School of Ecosystem and Forest Sciences, The University of Melbourne, Baldwin Spencer Building, Parkville, VIC 3010, Australia; Hawkesbury Institute for the Environment, Western Sydney University, Richmond, NSW 2753, Australia.
School of Ecosystem and Forest Sciences, The University of Melbourne, Baldwin Spencer Building, Parkville, VIC 3010, Australia.
Sci Total Environ. 2019 Dec 1;694:133551. doi: 10.1016/j.scitotenv.2019.07.357. Epub 2019 Jul 29.
Topography exerts control on eco-hydrologic processes via alteration of energy inputs due to slope angle and orientation. Further, water availability varies with drainage position in response to topographic water redistribution and the catena effect on soil depth and thus soil water storage capacity. Our understanding of the spatio-temporal dynamics and drivers of transpiration patterns in complex terrain is still limited by lacking knowledge of how systematic interactions of energy and moisture patterns shape ecosystem state and water fluxes and adaptation of the vegetation to these patterns. To untangle the effects of slope orientation and hillslope position on forest structure and transpiration patterns, we measured forest structure, sap flux, soil moisture, throughfall and incoming shortwave radiation along two downslope transects in a forested head water catchment in south-east Australia. Our plot locations controlled for three systematically varying drainage position levels (topographic wetness index: 5.0, 6.5 and 8.0) and two levels of energy input (aridity index: 1.2 and 1.8). Vegetation patterns were generally stronger related to drainage position than slope orientation, whereas sap velocity variations were less pronounced. However, in combination with stand sapwood area, consistent spatio-temporal transpiration patterns emerged in relation to landscape position, where slope orientation was the primary and drainage position the secondary controlling factor. On short temporal scales, radiation and vapor pressure deficit were most important in regulating transpiration rates, whereas soil water limitation only occurred on shallow soils during summer. The importance of stand structural parameters increased on longer time scales, indicating optimization of vegetation in response to the long-term hydro-climatic conditions at a given landscape position. Thus, vegetation patterns can be conceptualized as a 'time-integrated' predictor variable that captures large fractions of other factors contributing to transpiration patterns.
地形通过改变坡度角和方位的能量输入来控制生态水文过程。此外，由于地形水分再分配以及对土壤深度和土壤水分储量的阶地效应，排水位置的不同导致水分供应情况也会发生变化。由于缺乏系统地了解能量和水分模式的相互作用如何塑造生态系统状态和水分通量以及植被对这些模式的适应，我们对复杂地形中蒸腾模式的时空动态及其驱动因素的理解仍然有限。为了理清坡度方位和山坡位置对森林结构和蒸腾模式的影响，我们在澳大利亚东南部一个森林流域的上游集水区沿两条下坡横截测量了森林结构、树干液流、土壤水分、穿透雨和入射短波辐射。我们的样地位置控制了三个系统变化的排水位置水平（地形湿润指数：5.0、6.5 和 8.0）和两个能量输入水平（干旱指数：1.2 和 1.8）。植被模式通常与排水位置的关系比坡度方位更为密切，而树干液流速度的变化则不那么明显。然而，结合林分边材面积，与景观位置相关的一致时空蒸腾模式出现了，其中坡度方位是主要控制因素，排水位置是次要控制因素。在短时间尺度上，辐射和水汽压亏缺是调节蒸腾速率的最重要因素，而土壤水分限制仅在夏季发生在浅层土壤中。在较长时间尺度上，林分结构参数的重要性增加，这表明植被进行了优化，以适应给定景观位置的长期水热条件。因此，植被模式可以被概念化为一个“时间综合”的预测变量，它可以捕获对蒸腾模式有贡献的其他因素的大部分。
