Condalia

Abstract: Experimental fall burning of South Texas chaparral communities significantly reduced canopy of all brush species in untreated areas and in areas previously treated by roller chopping, shredding, and scalping. There was a highly significant (P < .01) reduction in frequency of occurrence of lotebush (Condalia obtusifolia (Hook.) Weberb.), lycium (Lycium berlandieri Dunal.), and creeping mesquite (Prosopis reptans Benth. var. cinerascens (Gray) Burkart). Frequencies of occurrence of brasil (Condalia obovata Hook.) and Mexican persimmon (Diospyros texana Scheele) were significantly reduced (P < .05). There was no sgnificant difference in total amount of grass on burned and unburned areas 1 year following the fire. Filly panic (Panicum filipes Scribn.), buffalograss (Buchloe dactyloides (Nutt.) Engelm.), and meadow dropseed (Sporobolus asper var. hookeri (Trin.) Vasey) were more abundant on burned than on unburned areas. Plains bristlegrass (Setaria leucopila Scribn. and Merr.) was less abundant on burned areas than on unburned areas. Forb production was significantly (P <. 01) less on burned than on unburned areas, mostly because of reduction in western ragweed (Ambrosia psilostachya DC.) and Texas broomweed (Xanthocephlum texanum (DC.) Shinners). Fire could have been responsible for the creation of the brush mottes described by early explorers. The study substantiates the theory that fire suppressed brush on south Texas grasslands.

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.