Submitted to: Soil Use and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/13/1999
Publication Date: N/A
Citation: Interpretive Summary: A lack of plant available water can be a problem when establishing forest seedlings in a hot, dry environment. Other management factors affecting soil water properties can also be important in determining forest seedling survival. A study was conducted to determine the effect of animal grazing on soil water properties in a recently established forest in a semiarid climate. The study was conducted in southwestern China where forest establishment is a high priority conservation practice. Two study sites were established on soils with different texture and parent material. Tree, shrub, and grass composition was the same at both sites. Treatment variables were grazing intensity (grazed and non-grazed). Results from this study showed many negative effects with grazing including decreased water infiltration into the soil profile, macropore volumes, and soil water retention. The combined negative effects on grazed compared to the non-grazed treatment were less plant available water on both soils resulting in a higher probability for failure in establishment of a healthy forest. These data can be used by conservation and forest managers in the effective establishment of forest plantations for protecting our natural resource base under limited water conditions.
Technical Abstract: In arid and semiarid environments, soil water deficit is a major constraint to vegetation establishment. While climatic conditions can be a constraint to soil water supply, other external factors are important in determining forest survival. The objective of this study was to quantify the changes in soil water properties in a recently established forest as affected by grazing. This study was conducted in the low mountain region of Yuanmou province, a dry and hot valley of the Jinsha River in the Upper Yangtze River Basin, southwestern China. Two areas of recently established tree (Eucalypus camaldulenis) and shrub (Dodonaea viscosa) plantations were selected for study. A grazed and non-grazed seeded grass condition (Heteropogon contortus) was established at each site. Soils at both sites were classified as dry red soils, Orthic Ferralsols (FAO/Unesco). Soil parent material was mudstone (34% clay, 53% sand) at site 1 and alluvial deposits (13% clay, 63% sand) at site 2. Initial infiltration (P<0.05) and steady state infiltration (P<0.01) were significantly reduced at both sites on the grazed treatment. Macropore volume with cylindrical diameters >0.05 mm was reduced in the grazed treatment in comparison with the non-grazed treatment (P<0.10). Differences in soil water retention occurred under low water tensions (P<0.01), indicating a soil structural difference between the grazed and non-grazed treatments. Total soil porosity was less for the grazed treatment where the reduction in pores >0.05 mm was observed indicating that this decrease in macropore volume was largely responsible for the decline in soil porosity. The combined negative effect of grazing on soil physical properties resulted in less plant available water capacity for both soil types.