Surface modelling of global terrestrial ecosystems under three climate change scenarios

A high accuracy and speed method (HASM) of surface modelling is developed to find a solution for error problem and to improve computation speed. A digital elevation model (DEM) is established on spatial resolution of 13.5 km × 13.5 km. Regression formulations among temperature, elevation and latitude are simulated in terms of data from 2766 weather observation stations scattered over the world by using the 13.5 km × 13.5 km DEM as auxiliary data. Three climate scenarios of HadCM3 are refined from spatial resolution of 405 km × 270 km to 13.5 km × 13.5 km in terms of the regression formulations. HASM is employed to simulate surfaces of mean annual bio-temperature, mean annual precipitation and potential evapotranspiration ratio during the periods from 1961 to 1990 (T₁), from 2010 to 2039 (T₂), from 2040 to 2069 (T₃), and from 2070 to 2099 (T₄) on spatial resolution of 13.5 km × 13.5 km. Three scenarios of terrestrial ecosystems on global level are finally developed on the basis of the simulated climate surfaces. The scenarios show that all polar/nival, subpolar/alpine and cold ecosystem types would continuously shrink and all tropical types, except tropical rain forest in scenario A1Fi, would expand because of the climate warming. Especially at least 80% of moist tundra and 22% of nival area might disappear in period T₄ comparing with the ones in the period T₁. Tropical thorn woodland might increase by more than 97%. Subpolar/alpine moist tundra would be the most sensitive ecosystem type because its area would have the rapidest decreasing rate and its mean center would shift the longest distance towards west. Subpolar/alpine moist tundra might be able to serve as an indicator of climatic change. In general, climate change would lead to a continuous reduction of ecological diversity.     

Impacts of daily weather variability on simulations of the Canadian boreal forest

This study examines the importance of climate variability when simulating forest succession using a process-based model of stand development. The FORSKA-2V forest gap model, originally developed for forcing with monthly mean climate data, was modified to accept daily weather data. The model's performance was compared using different temporal resolutions of forcing along a bioclimatic transect crossing the boreal region of central Canada, including the aspen-parkland and forest-tundra ecotones. Forcing the model with daily weather data improved the simulation of key attributes of present-day forest along the transect, particularly at the ecotones, compared to forcing with monthly data or long term averages. The results support the hypothesis that climatic variability at daily time-scales is an important determinant of present-day boreal forest composition and productivity. To simulate boreal forest response to climatic change it will be necessary to create climatic scenarios that include plausible projections of future daily scale variability.     

Long-term simulation of the effect of climate changes on the growth of main Central-European forest tree species

The simulation of forest production until 2100 under different environmental scenarios and current management practices was performed using a process-based model BIOME-BGC previously parameterized for the main Central-European tree species, and adapted to include forest management practices. Three climatic scenarios (HadCM3, NCAR-PCM, CSIRO) used were taken from the IPCC database created within the 3^rd Assessment Report. They were combined with a scenario of CO₂ concentration development and a scenario of N deposition. The control scenario considered no changes of climatic characteristics, CO₂ concentration and N deposition.     

Modeling the Effect of Climate Change on the Distribution of Oak and Pine Species of Mexico

Abstract:  We examined the vulnerability of 34 species of oaks ( Quercus ) and pines ( Pinus ) to the effects of global climate change in Mexico. We regionalized the HadCM2 model of climate change with local climatic data (mean annual temperature and rainfall) and downscaled the model with the inverse distance-weighted method. Databases of herbaria specimens, genetic algorithms (GARP), and digital covers of biophysical variables that affect oaks and pines were used to project geographic distributions of the species under a severe and conservative scenario of climate change for the year 2050. Starting with the current average temperature of 20.2 °C and average precipitation of 793 mm, under the severe warming scenario mean temperature and precipitation changed to 22.7 °C and 660 mm, respectively, in 2050. For the conservative warming scenario, these variables shifted to 21.8 °C and 721 mm. Responses to the different scenarios of climate change were predicted to be species-specific and related to each species climate affinity. The current geographic distribution of oaks and pines decreased 7–48% and 0.2–64%, respectively. The more vulnerable pines were Pinus rudis , P. chihuahuana , P. oocarpa , and P. culminicola , and the most vulnerable oaks were Quercus crispipilis , Q. peduncularis , Q. acutifolia , and Q. sideroxyla . In addition to habitat conservation, we think sensitive pine and oak species should be looked at more closely to define ex situ strategies (i.e., seed preservation in germplasm banks) for their long-term conservation. Modeling climatic-change scenarios is important to the development of conservation strategies.     

Climate Change,Multiple Stressors,and the Decline of Ectotherms

Climate change is believed to be causing declines of ectothermic vertebrates, but there is little evidence that climatic conditions associated with declines have exceeded critical (i.e., acutely lethal) maxima or minima, and most relevant studies are correlative, anecdotal, or short‐term (hours). We conducted an 11‐week factorial experiment to examine the effects of temperature (22 °C or 27 °C), moisture (wet or dry), and atrazine (an herbicide; 0, 4, 40, 400 μg/L exposure as embryos and larvae) on the survival, growth, behavior, and foraging rates of postmetamorphic streamside salamanders (Ambystoma barbouri), a species of conservation concern. The tested climatic conditions were between the critical maxima and minima of streamside salamanders; thus, this experiment quantified the long‐term effects of climate change within the noncritical range of this species. Despite a suite of behavioral adaptations to warm and dry conditions (e.g., burrowing, refuge use, huddling with conspecifics, and a reduction in activity), streamside salamanders exhibited significant loss of mass and significant mortality in all but the cool and moist conditions, which were closest to the climatic conditions in which they are most active in nature. A temperature of 27 °C represented a greater mortality risk than dry conditions; death occurred rapidly at this temperature and more gradually under cool and dry conditions. Foraging decreased under dry conditions, which suggests there were opportunity costs to water conservation. Exposure to the herbicide atrazine additively decreased water‐conserving behaviors, foraging efficiency, mass, and time to death. Hence, the hypothesis that moderate climate change can cause population declines is even more plausible under scenarios with multiple stressors. These results suggest that climate change within the noncritical range of species and pollution may reduce individual performance by altering metabolic demands, hydration, and foraging effort and may facilitate population declines of amphibians and perhaps other ectothermic vertebrates. Cambio Climático, Estresantes Múltiples y la Declinación de Ectotermos     

中国东部南北样带中南段典型植被类型NDVI变化分析

以IGBP第15条国际标准样带——中国东部南北样带中南段的植被为主要研究对象，对该区域应用NDVI(normalized difference vegetation index)数据进行植被类型划分，共划分为三大类35小类．在此基础上，选择6种不同气候区域典型的森林植被类型，对其NDVI变化进行分析，从而得出：NDVI随着纬度的降低变化逐渐减小；通过研究经向年内：NDVI变化，发现4月份研究区域南北：NDVI指数变化最明显；分析NDVI均值变化可知，从暖温带到北亚热带植被指数NDVI形成明显的阶跃，从而判定植被指数NDVI对短期气候变化具有明显的指示性，并发现通过植被指数NDVI的季节变化曲线，可以较为准确地判定森林、草原、农作物等大类型，图4表1参15。     

辽东栎叶片气孔特征参数的时空变异

利用数码图像显微镜处理系统 ,对 2 0世纪 30年代至 80年代不同植被区域内辽东栎叶片气孔特征参数进行了较为系统的观测 ,明确了辽东栎叶片气孔特征参数的变化范围 ,并对其时空变异规律进行研究 .结果表明 ,从时间分布角度 ,由 30年代至 80年代 ,暖温带落叶阔叶林区域中气孔长度、面积变化呈上升趋势 ,而气孔宽度、密度呈下降趋势 ;亚热带常绿阔叶林区域中 4个气孔特征参数均逐年递增 ;青藏高原高寒植被区域中除气孔长度下降外 ,其它 3个气孔特征参数均逐年递增 .从空间分布角度 ,在由北部至南部再到西南部分布的暖温带落叶阔叶林、亚热带常绿阔叶林至青藏高原高寒植被区域 ,30年代中 ,气孔长度、面积呈上升趋势 ,而气孔宽度、密度呈下降趋势 ;5 0年代中 ,不同植被类型区之间 ,除气孔密度差异较大外 ,其它 3个气孔特征参数差异均不明显 .图 1表 1参 9     

Multidecadal climate variability and climate interactions affect subalpine fire occurrence, western Colorado (USA)

This study investigates the influence of climatic variability on subalpine forest fire occurrence in western Colorado during the AD 1600-2003 period. Interannual and multidecadal relationships between fire occurrence and the El Ni?o Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) were examined, in addition to the effects of phase interactions among these oscillations. Fires occurred during short-term periods of significant drought and extreme cool (negative) phases of ENSO and PDO and during positive departures from mean AMO index. At longer time scales, fires exhibited 20-year periods of synchrony with the cool phase of the PDO, and 80-year periods of synchrony with extreme warm (positive) phases of the AMO. Years of combined positive AMO and negative ENSO and PDO phases represent "triple whammies" that significantly increased the occurrence of drought-induced fires. Fires were synchronous with this phase combination over 0-30 year periods and distinctly asynchronous with the opposite phase combination. Overall, because fires are synchronous at supra-annual to multidecadal time scales with warm AMO events, particularly when combined with cool ENSO and PDO phases, this suggests that we may be entering a qualitatively different fire regime in the next few decades due to the recent shift in 1998 to a likely long-term warm AMO phase. Although uncertainty remains regarding the effects of CO2-induced warming at regional scales, given the multidecadal persistence of the AMO there is mounting evidence that the recent shift to the positive phase of the AMO will promote higher fire frequencies in the region.     

Influence of Tibetan Plateau on vegetation distributions in East Asia: a modeling perspective

Understanding the current distribution of vegetation and its interaction with climate regularity and surface irregularity is important for predicting its future change. In comparison with other regions of the world, the vegetation distribution in East Asia is unique, such as the location of desert belt, subtropical evergreen forests and deciduous broadleaved forest; but the underlying causes are still not clear. While some researchers have proposed on the effect of monsoons as causal mechanisms, others have suggested that the direct cause might be the rising of the Tibetan Plateau (TP). However, the relative importance of these two mechanisms remains unknown, and cannot be directly tested at large spatial and temporal scales. Here we construct the possible vegetation distribution in this area (15°N–60°N, 60°E–150°E) with assumption that there were no TP (e.g., its elevation were 1000 m and roughly equal to its surroundings), using a General Circulation Model and the Holdridge Life Zones System. Our simulations demonstrated that TP affected the vegetation distribution and patterns in East Asia significantly. Without TP the area of warm temperate forest and subtropical forest would increase, but desert area would decrease. The effects of TP should be considered when studying vegetation dynamics in East Asia under climate change. The results are also useful for explaining the plant biogeography in this region.     

Woody plant richness and NDVI response to drought events in Catalonian (northeastern Spain) forests

The role of species diversity on ecosystem resistance in the face of strong environmental fluctuations has been addressed from both theoretical and experimental viewpoints to reveal a variety of positive and negative relationships. Here we explore empirically the relationship between the richness of forest woody species and canopy resistance to extreme drought episodes. We compare richness data from an extensive forest inventory to a temporal series of satellite imagery that estimated drought impact on forest canopy as NDVI (normalized difference vegetation index) anomalies of the dry summer in 2003 in relation to records of previous years. We considered five different types of forests that are representative of the main climatic and altitudinal gradients of the region, ranging from lowland Mediterranean to mountain boreal-temperate climates. The observed relationship differed among forest types and interacted with the climate, summarised by the Thorntwaite index. In Mediterranean Pinus halepensis forests, NDVI decreased during the drought. This decrease was stronger in forests with lower richness. In Mediterranean evergreen forests of Quercus ilex, drought did not result in an overall NDVI loss, but lower NDVI values were observed in drier localities with lower richness, and in more moist localities with higher number of species. In mountain Pinus sylvestris forests NDVI decreased, mostly due to the drought impact on drier localities, while no relation to species richness was observed. In moist Fagus sylvatica forests, NDVI only decreased in plots with high richness. No effect of drought was observed in the high mountain Pinus uncinata forests. Our results show that a shift on the diversity-stability relationship appears across the regional, climatic gradient. A positive relationship appears in drier localities, supporting a null model where the probability of finding a species able to cope with drier conditions increases with the number of species. However, in more moist localities we hypothesize that the proportion of drought-sensitive species would increase in richer localities, due to a higher likelihood of co-occurrence of species that share moist climatic requirements. The study points to the convenience of considering the causes of disturbance in relation to current environmental gradients and historical environmental constraints on the community.     

北方和温带森林生态系统的蒸腾耗水

北方和温带森林地处气候变化敏感的中高纬度地区,认识其蒸腾耗水过程的时卒动态及其控制因子是评价和预测森林在气候系统中作用的基础.本文综述了北方和温带森林蒸腾耗水的近期研究结果,从叶片、个体和林分3个尺度综合分析了树木蒸腾耗水的变异性及其影响因子,并探讨了其中的尺度转换问题.主要结论如下:尽管相同生活型树木的蒸腾耗水量变异性较大,但针叶树的平均蒸腾耗水量在叶片和个体尺度上显著低于阔叶树,而在林分尺度上针叶林和阔叶林之间差异不显著.3个尺度上的蒸腾作用均受太阳辐射、蒸汽压亏缺、土壤含水量等环境因子的影响,且存在因子间的交互作用,但主导控制因子因时空尺度而异.单株树木蒸腾量与胸径、边材面积和树高均呈显著正相关;林分日蒸腾量最大值与叶面积指数相关显著,而生长季日蒸腾量平均值则与年降水量和年均温呈正相关.这些蒸腾速率与生物环境因子之间的关系模型和不同空间尺度之间的联系是目前森林蒸腾过程尺度转换的基础.本文还讨论了该领域研究中存在的问题和研究热点.     

Impact of nutrient removal through harvesting on the sustainability of the boreal forest

The cycling of base cations (K, Ca, Mg, and Na) was investigated in a boreal balsam fir forest (the Lake Laflamme Watershed) between 1999 and 2005. Base cation budgets were calculated for the soil rooting zone that included atmospheric deposition and soil leaching losses, two scenarios of tree uptake (whole-tree and stem-only harvesting), and three scenarios of mineral weathering, leading to six different scenarios. In every scenario there was a net accumulation of Mg within the soil exchangeable reservoir, while Ca accumulated in four scenarios. Potassium was lost in five of the six scenarios. Contrary to Ca and Mg, immobilization of K within tree biomass (69 mol x ha(-1) x yr(-1)) was the main pathway of K losses from the soil exchangeable reservoir, being five times higher than losses via soil leaching (14 mol x ha(-1) x yr(-1)). The amounts of K contained within the aboveground biomass and the exchangeable soil reservoir were 3.3 kmol/ha and 4.2 kmol/ha, respectively. Whole-tree harvesting may thus remove 44% of the K that is readily available for cycling in the short term, making this forest sensitive to commercial forestry operations. Similar values of annual K uptake as well as a similar distribution of K between tree biomass and soil exchangeable reservoirs at 14 other coniferous sites, distributed throughout the boreal forest of Quebec, suggest that the Lake Laflamme Watershed results can be extrapolated to a much larger area. Stem-only harvesting, which would reduce K exports due to biomass removal by 60%, should be used for these types of forest.     

The Future of Tropical Species on a Warmer Planet

Abstract: Modern global temperature and land cover and projected future temperatures suggest that tropical forest species will be particularly sensitive to global warming. Given a moderate greenhouse gas emissions scenario, fully 75% of the tropical forests present in 2000 will experience mean annual temperatures in 2100 that are greater than the highest mean annual temperature that supports closed‐canopy forest today. Temperature‐sensitive species might extend their ranges to cool refuges, defined here as areas where temperatures projected for 2100 match 1960s temperatures in the modern range. Distances to such cool refuges are greatest for equatorial species and are particularly large for key tropical forest areas including the Amazon and Congo River Basins, West Africa, and the upper elevations of many tropical mountains. In sum, tropical species are likely to be particularly sensitive to global warming because they are adapted to limited geographic and seasonal variation in temperature, already lived at or near the highest temperatures on Earth before global warming began, and are often isolated from cool refuges. To illustrate these three points, we examined the distributions and habitat associations of all extant mammal species. The distance to the nearest cool refuge exceeded 1000 km for more than 20% of the tropical and less than 4% of the extratropical species with small ranges. The biological impact of global warming is likely to be as severe in the tropics as at temperate and boreal latitudes.     

Multi-season climate synchronized forest fires throughout the 20th century, northern Rockies, U.S.A

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 Ni?o-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.     

Effects of Clear-Cut Harvesting on Boreal Ground-Beetle Assemblages (Coleoptera: Carabidae) in Western Canada

We compared pitfall catches from four types of mature lodgepole pine—white spruce forest with those from five age classes of young forest regenerating subsequent to clear-cutting. Ground beetles were most abundant in the youngest sites (1–2 years since cutting) and in the mature stands on moist soil. Species richness was higher in regenerating sites than in mature forest. Cluster analysis grouped the ground-beetle fauna according to forest age and forest type, suggesting that there is a general pattern of recovery after logging. Responses of common species to forest cutting fell into three groups: (1) forest generalists (2 species) were not dramatically affected, (2) species of open habitat (27 species) appeared and/or increased in abundance, and (3) mature forest species (10 species) disappeared or decreased in abundance. Populations of many mature forest species appear to recover following logging, but several specialists did not recolonize even the oldest regenerating stands. Furthermore, fragmentation and creation of large areas of relatively homogeneous young forest stages through logging may have detrimental long-term effects even on the more abundant forest generalists. We must better understand subtle variations in habitat in order to maintain invertebrate diversity while harvesting the boreal forest.     

热带增宽及其对中国东部亚热带森林植被的影响

全球气候变暖已是不争的事实,现今气候变暖的趋势已由每百年（1901--2000）增加0．6℃的记录升高为0．74℃（1906—2005）。其中高纬度地区增温特别显著,成为世界关注的热点。与之对比,热带地区的气候变化以及热带森林对它的反应报道甚少。事实上,自1970s中期以来,热带温度是每lO年升高0．26oC;同时气候模型预测到本世纪末热带地区温度将上升2．1-4．5℃。这些预测是有根据的,但究竟不是直接的证据。因此,本文综合了许多专家对热带地球物理学和大气层特性的多年观测、分析和研究的成果,其结论认为：至少自1979年以来许多热带大气层固有的特征发生变化并向地球极地推进和位移,这些根据是：（1）热带高空的哈德利环流增强并向极地扩展;（21位于热带边缘的亚热带射流向极地移动;（3）热带亚热带对流层顶高度和位置的变化;（4）热带高空平流层臭氧柱总量浓度的变化。据上述特征的变化证明数十年来热带向极地增宽纬度2°～5°（～8°）,一般确认为2．5°。由于热带增宽的驱动,广东50年的气温记录表明气候持续变暖,按增暖趋势推算,预估到2020年,现在的雷州半岛南部可能变成中热带;广东东南沿海将由目前的南亚热带变为北热带（占全省面积约1／3）;其余大部分地区为南亚热带;中亚热带基本上将退出广东（仅剩下东北角一偶）。此预测意味着南岭地区将成为南亚热带的边缘地。     

Examining the effects of alternative management strategies on landscape-scale forest patterns in northeastern Minnesota using LANDIS

Spatial modeling of forest patterns can provide information on the potential impact of various management strategies on large landscapes over long time frames. We used LANDIS, a stochastic, spatially-explicit, ecological landscape model to simulate 120 years of forest change on the Nashwauk Uplands, a 328,000 ha landscape in northeastern Minnesota that lies in the transition between boreal and temperate forests. We ran several forest management scenarios including current harvesting practices, no harvests, varied rotation ages, varied clearcut sizes, clustered clearcuts, and landowner coordination. We examined the effects of each scenario on spatial patterns of forests by covertype, age class, and mean and distribution of patch sizes. All scenarios reveal an increase in the spruce-fir (Picea-Abies) covertype relative to the economically paramount aspen-birch (Populus-Betula) covertype. Our results also show that most covertypes occur in mostly small patches <5 ha in size and the ability of management to affect patch size is limited by the highly varied physiography and landuse patterns on the landscape. However, coordination among landowners, larger clearcuts, and clustered clearcuts were all predicted to increase habitat diversity by creating some larger patches and older forest patches. These three scenarios along with the no harvest scenario also create more old forest than current harvesting practices, by concentrating harvesting on some portion of the landscape. The no harvest scenario retained large, fire-regenerated aspen-birch patches. Harvests fragment large aspen-birch patches by changing the age structure and releasing the shade-tolerant understory species. More sapling forest, and larger sapling patches resulted from the shortened rotation scenario.     

Beurteilung des Ozonrisikos für die Waldregionen Bayerns am Beispiel des Jahres 2002 und des Extremtrockenjahres 2003 auf der Basis der externen Ozonexposition und der internen Ozonaufnahme

Background, aim, and scope Increasing background concentrations of ground-level tropospheric ozone and more frequent and prolonged summer drought incidences due to climate change are supposed to increase the stress on Bavarian forests. For such scenarios growth reduction and yield losses are predicted. Sustainable forest management in Bavaria aims to significantly increase the proportion of beech (Fagus sylvatica L.) because of its broad ecological amplitude. In our regional study different approaches for calculating ozone impact were used to estimate the risks for Bavarian forests in the average climatic, rather moist year 2002 and the extremely dry year 2003.Materials and methods Measurements were conducted for eleven forest ecosystem sites and two forest research sites representing typical Bavarian forest stands under different climatic conditions and situated in different altitudes. For risk assessment currently used approaches were applied either based on the calculation of the cumulative ozone exposure (external dose; MPOC maximal permitted ozone concentration; critical level AOT40_phen? accumulated ozone exposure over a threshold of 40 nl [O₃] l^–1, for the effective phenolgy of beech) or based on the calculation of the phytomedically relevant ozone flux into the stomata (internal dose, critical level AF_st>1,6, accumulated stomatal flux above a flux threshold of 1.6 nmol O₃?m^–2 PLA; PLA = projected leaf area). For calculations continuously recorded ozone concentrations and meteorological and phenological data from nearby rural open field background measuring stations from the national air pollution control and from forested sites were used. Additionally ozone induced leaf symptoms were assessed.Results The exposure-based indices AOT40_phen and MPOC as well as the flux-based index AF_st>1.6suggest that Bavarian forests are at risk from O₃ during a rather moist average year concerning climate conditions (2002) as well as in an extreme dry year (2003). Thus, growth reductions of 5?% are predicted when thresholds are exceeded. Threshold exceedance occurred in both years at all plots, mostly already at the beginning of the growing season and often even many times over. Ozone induced leaf symptoms could be detected only on a few plots in a very slight occurrence.Discussion The results for the applied critical level indices differed depending on climatic conditions during the growing seasons: Regarding exposure-based indices, the highest degree of threshold exceedance occurred in the dry year of 2003 at all plots; the flux-based approach indicated the highest stomatal ozone uptake and thus an increased risk at moist sites or during humid years, whereas the risk was decreasing at dry sites with prolonged water limitation. Hence, soil and accordingly plant water availability was the decisive factor for the flux-modelled internal ozone uptake via stomata. Drought and increased ozone impact can generate synergistic, but also antagonistic effects for forest trees. At water limited rather dry forest sites restricted transpiration and thus production, but concurrently lower ozone uptake and reduced risk for damage can be expected.Conclusions, recommendations, and perspectives For realistic site-specific risk assessment in forest stands the determination of the internal ozone dose via modeling flux based internal stomatal ozone uptake is more appropriate than the calculation of the external ozone dose. The predicted 5?% growth reductions are in discrepancy with the frequently observed increment increase during the last decades in forest stands. Comprehensive and significant statistical verification for ozone induced forest growth reduction as well as the systematic validation of thresholds for ozone in the field is still lacking. However, a multiplicity of different specific new and retrospective growth analysis data should allow closing the gap. Moreover, the determination of canopy transpiration with sap flow measurements is a novel approach to provide cause-effect related, site specific results for the effective internal ozone dose as well as for canopy water supply and consecutively for regional risk estimation. A further future objective is the refinement of O₃ flux modelling by further consideration of soil/water budget characteristics and the above mentioned improved estimations of crown and canopy transpiration. Further, the introduction of threshold ranges for forest trees in view of their specific regional climatic conditions and their validation in real forest stands is necessary for developing meaningful ozone risk predictions for forests.     

Relation of Terrestrial-Breeding Amphibian Abundance to Tree-Stand Age

There is a lack of research on the effects of logging on Canadian amphibians. We compared the abundance of terrestrial salamanders in old-growth forests with that in young and mature post-harvest stands. We also measured habitat features of amphibians and contrasted these with old-growth and harvested stands to assess the effects of forest harvest. Quadrat searches demonstrated that clearcut harvesting reduces terrestrial amphibian populations by up to 70% in coastal old-growth forests. We suggest that this reduction results from a decrease in availability of moist microhabitats. Salamander densities within 10 meters of streams in managed stands were similar to those near and away from streams in old growth. We recommend that forest managers recognize the needs of terrestrial amphibians and help maintain amphibian populations by preserving cool, moist habitats. This can be accomplished within cutblocks by (1) maintaining an even distribution of logs and snags as stable, moist microhabitats; (2) retaining some understory as sources of shade, and (3) preserving streamside buffers. Managers must also ensure some level of landscape connectivity to enable climate-sensitive amphibians to disperse and recolonize marginal habitats.     

Climate effects on fire regimes and tree recruitment in Black Hills ponderosa pine forests

Climate influences forest structure through effects on both species demography (recruitment and mortality) and disturbance regimes. Here, I compare multi-century chronologies of regional fire years and tree recruitment from ponderosa pine forests in the Black Hills of southwestern South Dakota and northeastern Wyoming to reconstructions of precipitation and global circulation indices. Regional fire years were affected by droughts and variations in both Pacific and Atlantic sea surface temperatures. Fires were synchronous with La Ni?as, cool phases of the Pacific Decadal Oscillation (PDO), and warm phases of the Atlantic Multidecadal Oscillation (AMO). These quasi-periodic circulation features are associated with drought conditions over much of the western United States. The opposite pattern (El Ni?o, warm PDO, cool AMO) was associated with fewer fires than expected. Regional tree recruitment largely occurred during wet periods in precipitation reconstructions, with the most abundant recruitment coeval with an extended pluvial from the late 1700s to early 1800s. Widespread even-aged cohorts likely were not the result of large crown fires causing overstory mortality, but rather were caused by optimal climate conditions that contributed to synchronous regional recruitment and longer intervals between surface fires. Synchronous recruitment driven by climate is an example of the Moran effect. The presence of abundant fire-scarred trees in multi-aged stands supports a prevailing historical model for ponderosa pine forests in which recurrent surface fires affected heterogenous forest structure, although the Black Hills apparently had a greater range of fire behavior and resulting forest structure over multi-decadal time scales than ponderosa pine forests of the Southwest that burned more often.