Shrub recruitment 10 years following fire on type-converted and native chaparral watersheds of San Dimas Experimental Forest, California

Abstract

Following the 1960 Johnstone wildfire, some areas on the San Dimas Experimental Forest, CA were type-converted from native chaparral to non-native grasses. In 2002, the Williams fire re-burned much of the same area. In 2012, vegetation was measured to document post-fire chaparral recruitment and recovery in the presence and absence of these previous typeconversions. Six 1-3 ha (2.5-7.5 ac) watersheds were studied: three type-converted and three native chaparral. Of 59 plant species identified, 49 were native. Mean cover values for subshrubs and grass were significantly greater in type-converted watersheds compared to native chaparral. In contrast, shrub, litter, total live and total cover values were significantly greater in native chaparral watersheds than type-converted. Tree, forb and bare soil cover values were similar among all watersheds. Shrubs and sub-shrubs combined provided 76 percent cover on type-converted watersheds and 114 percent on chaparral watersheds. Type-converted grass cover was mostly Ehrharta calycina with values between 4 and 40 percent compared to 6-8 percent in native chaparral watersheds. Over 52 years after type-conversion and 10 years following fire, results show that sub-shrubs and woody shrubs re-established in both typeconverted and native chaparral watersheds. While all watersheds were mostly soft and hard chaparral species, two of three type-converted watersheds had a significant component of non-native grass cover. Future disturbances such as close interval wildfire or climate change may further contribute to non-native annual and perennial grass expansion, possibly changing the community recovery dynamics. Further research is needed to identify how and if these historical disturbances will continue to affect this unique landscape and its associated plant assemblages.

Parent Publication

• Proceedings of the chaparral restoration workshop, California

Citation

Corcoran, Bonni M.; Narog, Marcia G.; Wohlgemuth, Peter M. 2019. Shrub recruitment 10 years following fire on type-converted and native chaparral watersheds of San Dimas Experimental Forest, California. In: Narog, Marcia, tech. coord. Proceedings of the chaparral restoration workshop, California. Gen. Tech. Rep. PSW-GTR-265. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 19-35.