Effects of variation in soil heating during fire on patterns of plant establishment and regrowth in maritime chaparral

I related patterns of chaparral regeneration to spatial variability of surface heating during fire and its effect on seeds and resprout propagules. Three burns were studied. All took place on the Burton Mesa in northern Santa Barbara County. Sites were on level terrain where eolian sand supports maritime chaparral. This chaparral is composed of the widespread dominant, Adenostoma fasciculatum, capable of resprouting, and locally endemic Ceanothus and Arctostaphylos, which can only regenerate from seed the first year after fire.;The first burn in 1986 (Chapter I) was used to test procedures for the more detailed studies to follow. Patterns in vegetation and seed assemblages along a 24 m transect were investigated in relation to soil temperatures during burning. Maximum soil temperatures were lowest in 1-2 m gaps in the pre-burn canopy. Post-burn vegetation was very patchy, with 4-6 m wide former understory areas nearly devoid of seedlings, and former gaps supporting high densities. Numbers of germinable seed after fire were highest in gaps. Direct soil heating effects could not be adequately determined because refractory seed in pre-burn samples was not quantified.;For the second and third fires in 1988 and 1989 (Chapters II-IV), I established transects consisting of 47 contiguous m;Seed populations diminished greatly with fire, and much more in areas of greater heating. This rearranged patterns in seed abundance and reflected the heating pattern imprinted into the soil by glowing combustion. Seedlings and resprouts in the field also exhibited this pattern. Depth of burial was important to seed survival, for example, seeds of Arctostaphylos and Ceanothus were deeper and suffered lower mortality than those of Adenostoma. Experimental reversal of gap and adjacent understory fuel reversed patterns in seeds and seedlings after fire, even though seeds were more abundant before fire in gaps. Regeneration patterns were not appreciably modified during 5 years of vegetation development following fires. Thus, species distributions after fire are directly linked to the pre-burn vegetation through its effect on patterns in seeds and resprouts during combustion, and these patterns are manifest in long-term community structure.