Synthesis of Watershed and Ecosystem Responses to Lehmann Lovegrass Invasion in a SE Arizona Desert Grassland Watershed
Abstract
Compared to aridland systems that have undergone rapid change in dominant vegetation growth form, the responses of watershed and ecosystem processes to a shift in dominance of similar growth forms have not been well-studied. Following a prolonged drought period (2000-2005) at the Walnut Gulch Experimental Watershed's Kendall grassland site (WS#112), near Tombstone, AZ, strong summer monsoon rains in 2006 were accompanied by widespread mortality most native perennial grasses, a transient increase in annual forbs, followed by establishment and sustained dominance by a single perennial grass, the invasive bunchgrass, Lehmann lovegrass (Eragrostis lehmanniana). This loss of ecological diversity occurred across a watershed already instrumented for quantifying long-term climate, watershed, hill-slope, and ecosystem-level gas exchange processes. Salient findings from these data sets were: 1) annual watershed sediment discharge rapidly returned to pre-invasion levels following a large spike in 2006 that accounted for 65% of the total sediment yield summed over 35 years, 2) plot-level experimental runoff studies showed hill-slope sediment yields consistently doubled, as did growing season soil evaporation contributions to ET, and 3) the grassland was a carbon sink during dry conditions under lovegrass dominance. These findings show that while some aspects of overall watershed and ecosystem function were not strongly affected (i.e. sediment yield and net primary productivity), processes acting at lower spatial and temporal scales have been negatively impacted by lovegrass dominance. We believe these lower-order processes underlie the strong ecological effects associated with Lehmann lovegrass invasion, and will also eventually alter landform processes and change the basic ecohydrological characteristics of desert grassland watersheds.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B24C..02H
- Keywords:
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- 0439 BIOGEOSCIENCES / Ecosystems;
- structure and dynamics;
- 1630 GLOBAL CHANGE / Impacts of global change;
- 1879 HYDROLOGY / Watershed