4.3 Environmental effects on forest productivity and stability
Unlike natural forests, plantation location is determined by humans. The location of these two forest types had a significant difference (Fig. 1). The plantation in this study was located in the southern portion of the rainy zone in West China (Sichuan Vegetation Cooperation Group, 1980); the annual precipitation (911.69±118.66 mm) is greater in this area than in the area of natural forest (787.08±137.08 mm). This may make natural forests in less precipitation environment more sensitive to annual precipitation changes. Higher forest productivity at sites with suitable conditions suggested that a favorable resource (e.g., soil depth and annual precipitation) increased productivity (Forrester and Bauhus, 2016). MAT did not significantly affect productivity. While, links between rainfall and total productivity are highly temperature-dependent, where at least at tropical mountain rainforest sites experiencing low temperatures (16 ℃), increasing rainfall exerted a negative effect on productivity (Taylor et al. 2017). This may stem from the climatic context in our study region, which is characterized by a low MAT (0 ~17 ℃). In addition, the response of forests to climate change strongly depends on forest composition and structure, and most of the natural forests in this study were composed of multiple late-successional Fir, Spruce and Betula in this study. It is consistent with Chen and Luo (2015), which showed that coniferous forest was more sensitive to climate change. The trees species and community compose in natural forest may explain differences between the two forest types.