Impact of a high-intensity fire on mixed evergreen and mixed conifer forests in the Peninsular Ranges of southern California, USA

Abstract

Fire is an important disturbance agent in the southern California landscape and plays a large role in the function and structure of its pine and mixed conifer forests. However, humans have changed the forest fire regime across the western United States by excluding fire. Fire suppression has been blamed for increasing stand densities and a shift from fire-tolerant trees to shade-tolerant but fire sensitive trees. These changes had been observed in Cuyamaca Rancho State Park (CRSP), Peninsular Ranges, San Diego County, California, USA. We surveyed an area in CRSP during the first two post-fire growing seasons following the October 2003 Cedar Fire, a historically large and severe fire, to determine patterns of tree mortality and vegetation recovery. This area is a mosaic of mixed evergreen and mixed conifer forest, oak woodland, chaparral and grassland. Most conifers were killed by the fire, especially smaller trees, and very few pine seedlings have established. Oaks were top-killed but most were resprouting by the second year, although larger oaks were more likely to have died than smaller. A rich herbaceous community of native annuals established in the first post-fire growing season. With a record rainy season during the winter of 2004–2005, all plant functional groups increased in abundance in the second year, including exotic annual grasses. The spread of exotic grasses in CRSP is a plant community change that may be of concern to resource managers. As forest succession is a long term process, it is important to continue monitoring vegetation recovery.