Structural Changes in Chamise (Adenostoma fasciculatum) along a Fire-induced Age Gradient

Abstract

Chamise (Adenostoma fasciculatum) undergoes major structural changes in above-ground biomass along a gradient of increasing stand age since fire. Shrub growth in volume and biomass is rapid through 16 years but levels off in older stands. In this early phase of linear biomass increase, net above-ground productivity has a mean of 430 g yr-1 for each shrub, or 60 g m-2 yr-1 over the period of 2-16 years stand age. Individual shrubs at 37 years in Sequoia in the southern Sierra Nevada have more than twice the biomass and four times the annual above-ground productivity of chamise of similar age in the San Gabriel Mountains of Los Angeles County. Between 16 and 37 years, shrub senescence increases with no increase in above-ground biomass and a sharp reduction of available photosynthetic surface area. Total stand biomass continues increasing with stand age up to 37 years as shrub biomass increases, with a maximum at approximately 15,000 kg ha-1. Fine fuels less than 10 mm comprise more than 500 g m-2 in all chamise canopy ages, providing an important structural element of flammability.