Thresholds for exotic forb control to restore coastal sage scrub vegetation

Дата канвертавання19.04.2016
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Thresholds for exotic forb control to restore coastal sage scrub vegetation

Kristin Weathers & Edith Allen, Department of Botany and Plant Sciences

University of California Riverside, CA 92521-0124

Many damaged ecosystems do not recover after a management action. This suggests that restoration thresholds, or barriers, exist that prevent the system from returning to a less degraded state. Identifying these thresholds helps to prioritize management activities , as well as improve restoration success. The coastal sage scrub plant community (CSS) is being widely replaced by thick stands of invasive annual grasses. Studies have documented that when the cover of exotic grasses is removed, establishment of the native shrubs species fails to occur, even with the addition of seed. Native forbs return, but in lesser proportions than exotic annual forbs of the genus Erodium. Our objectives are to test whether high densities of exotic forbs in the genus Erodium act as a constraint on restoration of the coastal sage scrub community and, if so, to identify density thresholds where significant reductions in the establishment of native species occur. Two experiments will be initiated. In the additive competiton seeding experiment seven densities of Erodium cicutarium will be seeded with a single density of one of two natives, a native annual forb, Cryptantha intermedia, a native shrub, Artemisia californica. The second is a removal experiment at a northeastern San Diego County Park burned by wildfire in 2003, following which dense stands of Erodium botrys became established. Erodium botrys will be removed from the plots by hand in order to establish same 7 different Erodium density treatments as in the first experiment. Half of these plot will be seeded with Cryptantha and the other half with Artemisia. For both experiments the density and percent cover of Erodium and of native plants in each plot will be determined at the peak of the growing season. The response of the native species will be measured so that a regression of response of native emergence and growth based on Erodium density can be calculated.

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