Abstract
The coexistence of different species within arid and semi-arid ecosystems depend on numerous variables, including the amount of precipitation and the phenologies of constituent species. Since water availability in arid and semi-arid ecosystems is often the crucial limiting factor, the timing and magnitude of precipitation events can have a significant impact on plant growth, aboveground annual net primary productivity (ANPP), and species composition. In order to investigate how overall increases in seasonal precipitation due to global climate change may affect the plant growth, ANPP, species richness, and plant density of a Sotol Grassland ecosystem in Big Bend National Park, plots were set up using the following experimental manipulations: 1) no water addition, 2) summer water addition (25% of summer precipitation), 3) winter water addition (25% of winter precipitation), and 4) summer and winter water addition (25% of seasonal precipitation). For three years (2002-2004), precipitation was altered and plant growth and ANPP measurements focused on the three dominant species: Dasylirion leiophyllum - shrub; Bouteloua curtipendula – grass; Opuntia phaeacantha – succulent. Species richness and plant density was determined for each functional group (shrubs, succulents, herbs, and grasses). Past precipitation records within Big Bend National Park and regional records for the Trans Pecos area were also examined to see if precipitation patterns were following possible global climate model predictions. The climate records showed no significant patterns of greater or lesser annual or seasonal precipitation for the past 110 years. Most precipitation occur in small (
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