Temperature-driven changes in tree species abundance and carbon cycling along latitudinal and altitudinal gradients

树木物种丰富度和碳循环沿着纬度和海拔梯度的温度驱动变化 预计全球变暖将改变森林的组成和生产力，特别是在气温上升最多的高纬度和高海拔地区。这些变化可能会产生重大的经济和社会后果，以及连锁的环境影响，例如森林碳储存的变化可能对气候变化的速度产生积极或消极的反馈。预测全球变暖的影响需要更好地了解温度如何影响森林的物种组成和生产力。为此，拟议中的研究将使用森林清查数据来研究树木和森林如何对温度的空间变化作出反应。采用空间换时间的替代办法，清单数据还将用于确定一个模型的参数，以预测森林将如何应对全球变暖，包括可能对气候变化产生积极或消极反馈的反应。 这两个研究区域跨越广泛的纬度和海拔梯度：a）北方森林，跨越北美东部的温带-寒带交错带，从35°到50°纬度; B）山地森林，跨越瑞士的落叶针叶林交错带和阿尔卑斯山，从海拔500米到1 500米。 研究的主要目的是：1）确定温度的地理变化如何影响不同树种的补充、生长和死亡; 2）评估补充、生长和死亡在限制物种分布区附近的丰富度方面的相对重要性; 3）阐明温度的地理变化如何直接通过树木生长和死亡的变化影响森林生产力和生物量周转，间接通过物种组成的变化; 4）预测温度的直接和间接影响将如何改变下一个世纪全球变暖的碳循环。 这项拟议的研究将引起研究气候变化的科学家的广泛兴趣，因为它将检验有关在全球碳循环中发挥关键作用的森林生态系统的物种组成和生产力的基本假设。研究结果对整个社会也很有价值，包括自然资源管理者和政策制定者，他们需要知道气候变化将如何影响森林以及栖息在森林中的野生动物和人类。最后，关于森林组成和生产力变化的预测对林业部门具有经济意义，因为林业部门的造林战略和生产预测必须适应全球变暖的影响。

Temperature-driven changes in tree species abundance and carbon cycling along latitudinal and altitudinal gradients  Global warming is expected to alter the composition and productivity of forests, particularly at high latitudes and altitudes where temperature will increase the most. These changes may have significant economic and social consequences, as well as cascading environmental impacts, such as changes in forest carbon storage that may exert a positive or negative feedback on the rate climate change. Predicting the impacts of global warming requires a better understanding of how temperature influences the species composition and productivity of forests. Toward this end, the proposed research will use forest inventory data to examine how trees and forests respond to spatial variation in temperature. Employing space-for-time substitution, the inventory data will also be used to parameterize a model for predicting how forests will respond to global warming, including responses that may exert a positive or negative feedback on climate change. The two study regions span broad latitudinal and altitudinal gradients: a) northern forests spanning the temperate-boreal ecotone in eastern North America, from 35° to 50° latitude; b) montane forests spanning the deciduous-coniferous ecotone in the Swiss the Alps, from 500 to 1500 meters above sea level.   The four main objectives of the research are: 1) to determine how geographic variation in temperature influences the recruitment, growth and mortality of different tree species; 2) to assess the relative importance of recruitment, growth, and mortality in limiting abundance near species’ range limits; 3) to elucidate how geographic variation in temperature influences forest productivity and biomass turnover, both directly though changes in tree growth and mortality, and indirectly via changes in species composition; 4) to predict how the direct and indirect effects of temperature will alter carbon cycling over the next century of global warming. The proposed research will be of broad interest to scientists studying climate change because it will test fundamental hypotheses regarding the species composition and productivity of forest ecosystems that play a key role in the global carbon cycle. The results will also be valuable to society at large, including natural resource managers and policy makers who need to know how climate change will impact forests and the wildlife and humans that inhabit them. Finally, the predictions regarding changes in forest composition and productivity will be of economic interest to the forest sector, whose silvicultural strategies and production forecasts must adjust to the impacts of global warming.