Faculty of Natural Resources, University of Tehran, Iran.
Department of Technology and Society, Faculty of Engineering, Lund University, Box 118, 221 00, Lund, Sweden.
J Environ Manage. 2021 May 15;286:112249. doi: 10.1016/j.jenvman.2021.112249. Epub 2021 Mar 4.
Understanding vegetation response to natural and anthropogenic forcings is vital for managing watersheds as natural ecosystems. We used a novel integrated framework to separate the impacts of natural factors (e.g. drought, precipitation and temperature) from those of anthropogenic factors (e.g. human activity) on vegetation cover change at the watershed scale. We also integrated several datasets including satellite remote sensing and in-situ measurements for a twenty-year time period (2000-2019). Our results show that despite no significant trend being observed in temperature and precipitation, vegetation indices expressed an increasing trend at both the control and treated watersheds. The vegetation cover was not significantly affected by the natural factors whereas the watershed management practice (as a human activity) had significant impacts on vegetation change in the long-term. Further, the vegetation cover long-term response to watershed management practice was mainly linear. We also found that the vegetation indices values in the 2011-2019 period (as the treated period in treated watershed) were significantly higher than those in the 2000-2010 period. In the short-term, however, the drought condition and decreased precipitation (as natural factors) explained the majority of the change in vegetation cover. For example, the majority of the breakpoints occurred in 2008, and it was related to a widespread extreme drought in the area. The watershed management practice as a human activity along with extreme climatic events could explain a large part of the vegetation changes observed in the treated and control watersheds.
了解植被对自然和人为胁迫的响应对于管理作为自然生态系统的流域至关重要。我们使用了一种新的综合框架，将自然因素（如干旱、降水和温度）的影响与人为因素（如人类活动）的影响分开来，以了解流域尺度上植被覆盖变化的原因。我们还整合了多个数据集，包括卫星遥感和现场测量数据，时间跨度为二十年（2000-2019 年）。我们的研究结果表明，尽管温度和降水没有明显的趋势，但在对照和处理流域，植被指数都表现出了上升的趋势。植被覆盖不受自然因素的显著影响，而流域管理实践（作为一种人类活动）对植被变化的长期影响显著。此外，植被覆盖对流域管理实践的长期响应主要是线性的。我们还发现，在处理流域的 2011-2019 年期间（作为处理期），植被指数值明显高于 2000-2010 年期间。然而，在短期内，干旱条件和降水减少（作为自然因素）解释了植被覆盖变化的大部分原因。例如，大多数转折点出现在 2008 年，这与该地区广泛发生的极端干旱有关。流域管理实践作为一种人类活动，加上极端气候事件，可以解释在处理和对照流域中观察到的大部分植被变化。
