2.1 Study area
The sandy land in Horqin is part of north-eastern China’s Inner Mongolia
desert zone, from the North-East China Plain to the transition zone of
the Inner Mongolia plateau (42°41′–45°15′ N,118°35′–123°30′ E,
178.5–631.9 m above the sea level), and is spread over approximately
51.75 km². The climate ranges from temperate semi-arid to semi-humid
continental monsoon. The study site was at the Daqinggou Ecological
Station, Institute of Applied Ecology, Chinese Academy of Science.
Average annual temperature in the area is 3–7 °C (ranging from −12.6 °C
to −16.2 °C, in January, to 20.3–23.9 °C, in July), with 140–160
frost-free days a year. Average annual precipitation is 343–500 mm,
about 70% of which is received between June and August. Spring is
fairly dry with hardly any rainfall in most places. Average annual
evaporation is 1500–2500 mm; average annual wettability is 0.3–0.5;
the drying coefficient ranges from 1 to 1.8; cumulative active
temperature (≥10 °C) is 3032–3168 °C; and annual daily mean sunshine
hours are 2837–2892, with 120 kcal/cm² of global radiation. Annual
average wind speed is 3.4–4.4 m/s (4.2–5.9 m/s in spring); for
210–310 days a year, and even up to 330 d in some years, the wind is
laden with sand and its speed is more than 5 m/s. Each year also sees
25–40 gale days (wind speeds exceeding 17.2 m/s), including 10–15
days, mainly in the spring, of sand storms. The annual sunshine hours
are 2900–3100, maximum in May and minimum in December. The soils are
mainly aeolian sandy soils and meadow soils. Substratum mobility varies
from fixed sand dunes, semi-fixed sand dunes, and mobile dunes. The
zonal soils in the Horqin sandy lands are dark brown, chestnut, and
loess soils whereas the non-zonal soils are mainly sandy, meadow, and
saline. Due to desertification, the zonal soils are gradually turning
into sandy soils. Sandy plains are widely distributed, consisting mainly
of sandy soils, and, following the standard soil classification, can be
divided into raw grass sandy soils, flowing sand soils, and aeolian
sandy chestnut soils. The area is a typical agro-pastoral transition
zone in northern China and comprises many different ecosystems including
natural deciduous broad-leaved forests, forest plantations, grasslands,
wetlands, and farmlands. The vegetation consists of mainly psammophytes
of the Mongolian and Huabei floras.