The effects of land use and climate change on the carbon cycle of Europe over the past 500 years

The long residence time of carbon in forests and soils means that both the current state and future behavior of the terrestrial biosphere are influenced by past variability in climate and anthropogenic land use. Over the last half‐millennium, European terrestrial ecosystems were affected by the cool temperatures of the Little Ice Age, rising CO₂ concentrations, and human induced deforestation and land abandonment. To quantify the importance of these processes, we performed a series of simulations with the LPJ dynamic vegetation model driven by reconstructed climate, land use, and CO₂ concentrations. Although land use change was the major control on the carbon inventory of Europe over the last 500 years, the current state of the terrestrial biosphere is largely controlled by land use change during the past century. Between 1500 and 2000, climate variability led to temporary sequestration events of up to 3 Pg, whereas increasing atmospheric CO₂ concentrations during the 20th century led to an increase in carbon storage of up to 15 Pg. Anthropogenic land use caused between 25 Pg of carbon emissions and 5 Pg of uptake over the same time period, depending on the historical and spatial pattern of past land use and the timing of the reversal from deforestation to afforestation during the last two centuries. None of the currently existing anthropogenic land use change datasets adequately capture the timing of the forest transition in most European countries as recorded in historical observations. Despite considerable uncertainty, our scenarios indicate that with limited management, extant European forests have the potential to absorb between 5 and 12 Pg of carbon at the present day.     

Climatic changes during the past 1300 years as deduced from the sediments of Lake Nakatsuna, central Japan

Limnological features and sediment characteristics were studied in Lake Nakatsuna, a mesotrophic lake in central Japan. The lake is dimictic, and is anoxic in the hypolimnion during thermal stratification from May to September. In an attempt to reconstruct paleoclimatic changes around the lake, a sediment core taken from the lake center spanning the past 1300 years was analyzed for its organic and inorganic contents. Climatic influences were examined on the variation of total organic carbon (TOC), total nitrogen (TN), and sand contents. Short- and long-term fluctuations in TOC, TN, and sand contents are evident, and variation in atmospheric temperature appears to be important for their long-term variability. The sediment record from AD 900 to 1200 indicates hot summers and warm winters with less snow accumulation, whereas the record from AD 1200 to 1950 is characterized by high variation of temperature, with three cool phases from AD 1300 to 1470, 1700 to 1760, and 1850 to 1950. The warm period from AD 900 to 1200 corresponds well to the Medieval Warm Period, and the second and third cool phases are related to the Little Ice Age. Received: February 16, 2001 / Accepted: June 7, 2001     

南亚热带森林演替过程中小气候的改变及对气候变化的响应

区域水热格局变化和系统演替深刻影响森林内部小气候,不同演替阶段森林内部水热环境对气候变化的响应和反馈作用有待进一步认识和评估。以南亚热带地区的3种不同演替阶段代表性森林生态系统统(人工恢复的马尾松针叶林(Pinus massoniana coniferous forest,PF)、马尾松针阔叶混交林(mixed Pinus massoniana/broad-leaved forest,MF)和季风常绿阔叶林(monsoon evergreen broad-leaved forest,MEBF))为研究对象,通过分析其林内小气候林型间差异以及时间序列上的动态变化,探讨森林系统内部水热环境的改变机理。结果表明:演替驱动下,随着PF→MF→MEBF的正向发展,林内温度条件如气温、土壤温度逐渐降低,林内相对湿度、土壤层及凋落物含水量等水分状况逐步升高。不同林型在"雨热同期"的南亚热带地区其"降温效应"有差,演替初期的PF干、湿季"降温效应"分别为7.9%和3.6%,中期MF分别为11.6%和6.4%,顶级群落MEBF干、湿季"降温效应"可达15.7%和10.5%。总体上,随演替"降温增湿"效应越来越显著,且"降温"表现为干季更明显,而"增湿"表现为湿季明显。此外,演替驱动下后期森林对高温及土壤温度的调节作用更为突出。时间序列上,区域降水趋于"极端化"的格局影响下,森林生态系统的水分固持能力下降。主要表现为:自1984年以来,3种林型0—50cm土壤含水量均呈显著降低的趋势(P0.001),且湿季土壤含水量下降速率高于干季,林型间在全年及湿季均为MFMEBFPF,干季为MEBFMFPF。虽然研究期间3种林型林内气温、土壤温度无明显趋势性变化,但顶级群落MEBF林内相对湿度(P=0.021)、凋落物自然状态下含水量(P=0.003)在年际尺度上均呈现显著下降的趋势。与土壤含水量干、湿季下降速率的格局一致,二者也均为湿季大于干季。研究认为,成熟森林可能在当前南亚热带区域气候变化及水热格局改变背景影响下更为敏感和脆弱。     

Elevation‐dependent responses of tree mast seeding to climate change over 45 years

We use seed count data from a New Zealand mono‐specific mountain beech forest to test for decadal trends in seed production along an elevation gradient in relation to changes in climate. Seedfall was collected (1965 to 2009) from seed trays located on transect lines at fixed elevations along an elevation gradient (1020 to 1370 m). We counted the number of seeds in the catch of each tray, for each year, and determined the number of viable seeds. Climate variables were obtained from a nearby (<2 km) climate station (914‐m elevation). Variables were the sum or mean of daily measurements, using periods within each year known to correlate with subsequent interannual variation in seed production. To determine trends in mean seed production, at each elevation, and climate variables, we used generalized least squares (GLS) regression. We demonstrate a trend of increasing total and viable seed production, particularly at higher elevations, which emerged from marked interannual variation. Significant changes in four seasonal climate variables had GLS regression coefficients consistent with predictions of increased seed production. These variables subsumed the effect of year in GLS regressions with a greater influence on seed production with increasing elevation. Regression models enforce a view that the sequence of climate variables was additive in their influence on seed production throughout a reproductive cycle spanning more than 2 years and including three summers. Models with the most support always included summer precipitation as the earliest variable in the sequence followed by summer maximum daily temperatures. We interpret this as reflecting precipitation driven increases in soil nutrient availability enhancing seed production at higher elevations rather than the direct effects of climate, stand development or rising atmospheric CO₂ partial pressures. Greater sensitivity of tree seeding at higher elevations to changes in climate reveals how ecosystem responses to climate change will be spatially variable.     

林窗模型及其在全球气候变化研究中的应用

林窗模型是基于个体的广泛应用于森林长期动态变化的模拟与预测的模型,是研究森林生态系统对气候变化响应的有效工具。本文把林窗模型的发展与演变过程概括为3个阶段:萌芽阶段、飞速发展阶段和提高阶段;展望了林窗模型的未来发展趋势;简要阐述了在全球气候变化背景下应用模型研究森林与气候间关系的可行性与必要性;对国际上相关的研究热点和前沿问题进行了探讨;综述了国内的研究现状,指出国内林窗模型的预测研究应以改进现有模型、构建新模型、耦合多模型作为未来的发展方向。     

Changes in soil bacterial community triggered by drought‐induced gap succession preceded changes in soil C stocks and quality

The aim of this study was to understand how drought‐induced tree mortality and subsequent secondary succession would affect soil bacterial taxonomic composition as well as soil organic matter (SOM) quantity and quality in a mixed Mediterranean forest where the Scots pine (Pinus sylvestris) population, affected by climatic drought‐induced die‐off, is being replaced by Holm‐oaks (HO; Quercus ilex). We apply a high throughput DNA pyrosequencing technique and ¹³C solid‐state Nuclear Magnetic Resonance (CP‐MAS ¹³C NMR) to soils within areas of influence (defined as an surface with 2‐m radius around the trunk) of different trees: healthy and affected (defoliated) pines, pines that died a decade ago and healthy HOs. Soil respiration was also measured in the same spots during a spring campaign using a static close‐chamber method (soda lime). A decade after death, and before aerial colonization by the more competitive HOs have even taken place, we could not find changes in soil C pools (quantity and/or quality) associated with tree mortality and secondary succession. Unlike C pools, bacterial diversity and community structure were strongly determined by tree mortality. Convergence between the most abundant taxa of soil bacterial communities under dead pines and colonizer trees (HOs) further suggests that physical gap colonization was occurring below‐ground before above‐ground colonization was taken place. Significantly higher soil respiration rates under dead trees, together with higher bacterial diversity and anomalously high representation of bacteria commonly associated with copiotrophic environments (r‐strategic bacteria) further gives indications of how drought‐induced tree mortality and secondary succession were influencing the structure of microbial communities and the metabolic activity of soils.     

Fire‐induced tree mortality in a neotropical forest: the roles of bark traits,tree size,wood density and fire behavior

Large‐scale wildfires are expected to accelerate forest dieback in Amazônia, but the fire vulnerability of tree species remains uncertain, in part due to the lack of studies relating fire‐induced mortality to both fire behavior and plant traits. To address this gap, we established two sets of experiments in southern Amazonia. First, we tested which bark traits best predict heat transfer rates (R) through bark during experimental bole heating. Second, using data from a large‐scale fire experiment, we tested the effects of tree wood density (WD), size, and estimated R (inverse of cambium insulation) on tree mortality after one to five fires. In the first experiment, bark thickness explained 82% of the variance in R, while the presence of water in the bark reduced the difference in temperature between the heat source and the vascular cambium, perhaps because of high latent heat of vaporization. This novel finding provides an important insight for improving mechanistic models of fire‐induced cambium damage from tropical to temperate regions. In the second experiment, tree mortality increased with increasing fire intensity (i.e. as indicated by bark char height on tree boles), which was higher along the forest edge, during the 2007 drought, and when the fire return interval was 3 years instead of one. Contrary to other tropical studies, the relationship between mortality and fire intensity was strongest in the year following the fires, but continued for 3 years afterwards. Tree mortality was low (≤20%) for thick‐barked individuals (≥18 mm) subjected to medium‐intensity fires, and significantly decreased as a function of increasing tree diameter, height and wood density. Hence, fire‐induced tree mortality was influenced not only by cambium insulation but also by other traits that reduce the indirect effects of fire. These results can be used to improve assessments of fire vulnerability of tropical forests.     

The role of climate,habitat, and species co‐occurrence as drivers of change in small mammal distributions over the past century

Species distribution models are commonly used to predict species responses to climate change. However, their usefulness in conservation planning and policy is controversial because they are difficult to validate across time and space. Here we capitalize on small mammal surveys repeated over a century in Yosemite National Park, USA, to assess accuracy of model predictions. Historical (1900–1940) climate, vegetation, and species occurrence data were used to develop single‐ and multi‐species multivariate adaptive regression spline distribution models for three species of chipmunk. Models were projected onto the current (1980–2007) environmental surface and then tested against modern field resurveys of each species. We evaluated models both within and between time periods and found that even with the inclusion of biotic predictors, climate alone is the dominant predictor explaining the distribution of the study species within a time period. However, climate was not consistently an adequate predictor of the distributional change observed in all three species across time. For two of the three species, climate alone or climate and vegetation models showed good predictive performance across time. The stability of the distribution from the past to present observed in the third species, however, was not predicted by our modeling approach. Our results demonstrate that correlative distribution models are useful in understanding species' potential responses to environmental change, but also show how changes in species‐environment correlations through time can limit the predictive performance of models.     

Climatic and biotic velocities for woody taxa distributions over the last 16 000 years in eastern North America

We estimated the latitudinal velocity (km/decade) of northern and southern boundaries of core distributions for 30 woody taxa over the last 16 000 years (biotic velocities) using networks of fossil pollen records, and compared these with climate velocities estimated from CCSM3 simulations. Biotic velocities were faster during periods of rapid temperature change (i.e. 16 to 7 ka) than times of relative stability (i.e. 7 to 1 ka), with a consistent northward movement of northern and southern boundaries. For most taxa, biotic velocities were faster for northern than for southern boundaries between 12 and 7 ka, resulting in expanding distributions. For individual time periods, biotic velocities were as fast or faster than climate velocities calculated using multivariate approaches. These results indicate that climate change paced the rate of distribution shifts in both northern and southern populations while suggesting that northern populations were more sensitive. A similar sensitivity and pacing is expected under 21st century climate change.     

Emergence patterns of novelty in European vegetation assemblages over the past 15 000 years

Plant communities are not stable over time and biological novelty is predicted to emerge due to climate change, the introduction of exotic species and land‐use change. However, the rate at which this novelty may arise over longer time periods has so far received little attention. We reconstruct the emergence of novelty in Europe for a set of baseline conditions over the past 15 000 years to assess past rates of emergence and investigate underlying causes. The emergence of novelty is baseline specific and, during the early‐Holocene, was mitigated by the rapid spread of plant taxa. Although novelty generally increases as a function of time, climate and human‐induced landscape changes contributed to a non‐linear post‐glacial trajectory of novelty with jumps corresponding to periods of rapid changes. Emergence of novelty accelerated during the past 1000 years. Historical cultural landscapes experienced a faster novelty development due to the contribution from anthropogenic land‐cover changes.     

Impacts of human activity and climate change on the distribution of snub‐nosed monkeys in China during the past 2000 years

Aim

In this article, we analysed two millennia of historical records and environmental information to reconstruct the past distribution and examine the current distribution of snub‐nosed monkeys (Rhinopithecus) in China.

Location

China.

Methods

We applied trend surface analysis (TSA) to document patterns of range shifting in snub‐nosed monkeys over time. Random forest was used to study the association between explanatory variables and changes in the distribution of snub‐nosed monkeys over the past 2000 years.

Results

Our results showed that both the longitude and latitude of snub‐nosed monkeys contracted from 0 to 2000 AD. We found that the integrated effects of human population size and changes in temperature in the Northern Hemisphere resulted in a westward and northward contraction of the snub‐nosed monkey distributional range. However, the impact of fluctuating temperature was greatest during periods of low human population density (0–1200 AD), whereas from 1200 to 2000 AD, marked increases in human population size in China leading to extensive deforestation, agricultural expansion, hunting, logging and land terracing have had the greatest negative effects. Further analyses highlighted the fact that the rapid expansion of human population density in regions occupied by snub‐nosed monkeys between 1700 and 2000 has resulted in the recent extirpation of this primate radiation in eastern, south‐eastern and central China.

Main conclusions

We examined the interactive effects of human population growth, deforestation, agricultural expansion and climate variation on the past and current distribution of snub‐nosed monkeys. Our data provide clear evidence that climate change, human population increase and human activities have differentially affected the viability and distribution of snub‐nosed monkey populations over time. In particular, the marked expansion of the human population in China over the past 300 years has resulted in the extinction of Rhinopithecus populations across much of its range.