Plant-water use in a Woody Encroached Subtropical Savanna: Have we been blaming Mesquites too long for too little?
Abstract
South Texas has seen extensive woody encroachment in the last century. Since its grassland state in the 1800s, these landscapes have undergone a dramatic shift in its vegetation structure. In addition to Prosopis glandulosa (Honey Mesquite) and Vachellia farnesiana (Sweet Acacia), these shrublands are also composed of several other woody plant species, such as Diospyros texana (Texas persimmon). These plant species thrive despite a subtropical climate marked by extreme heat and precipitation events with high inter-annual variability. However, little is known about the ecohydrological traits that allows for such adaptation. The objective of this study was to a) estimate the amount of water used by two co-occurring tree species (P. glandulosa, D. texana) in two different landform locations (upland and drainage) and b) identify the abiotic drivers and limitations for transpiration in these two species. We hypothesized that the trees in the drainage plot would have greater transpiration rates than the upland plot, and that mesquites would have greater water use than persimmons owing to their deeper roots. To assess these objectives, Granier type TDP probes were used to monitor sap flux density of seven tree individuals of each species from Aug 2017 until July 2018. Micrometeorological data was collected from an eddy covariance tower at a neighboring shrubland site. Contrary to our hypotheses, transpiration rates were higher for upland locations indicating a possible role of lateral root spreads and more soil moisture exploration. Daily water uptake in persimmon was higher than mesquites and this persisted over the winter too. While vapor pressure deficits exerted control on a shorter time-scale, soil moisture availability was a dominant driver of transpiration at the seasonal level. Our results provide three broad implications for these landscapes: 1) lowland locations do not necessarily confer a competitive advantage to woody plants; 2) secondary succession species contribute more than the pioneer species to the ET budget in these shrublands; 3) coupling between drought-deciduous phenology with the seasonality of precipitation could be an important control for the productivity of these systems.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B21M2531B
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCESDE: 1630 Impacts of global change;
- GLOBAL CHANGEDE: 1813 Eco-hydrology;
- HYDROLOGY