*2.1. Study Area*

Xuanwei County in Yunnan Province, Western China was selected as the study area. Xuanwei has a land area of 6502 km2, with a low-latitude highland monsoonal climate, average annual precipitation of 986 mm, and an average annual temperature of 13.3 ◦C. The area is located in the watershed zone between Yangtze River and Pearl River, which has a maximum elevation of 2868 m, a minimum elevation of 920 m, a relative altitude difference of 1948 m, numerous sloping fields, and few mountainous areas, and a relatively large slope gradient. The karst landform in the area spreads widely, with the outcrop reaching 3300 km2 and accounting for 52.74% of the entire land area of the county. The soil in the study area mainly consists of red earth and limestone. Xuanwei County is located in the "Hump Course" of World War II. The critical section of Yunnan–Burma, and Yunnan–Guizhou Highway played a significant role in the victory of the Allies during World War II (Figure 1). To guarantee smooth passage in this important transport corridor during the war, the U.S. army conducted several detailed works to study the geographical elements of the forests in this region, and the resulting historical military maps reflect the actual and ecological landscapes in the area during that period.

**Figure 1.** The maps of the location and main natural background of the study area. Note the following: (**a**) location; (**b**) elevation; (**c**) elevation classification; (**d**) slope grade; (**e**) soil type; (**f**) lithology. (We constructed this map using ArcGIS9.3 (http://www.esri.com/arcgis/about-arcgis) (accessed on 12 November 2021)).
