Nutrient Changes in Two Chaparral Shrubs Along a Fire‐induced Age Gradient

Adenostoma fasciculatum H. & A. and Ceanothus leucodermis Green in chaparral stands of the foothill zone of Sequoia National Park, California, show a rapid decline in foliage concentrations of nitrogen over the first six years following fire. This is followed by a more gradual decline over succeeding years. Phosphorus concentrations show a similar early decline, followed by an increase in older age stands. Considerable data suggest luxury consumption of nutrients in both species following fire. Following a sharp increase in aboveground nutrients per unit of Adenostoma canopy area for the first 16 years of growth, a plateau is reached. The contemporaneous occurrence of restricted net nutrient uptake and observed stand senescence suggest a possibility of a causal relationship. Natural chaparral fire frequencies promote fire‐cycling of nutrients at intervals consistent with periods when nutrient availability becomes limiting. The fire‐nutrient interactions are of critical importance in influencing quality and quantity of suitable browse for vertebrate herbivores.