Soil Moisture Redistribution as Affected by Throughfall and Stemflow in an Arid Zone Shrub Community

Abstract

Changes in soil moisture under various densities of mulga (Acacia aneura F. Muell.) were followed from December 1971 to October 1973. Stemflow was instrumental in storing water at depth in the soil, being particularly noticeable with medium falls of rain (~ 75 mm); heavy (~ 160 mm) falls tended to mask the effect.

Throughfall increased linearly with aggregate rainfall, and percentage throughfall decreased with increasing tree density. Of incoming precipitation, 94% was partitioned as throughfall under a tree density of 40 trees/ha^-1 compared with 86% at a density of 4000 trees/ha. No distinct soil moisture patterns due to throughfall were found.

Infiltration rates of water into the soil decreased with increasing distance from trees, being 46, 22 and 17 mm/h^-1 after 10 min at distances 0.25, 0.5 and 2 m from a tree bole respectively, thus demonstrating that stemflow waters are absorbed at close proximity to the tree bole.

The results are discussed in terms of the ecological importance of stem flow and soil moisture patterning to the survival and growth of mulga and associated ground flora.