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Chaparral shrublands burn in large high intensity crown fires. Managers interested in 23 how these wildfires affect ecosystem processes generally rely on surrogate measures of fire intensity 24 known as fire severity metrics, which typically measure organic matter loss aboveand 25 belowground. In California shrublands burned in the autumn of 2003, a study of 250 sites 26 distributed across five fires, investigated factors determining fire severity in these ecosystems and 27 the extent to which fire severity ecosystem responses. 28 Using structural equation modeling we showed that stand age, prefire shrub density and the 29 shortest interval of the prior fire history had significant direct effects on fire severity, explaining 30 over 50% of the variation in severity. 31 Fire severity per se is of interest to resource managers primarily because it is presumed to be an 32 indicator of important ecosystem processes such as vegetative regeneration, community recovery 33 and erosion. Our bivariate models as well as structural equation modeling showed that fire severity 34 contributed relatively little to explaining patterns of vegetative regeneration after fire, measured as 35 cover of all species or as resprouting success of shrubs. Where fire severity did affect recovery, two 36 generalizations can be drawn: fire severity effects are mostly short-lived, i.e., by the second year 37 they are greatly diminished, and fire severity may have opposite effects on different functional 38 types. 39 Species richness exhibited a highly significant negative relationship to fire severity in the first 40 year but fire severity impacts were substantially less in the second postfire year and varied by 41 functional type. Much of this relationship was due to alien plants that are sensitive to high fire 42 severity; at all scales from 1 – 1000 m, the percentage of alien species in the postfire flora declined 43 with increased fire severity. Other aspects of disturbance history are also important determinants of 44 alien cover and richness as both increased with the number of times the site had burned and 45 decreased with time since last fire. 46