Critical junctures in eco-hydrologic control of forest water balance

森林采伐以及野火和昆虫造成的自然干扰使较老的森林转变为较年轻的森林，这对水源地区森林的水生产调节有很大影响。随着幼林的生长，冠层叶面积的增长增加了水的消耗，增加了光合作用过程中蒸腾作用损失的水量，减少了通过拦截雨水或降雪进入森林的水量。因此，叶面积调节森林植被通过截留和蒸腾消耗多少水，这反过来又调节森林如何产生径流。因此，随着森林的建立、成熟和发展到老的生长阶段，森林结构的变化可以使水源地区的水分生产产生很大的变化。森林植被的其他变化，例如随着森林演替物种组成的缓慢变化，也可能导致森林植被消耗的水量发生巨大变化，因为有些物种比其他物种消耗更多的水。发展一个更好地了解多少水是由不同年龄的森林和不同的森林树种使用是很重要的，能够预测加拿大的水供应可能会随着森林的自然变化，随着时间的推移和那些与人类使用的森林。

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.