2.1. Study area
Miyun County is located in the Northeast of Beijing, with geographical
coordinates of 116°39′–117°30′ E and 40°13′–40°47′ N. It is flanked by
the Pinggu, Shunyi, and Huairou Counties of Beijing in the Southeast to
Northwest regions and Hebei Province in the North and East regions and
has a total area of approximately 2229.45 km2, making
it the largest district in Beijing.
Miyun belongs to the Yanshan Mountains and North China Plain junction,
and mountains surround the terrain of the entire area on three sides
(East, North, and West). The Miyun area has a warm temperate monsoon
continental semi-humid and semi-arid climate with four seasons and
apparent changes in dry, wet, cold, and warm conditions. The annual
average temperature is 6–19 °C; the frost-free period is about 150 d;
sunshine is sufficient; and precipitation is mainly concentrated from
June to August. The precipitation distribution generally decreases from
Southeast to Northwest, giving an average annual of 300–700 mm.
In 2020, the main ecosystem types in Miyun County were forests (41.6%)
and shrubs (22.9%), followed by farmlands (21.9%) and wetlands
(6.6%). Natural ecosystems (forests, shrubs, grasslands, and wetlands)
account for 72.4% of the total area of Miyun County. The quality of the
ecosystem in Miyun County is good, and natural resources are abundant.