Plant Accessible Water Storage Capacity and Tree-Scale Root Interactions Determine How Forest Density Reductions Alter Forest Water Use and Productivity
Plant Accessible Water Storage Capacity and Tree-Scale Root Interactions Determine How Forest Density Reductions Alter Forest Water Use and Productivity
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植物可利用的储水能力和树尺度根部相互作用决定森林密度降低如何改变森林用水和生产力
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发表时间：
2019
期刊：
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通讯作者：
M. Moritz
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作者：
C. Tague;M. Moritz
森林干扰，如野火和干旱相关的疾病往往导致生产力下降，影响森林用水，特别是在美国西部的半干旱环境中。人们经常提议对燃料进行处理，以减少易受这些干旱影响的脆弱性，在某些情况下，还将其作为增加产水量的一种方法。通过改变生态系统结构，燃料处理改变生态系统功能（包括水文循环、碳固存、能量分配和地球化学循环）。对通过积极的森林管理或自然干扰改变生态系统结构所产生的影响进行的实证研究表明，森林用水量的增加和减少都是一种广泛的反应。气候和物种的变化，以及森林密度减少的幅度，通常被认为是这种变化的原因。在本文中，我们使用一个耦合的生态水文模型来证明，地下功能可能是一个关键的，但往往被忽视的因素，影响森林用水和再生密度降低治疗。使用一个案例研究网站在南部的内华达州山脉的加州，我们表明，森林用水是否增加或减少密度降低，以及恢复水文变化的幅度和速度，在很大程度上取决于植物可访问的储水能力内生根区和相邻树木的根结构相互作用和共享水的程度。我们发现，在某些情况下，密度降低可以增加剩余树木的产水量和生产力的头几年治疗后。然而，我们也表明，当土壤浅，根系重叠，反直觉的增加用水和相关的生产力下降，可能会发生由于水分胁迫。结果强调了在评估燃料处理如何与生态系统用水和干旱脆弱性相互作用以及最终对径流的下坡影响时，考虑特定地点变化（如土壤蓄水能力）的重要性。
Forest disturbances such as wildfire and drought-related disease often lead to declines in productivity that both influence and are influenced by forest water use, particularly in the semi-arid environments of the Western US. Fuel treatments are frequently proposed to reduce vulnerability to these drought-related impacts and in some cases as an approach to increase water yield. By changing ecosystem structure, fuel treatments alter ecosystem function (including hydrologic cycling, carbon sequestration, energy partitioning and biogeochemical cycling). Empirical studies of the impacts of changing ecosystem structure, either through active forest management or through natural disturbances, show a wide range of responses that include both increases and decreases in forest water use. Variation in climate and species, as well as the magnitude of forest density reduction, are commonly proposed as explanations for this variation. In this paper we use a coupled eco-hydrologic model to demonstrate that subsurface features are likely to be a critical, but often over-looked, factor that influences forest water use and regeneration following density reduction treatments. Using a case study site in the southern Sierra Nevada Mountains of California, we show that whether forest water use increases or decreases following density reduction, as well as the magnitude and rate of recovery of hydrologic changes, depends strongly on plant accessible water storage capacity within the rooting zone and the extent to which the root structures of neighboring trees interact and share water. We find that in some cases density reduction can increase water yield and productivity of remaining trees for the first few years following treatment. However we also show that when soils are shallow and roots systems overlap, counter-intuitive increases in water use and related declines in productivity can occur due to water stress. Results highlight the importance of accounting for site-specific variation, such as soil water storage capacity, in assessing how fuel treatments may interact with ecosystem water use and drought vulnerability, and ultimately downslope impacts on streamflow.