TIPPING THE BALANCE IN THE RESTORATION OF NATIVE PLANTS: EXPERIMENTAL APPROACHES TO CHANGING THE EXOTIC: NATIVE RATIO IN CALIFORNIA GRASSLAND.

Authors: CORBIN, JEFFREY - UNIV OF CA, BERKELEY; D Antonio, Carla; BAINBRIDGE, SUSAN - UNIV OF CA, BERKELEY

Submitted to: University of California Press-Cooperative Extension
Publication Type: Book / Chapter
Publication Acceptance Date: 1/1/2003
Publication Date: 6/1/2004
Citation: Corbin, J.D., D Antonio, C.M., Bainbridge, S.J. 2004. Tipping the balance in the restoration of native plants: experimental approaches to changing the exotic: native ratio in California grassland. In: Gordon, M., and Bartol, L. editors. University of California Press-Cooperative Extension. p. 154-179.

Interpretive Summary: California grasslands today are largely dominated by European grasses and forbs. Recently introduced shrubs are also successful invaders of many grassland sites. Some introduced species in California grassland are considered noxious and many are a detriment to sustaining ecosystem functions or societal values provided by these rangelands. Hence methods are being sought to reduce unwanted plant species while simultaneously increasing the abundance of native plant species on these sites. Here, we reviewed studies that attempted to shift the balance from non-native to native plant species in California grasslands using controlled experimental procedures. We focused mainly on the use of carbon applications (to reduce N availability), grazing, fire and biological control to reduce unwanted species and at the same time favor native species. We did not find any one procedure that was successful at tipping the balance. Several approaches and specific studies were successful in reducing the abundance of particular unwanted exotic species but native species did not simultaneously increase during or after control efforts. We conclude that more research is needed that combines different control methods while actively increasing native seed availability during removal and restoration.

Technical Abstract: As exotic species increasingly threaten native biodiversity, habitat managers have turned to a variety of tools designed to increase the efficiency of plant restoration projects. These efforts include eliminating exotic competitors through mechanical removal, herbicide application, or fire, and increasing native species' competitiveness relative to that of exotic species through reduction of soil nitrogen availability, grazing, prescribed burning, or biological control. In this chapter we evaluate the ability of experimental tests of these techniques to favor native species in California grassland ecosystems. We did not find evidence that any of the strategies consistently favored native species relative to exotic species. Outcomes were highly case specific, and likely varied with biotic and abiotic conditions in the experimental systems. Several studies suggest that these techniques are more successful in reducing specific invasive plant species in California grasslands rather than increasing the success of native revegetation. Limited availability of native propagules in the experimental systems likely limited the extent to which restoration techniques actually promoted native species. The most promising strategy for increasing native components in invaded ecosystems is likely to be the coordination of multiple strategies that address exotic species abundance, native seed or seedling availability, and the post-establishment competitiveness of the native species. Such an application of an integrated 'pest' management approach to the restoration of degraded habitats holds greater promise for the successful reestablishment of native biodiversity than simply targeting exotic species for removal.