Patterns of Re-vegetation on Western Santa Cruz Island, CA in the Post-grazing era
Abstract
Recent reports suggest that land degradation continues to be a problem of increasing severity and extent around the world, with an estimated 1.5 billion people depending directly on degrading land for their livelihood (2005 Millennium Ecosystem Assessment). Causes for degradation range from the direct pressures applied by a growing population to unsuitable land tenure practices. In a degraded landscape, some of the areas most susceptible to erosion are the completely denuded zones, lacking any protective cover from the wind and rain. Mitigation efforts include active measures such as terracing or reforestation programs as well as passive measures such as leaving land fallow. But given a chance to recover, how long will denuded areas remain bare? And can we predict which areas will re-vegetate more quickly or completely than others? Santa Cruz Island, CA, formerly an overgrazed sheep and cattle ranch, presents an opportunity to address these questions over a variety of geologic substrates in a Mediterranean climate. In this study, a spatial analysis of denuded land was conducted using a time series of orthorectified aerial imagery dating back to 1929. High resolution (1.5m) LiDAR data from the Carnegie Airborne Observatory was also used to investigate topographic factors in predicting the presence/absence and degree of re-vegetation since the 1989 eradication of sheep. Our findings show that the most important factor for the re-vegetation of denuded areas is the degree of pre-existing channelization. Some denuded but non-gullied areas were observed to contract in size >50% within a decade of the removal of grazing animals while established gully networks generally persisted or expanded. In areas that did experience significant re-vegetation, the most common pattern of recovery was an encroachment of surrounding vegetation inward into denuded areas. Although most degraded rangelands around the world cannot be completely taken out of production as has been done on Santa Cruz Island, our results support previous research suggesting that mitigation efforts focused on non-channeled areas will have a greater lasting impact than those directed at active gullies.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.H51D0858P
- Keywords:
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- 1815 Erosion;
- 1826 Geomorphology: hillslope (1625);
- 1834 Human impacts;
- 1872 Time series analysis (3270;
- 4277;
- 4475)