The role of precipitation and woody cover deficit in juniper encroachment in Texas savanna

摘要

A lot of studies have been devoted to understanding the underlying mechanism of woody plant encroachment in savanna ecosystems for informed management strategy. However, many of them take their study area as a whole and do not consider the encompassed environmental gradient, which may modulate the role of different factors in the encroachment. This study aims to test the hypothesis that the role of different factors varies over environmental gradient. The test was conducted in the semiarid and mesic regions of the savanna in central Texas, USA. Tentatively, the role of mean annual precipitation (MAP) and woody cover deficit in juniper encroachment was investigated and compared in these two regions. Results suggest that MAP has a positive effect on the encroachment rate in the semiarid region, but not in the mesic region. The encroachment rate increases with woody cover deficit in the semiarid region. In the mesic region, however, the encroachment rate increases with woody cover deficit till a threshold level, then starts decreasing with it. This study demonstrates the varying role of precipitation and woody cover deficit in juniper encroachment across the rainfall gradient of Texas savanna. It furthers our understanding of the underlying mechanism of woody plant encroachment.