OOS 5-6
Chaparral shrub re-establishment on type-converted slopes in southern California
Too-frequent fire and grazing can lead to conversion of chaparral to non-native annual grassland. Interest in chaparral restoration is growing among land managers and practitioners, as invasive annual grasses promote frequent fires, outcompete chaparral shrub seedlings, reduce biological diversity, and increase slope failures endangering downslope communities. We compared the effectiveness of two widely used herbicides (fluazifop, a grass-specific herbicide, and glyphosate, a broad-spectrum herbicide) in reducing non-native annual grass competition and promoting shrub establishment on type-converted slopes in southern California. We used a factorial design with three replicates: two restoration treatments (no restoration and planting seedlings) across three herbicide treatments (a January glyphosate application followed by an early-March fluazifop treatment, an early-March fluazifop treatment only, and a control treatment with no herbicide). Seedlings of Adenostoma fasciculatum, Eriogonum fasciculatum, Quercus berberidifolia, and Rhus ovata were planted into plots in January. Glyphosate was applied prior to planting. Seedlings were watered semi-monthly for one year. Soil water content was measured in April to assess the effect of herbicide treatments on soil moisture depletion with and without the presence of watered seedlings. Seedling survival and live plant canopy volume were measured to asses the effect of herbicide treatments on shrub establishment.
Results/Conclusions
In general, the early-season glyphosate treatment with a fluazifop follow-up was more effective at reducing grass competition with shrub seedlings than the late-season fluazifop-only treatment. The planted species did not behave similarly. No Q. berberidifolia seedlings survived the first year in any treatment. A. fasciculatum seedlings had higher survivorship in the glyphosate treatment than in other treatments. E. fasciculatum survivorship did not differ significantly between the glyphosate and the fluazifop-only treatments, but seedlings achieved higher live plant canopy volume in the glyphosate treatment. For R. ovata, the glyphosate treatment significantly increased survivorship over control levels, but the fluazifop-only treatment did not. Similarly, the glyphosate treatment increased soil moisture content over control levels, but the March fluazifop-only treatment did not. We suggest that winter herbicide application in a Mediterranean-type climate might benefit shrub re-establishment better than spring treatment by eliminating non-native annual grass competition for soil moisture sooner in the growing season.