Document: DAV-3-35-27

Ecophysiology and phenology of chaparral shrubs: A multivariate, comparative study.

ACKERLY, D.D.* and K.P.STARMER

Stanford University, Stanford, CA, USA ¹

Abstract:
Studies of functional variation in chaparral shrubs have focused on three features: carbon gain strategies, water relations, and post-fire regeneration strategies. In this study, we examined numerous ecophysiological, functional, and phenological attributes in 20 coexisting shrub species to test whether these three axes are independent of each other, and to determine the major axes of functional variation which may contribute to species' coexistence. Quantitative analysis of vegetative phenology demonstrated that there was a continuum of leaf life span, which was negatively correlated with specific leaf area (SLA), leaf nitrogen content, and assimilation rates. The deciduous vs. evergreen distinction reflected this variation, but there was no evidence of discrete functional groups along this continuum. SLA was also significantly correlated with realized niche distributions along an exposure gradient of north- to south-facing slopes (i.e., lower SLA in species occupying more exposed locations). Predawn and midday water potentials were positively correlated with leaf size and negatively correlated with basal stem number (a measure of "shrubbiness"), suggesting a major functional axis related to growth form and drought tolerance. This variation was largely independent of SLA and associated traits. There were no significant differences in functional traits between species exhibiting different post-fire regeneration strategies (facultative vs. obligate resprouters). These results demonstrate that leaf size and SLA define two independent axes of functional variation associated with resource acquisition and stress tolerance.

Keywords:

This abstract is being presented at: 1:00 PM in session:
Oral Session #16: Plant Demography: Trees and Shrubs.