The comprehensive evaluation of how water level fluctuation and temperature change affect vegetation cover variations at a lake of ecological importance (Poyang Lake), China

Wetland vegetation is crucial to ecosystem services provided by lake wetlands worldwide. While environmental elements like hydrological factors and temperature have a wide impact on vegetation cover changes in lake wetlands, their effects on vegetation cover changes haven't been well separated and evaluated in the context of local temperature change worldwide. Here, we developed a novel indicator (Rtaw) to decouple and evaluate the effects of temperature change and the change of a typical hydrological factor, namely water level, on vegetation cover changes in the Poyang Lake wetland (PLW) from 2003 to 2014. Rtaw compares the vegetation cover changes in the PLW caused by water level fluctuation to those caused by temperature change. The impact of each environmental factor on wetland vegetation changes was measured by the change in area of vegetation-covered PLW (Ap). Our results demonstrate that the PLW experiences the most significant vegetation cover decrease and increase in June and September, respectively. Annual Ap generally increases from 2003 to 2014. The vegetation cover-changed PLW generally extends from the Poyang Lake's center to its coast. Furthermore, while the water level fluctuation-induced vegetation cover variations in the PLW are typically 0.6 times stronger than that caused by temperature change, the latter is 0.17 similar to 2.99 times stronger than the former around every three years and when seasons change. This is caused by the extreme water level, temperature, and their changes with particular values. Meanwhile, the anomalous impact of temperature change occurs in the PLW's vast region. Overall, the applied Rtaw in the PLW revealed the periodic control of temperature change on vegetation cover changes which are widely thought to be dominated by hydrological variations. Therefore, our work could contribute to a more comprehensive assessment of the vegetation cover changes in lake wetlands. This also implies that the effects of extreme temperature events on vegetation cover changes in lake wetlands should be paid enough attention.