Desertification models predict that arid grasslands exist in one of two stable states: grassland or desertified shrubland. This prediction is derived from an assumed positive relationship between grass cover and water infiltration rate: once grass cover is reduced, water infiltration rates are insufficient to support perennial grass. These models assume that other factors known to affect water infiltration rate are unimportant. While this alternate stable state view is widely accepted and suggests that restoration of desertified grasslands will be difficult, there have been four recent reports of the reversal of desertification (significant increases in the abundance of perennial grasses) following long-term livestock removal. At one site, recovery of perennial grass inside a long-term grazing exclosure was associated with increased water infiltration rates due to release from soil compaction. To assess the generality of this finding, I examined water infiltration rates inside and outside five other long-term livestock exclosure sites in southwestern North America that differ in degree of desertification and time since livestock removal. At each site, water infiltration rates were significantly higher inside compared to outside the grazing fence. The relative difference in water infiltration rate across the sites increased with time since livestock removal at a rate of approximately 1.7% per year. These data show that increased water infiltration rate following livestock removal appears to be a general phenomenon in arid grassland systems. In addition, they suggest that the effect of livestock on water infiltration rates should be included in desertification models to better understand the dynamics of vegetation in these systems. Finally, this work suggests that restoration of desertified grasslands may be possible given sufficient time to allow changes in soil properties including release from soil compaction and the concomitant increases in water infiltration rate that follow.
Was this article helpful?