This is the accepted manuscript of an article published by Wiley.Disturbance is widely believed to facilitate invasions by exotic plants, but also is important for the persistence of many native species. Here, I report the results of a series of field experiments designed to investigate the effects of soil disturbance on natives and aliens in Californian grassland vegetation. I also compare the effects of different types of soil disturbance to establish whether some favour aliens to a greater degree than others.
In two experiments, conducted at two different locations, three types of soil disturbance (excavation, burial, and simulated gopher mounds) were created, and their revegetation was compared with changes in undisturbed control plots over the next three years. A third experiment was used to provide data on the effects of soil disturbance on soil temperature, moisture, and KCl-extractable nitrogen.
Disturbance affected both soil temperature and chemistry. Buried plots contained the most KCl-extractable nitrogen, and also were the warmest. Effects on soil moisture were relatively small.
Initially, most disturbances greatly reduced the numerical abundance of both groups dominated by natives (perennial graminoids and bulbs) and those dominated by aliens (annual graminoids). Disturbance also reduced maximal (summer) species richness, but in some cases increased the fraction of richness contributed by natives.
In subsequent years, richness rebounded as natives and exotics re-invaded. Native bulbs and perennial graminoids were slow to recover; instead, most disturbances increasingly became numerically dominated by exotic annual grasses, accentuating the effects of a multi-year drought.
The differing effects of experimental disturbances on aliens and natives can best be explained by considering relationships between sources of propagules, life histories, and geographic origins.
Some types of disturbance were less damaging to native-dominated groups than others, but most ultimately favoured exotics. Consequently, it may be difficult to develop management strategies that preserve the diversity of disturbance-dependent natives while still excluding weedy aliens.Funding was provided by the Nature Conservancy of California (CARO 042491-K), the University of California Natural Reserve System, an NSF Doctoral Dissertation Improvement Grant (DEB-9122821), a Postgraduate Fellowship of the Natural Sciences and Engineering Research Council of Canada, the Hardman Foundation, and the Department of Integrative Biology at U.C. Berkeley
