Effects of aridity on the demography, distribution, and biomass of trees and forests in western Canada

最近的观察表明，日益严重的干旱和缺水将是森林应对全球气候变化的主要驱动力。这一预测似乎是特别真实的加拿大西部的北方森林，在那里与干旱有关的树木死亡率和水分有限的增长和招聘率的增加证实，森林动态与水的供应紧密相连。然而，尽管有很好的经验证据表明西部森林的水分胁迫的影响，生态学家对干旱增加对树木数量的影响（即，生长、死亡率和再生）可能转化为森林生物群落的地理分布和现存生物量的更广泛变化。我计划进行一套协调的实地研究和模拟实验，以量化加拿大西部的森林将如何应对下一个世纪增加的水压力。这项研究计划将测试假设：（1）树木死亡率和招聘如何随水的可用性而变化;（2）与水分有关的人口变化如何控制西部北方森林的分布和生物量;以及（3）该森林地区如何应对未来的干旱。首先，我将使用无人机收集柏树山地区森林景观的高分辨率3D图像;这些数据将用于量化降水和土壤水分在海拔梯度上冠层树木死亡率的时空变化。其次，我将建立和重新普查一组永久性的森林样地，以确定不同程度的郁闭度下的光和水对幼树动态的影响。第三，我将使用航空和基于地块的人口数据来参数化基于个人的森林动态模型，该模型可以模拟树种的区域分布和丰富度如何随气候梯度和森林年龄而变化。通过将实地研究的数据和结果整合到一个动态森林模型中，这项研究将对与气候相关的人口变化如何导致加拿大西部森林覆盖率，物种组成和碳储量的未来变化做出有充分依据的定量预测。这项研究的结果将最终导致更好地代表全球陆地碳循环模型中的人口过程，并将使环境变化下的植被动态预测更加稳健。这些进展对于加拿大和国际决策者寻求减轻或适应气候变化对森林生态系统服务的影响将是宝贵的。

Recent observations indicate that increasing drought and water stress will be major drivers of forest responses to global climate change. This forecast appears to be particularly true for boreal forests of western Canada, where drought-related increases in tree mortality and moisture-limited growth and recruitment rates confirm that forest dynamics are tightly coupled with water availability. Yet, despite good empirical evidence for the effects of water stress in western forests, ecologists have a limited understanding of how impacts of increasing aridity on tree-level demography (i.e., growth, mortality, and regeneration) could translate to broader changes in the geographic distribution and standing biomass of forest biomes. I plan to undertake a coordinated set of field studies and modelling experiments to quantify how forests in western Canada will respond to increased water stress over the next century. This research program will test hypotheses regarding: (1) how tree mortality and recruitment vary with water availability; (2) how moisture-related demographic variation governs the distribution and standing biomass of western boreal forests; and (3) how this forest region may respond to future aridity. Firstly, I will use an Unmanned Aerial Vehicle to collect very high resolution 3D imagery of forest landscapes in the Cypress Hills region; these data will be used to quantify spatial and temporal variation in canopy tree mortality across elevational gradients in precipitation and soil moisture. Secondly, I will establish and re-census a set of permanent forest plots to determine the effects of light and water on juvenile tree dynamics under different levels of canopy closure. Thirdly, I will use aerial and plot-based demographic data to parameterize an individual-based model of forest dynamics that can simulate how the regional distribution and abundance of tree species vary across climate gradients and with forest age. By integrating data and results from field studies into a dynamic forest model, this research will produce well-grounded, quantitative predictions of how climate-related demographic variation could lead to future changes in forest cover, species composition, and carbon storage in western Canada. Findings from this research will ultimately lead to better representations of demographic processes in models of the global terrestrial carbon cycle, and will enable more robust projections of vegetation dynamics under environmental change. These advances will be valuable to Canadian and international policy makers seeking to either mitigate or adapt to climate change impacts on forest ecosystem services.