Effects of experimental soil disturbance on revegetation by natives and exotics in coastal Californian meadows

  • Published source details Kotanen P.M. (1997) Effects of experimental soil disturbance on revegetation by natives and exotics in coastal Californian meadows. Journal of Applied Ecology, 631-644.


Soil disturbance is widely believed to facilitate invasions by non-native plants but is also important for the persistence of many native species. The results of field experiments designed to investigate the effects of different types of soil disturbance on native and alien species in Californian grassland vegetation are described.

Study areas:A pair of experiments were conducted at the White House and South Meadows at the Northern California Coast Range Preserve of the University of California (123º37'W, 39º45'N), California, southwest USA.

Soil disturbance: At both sites 72, 25 x 25 cm plots were established in a c. 10 x 10 m grid. Three types of soil disturbance: excavation; burial; simulated gopher mounds; and also undisturbed controls, were applied in the winter of 1990-1991. Their revegetation was compared with changes in undisturbed control plots over the next three years.

Soil characteristics: A third experiment was used to provide data on the effects of soil disturbance on soil temperature, moisture and KCl-extractable nitrogen. About 100 m from the White House Meadows experiment, 12 plots of each disturbance type, (excluding simulated gopher mounds) were established in December 1991. The temperature of the top 1 cm of soil was recorded on six sunny afternoons between May 1992 and April 1993. In December, February, April and June, soil core samples (100 mm deep x 18 mm diameter) were taken and analysed for NO3, NH4 and soil moisture.

Effects of disturbance on vegetation: At the two sites, summer species richness and abundance of most plant functional groups were initially reduced by most disturbance types. It especially greatly reduced the numerical abundance both of groups dominated by natives (perennial graminoids and bulbs) and of groups dominated by aliens (annual graminoids).

In subsequent years, richness rebounded as natives and exotics re-invaded. Native bulbs and perennial graminoids were slow to recover if at all, remaining less common in most disturbances treatments than controls. Dicotyledons responded erratically and differed in behaviour between the two sites. Most disturbances increasingly became dominated by exotic annual grasses, which often equaled of exceeded those densities observed in the controls.

Effects of disturbance on soil characteristics: Disturbance affected both soil temperature and chemistry. Buried plots contained the most KCl-extractable nitrogen, and were also the warmest. Effects on soil moisture were relatively small.

Conclusions: Some types of disturbance were less damaging to native-dominated groups than others but most ultimately favoured the exotic species present on the experimental grasslands. Consequently the authors conclude that it may be difficult to develop management strategies that preserve the diversity of disturbance-dependent native plant species but exclude unwanted aliens.

Note: If using or referring to this published study, please read and quote the original paper.

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