PS 31-183 - Effects of fire on belowground biomass in a black grama grassland

Tuesday, August 9, 2011
Exhibit Hall 3, Austin Convention Center
Shayla A. Burnett, Plant Sciences, University of Wyoming, Laramie, WY, Scott L. Collins, Department of Biology, University of New Mexico, Albuquerque, NM, Jeffory A. Hattey, Plant and Soil Sciences, Oklahoma State University, Stillwater, OK, Jennifer E. Johnson, Biology Department, Stanford University, Palo Alto, CA and Amaris L. Swann, Biology, University of New Mexico, Sevilleta LTER, Albuquerque, NM

Chihuahuan Desert grasslands occupy large areas north of and interspersed within shrub-dominated vegetation in southwestern North America. These grasslands, dominated by Bouteloua eriopoda, are subjected to periodic drought, along with natural disturbances including fire and grazing. Previous work has shown that B. eriopoda is particularly sensitive to disturbance, but much of this work is based on aboveground responses, such as primary production. Recovery of belowground production and biomass in a B. eriopoda-dominated grassland was evaluated during the summer monsoon in 2010, the first full growing season following a lightning-caused wildfire the previous summer. Two sites were established, one in the burned area and one immediately across a dirt road that served as a firebreak. Root standing crop biomass was collected three times during the growing season using a bucket auger (0-15 cm, N=10), and belowground production was measured using root ingrowth bags buried in the top 15 cm of soil six times (N=10 per sample period) over the growing season.  Samples were collected from three different patch types in burned and unburned areas: bare soil, beneath clumps of B. eriopoda, and beneath clumps of B. eriopoda that were watered to simulate the start of the summer monsoon.


Belowground standing crop biomass did not change seasonally and did not differ between burned and unburned areas. However, patch types were significantly different in that belowground standing crop biomass was higher in soils under clumps of B. eriopoda (ranging from 1.05-1.40 g/L of soil) compared to patches of bare soil (0.15-0.4 g/L). Patterns of belowground production differed between patch types as well as over time in burned and unburned areas. Again, production was significantly higher in soils below clumps of B. eriopoda than in bare soil patches through out the monsoon season. Moreover, patterns of belowground production differed significantly in burned and unburned areas. Production in the burned area was significantly greater during the first three sample periods compared to belowground production in the unburned area. At the fourth sample period (early August), production increased rapidly in the unburned area and was significantly higher than in the burned area. Rates of production were comparable in burned and unburned areas during the last two sample periods. Watering early in the monsoon season had no effects on belowground production. These results demonstrate that despite the years it takes for aboveground production to recover following fire, belowground production can recover rapidly following burning.

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