Unsworth, M.H., Marks, D., 2004. The dynamics of rainfall interception by a seasonal temperate rainforest. Agric. Forest Meteorol. 124, 171-191.]. The young forest had significantly different S (1.40 mm +/- 0.27) and p (0.12 +/- 0.07) relative to the old-growth forest (S = 3.32 +/- 0.35; p = 0.42 +/- 0.07). Seasonal variation in canopy structure, such as deciduous leaf senescence and coniferous needle drop, were correlated with decreases in S. The differences in S and p between the two forests resulted in an I(n) that was only slightly larger in the old-growth forest because the E/R for the two forests were similar (young = 0.18 +/- 0.06; old-growth = 0.17 +/- 0.08). E/R in the young and old-growth forests may have been similar because developmental changes associated with old-growth forest may alter the external resistance (r(a)) and the effective area for evaporation. The Gash model successfully predicted I(n) for the young forest on a seasonal basis (3.29% error), but experienced larger errors (range = -91 to 36% error) for individual storms. The seasonal error and the error for individual storms improved when seasonal variations in canopy characteristics were incorporated in the model (seasonal error = 2.37%; individual storm error range = -12.0 to 21.7%). Therefore, short-term (seasonal) changes in phenology and long-term (decades to centuries) horizontal and vertical development of the forest canopy influence S, p, I(n) and E/R of Douglas-fir forests.

Forage frost protection potential of conifer silvopastures
About this Resource: In temperate climates, forages are frequently held in a near dormant state at both ends of the growing season due to episodic radiation frost. During these periods, air temperature is frequently adequate for forage growth to supply feed for grazing animals. The effect of thermal radiation from conifer tree canopies on forage canopy temperature was evaluated for a silvopasture with variable tree density. A long-wave radiation-sensitive sensor for measuring temperature at the forage canopy level was designed, tested, and used to approximate night time forage canopy temperature during the autumn of 1999 and 2000 and spring of 2000. Temperature from the designed sensor correlated linearly with forage canopy temperature measured with an infrared thermometer with a slope of 1.0, a 0.9 °C offset, and an r2 of 0.999. The response of sensor temperature to night sky shading by trees was also linear. Under 77% tree cover sensor temperature remained within half a degree of air temperature, however, under 7% cover averaged 10.4 °C below air temperature during radiation frost events. The results of this study indicate that a well designed silvopasture can potentially extend the grazing season period on both ends in regions were radiation frosts are prevalent.

Transmission of Phytophthora ramorum in mixed-evergreen forest in California.
About this Resource: During 2001 to 2003, the transmission biology of Phytophthora ramorum, the causal agent of sudden oak death, was studied in mixed-evergreen forest, a common forest type in northern, coastal California. Investigation of the sources of spore production focused on coast live oak (Quercus agrifolia) and bay laurel (Umbellularia californica), dominant hosts that comprised 39.7 and 46.2% of the individuals at the study site, respectively. All tests for inoculum production from the surface of infected coast live oak bark or exudates from cankers were negative. In contrast, sporangia and chlamydospores were produced on the surface of infected bay laurel leaves. Mean number of zoospores produced from infected bay laurel leaves under natural field conditions during rainstorms was 1,173.0 +/- SE 301.48, and ranged as high as 5,200 spores/leaf. P. ramorum was recovered from rainwater, soil, litter, and streamwater during the mid- to late rainy season in all 3 years of the study. P. ramorum was not recovered from sporadic summer rains or soil and litter during the hot, dry summer months. Concentrations of inoculum in rainwater varied significantly from year to year and increased as the rainy season progressed for the two complete seasons that were studied. Potential dispersal distances were investigated for rainwater, soil, and streamwater. In rainwater, inoculum moved 5 and 10 m from the inoculum source. For soil, transmission of inoculum was demonstrated from infested soil to bay laurel green leaf litter, and from bay laurel green leaf litter to aerial leaves of bay laurel seedlings. One-third to one-half of the hikers tested at the study site during the rainy season also were carrying infested soil on their shoes. In streamwater, P. ramorum was recovered from an unforested site in pasture approximately equal to 1 km downstream of forest with inoculum sources. In total, these studies provide details on the production and spread of P. ramorum inoculum in mixed-evergreen forest to aid forecasting and managing disease transmission of this environmentally destructive pathogen.

Effects of forest cover, topography, and sampling extent on the measured density of shallow, translational landslides
About this Resource: We use regionally available digital elevation models and land cover data, calibrated with ground- and photo-based landslide inventories, to produce spatially distributed estimates of shallow, translational landslide density (number/unit area). To discern effects of land use, we focus on resolving landslide density relationships with forest cover. We account for topographic variability between sites and landslide detection bias in air photo mapping. Even so, for sites in the Oregon Coast Range, we find great variability in the ratios of landslide density in forest classes among sites. We present strategies for subsampling available data to quantify this variability. For these data, we find that older forests, when sampled over tens of square kilometers, commonly exhibited the highest landslide densities but over hundreds of square kilometers always exhibited the lowest densities, averaging 30% of that in recently harvested areas and 79% of that in younger, managed forests.

A comparison of daily water use estimates derived from constant-heat sap-flow probe values and gravimetric measurements in pot-grown saplings
About this Resource: Use of Granier-style heat dissipation sensors to measure sap flow is common in plant physiology, ecology and hydrology. There has been concern that any change to the original Granier design invalidates the empirical relationship between sap flux density and the temperature difference between the probes. Here, we compared daily water use estimates from gravimetric measurements with values from variable length heat dissipation sensors, which are a relatively new design. Values recorded during a one-week period were compared for three large pot-grown saplings of each of the tropical trees Pseudobombax septenatum (Jacq.) Dugand and Calophyllum longifolium Willd. For five of the six individuals, P values from paired t-tests comparing the two methods ranged from 0.12 to 0.43 and differences in estimates of total daily water use over the week of the experiment averaged < 3%. In one P. septenatum sapling, the sap flow sensors underestimated water use relative to the gravimetric measurements. This discrepancy could have been associated with naturally occurring gradients in temperature that reduced the difference in temperature between the probes, which would have caused the sensor method to underestimate water use. Our results indicate that substitution of variable length heat dissipation probes for probes of the original Granier design did not invalidate the empirical relationship determined by Granier between sap flux density and the temperature difference between probes.

Invasion of tallow tree into southern US forests: influencing factors and implications for mitigation
About this Resource: We identify species-environment relationships to predict the occurrence of Chinese tallow (Triadica sebifera (L.) Small) on forestlands in the southern US, where it has emerged as the most pervading, stand-replacing, alien tree species. Tallow invasions are more likely to be observed on low and flat lands, areas adjacent to water and roadways, sites recently harvested or disturbed, younger stands, and private forestlands. The winter extreme minimum temperature tends to restrain tallow northward migration. Increases in both range and severity of tallow invasions are predicted with a warming climate trend, and the situation could be worse if the warming is coupled with an increased frequency and intensity of disturbances. Monitoring and mitigation strategies are proposed to assist this region and other countries threatened by tallow invasions.

Sources of Inoculum for Phytophthora ramorum in a Redwood Forest
About this Resource: Sources of inoculum were investigated for dominant hosts of Phytophthora ramorum in a redwood forest. Infected trunks, twigs, and/or leaves of bay laurel (Umbellularia californica), tanoak (Lithocarpus densiflorus), and redwood (Sequoia sempervirens) were tested in the laboratory for sporangia production. Sporangia occurred on all plant tissues with the highest percentage on bay laurel leaves and tanoak twigs. To further compare these two species, field measurements of inoculum production and infection were conducted during the rainy seasons of 2003-04 and 2004-05. Inoculum levels in throughfall rainwater and from individual infections were significantly higher for bay laurel as opposed to tanoak for both seasons. Both measurements of inoculum production from bay laurel were significantly greater during 2004-05 when rainfall extended longer into the spring, while inoculum quantities for tanoak were not significantly different between the 2 years. Tanoak twigs were more likely to be infected than bay laurel leaves in 2003-04, and equally likely to be infected in 2004-05. These results indicate that the majority of P. ramorum inoculum in redwood forest is produced from infections on bay laurel leaves. Years with extended rains pose an elevated risk for tanoak because inoculum levels are higher and infectious periods continue into late spring.

Carbon exchange and venting anomalies in an upland deciduous forest in northern Wisconsin, USA
About this Resource: Turbulent fluxes of carbon, water vapor, and temperature were continuously measured above an upland forest in north central Wisconsin during 1999 and 2000 using the eddy covariance method. Maple (Acer saccharum), basswood (Tilia americana), and green ash (Fraxinus pennsylvanica) species found in this forest also comprise a substantial portion of the landscape in the northern Great Lakes region and area, and it has been hypothesized that forests of this age (60-80 years) are responsible for net uptake of atmospheric CO2 over North America. Mean CO2, water vapor, and temperature profile measurements were used to improve flux estimates during periods of low turbulence, and were effective for friction velocities (u*) >0.3 m s-1. Unique observations at this site included nighttime and early morning venting anomalies that seemed to originate from a seemingly homogenous area within the forest. These elevated NEE measurements, some as high as 80 mol m-2 s-1, appeared in valid turbulent flux observations for hours at a time, and provided circumstantial evidence for preferential venting and/or existence of pooled CO2 in low-lying areas. We observed that the forest was a moderate sink for atmospheric carbon, and cumulative NEE of CO2 was estimated to be -334 g C m-2 year-1 during 2000. Sensitivity to low-turbulence flux corrections was very small (21 g C m-2 year-1), and discrepancies between annual estimates of NEE and NEP were similar to other sites. A normalized measure of ecosystem respiration, the free energy of activation, was presented and its seasonal variations were analyzed. Gross ecosystem production (GEP) was high (1165 g C m-2 year-1) and ecosystem respiration (ER) was low (817 g C m-2 year-1) in comparison to spatially integrated, landscape-scale observations from WLEF (914 and 1005 g C m-2 yea-1, respectively), a 477 m tower located 22 km to the northeast [Glob. Change Biol. 9 (2003) 1278]. Forest transpiration was responsible for most of the water released to the atmosphere. Stomata closed under intense sunlight and high vapor pressure deficits (VPD > 1.5 kPa). Effect of stomotal closure on annual CO2 uptake was minimal due to adequate soil moisture and moderate VPD during the growing season.

Multi-season Climate Synchronized Forest Fires Throughout the 20th Century, Northern Rockies, USA
About this Resource: We inferred climate drivers of 20th-century years with regionally synchronous forest fires in the U.S. northern Rockies. We derived annual fire extent from an existing fire atlas that includes 5038 fire polygons recorded from 12 070 086 ha, or 71% of the forested land in Idaho and Montana west of the Continental Divide. The 11 regional-fire years, those exceeding the 90th percentile in annual fire extent from 1900 to 2003 (>102 314 ha or approximately 1% of the fire atlas recording area), were concentrated early and late in the century (six from 1900 to 1934 and five from 1988 to 2003). During both periods, regional-fire years were ones when warm springs were followed by warm, dry summers and also when the Pacific Decadal Oscillation (PDO) was positive. Spring snowpack was likely reduced during warm springs and when PDO was positive, resulting in longer fire seasons. Regional-fire years did not vary with El Niño-Southern Oscillation (ENSO) or with climate in antecedent years. The long mid-20th century period lacking regional-fire years (1935-1987) had generally cool springs, generally negative PDO, and a lack of extremely dry summers; also, this was a period of active fire suppression. The climate drivers of regionally synchronous fire that we inferred are congruent with those of previous centuries in this region, suggesting a strong influence of spring and summer climate on fire activity throughout the 20th century despite major land-use change and fire suppression efforts. The relatively cool, moist climate during the mid-century gap in regional-fire years likely contributed to the success of fire suppression during that period. In every regional-fire year, fires burned across a range of vegetation types. Given our results and the projections for warmer springs and continued warm, dry summers, forests of the U.S. northern Rockies are likely to experience synchronous, large fires in the future.

Twentieth-century warming and the dendroclimatology of declining yellow-cedar forests in southeastern Alaska
About this Resource: Decline of yellow-cedar (Chamaecyparis nootkatensis ((D. Don) Spach) has occurred on 200 000 ha of temperate rainforests across southeastern Alaska. Because declining forests appeared soon after the Little Ice Age and are limited mostly to low elevations (whereas higher elevation forests remain healthy), recent studies have hypothesized a climatic mechanism involving early dehardening, reduced snowpack, and freezing injury. This hypothesis assumes that a specific suite of microclimatic conditions occurs during late winter and declining cedar populations across the region have responded similarly to these conditions. Based on the first geographically extensive tree ring chronologies constructed for southeastern Alaska, we tested these assumptions by investigating regional climatic trends and the growth responses of declining cedar populations to this climatic variation. Warming winter trends were observed for southeastern Alaska, resulting in potentially injurious conditions for yellow-cedar due to reduced snowfall and frequent occurrence of severe thaw-freeze events. Declining cedar forests shared a common regional chronology for which late-winter weather was the best predictor of annual growth of surviving trees. Overall, our findings verify the influence of elevational gradients of temperature and snow cover on exposure to climatic stressors, support the climatic hypothesis across large spatial and temporal scales, and suggest cedar decline may expand with continued warming.

Influence of Elevation on Bark Beetle (Coleoptera: Curculionidae, Scolytinae) Community Structure and Flight Periodicity in Ponderosa Pine Forests of Arizona
About this Resource: We examined abundance and flight periodicity of five Ips and six Dendroctonus species (Coleoptera: Curculionidae, Scolytinae) among three different elevation bands in ponderosa pine (Pinus ponderosa Douglas ex. Lawson) forests of northcentral Arizona. Bark beetle populations were monitored at 10 sites in each of three elevation bands (low: 1,600-1,736 m; middle: 2,058-2,230 m; high: 2,505-2,651 m) for 3 yr (2004-2006) using pheromone-baited Lindgren funnel traps. Trap contents were collected weekly from March to December. We also studied temperature differences among the elevation bands and what role this may play in beetle flight behavior. Bark beetles, regardless of species, showed no consistent elevational trend in abundance among the three bands. The higher abundances of Ips lecontei Swaine, I. calligraphus ponderosae Swaine, Dendroctonus frontalis Zimmerman, and D. brevicomis LeConte at low and middle elevations offset the greater abundance of I. knausi Swaine, D. adjunctus Blandford, D. approximatus Dietz, and D. valens LeConte at high elevations. I. pini (Say) and I. latidens LeConte were found in similar numbers across the three bands. Flight periodicity of several species varied among elevation bands. In general, the flight period shortened as elevation increased; flight initiated later and terminated earlier in the year. The timing, number, and magnitude of peaks in flight activity also varied among the elevation bands. These results suggest that abundance and flight seasonality of several bark beetles are related to elevation and the associated temperature differences. The implications of these results are discussed in relation to bark beetle management and population dynamics.

Forest floor temperature and relative humidity following timber harvesting in southern New England, USA
About this Resource: Forest amphibians, especially salamanders, prefer forests with shaded, cool, and moist forest floors. Timber harvesting opens the forest canopy and exposes the forest floor to direct sunlight, which can increase forest floor temperatures and reduce soil moisture. These microclimatic changes can potentially degrade the harvested stand for amphibian habitat or affect other biotic resources or ecological processes at the forest floor and in the understory. The degree of forest floor disturbance is directly related to the intensity of harvesting, however, the duration of this effect is unknown. We conducted a study of forest floor temperature and relative humidity over a 12-year chronosequence (1993-2004) of timber harvests. We compared simultaneous, paired measurements of temperature and relative humidity at three positions (soil, forest floor, air) in harvested and control sites over three seasonal survey sessions. Vegetation composition and structure were measured at each survey location. Ambient weather conditions were recorded at three open-field locations across the study area. We recorded over 23,000 paired measures of temperature and relative humidity at all 12 harvested and control sites during each survey session. While we found significant effects of time-since-harvesting on differences in temperature between harvested and uncut sites, the average differences were generally small (<1°C). We observed no temporal pattern in temperatures with time-since-harvest in the harvested sites compared to uncut conditions. Time-since-harvest had no effect on differences in relative humidity between cut and uncut sites. The variation in forest floor microclimate among sites was large, likely due to small-scale differences in cutting intensity (retained canopy), understory vegetation growth, and microtopography or aspect. We conclude that timber harvesting, within the range of intensities assessed in this study, would have only minimal and short-term effects on forest floor microclimate. We suggest that the small differences we observed in forest floor temperatures and moisture between cut and uncut forest parcels would likely have minor effects on climatic aspects of forest amphibian habitat, and on climatic influences on other forest floor biota and ecological processes.

Utility of thermal sharpening over Texas high plains irrigated agricultural fields
About this Resource: Irrigated crop production in the Texas high plains (THP) is dependent on water extracted from the Ogallala Aquifer, an area suffering from sever water shortage. Water management in this area is therefore highly important. Thermal satellite imagery at high temporal (~daily) and high spatial (~100 m) resolutions could provide important surface boundary conditions for vegetation stress and water use monitoring, mainly through energy balance models such as DisALEXI. At present, however, no satellite platform collects such high spatiotemporal resolution data. The objective of this study is to examine the utility of an image sharpening technique (TsHARP) for retrieving land surface temperature at high spatial resolution (down to 60 m) from moderate spatial resolution (1 km) imagery, which is typically available at higher (~daily) temporal frequency. A simulated sharpening experiment was applied to Landsat 7 imagery collected over the THP in September 2002 to examine its utility over both agricultural and natural vegetation cover. The Landsat thermal image was aggregated to 960 m resolution and then sharpened to its native resolution of 60 m and to various intermediate resolutions. The algorithm did not provide any measurable improvement in estimating high-resolution temperature distributions over natural land cover. In contrast, TsHARP was shown to retrieve high-resolution temperature information with good accuracy over much of the agricultural area within the scene. However, in recently irrigated fields, TsHARP could not reproduce the temperature patterns. Therefore we conclude that TsHARP is not an adequate substitute for 100-m-scale observations afforded by the current Landsat platforms. Should the thermal imager be removed from follow-on Landsat platforms, we will lose valuable capacity to monitor water use at the field scale, particularly in many agricultural regions where the typical field size is ~100 x 100 m. In this scenario, sharpened thermal imagery from instruments like MODIS or VIIRS would be the suboptimal alternative.

Spatial variability in forest growth - climate relationships in the Olympic Mountains, Washington
About this Resource: For many Pacific Northwest forests, little is known about the spatial and temporal variability in tree growth - climate relationships, yet it is this information that is needed to predict how forests will respond to future climatic change. We studied the effects of climatic variability on forest growth at 74 plots in the western and northeastern Olympic Mountains. Basal area increment time series were developed for each plot, and Pearson's correlation analysis and factor analysis were used to quantify growth-climate relationships. Forest growth in the Olympic Mountains responds to climatic variability as a function of mean climate and elevation. Low summer moisture limits growth across all elevations in the dry northeastern Olympics. Growth at low elevations in the wet western Olympics is associated with phases of the Pacific Decadal Oscillation and with summer temperature. Heavy winter snowpack limits growth at high elevations in the western Olympics. In the warmer greenhouse climate predicted for the Olympic Mountains, productivity at high elevations of the western Olympics will likely increase, whereas productivity at high elevations in the northeastern region and potentially in low elevations of the western region will likely decrease. This information can be used to develop adaptive management strategies to prepare for the effects of future climate on these forests. Because growth-climate relationships on the Olympic Peninsula vary at relatively small spatial scales, those relationships may assist modeling and other efforts to provide more accurate predictions at local to regional scales.

Temperature and vegetation effects on soil organic carbon quality along a forested mean annual temperature gradient in North America
About this Resource: Both climate and plant species are hypothesized to influence soil organic carbon (SOC) quality, but accurate prediction of how SOC process rates respond to global change will require an improved understanding of how SOC quality varies with mean annual temperature (MAT) and forest type. We investigated SOC quality in paired hardwood and pine stands growing in coarse textured soils located along a 22 °C gradient in MAT. To do this, we conducted 80-day incubation experiments at 10 and 30 °C to quantify SOC decomposition rates, which we used to kinetically define SOC quality. We used these experiments to test the hypotheses that SOC quality decreases with MAT, and that SOC quality is higher under pine than hardwood tree species. We found that both SOC quantity and quality decreased with increasing MAT. During the 30 °C incubation, temperature sensitivity (Q₁₀) values were strongly and positively related to SOC decomposition rates, indicating that substrate supply can influence temperature responsiveness of SOC decomposition rates. For a limited number of dates, Q₁₀ was negatively related to MAT. Soil chemical properties could not explain observed patterns in soil quality. Soil pH and cation exchange capacity (CEC) both declined with increasing MAT, and soil C quality was positively related to pH but negatively related to CEC. Clay mineralogy of soils also could not explain patterns of SOC quality as complex (2 : 1), high CEC clay minerals occurred in cold climate soils while warm climate soils were dominated by simpler (1 : 1), low CEC clay minerals. While hardwood sites contained more SOC than pine sites, with differences declining with MAT, clay content was also higher in hardwood soils. In contrast, there was no difference in SOC quality between pine and hardwood soils. Overall, these findings indicate that SOC quantity and quality may both decrease in response to global warming, despite long-term changes in soil chemistry and mineralogy that favor decomposition.

Rapid mortality of Populus tremuloides in southwestern Colorado, USA
About this Resource: Concentrated patches of recent trembling aspen (Populus tremuloides) mortality covered 56,091ha of Colorado forests in 2006. Mortality has progressed rapidly. Area affected increased 58% between 2005 and 2006 on the Mancos-Dolores Ranger District, San Juan National Forest, where it equaled nearly 10% of the aspen cover type. In four stands that were measured twice, incidence of mortality increased from 7-9% in 2002/2003 to 31-60% in 2006. Mortality generally decreased with increasing elevation over the primary elevation range of aspen and occurred on less steep slopes than healthy aspen. Slope-weighted mean aspects of aspen cover type were northern at low elevations and generally southern at high elevations. Relative frequency of mortality was generally highest on southern to western aspects. In 31 stands measured in detail, mortality ranged from 0 to 100% (mean 32%) and was negatively correlated with stand density (P =0.033). Size of trees affected was strongly correlated with amount of current mortality (P <0.001), and current mortality was skewed toward larger diameter classes. Density of regeneration was in a low range typical of undisturbed stands and did not increase with overstory mortality. Agents that typically kill mature trees in aspen stands were unimportant in this mortality. Instead, a group of interchangeable, usually secondary agents was most commonly associated with mortality, including Cytospora canker (usually caused by Valsa sordida), aspen bark beetles (Trypophloeus populi and Procryphalus mucronatus), poplar borer (Saperda calcarata), and bronze poplar borer (Agrilus liragus). The rapidity of mortality, mortality agents involved, and probably other causal factors distinguish this phenomenon from the long-term loss of aspen cover usually attributed to successional processes operating in an altered disturbance regime (and often exacerbated by ungulate browsing). Our data are consistent with a hypothesis that (a) predisposing factors include stand maturation, low density, southern aspects and low elevations; (b) a major inciting factor was the recent, acute drought accompanied by high temperatures, and; (c) contributing factors and proximate agents of mortality are the common biotic agents observed. On sites with poor regeneration and weak root systems, clones may die, resulting in the long-term loss of aspen forest cover.

UINTAS 2006: the Uinta Interdisciplinary Assessment Symposium, Snowbird, Utah, May 2006--Introduction
About this Resource: The Uinta Mountains are a spectacular and unique range of the Rocky Mountain system. Running east-west for more than 150 km across northeastern Utah and northwestern Colorado, they contain the highest summits in Utah (elevations greater than 4000 m a.s.l.), vast areas of alpine tundra, glacial lakes, immense compound cirques, and deep fluvial canyons. The range forms the northern and southern boundaries for many forest species common to the Colorado Plateau and the northern Rockies, respectively. It is also characterized by steep temperature and moisture gradients and is situated at the boundary between three air masses of the interior western United States (Mitchell, 1976). Indeed, the Uinta Mountains are an exceptional natural laboratory where questions germane to ecology, climatology, geology, and numerous other disciplines in alpine research can be effectively investigated. For example, recent research in the Uinta Mountains spans topics ranging from Pleistocene glacial chronology and climate (e.g., Munroe et al., 2006); to studies of lake and fluvial-sediment records exploring the impact of grazing, air-quality changes (e.g., Moser, 2005), and geomorphic processes on sedimentation (e.g., Carson, 2005); to Holocene treeline elevation responses to climate change (Siderius, 2004). In an effort to provide a forum in which researchers interested in these and other topics could meet to share and discuss their research, Jeff Munroe organized UINTAS 2006: the Uinta Interdisciplinary Assessment Symposium. This special section of Arctic, Antarctic, and Alpine Research includes 10 articles describing results of Uinta Mountain research presented at the symposium, all of which either build upon previous studies in the range or explore topics of alpine research, chiefly geomorphology, limnogeology, biogeography, paleoclimatology, and ecology. The underlying goal of this special section is to highlight the importance of current and future research in this relatively understudied, yet accessible, region of western North America.

Oligocene terrestrial strata of northwestern Ethiopia: a preliminary report on paleoenvironments and paleontology
About this Resource: The Paleogene record of Afro-Arabia is represented by few fossil localities, most of which are coastal. Here we report sedimentological and paleontological data from continental Oligocene strata in northwestern Ethiopia. These have produced abundant plant fossils and unique assemblages of vertebrates, thus filling a gap in what is known of Paleogene interior Afro-Arabia. The study area is approximately 60 km west of Gondar, Chilga Woreda; covers about 100 km2; and represents as few as 1 Myr based on radiometric dates and paleomagnetic chronostratigraphy. The sedimentary strata are 150 m thick, and dominated by kaolinitic and smectitic mudstones and airfall tuff deposits. Five main paleosol types are interpreted as representing Protosols (gleyed or ferric), Histosols, Gleysols, Vertisols, and Argillisols. Varied, poor drainage conditions produced lateral variation in paleosols, and stratigraphic variation probably resulted from lateral changes in drainage conditions through time. Vertebrate fossils occur in sediments associated with ferric Protosols and occur with fruits, seeds, and leaf impressions. Plant fossils also occur as in situ forests on interfluves, leaf and flower compressions associated with in situ carbonized trees in overbank deposits (Gleyed Protosols), and compressions of leaves, twigs and seeds in tuffs. Plant fossil assemblages document diverse forests, from 20-35 m tall, of locally heterogeneous composition, and representing families occurring commonly (legumes) or uncommonly (palms) in forests today. Sedimentological and paleobotanical data are consistent with a nearly flat landscape where a meandering river and ample rainfall supported lush vegetation. Over time, the region was subject to intermittent ashfalls. A unique fauna of archaic mammalian endemics, such as arsinoitheres and primitive hyracoids, lived here with the earliest deinotheres.

Allometric Models for Predicting Aboveground Biomass in Two Widespread Woody Plants in Hawaii
About this Resource: Allometric models are important for quantifying biomass and carbon storage in terrestrial ecosystems. Generalized allometry exists for tropical trees, but species- and site-specific models are more accurate. We developed species-specific models to predict aboveground biomass in two of the most ubiquitous natives in Hawaiian forests and shrublands, Metrosideros polymorpha and Dodonaea viscosa. The utility of the M. polymorpha allometry for predicting biomass across a range of sites was explored by comparing size structure (diameter at breast height vs. tree height) of the trees used to develop the models against trees from four M. polymorpha-dominated forests along a precipitation gradient (1630-2380 mm). We also compared individual tree biomass estimated with the M. polymorpha model against existing generalized equations, and the D. viscosa model with an existing species-specific model. Our models were highly significant and displayed minimal bias. Metrosideros polymorpha size structures from the three highest precipitation sites fell well within the 95% confidence intervals for the harvested trees, indicating that the models are applicable at these sites. However, size structure in the area with the lowest precipitation differed from those in the higher rainfall sites, emphasizing that care should be taken in applying the models too widely. Existing generalized allometry differed from the M. polymorpha model by up to 88 percent, particularly at the extremes of the data range examined, underestimating biomass in small trees and overestimating in large trees. The existing D. viscosa model underestimated biomass across all sizes by a mean of 43 percent compared to our model. The species-specific models presented here should enable more accurate estimates of biomass and carbon sequestration in Hawaiian forests and shrublands.

Development of equations for predicting Puerto Rican subtropical dry forest biomass and volume
About this Resource: Carbon accounting, forest health monitoring and sustainable management of the subtropical dry forests of Puerto Rico and other Caribbean Islands require an accurate assessment of forest aboveground biomass (AGB) and stem volume. One means of improving assessment accuracy is the development of predictive equations derived from locally collected data. Forest inventory and analysis (FIA) measured tree diameter and height, and then destructively sampled 30 trees from 6 species at an upland deciduous dry forest site near Ponce, Puerto Rico. This data was used to develop best parsimonious equations fit with ordinary least squares procedures and additive models fit with nonlinear seemingly unrelated regressions that estimate subtropical dry forest leaf, woody, and total AGB for Bucida buceras and mixed dry forest species. We also fit equations for estimating inside and outside bark total and merchantable stem volume using both diameter at breast height (d.b.h.) and total height, and diameter at breast height alone for B. buceras and Bursera simaruba. Model fits for total and woody biomass were generally good, while leaf biomass showed more variation, possibly due to seasonal leaf loss at the time of sampling. While the distribution of total AGB into components appeared to remain relatively constant across diameter classes, AGB variability increased and B. simaruba and B. buceras allocated more carbon into branch biomass than the other species. When comparing our observed and predicted values to other published dry forest AGB equations, the equation developed in Mexico and recommended for areas with rainfall >900 mm/year gave estimates substantially lower than our observed values, while equations developed using dry forest data from forest in Australia, India and Mexico were lower than our observed values for trees with d.b.h. <25 cm and slightly higher for trees with d.b.h. >30 cm. Although our ability to accurately estimate merchantable stem volume and live tree AGB for subtropical dry forests in Puerto Rico and other Caribbean islands has been improved, much work remains to be done to sample a wider range of species and tree sizes.

First direct landscape-scale measurement of tropical rain forest Leaf Area Index, a key driver of global primary productivity
About this Resource: Leaf Area Index (leaf area per unit ground area, LAI) is a key driver of forest productivity but has never previously been measured directly at the landscape scale in tropical rain forest (TRF). We used a modular tower and stratified random sampling to harvest all foliage from forest floor to canopy top in 55 vertical transects (4.6 m²) across 500 ha of old growth in Costa Rica. Landscape LAI was 6.00 ± 0.32 SEM. Trees, palms and lianas accounted for 89% of the total, and trees and lianas were 95% of the upper canopy. All vertical transects were organized into quantitatively defined strata, partially resolving the long-standing controversy over canopy stratification in TRF. Total LAI was strongly correlated with forest height up to 21 m, while the number of canopy strata increased with forest height across the full height range. These data are a benchmark for understanding the structure and functional composition of TRF canopies at landscape scales, and also provide insights for improving ecosystem models and remote sensing validation.

Phenology of a northern hardwood forest canopy
About this Resource: While commonplace in other parts of the world, long-term and ongoing observations of the phenology of native tree species are rare in North America. We use 14 years of field survey data from the Hubbard Brook Experimental Forest to fit simple models of canopy phenology for three northern hardwood species, sugar maple (Acer saccharum), American beech (Fagus grandifolia), and yellow birch (Betula alleghaniensis). These models are then run with historical meteorological data to investigate potential climate change effects on phenology. Development and senescence are quantified using an index that ranges from 0 (dormant, no leaves) to 4 (full, green canopy). Sugar maple is the first species to leaf out in the spring, whereas American beech is the last species to drop its leaves in the fall. Across an elevational range from 250 to 825 m ASL, the onset of spring is delayed by 2.7±0.4 days for every 100 m increase in elevation, which is in reasonable agreement with Hopkin's law. More than 90% of the variation in spring canopy development, and just slightly less than 90% of the variation in autumn canopy senescence, is accounted for by a logistic model based on accumulated degree-days. However, degree-day based models fit to Hubbard Brook data appear to overestimate the rate at which spring development occurs at the more southerly Harvard Forest. Autumn senescence at the Harvard Forest can be predicted with reasonable accuracy in sugar maple but not American beech. Retrospective modeling using five decades (1957-2004) of Hubbard Brook daily mean temperature data suggests significant trends (P<=0.05) towards an earlier spring (e.g. sugar maple, rate of change=0.18 days earlier/yr), consistent with other studies documenting measurable climate change effects on the onset of spring in both North America and Europe. Our results also suggest that green canopy duration has increased by about 10 days (e.g. sugar maple, rate of change=0.21 days longer/yr) over the period of study.

Invasive plants transform the three-dimensional structure of rain forests
About this Resource: Biological invasions contribute to global environmental change, but the dynamics and consequences of most invasions are difficult to assess at regional scales. We deployed an airborne remote sensing system that mapped the location and impacts of five highly invasive plant species across 221,875 ha of Hawaiian ecosystems, identifying four distinct ways that these species transform the three-dimensional (3D) structure of native rain forests. In lowland to montane forests, three invasive tree species replace native midcanopy and understory plants, whereas one understory invader excludes native species at the ground level. A fifth invasive nitrogen-fixing tree, in combination with a midcanopy alien tree, replaces native plants at all canopy levels in lowland forests. We conclude that this diverse array of alien plant species, each representing a different growth form or functional type, is changing the fundamental 3D structure of native Hawaiian rain forests. Our work also demonstrates how an airborne mapping strategy can identify and track the spread of certain invasive plant species, determine ecological consequences of their proliferation, and provide detailed geographic information to conservation and management efforts.

Climate response of five oak species in the eastern deciduous forest of the southern Appalachian Mountains, USA
About this Resource: The climatic response of trees that occupy closed canopy forests in the eastern United States (US) is important to understanding the possible trajectory these forests may take in response to a warming climate. Our study examined tree rings of 664 trees from five oak species (white (Quercus alba L.), black (Quercus velutina Lam.), chestnut (Quercus prinus L.), northern red (Quercus rubra L.), scarlet (Quercus coccinea Münchh.)) from 17 stands in eastern Tennessee, western North Carolina, and northern Georgia to determine their climatic response. We dated the samples using skeleton plots, measured the cores, and compared the site- and regional-level tree-ring chronologies of each separate species with divisional climate data. The oldest trees in each chronology dated back to 203 years for black oak, 299 years for chestnut oak, 171 years for northern red oak, 135 years for scarlet oak, and 291 years for white oak. We successfully developed climate models via multiple regression analyses with statistically significant (P < 0.05) variables representing the Palmer Drought Severity Index and average monthly temperature for most of the site-species chronologies (average R2 = 0.15). All regional climate response models included the Palmer Drought Severity Index from either June or July as the most significant variable in the climate response, suggesting that growing-season drought is the most important factor limiting oak growth in the southeastern US. An increase in temperature and reduction in moisture is likely to reduce their competitiveness in their current locations and force these species to migrate to cooler climates, thereby greatly changing ecosystem health and stability in the southern Appalachians.

Environmental controls over carbon dioxide and water vapor exchange of terrestrial vegetation
About this Resource: The objective of this research was to compare seasonal and annual estimates of CO₂ and water vapor exchange across sites in forests, grasslands, crops, and tundra that are part of an international network called FLUXNET, and to investigating the responses of vegetation to environmental variables. FLUXNETs goals are to understand the mechanisms controlling the exchanges of CO₂, water vapor and energy across a spectrum of time and space scales, and to provide information for modeling of carbon and water cycling across regions and the globe. At a subset of sites, net carbon uptake (net ecosystem exchange, the net of photosynthesis and respiration) was greater under diffuse than under direct radiation conditions, perhaps because of a more efficient distribution of non-saturating light conditions for photosynthesis, lower vapor pressure deficit limitation to photosynthesis, and lower respiration associated with reduced temperature. The slope of the relation between monthly gross ecosystem production and evapotranspiration was similar between biomes, except for tundra vegetation, showing a strong linkage between carbon gain and water loss integrated over the year (slopes=3.4 g CO₂/kg H₂O for grasslands, 3.2 for deciduous broadleaf forests, 3.1 for crops, 2.4 for evergreen conifers, and 1.5 for tundra vegetation). The ratio of annual ecosystem respiration to gross photosynthesis averaged 0.83, with lower values for grasslands, presumably because of less investment in respiring plant tissue compared with forests. Ecosystem respiration was weakly correlated with mean annual temperature across biomes, in spite of within site sensitivity over shorter temporal scales. Mean annual temperature and site water balance explained much of the variation in gross photosynthesis. Water availability limits leaf area index over the long-term, and inter-annual climate variability can limit carbon uptake below the potential of the leaf area present.

Effects of postfire seeding and fertilizing on hillslope erosion in north-central Washington, USA
About this Resource: After the 1998 North 25 Fire in the Wenatchee National Forest, eight study sites were established on steep, severely burned hillslopes to examine the effectiveness of postfire seeding and fertilizing treatments in increasing cover to reduce hillslope erosion, and to measure the nutrient content of the eroded sediment. At each site, four 4 by 9 m plots were located with four randomly applied treatments: seed (winter wheat, Triticum estivum) at 34 kg ha- 1, fertilizer (75% ammonium nitrate and 25% ammonium sulfate) at 31 kg ha- 1, seed and fertilizer, and untreated control. Sediment fences were installed at the base of each plot to measure erosion rates and sample the eroded sediments. In addition, precipitation amounts and intensities, surface cover, canopy cover, and nutrient concentrations in the eroded sediments were measured for four years after the fire. Total precipitation was below average during the four-year study period, and most erosion occurred during short duration, moderate intensity summer rainfall events. The overall first year mean erosion rate was 16 Mg ha- 1 yr- 1, and this decreased significantly in the second year to 0.66 Mg ha- 1 yr- 1. There were no significant differences in erosion rates between treatments. In the first year, the seeded winter wheat provided 4.5% canopy cover, about a fourth of the total canopy cover, on the seeded plots; however, the total canopy cover on the seeded plots did not differ from the unseeded plots. The below average precipitation in the spring after seeding may have affected the winter wheat survival rate. In the fourth year of the study, the mean canopy cover in the fertilization treatment plots was 74%, and this was greater than the 55% mean canopy cover in the unfertilized plots (p = 0.04); however, there was no accompanying reduction in erosion rate for either the seeding or fertilization treatments. Revegetation by naturally occurring species was apparently not impacted by seeding during the four years of this study. The pH of the sediment as well as the concentrations of NO3-N, NH4-N, and K was not affected by seeding or fertilizing. The nutrient loads in the eroded sediment were minimal, with most of the nutrient loss occurring in the first postfire year. These results confirm that seeding success is highly dependent on rainfall intensity, amounts, and timing, and that soil nutrients lost in eroded sediments are unlikely to impair the site productivity.

Forest Fires in the Insular Caribbean
About this Resource: This paper presents a summary of the forest fire reports in the insular Caribbean derived from both management reports and an analysis of publicly available Moderate Resolution Imaging Spectrodiometer (MODIS) satellite active fire products from the region. A vast difference between the amount of fires reported by land managers and fire points in the MODIS Fire Information for Resource Management System data can be observed. Future research is recommended to better understand the nature of these differences. While there is a general lack of available statistical data on forest fires in the Caribbean, a few general observations can be made: Forest fires occur mainly in dry forest types (500 to 1000 mm of mean annual rainfall). These are also the areas where most human settlements are located. Lowland high forests and montane forests with higher rainfall (1000 and more mm y-1) are less susceptible to forest fire, but they can burn in exceptionally dry years. Most of the dry forest ecosystems in the Caribbean can be considered to be fire-sensitive ecosystems, while the pine forests in the Caribbean (Cuba, Dominican Republic, and the Bahamas) are maintained by wildfires. In fire-sensitive ecosystems, uncontrolled burning often encourages the spread of alien invasive species. A Caribbean Fire Management Cooperation Strategy was developed between 2005 and 2006 under auspices of the Food and Agriculture Organization of the United Nations. This regional strategy aims to strengthen Caribbean fire management networking by encouraging closer collaboration among countries with similar ecological conditions. The strategy for the Caribbean identifies a number of research, training, and management activities to improve wildfire management capacity in the Caribbean.

Effects of reduced-impact logging and forest physiognomy on bat populations of lowland Amazonian forest
About this Resource: 1. As human population size increases, demand for natural resources will increase. Logging pressure related to increasing demands continues to threaten remote areas of Amazonian forest. A harvest protocol is required to provide renewable timber resources that meet consumer needs while minimizing negative effects on biodiversity and ecosystem services. Reduced-impact logging (RIL) may be a viable option to achieve these goals. 2. Effects of RIL (18 m³ ha⁻¹) and forest physiognomy were assessed for populations of bats from Amazonian terra firme forest in Brazil at 20-42 months postharvest. 3. Based on 64 512 meter-hours of netting, 1468 bats were captured representing 47 species, 30 genera, four families and five feeding ensembles. Five species (one nectarivore and four frugivores) responded to management in a consistent manner: four were more abundant in logged forest and one was more abundant in undisturbed forest. Ten species (one nectarivore, two gleaning animalivores and seven frugivores) responded to forest physiognomy in a consistent manner: nine were more abundant in closed-canopy sites and one was more abundant in gaps. Three species (all frugivores) exhibited idiosyncratic responses to management that were contingent on physiognomy. 4. Using qualitative measures (changes in status from common to rare, or from present to absent), RIL elicited negative responses from 16 species, mostly rare taxa. After accounting for differences in total number of collected individuals, control forest harboured seven to 15 more rare species than did forest subjected to RIL. 5. Synthesis and applications. In the short term, RIL generally did not negatively affect populations of abundant bats. In contrast, reductions in abundance or local extirpation in response to RIL generally characterized uncommon or rare species. Arrangement of RIL sites in a matrix of undisturbed forest may allow source-sink dynamics to mitigate effects of RIL on rare or sensitive species and enhance sustainability at a regional scale.

Forest dynamics in Oregon landscapes: Evaluation and application of an individual-based model
About this Resource: The FORCLIM model of forest dynamics was tested against field survey data for its ability to simulate basal area and composition of old forests across broad climatic gradients in western Oregon, USA. The model was also tested for its ability to capture successional trends in ecoregions of the west Cascade Range. It was then applied to simulate present and future (1990-2050) forest landscape dynamics of a watershed in the west Cascades. Various regimes of climate change and harvesting in the watershed were considered in the landscape application. The model was able to capture much of the variation in forest basal area and composition in western Oregon even though temperature and precipitation were the only inputs that were varied among simulated sites. The measured decline in total basal area from tall coastal forests eastward to interior steppe was matched by simulations. Changes in simulated forest dominants also approximated those in the actual data. Simulated abundances of a few minor species did not match actual abundances, however. Subsequent projections of climate change and harvest effects in a west Cascades landscape indicated no change in forest dominance as of 2050. Yet, climate-driven shifts in the distributions of some species were projected. The simulation of both stand-replacing and partial-stand disturbances across western Oregon improved agreement between simulated and actual data. Simulations with fire as an agent of partial disturbance suggested that frequent fires of low severity can alter forest composition and structure as much or more than severe fires at historic frequencies.

Amazon Forest Structure from IKONOS Satellite Data and the Automated Characterization of Forest Canopy Properties
About this Resource: We developed an automated tree crown analysis algorithm using 1-m panchromatic IKONOS satellite images to examine forest canopy structure in the Brazilian Amazon. The algorithm was calibrated on the landscape level with tree geometry and forest stand data at the Fazenda Cauaxi (3.75° S, 48.37° W) in the eastern Amazon, and then compared with forest stand data at Tapajos National Forest (3.08° S, 54.94° W) in the central Amazon. The average remotely sensed crown width (mean ± SE) was 12.7 ± 0.1 m (range: 2.0-34.0 m) and frequency of trees was 76.6 trees/ha at Cauaxi. At Tapajos, remotely sensed crown width was 13.1 ± 0.1 m (range: 2.0-38.0 m) and frequency of trees was 76.4 trees/ha. At both Cauaxi and Tapajos, the remotely sensed average crown widths were within 3 percent of the crown widths derived from field measurements, although crown distributions showed significant differences between field-measured and automated methods. We used the remote sensing algorithm to estimate crown dimensions and forest structural properties in 51 forest stands (1 km²) throughout the Brazilian Amazon. The estimated crown widths, tree diameters (dbh), and stem frequencies differed widely among sites, while estimated biomass was similar among most sites. Sources of observed errors included an inability to detect understory crowns and to separate adjacent, intermingled crowns. Nonetheless, our technique can serve to provide information about structural characteristics of large areas of unsurveyed forest throughout Amazonia.

Comparing simple respiration models for eddy flux and dynamic chamber data
About this Resource: Selection of an appropriate model for respiration (R) is important for accurate gap-filling of CO2 flux data, and for partitioning measurements of net ecosystem exchange (NEE) to respiration and gross ecosystem exchange (GEE). Using cross-validation methods and a version of Akaike's Information Criterion (AIC), we evaluate a wide range of simple respiration models with the objective of quantifying the implications of selecting a particular model. We fit the models to eddy covariance measurements of whole-ecosystem respiration (R(eco)) from three different ecosystem types (a coniferous forest, a deciduous forest, and a grassland), as well as soil respiration data from one of these sites. The well-known Q(10) model, whether driven by air or soil temperature, performed poorly compared to other models, as did the Lloyd and Taylor model when used with two of the parameters constrained to previously published values and only the scale parameter being fit. The continued use of these models is discouraged. However, a variant of the Q(10) model, in which the temperature sensitivity of respiration varied seasonally, performed reasonably well, as did the unconstrained three-parameter Lloyd and Taylor model. Highly parameterized neural network models, using additional covariates, generally provided the best fits to the data, but appeared not to perform well when making predictions outside the domain used for parameterization, and should thus be avoided when large gaps must be filled. For each data set, the annual sum of modeled respiration (annual ΣR) was positively correlated with model goodness-of-fit, implying that poor model selection may inject a systematic bias into gap-filled estimates of annual ΣR.

Responses of native and invasive plant species to selective logging in an Acacia koa-Metrosideros polymorpha forest in Hawai'i
About this Resource: Questions: Is the introduced timber species Fraxinus uhdei invasive in Hawai'i? Has logging disturbance facilitated the spread of Fraxinus and other alien species? Location: Windward Mauna Kea, island of Hawai'i. Methods: We surveyed 29 plots which were established before selective logging of the native tree Acacia koa in 1971 to determine if Fraxinus spread beyond the borders of an existing plantation and if other alien species increased. We created gaps in the canopy of the Fraxinus plantation and measured seed rain and regeneration, and we sampled foliar and soil nutrients inside and around the plantation. Results: Basal area of Fraxinus increased from 0.7 m2.ha-1in 1971 to 10.8 m2.ha-1 in 2000. Fraxinus was not found in plots that were located more than 500 m from those where it occurred in 1971 except along a road. Basal area of Acacia koa decreased after logging but subsequently recovered. Occurrence of the alien vine Passiflora tarminiana and alien grass Ehrharta stipoides decreased. Seedling regeneration of Fraxinus was prolific in gaps but did not occur under the canopy. Basal area of Fraxinus did not correlate with soil nutrient concentrations. Conclusions: Fraxinus was able to regenerate following logging more rapidly than native tree species. Basal area growth of Fraxinus was great enough to offset a decline in native trees and cause an increase in forest productivity. If the Fraxinus plantation is harvested, managers should plan ways of favoring regeneration of the native Acacia which is more valuable both for timber and for conservation.

Climate effects on cork growth in Cork oak plantations in Sicily (Italy)
About this Resource: Cork oak (Quercus suber L.) is usually dominant in silvopastoral systems in many areas of Sicily, where the trees are debarked periodically for cork production. In spite of the importance of cork and cork oak stands in Sicilian forests and the potential economic scenarios, few research works have been carried out on these systems. Given the importance of cork thickness in cork quality evaluation, the main objective of this work is to study cork growth in cork oak productive stands spread on the north (Nebrodi Mountains) and south-east (Iblei Mountains) of Sicily. Image analysis techniques were used on cork surfaces of transverse sections of planks to measure cork rings. Dendrochronological analysis was applied to study annual fluctuation on rings growth in relation to various climate parameters in a cork cycle production. Results showed that rainfall, summer drought and temperature are determining factors in controlling cork growth. In siliceous areas of Nebrodi Mountains correlation between cork growth index and rainfall indicates that the rain period from May to September strongly influences phellogen activity. Temperature and water stress indices, on the other hand, show a negative correlation with cork growth. In clay and evolved soils of volcanic plateau of Iblei Mountains January precipitation shows a positive correlation with cork growth index. Also absolute minimum temperature in June and absolute maximum temperature in September show a positive correlation when temperature possibly has influence on phellogen activity during growing season.

Drought-induced nitrous oxide flux dynamics in an enclosed tropical forest
About this Resource: El Niño-La Niña cycles strongly influence dry and wet seasons in the tropics and consequently nitrous oxide (N2O) emissions from tropical rainforest soils. We monitored whole-system and soil chamber N2O fluxes during 5-month-long droughts in the Biosphere 2 tropical forest to determine how rainfall changes N2O production. A consistent pattern of N2O flux changes during drought and subsequent wetting emerged from our experiments. Soil surface drying during the first days of drought, presumably increased gas transport out of the soil, which increased N2O fluxes. Subsequent drying caused an exponential decrease in whole-system (4.0±0.1% day-1) and soil chamber N2O flux (8.9±0.8% day-1; south chamber; and 13.7±1.1% day-1; north chamber), which was highly correlated with soil moisture content. Soil air N2O concentration ([N2O]) and flux measurements revealed that surface N2O production persisted during drought. The first rainfall after drought triggered a N2O pulse, which amounted to 25% of drought-associated reduction in N2O flux and 1.3±0.4% of annual N2O emissions. Physical displacement of soil air by water and soil chemistry changes during drought could not account for the observed N2O pulse. We contend that osmotic stress on the microbial biomass must have supplied the N source for pulse N2O, which was produced at the litter-soil interface. After the pulse, N2O fluxes were consistently 90% of predrought values. Nitrate change rate, nutrient, [N2O], and flux analyses suggested that nitrifiers dominated N2O production during the pulse and denitrifiers during wet conditions. N2O flux measurements in Biosphere 2, especially during the N2O pulse, demonstrate that large-scale integration methods, such as flux towers, are essential for improving ecosystem N2O flux estimates.

Landscape Models to Predict the Influence of Forest Structure on Tassel-Eared Squirrel Populations
About this Resource: The tassel-eared squirrel (Sciurus aberti) is often used as an indicator species in southwestern ponderosa pine (Pinus ponderosa) forests. Because of more than a century of fire suppression, grazing, and timber harvest, these forests have become increasingly prone to catastrophic wildfire, resulting in pressure to implement large-scale treatments to reduce fire threat and restore ecosystem function. However, such treatments could have dramatic effects on tassel-eared squirrels and other wildlife. Because of emerging plans for thinning southwestern forests to reduce fire threat, we undertook a modeling effort to produce spatial data to examine the results of proposed management actions on squirrel habitat. We used squirrel density and recruitment data from 9 study areas located in the Flagstaff region of northern Arizona, USA, linked with spatial data on forest structure developed from remote-sensing imagery. We used a multiscale approach to analyze relationships between forest structure and squirrel density and recruitment. We then used an information-theoretic approach to identify the most parsimonious models for both squirrel density and recruitment. The most strongly supported models of squirrel density included local-scale basal area and .60% canopy cover at the 65-ha spatial scale. For squirrel recruitment, 4 different models that included both local-scale basal area (m2/ha) and variations of canopy cover over extents of approximately 160-305 ha were strongly supported. Using the most parsimonious models, we created spatial data layers representing both squirrel density and recruitment across an 800,000-ha landscape in northern Arizona. Our approach resulted in spatially explicit models that can be used in efforts to predict the effects of forest management on squirrel populations.

Air pollution and climate gradients in western Oregon and Washington indicated by epiphytic macrolichens
About this Resource: Human activity is changing air quality and climate in the US Pacific Northwest. In a first application of non-metric multidimensional scaling to a large-scale, framework dataset, we modeled lichen community response to air quality and climate gradients at 1416 forested 0.4 ha plots. Model development balanced polluted plots across elevation, forest type and precipitation ranges to isolate pollution response. Air and climate scores were fitted for remaining plots, classed by lichen bioeffects, and mapped. Projected 2040 temperatures would create climate zones with no current analogue. Worst air scores occurred in urban-industrial and agricultural valleys and represented 24% of the landscape. They were correlated with: absence of sensitive lichens, enhancement of nitrophilous lichens, mean wet deposition of ammonium >0.06 mg l-1, lichen nitrogen and sulfur concentrations >0.6% and 0.07%, and SO2 levels harmful to sensitive lichens. The model can detect changes in air quality and climate by scoring re-measurements. Lichen-based air quality and climate gradients in western Oregon and Washington are responsive to regionally increasing nitrogen availability and to temperature changes predicted by climate models.

Ecophysiology of a Mangrove Forest in Jobos Bay, Puerto Rico
About this Resource: We studied gas exchange, leaf dimensions, litter production, leaf and litterfall chemistry, nutrient flux to the forest floor, retranslocation rates, and nutrient use efficiency of mangroves in Jobos Bay, Puerto Rico. The fringe forest had a salinity gradient from the ocean (35 per thousand) to a salt flat (100 per thousand) and a basin (about 80 per thousand). Red (Rhizophora mangle), white (Laguncularia racemosa), and black (Avicennia germinans) mangroves were zoned along this gradient. Photosynthetic rates, stomatal conductance, leaf area and weight, leaf specific area, and nutrient use efficiency decreased with increasing salinity, while xylem tension, nutrient retranslocation, and leaf respiration increased with increasing salinity. The concentration of some leaf elements increased with salinity (N, P, Mg, Na) while others decreased (Ca). Leaf specific area was less variable than leaf area or weight. Maximum photosynthesis (12.7 μmol CO2 m-2s-1), leaf conductance (283 mmol CO2 m-2s-1), and litterfall (16.9 Mg ha-1 yr-1) in the fringe were high in comparison with those of other world mangroves. Nutrient flux to the forest floor was also high and nutrient use efficiency was low in this forest. Part of the reason for these high values and low use-efficiencies was the high proportion of nutrient-rich flowers and propagules in litterfall. Nevertheless, access to freshwater in the form of groundwaterdischarge and about 1 m of annual rainfall play a role in the high productivity of the Jobos mangroves.

Conversion and recovery of Puerto Rican mangroves: 200 years of change
About this Resource: Human activities have dramatically reduced the world's area of mangroves just as the ecological services they provide are becoming widely recognized. Improving the conservation tools available to restore lost mangroves would benefit from a better understanding of how human activities influence the conservation of these ecosystems. We took advantage of historical information and long-term landscape analyses to relate land use change with the area of mangroves in Puerto Rico. We found that mangroves experienced dramatic changes over the last 200 years, and four distinct eras of change were visible. During the agricultural era (1800-1940) the area of mangroves declined 45%. As the economy changed to industrial in the late 1940s the area of mangrove increase due to reduced land use pressure on the wetlands. Nevertheless, urban expansion between 1960s and 1970s produced another decline. Public concern for mangrove conservation resulted in the legal protection of all the mangroves in 1972, and since then their area has expanded. We found that past human activity altered the original proportion of mangrove species. The number and size of mangrove-forest fragments was impacted by land use, and urban areas had fewer and smaller fragments than vegetated areas. Uncontrolled expansion of urban areas emerged as a major threat to mangrove conservation. Mangroves are resilient and recover quickly when given an opportunity if the geomorphological and hydrological features of the habitat are not changed by their use. The key to conservation appears to be a combination of the type of human activity in mangrove watersheds combined with strong legal protection. The following steps are recommended: (1) identify the areas that satisfy the ecological requirements of mangrove development; (2) incorporate better zoning regulations to maintain these areas natural and to protect the fluxes of water, nutrients, and organisms in and out of the system; and (3) monitor results.

Initial tree regeneration responses to fire and thinning treatments in a Sierra Nevada mixed-conifer forest, USA
About this Resource: Fire is a driver of ecosystem patterns and processes in forests globally, but natural fire regimes have often been altered by decades of active fire management. Following almost a century of fire suppression, many western U.S. forests have greater fuel levels, higher tree densities, and are now dominated by fire-sensitive, shade-tolerant species. These fuel-loaded conditions can often result in high-intensity crown fires replacing historic low- to moderate-intensity fire regimes. In the mixed-conifer forests of the California Sierra Nevada, thinning and prescribed fire are widely used to reduce fuels and shift future stand composition from shade-tolerant species to more fire-resistant pines (Pinus lambertiana and Pinus jeffreyi) that were historically more abundant. The impacts of these treatments, however, on forest regeneration composition and abundance are unclear. We examined the effects of prescribed fire and common thinning treatments (understory and overstory thinning) on microsite conditions, seed rain, and tree regeneration in an old-growth, mixed-conifer forest in the Sierra Nevada, California, USA. Treatments significantly altered environmental conditions, but there was substantial variation and overlap in conditions among treatments. Seed rain of shade-tolerant Abies concolor and Calocedrus decurrens was 5-26 times greater than P. jeffreyi and P. lambertiana, creating inertia in efforts to shift stands towards increased pine abundance. Survival of Pinus germinants was greatest in burned microsites. The burn-overstory thin treatment had both the highest mortality of advanced A. concolor and C. decurrens regeneration and the greatest increase in pine regeneration. Species occupied microsites gradating from low light/high moisture to high light/low moisture in the order: C. decurrens, A. concolor, P. lambertiana, and P. jeffreyi. Results suggest prescriptions may need to thin mature A. concolor and C. decurrens to significantly reduce their seed rain, create an abundance of burned open microsites, or plant Pinus seedlings to shift regeneration composition in treated stands.

White-tailed deer herbivory and timber harvesting rates: Implications for regeneration success
About this Resource: Herbivory by white-tailed deer (Odocoileus virginianus) can affect forest regeneration. Typical measures to ensure forest regeneration have included physical barriers or direct manipulation of deer densities. However, altering silvicultural practices to provide abundant deer forage has not been tested thoroughly. We examined browse species preferences and changes in herbivory rates in 1-6 year old regeneration areas from 2001 to 2004 in the central Appalachians on the MeadWestvaco Wildlife and Ecosystem Research Forest in West Virginia. Woody vegetation reached the maximum plot coverage by the 4th growing season. However, the establishment of less abundant woody species, such as northern red oak (Quercus rubra), may be inhibited when browsed greater than or proportionally to occurrence. Herbivory rates declined precipitously as the amount of early successional habitat increased on our study site. We conclude that providing approximately 14% of an area in well-distributed, even-aged managed forests can have substantial impacts on reducing herbivory rates. However, management practices also should consider harvesting effects on hard mast production, habitat requirements of other species, and hardwood lumber marketability.

Changes in conifer and deciduous forest foliar and forest floor chemistry and basal area tree growth across a nitrogen (N) deposition gradient in the northeastern US
About this Resource: We evaluated foliar and forest floor chemistry across a gradient of N deposition in the Northeast at 11 red spruce (Picea rubens Sarg.) sites in 1987/1988 and foliar and forest floor chemistry and basal area growth at six paired spruce and deciduous sites in 1999. The six red spruce plots were a subset of the original 1987/1988 spruce sites. In 1999, we observed a significant correlation between mean growing season temperature and red spruce basal area growth. Red spruce and deciduous foliar %N correlated significantly with N deposition. Although N deposition has not changed significantly from 1987/1988 to 1999, net nitrification potential decreased significantly at Whiteface. This decrease in net potential nitrification is not consistent with the N saturation hypothesis and suggests that non-N deposition controls, such as climatic factors and immobilization of down dead wood, might have limited N cycling. Data from the 1999 remeasurement of the red spruce forests suggest that N deposition, to some extent, is continuing to influence red spruce across the northeastern US as illustrated by a significant correlation between N deposition and red spruce foliar %N. Our data also suggest that the decrease in forest floor %N and net nitrification potential across sites from 1987 to 1999 may be due to factors other than N deposition, such as climatic factors and N immobilization in fine woody material (<5 cm diameter).

Grazing impacts on spatial distribution of soil and herbaceous characteristics in an Australian tropical woodland
About this Resource: This study examined effects of different levels of applied grazing pressures on herbaceous vegetation (standing crop, basal area, size and spacing of grass tussocks) and soil properties (total soil C, total N, total P, and soil-borne plant material [roots and surface litter] in the A horizon) around grass tussocks of a dry eucalypt woodland (dominant woody components; Eucalyptus xanthoclada and Corymbia erythrophloia of northern Australia. Grass tussocks influenced total soil C and N at small (<20 cm) spatial scales, and applied grazing pressures significantly (p<0.05) affected all soil properties except total P. Concentrations of N and C were highest at locations close to plants, and levels in proximity to plants declined under sustained heavy grazing. Paddocks receiving heavier grazing pressures also produced less standing crop and tussocks were smaller and more widely dispersed. Further, areas with high amounts of soil C, N and soil-borne plant materials were smaller and more widely dispersed under heavy grazing. Alternatively, conservative grazing pressure in combination with wet season grazing deferments allowed conservation of landscape condition. Eucalypt woodlands in northern Australia have low resistance to disturbance, and limited resilience to recover following disturbance. As such, the effects of disturbance on these areas should be monitored by combinations of plant (basal area, plant spacing) and soil (soil-borne plant material, total N) characteristics capable of detecting degradation at the earliest stages possible.

TOASTED FORESTS - EVERGREEN RAIN FORESTS OF TROPICAL ASIA UNDER DROUGHT STRESS
About this Resource: This paper has been written to make an enormous threat known to the public. We all know about the forest fires that raged in Indonesia and parts of Malaysia in 1997, and about the noxious haze covering the whole region, but only a few experts are aware of the threat of extinction of the last rain forest areas in Southeast Asia. As this paper will show, droughts have always been a part of these ecosystems, which normally receive plenty of rain. Mild droughts can be regarded as slight or medium disturbances, which can even have a stimulating effect according to the Intermediate Disturbance Hypothesis. However, severe droughts and fires have a destructive effect, which will only be overcome in successional stages. Logging and forest fragmentation reduce the ability of forests to overcome severe droughts. Forest fires rage in selectively logged forests, whereas they are extremely rare in undisturbed rain forests. Forest regeneration in fragmented forests is disturbed, so that we have to expect a total degradation of even effectively protected forest areas. Due to drought and fire, the remnant rain forest areas are being roasted like slices of toast . New research is also revealing that rain forests under drought stress consume more oxygen than they produce. The "green lung" and carbon sink are thus out of function. Furthermore, severe ENSO-(El Niño/Southern Oscillation)-droughts have been increasing in recent years. The consequences both for development of the region and for the whole atmosphere are imminent. Forest fires during ENSO droughts have caused extensive damage to forests and plantations, and noxious haze clouds in the whole region. Awareness about ENSO and droughts exists and is growing within the local population. Strict regulations, drought and fire alerts, and law enforcement can reduce at least the effects of drought. A logging ban, also including selective logging, may have to be considered. While this paper covers the whole of tropical Asia, it focuses on Sumatra, Borneo and the Malay Peninsula, which are the main evergreen rain forest areas. Other areas in the region have either seasonal vegetation, which is more drought adapted, or only small pockets of evergreen rain forest depending on local rain exposure - or the lowland forests have disappeared. The paper concentrates on Western Indonesia, Malaysia and the very south of Thailand.

Thirty thousand years of vegetation development and climate change in Angola (Ocean Drilling Program Site 1078)
About this Resource: ODP Site 1078 situated under the coast of Angola provides the first record of the vegetation history for Angola. The upper 11 m of the core covers the past 30 thousand years, which has been analysed palynologically in decadal to centennial resolution. Alkenone sea surface temperature estimates were analysed in centennial resolution. We studied sea surface temperatures and vegetation development during full glacial, deglacial, and interglacial conditions. During the glacial the vegetation in Angola was very open consisting of grass and heath lands, deserts and semi-deserts, which suggests a cool and dry climate. A change to warmer and more humid conditions is indicated by forest expansion starting in step with the earliest temperature rise in Antarctica, 22 thousand years ago. We infer that around the period of Heinrich Event 1, a northward excursion of the Angola Benguela Front and the Congo Air Boundary resulted in cool sea surface temperatures but rain forest remained present in the northern lowlands of Angola. Rain forest and dry forest area increase 15 thousand years ago. During the Holocene, dry forests and Miombo woodlands expanded. Also in Angola globally recognised climate changes at 8 thousand and 4 thousand years ago had an impact on the vegetation. During the past 2 thousand years, savannah vegetation became dominant.

CARACTERIZATION OF SCOLYTIDAE FAMILY (INSECTA: COLEOPTERA) IN THREE FOREST ENVIRONMENTS
About this Resource: Insects are potential cause of damage in forests and the family Scolytidae is responsible for major death of trees in the world. This research studied Scolytidae insects at three areas, two in rain forests and one in an eucalyptus plantation, through faunistic indexes, and to determined the correlation between number of Scolytidae and temperature and relative humidity. A total of fifteen ethanolic traps were used from July 1998 to June 1999. A total of 35 species of Scolytidae was identified, with 48.6% of then occurring at all areas. Twenty nine species were xylomicetophagus. The genus Xyleborus presented the higher number of species. In the Eucalyptus plantation area, six species constantly appeared and positive correlation (54.5%) was found between the number of insects and monthly mean temperature.

Environmental and Biotic Controls over Aboveground Biomass Throughout a Tropical Rain Forest
About this Resource: The environmental and biotic factors affecting spatial variation in canopy three-dimensional (3-D) structure and aboveground tree biomass (AGB) are poorly understood in tropical rain forests. We combined field measurements and airborne light detection and ranging (lidar) to quantify 3-D structure and AGB across a 5,016 ha rain forest reserve on the northeastern flank of Mauna Kea volcano, Hawaii Island. We compared AGB among native stands dominated by Metrosideros polymorpha found along a 600-1800 m elevation/climate gradient, and on three substrate-age classes of 5, 20, and 65 kyr. We also analyzed how alien tree invasion, canopy species dominance and topographic relief influence AGB levels. Canopy vertical profiles derived from lidar measurements were strong predictors (r ² = 0.78) of AGB across sites and species. Mean AGB ranged from 48 to 363 Mg ha⁻¹ in native forest stands. Increasing elevation corresponded to a 53-84% decrease in AGB levels, depending upon substrate age. Holding climate constant, changes in substrate age from 5 to 65 kyr corresponded to a 23-53% decline in biomass. Invasion by Psidium cattleianum and Ficus rubiginosa trees resulted in a 19-38% decrease in AGB, with these carbon losses mediated by substrate age. In contrast, the spread of former plantation tree species Fraxinus uhdei corresponded to a 7- to 10-fold increase in biomass. The effects of topographic relief at both local and regional scales were evident in the AGB maps, with poorly drained terrain harboring 76% lower biomass than forests on well-drained relief. Our results quantify the absolute and relative importance of environmental factors controlling spatial variation in tree biomass across a rain forest landscape, and highlight the rapid changes in carbon storage incurred following biological invasion.

Seed Invasion Filters and Forest Fire Severity
About this Resource: Forest seed dispersal is altered after fire. Using seed traps, we studied impacts of fire severity on timing of seed dispersal, total seed rain, and seed rain richness in patches of high and low severity fire and unburned Douglas-fir (Pseudotsuga menziesii) forests in the Fischer and Tyee fire complexes in the eastern Washington Cascades. Unburned plots had the lowest average seed production. The high severity fire patches in the Fischer Fire Complex had a higher total seed production than low severity fire patches of the same complex. At the Tyee Fire Complex, the total seed production for each of the two fire severities was similar, but the period of maximum seed dispersal was later for high severity than low severity fire. Seed rain at the Fischer Fire patches (sampled one year after the fire) was predominantly composed of annual species, while that of the Tyee Fire patches (sampled nine years after fire) was predominantly perennial species. Seed rain richness was greater in Tyee high severity patches than paired low severity fire patches. In these paired Tyee patches the average number of new seed species (species not found in the extant plot vegetation) was greater for high severity than low severity fire. Our results suggest that high severity fire plots are more porous to seed rain than low severity plots. Intact forest canopies may filter seed rain and reduce seed influx, while high severity fires are more open to invasion by seed dispersal.

Neogene woods from western Peruvian Amazon and palaeoenvironmental interpretation
About this Resource: Vegetation dynamics in the Western Amazonian Basin are studied using knowledge of palaeobotany. Fossil wood specimens from eroded sediments on the banks of the Amazon in the Iquitos region of Peru come from layers dated as Middle Miocene to Pliocene. Samples include branch fragments or entire tree trunks either as compressed lignites or silicified stems. The wood can be assigned to modern genera of various families still present in the South American flora. Samples from the Middle Miocene Pebas Formation show affinities with taxa now occurring in rain forests: Anacardium (Anacardiaceae), Calophyllum (Clusiaceae), Buchenavia and Terminalia (Combretaceae), Andira / Hymenolobium (Fabaceae), Humiriastrum (Humiriaceae), Cariniana and Eschweilera (Lecythidaceae), Guarea (Meliaceae) and Mimosaceae, which indicates that part of the Recent Amazon Basin flora pre-dates contact with North America. Growth rings are absent or indistinct in the fossils, a characteristic feature of low-elevation rain forests. The fossil assemblage evokes “Hylaea Amazonia” and especially the “terra firme” forests of the modern Amazon delta and surroundings. Fossil wood samples from the Pliocene Amazonas Formation resemble Cedrela (Meliaceae) and are semi ring-porous. The Cedrela wood occurence shows a vegetation change between mid-Miocene and now in the western Amazon Basin.