Critical junctures in eco-hydrologic control of forest water balance

森林采伐以及野火和昆虫的自然干扰会将老森林转变为年轻森林，这可能对调节源头地区森林的产水量产生很大影响。随着幼林的生长，由于树冠叶面积的增长而增加的耗水量增加了光合作用过程中蒸腾损失的水量，并减少了通过拦截雨或雪进入森林的水量。因此，叶面积调节森林植被通过拦截和蒸腾消耗多少水分，而蒸腾作用又调节森林如何产生径流。因此，随着森林的建立、成熟和发展进入老的生长阶段，森林结构的变化可能会对源头地区的水生产产生非常大的变化。森林植被的其他变化，如随着森林演替而缓慢变化的物种组成，也可能导致森林植被耗水量的巨大变化，因为某些物种比其他物种消耗更多的水。更好地了解不同年龄的森林和不同森林树种的用水量，对于能够预测加拿大的供水可能随着时间的推移森林的自然变化和与人类对森林的利用有关的变化是很重要的。这项研究将探索随着森林成熟或进入老生长期，森林的用水量如何变化，以及森林树种组成的变化如何导致类似的水生产变化。一系列研究将比较新老森林通过上层/下层植被的蒸腾作用和因截留降水而损失的水分组合使用的总用水量的差异。另一系列研究将探讨森林演替中典型的森林树种组成的变化如何产生总体变化、蒸腾和截留损失，以确定老生长森林比早期演替森林用水量多还是少。这些研究将使人们能够更好地了解和预测森林管理、自然干扰和气候变化可能影响加拿大的供水。

Forest harvesting and natural disturbance by wildfire and insects converts older forests into younger forests and this can have a large effect on regulation of water production from forests in headwaters regions. As young forests grow, increasing water consumption by growth of canopy leaf area increases the amount of water lost by transpiration during photosynthesis and reduces the amount of water entering the forest by intercepting rain or snowfall. Therefore leaf area regulates how much water the forest vegetation consumes through interception and transpiration, which in turn, regulates how streamflow is produced by forests. Thus changes in forest structure can produce very large changes in water production from headwater regions as forests establish, mature, and develop into old growth phases. Other changes in forest vegetation such as slowly changing species composition with forest succession can also cause large changes in the amount of water the forest vegetation consumes because some species use more water than others. Developing a better understanding how much water is used by forests of differing age and by different forest tree species is important to be able to predict how Canadian water supplies might change with both natural changes in forests over time and those related to human use of the forest.This research will explore how the water consumption by forests changes as forests mature or reach old growth phases and how changes in forest tree species composition drive similar changes in water production.  A series of studies will compare differences in total water use by younger & old forests by combined water use through transpiration in the overstory/understory vegetation and water lost to interception of precipitation. Another series of studies will explore how changes in forest tree species composition that are typical in forest succession produce overall changes transpiration and interception losses to determine if old growth forests use more or less water than early successional forests. These studies will allow for much better understanding and prediction of forest management, natural disturbances, and climate change may affect Canadian water supplies.