Journal of Vegetation Science 24 (2013) 395–404 Changes in fire intensity have carry-over effects on plant responses after the next fire in southern California chaparral Jose ´ M. Moreno, Iva ´ n Torres, Bele ´ n Luna, Walter C. Oechel & Jon E. Keeley Keywords Adenostoma; Ceanothus; Fire cycle; Fire regime; Fire season; Fire severity; Post-fire recruitment; Seeder Nomenclature Munz (1974) Received 6 November 2011 Accepted 15 July 2012 Co-ordinating Editor: Kerry Woods Moreno, J.M. (corresponding author, josem.moreno@uclm.es), Torres, I. (ivan.torres@uclm.es) & Luna, B. (belen.luna@uclm.es): Department of Environmental Sciences, Universidad de Castilla-La Mancha, Toledo, 45071, Spain Oechel, W.C. (oechel@sunstroke.sdsu.edu): Global Change Research Group and Department of Biology, San Diego State University, San Diego, CA, 92182, USA Oechel, W.C.: CRI Fondazione Edmund Mach, San Michele all’Adige (TN), 38010, Italy Keeley, J.E. (jon_keeley@usgs.gov): U.S. Geological Survey, Western Ecological Research Center, Sequoia National Park, Three Rivers, CA, 93271, USA Keeley, J.E.: Department of Ecology & Evolutionary Biology, University of California, Los Angeles, CA, 90095, USA Abstract Question: Do variations in fire intensity within a stand determine changes in fire intensity and plant demographics in a subsequent fire? Location: San Diego (CA, USA); chaparral dominated by Adenostoma fascicula- tum (resprouter) and Ceanothus greggii (seeder). Methods: In 2003, a wildfire burned a young (16-yr-old) stand containing a set of experimental plots burned in 1987 with various levels of fire intensity. In 2004, all the 1987 plots were sampled for Adenostoma survival and the recruit- ment of both species. Similar measures were carried out in the adjacent old (75- yr) stand. Fire intensity in 2003 was estimated by a surrogate fire severity mea- sure [minimum diameter of burned branches (branch diameter)]. Results: In the young stand, branch diameter in 2003 was similar to the control plots in 1987, but lower than in the old stand. Fire intensity in 1987 did not sig- nificantly affect branch diameter in 2003. Survival of Adenostoma in the young stand was very low, much lower than after the 1987 burn and that in the old stand. Fire intensity in 1987 did not affect Adenostoma survival. Recruitment in Adenostoma increased, and in Ceanothus decreased, with increased fire intensity in 1987. Conclusions: We demonstrate that there is a carry-over effect of fire intensity across a whole fire cycle on plant recruitment of the two dominant species. The 2003 fire partially reversed the relative effects on recruitment caused by elevated fire intensity in 1987. Arguably, this effect was driven by the contrasted relation- ships of the two species to fire intensity. Adenostoma survival in the young stand was much lower in 2003 than in 1987, despite similar branch diameter, and was also lower than in the old stand, despite higher branch diameter in this case. The causes of such mortality are unknown. Introduction The energy liberated through combustion during a wild- fire is highly variable in space and time. As a fire spreads, fire-line intensity and spread rate will change across the landscape due to variations in fuel quantity and quality, wind and topography (Rothermel 1972). Furthermore, for any given place, similar changes can occur across seasons and years, because of variations in weather, climate and fuel as vegetation develops with time (Rothermel & Philpot 1973). Therefore, variations in the degree of heating to which plants may be exposed during fire are common within a fire (Odion & Davis 2000) and across fires (Hodgkinson 1991; Knapp & Keeley 2006). In general, as heating at the soil surface increases, plant mortality, including seeds, increases, and changes in species composition, dominance and spatial distribution may follow, as shown by numerous studies across many world ecosystems (Segura et al. 1998; Mor- rison 2002; Govender et al. 2006; Knox & Clarke 2006; Penman & Towerton 2008), including California chapar- ral (Moreno & Oechel 1991b, 1992, 1993; Rice 1993; Tyler 1996; Odion & Davis 2000; Keeley et al. 2005, 2008). Nevertheless, given the varying sensitivity of plants to heating in space and time (Wright 1970; Kauffman & Journal of Vegetation Science Doi: 10.1111/j.1654-1103.2012.01466.x © 2012 International Association for Vegetation Science 395