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 profiles 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. Covariance
analysis showed that plant communities
allocate biomass components differently;
Tamaulipan thornscrub species have larger
root biomass allocation per unit Db than dry
temperate pine forests in early stages of development. Tamaulipan thornscrub roots are
more numerous, smaller and thinner, 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) play
an important role in explaining higher BGB:
ABG ratios, but differences can be eventually obscured by the developmental stage of
these plant communities.