Response of Adenostoma Fasciculatum and Ceanothus Greggii Chaparral to Nutrient Additions

Abstract

(1) The purposes of this study were to determine if small quantities of fertilizer enhance the biomass production of annual plants and shrubs and influence the flowering and branching patterns of shrubs in chaparral vegetation. (2) Urea (8 g N m-2), superphosphate (4 g P m-2) and urea plus superphosphate ((8 g N + 4 g P) m-2), were applied in early spring 1978 to 26-year-old chaparral, with Adenostoma fasciculatum and Ceanothus greggii the predominant shrubs. Adenostoma responded to the three treatments by producing larger shoots in 1978. In 1979, without additional fertilizer, only the N treatment remained effective. For Ceanothus the largest response was to the P and N + P treatments in 1978. In 1979 shoots in all treatments were similar to or smaller than those in the control plots. (3) Phosphorus addition significantly increased the number of inflorescences in Adenostoma, although this effect did not last into the second year after fertilization. Likewise, N, P, and N + P produced a significant increase in the number of new shoots m-2 of canopy. In Ceanothus a fertilizer effect was not found on either inflorescence growth or the number of new shoots. (4) The above-ground biomass of annual species was significantly increased in 1978 and 1979 by N, and particularly by N + P. Phosphorus reduced the growth of annual species, especially grasses.