CHARACTERISTICS OF SOIL MOISTURE CONTENT ON SAND DUNES IN MU US SANDY GRASSLAND:WHY ARTEMISIA ORDOSICADECLINES ON OLD FIXED SAND DUNES

Abstract

Soil moisture content of a drifting sand dune and a fixed sand dune in the Mu Us sandy grassland of Inner Mongolia was measured over a period of one year. The surficial dry soil layer was significantly thicker in the winter and spring than in the summer and autumn. This dry soil layer was significantly thicker during the winter and spring, and slightly thinner during the summer and autumn, on the drifting sand dune than on the fixed dune. Soil moisture content, generally being lower in the winter and spring than in the summer and autumn, was higher on the drifting sand dune than on the fixed sand dune. The difference of the soil moisture content between the drift sand dune and the fixed sand dune was less in the winter and spring than in the plant growing season. The fine texture of upper soil layer on the fixed sand dune appeared to reduce the replenishment of moisture to the soil of the shrub root layer. The measured results and calculation suggest that rains of more than 1 mm are able to effectively replenish soil moisture on drifting sand dunes, but rains less than 5mm usually permeate no more than 5 cm from the soil surface on fixed sand dunes. Heavy rains may result in water runoff on fixed sand dunes. In combination with the relatively high frequency of small rains in the area, the soil texture and moisture content of fixed sand dunes seem to favor herbs over semi shrubs. This may be a main reason leading to the succession from Artemisia ordosica community to climax steppe in less grazing condition.