Plant Ecology 160: 193–205, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. 193 Leaf demography and growth responses to altered resource availability in woody plants of contrasting leaf habit in a subtropical savanna Jim A. Nelson 1,∗ , Paul W. Barnes 1 & Steve Archer 2 1 Department of Biology, Southwest Texas State University, San Marcos, Texas 78666-4616, USA; 2 Department of Rangeland Ecology and Management, Texas A&M University, College Station, Texas 77843-2126, USA; ∗ Current address: USDA/ARS Crops Research Laboratory, 1701 Centre Ave, Fort Collins, CO 80526, USA (E-mail: janelson@lamar.colostate.edu) Received 29 July 2000; accepted in revised form 30 January 2001 Key words: Functional groups, Leaf longevity, Leaf habit, Resource partitioning, Soil moisture Abstract Leaf demography and growth of six common, co-occurring woody plant species that varied in stature (tree vs. shrub) and leaf texture (sclerophyllous, coriaceous, malacophyllous) were examined in a subtropical savanna parkland in southern Texas, USA. We tested the hypotheses that, (a) leaves of plants with evergreen canopies would have longer life spans than those of deciduous species; (b) supplementation of soil moisture would decrease leaf life span in both evergreen and deciduous species; (c) species responses to increased soil moisture availability would be inversely related to leaf longevity; and (d) deciduous growth forms would exhibit a greater growth response to increased soil moisture availability than their evergreen counterparts. A variety of seasonal leaf habits (evergreen, winter-deciduous and summer-deciduous canopies) and leaf life spans (median = 66 to 283 days) were represented by the targeted species, but there was no clear relationship between seasonal leaf habit and leaf longevity. Among species with evergreen canopies, median leaf longevity ranged from short (Zanthoxylum fagara = 116 days; Condalia hookeri = 158 days) to long (Berberis trifoliolata = 283 days) but did not exceed 1 yr. In fact, leaf longevity in evergreen shrubs was often comparable to, or shorter than, that of species with deciduous canopies (Ziziphus obtusifolia = 66 days; Diospyros texana = 119 days; Prosopis glandulosa = 207 days). Augmentation of surface soil moisture had no detectable effect on median leaf life span in any species and there was no clear relationship between leaf longevity and species growth responses to irrigation. Contrary to expectations, species with evergreen canopies responded to irrigation by producing more leaf biomass, longer shoots and more leaf cohorts/year than did deciduous species. Species differences in the annual cycle of leaf initiation, leaf longevity and canopy development, combined with contrasts in root distributions and a highly variable climate, may allow for spatial and temporal partitioning of resources and hence, woody species coexistence and diversity in this system. However, the lack of expected relationships between leaf longevity, leaf habit and plant responses to resource enhancement suggests that structure- function relationships and functional groupings developed in strongly seasonal environments cannot be applied with confidence to these subtropical savannas and thorn woodlands. Introduction Leaf life span and leaf habit (i.e., evergreen, decid- uous, etc.) are important plant life history traits that have been linked to a number of plant and ecosystem- level processes, including photosynthetic capacity, growth rate, primary productivity and nutrient cycling (e.g., Shaver 1981; Coley 1988; Reich et al. 1992; Gower et al. 1993). Thus, these traits are widely re- garded as important attributes in the classification of plant functional types (Chabot & Hicks 1982; Mooney & Gulmon 1982; Box 1995; Chapin et al. 1996; Reich et al. 1997).