PLASTICITY OF BIOMASS COMPONENT ALLOCATION PATTERNS IN SEMIARID TAMAULIPAN THORNSCRUB AND DRY TEMPERATE PINE SPECIES OF NORTHEASTERN MEXICO

Abstract

The question of how plant communities respond to variation in the availability of resources in the environment was answered by testing the hypotheses of true adjustments and ontogenetic drift in biomass allocation patterns. The slopes of allometric equations that estimate biomass components as a function of diameter at breast height, D; root profi les, and the ratio of belowground to aboveground biomass, BGB:AGB, vs. basal diameter, Db, supported these hypotheses in Mexico’s northeast Tamaulipan thornscrub and dry temperate pine forests. The results showed through a covariance analysis that plant communities allocate biomass components differently; Tamaulipan thornscrub species having larger root biomass allocation per unit Db than dry temperate pine forests in the early stages of development. Tamaulipan thornscrub roots are smaller and less thick and larger in number, and differences in taper were noted for both lateral and tap root systems. This report concludes that environmental factors (more abundant soil nutrients, but less water availability in Tamaulipan thornscrub communities) plays an important role in explaining higher BGB: ABG ratios but differences can be eventually obscured by the developmental stage of these plant communities.