COS 93-7 - Fire disturbance impacts on woodland dynamics

Thursday, August 11, 2011: 10:10 AM
9AB, Austin Convention Center
Jian Yao, The Institute of Ecological, Earth, and Environmental Sciences, Baylor University, Waco, TX, Joseph D. White, The Institute of Ecological, Earth, and Environmental Science, Baylor University, Waco, TX and Darrel B. Murray, Biology, Baylor University, Waco, TX

Woodland ecosystems play an important role in the mitigation of climate change as they are a large pool of terrestrial carbon. Fire has been the primary disturbance in woodland ecosystem and has profound impact on woodland dynamics, including carbon sequestration process, alteration of community structure, and biogeochemical cycling. We conducted a field survey in the woodlands of the Balcones Canyonlands National Wildlife Refuge (BCNWR) to study these impacts. Based on the fire disturbance information from the previous regional tree ring study and historical aerial photographic analysis, sixty study sites with different fire histories were selected and separated into three groups: no fire treatment, old fire treatment (>=30 years), and recent fire treatment (<30 year). At each study site, parameters such as species name, tree cover, tree diameter at breast height (dbh), and tree height were recorded. Four soil samples were also collected from each site. Total biomass was calculated from the published allometric equations and total soil carbon was assessed by an elemental analyzer from collected soil samples. The soil C/N ratio and charcoal content were also analyzed to study the impact of fire on biogeochemical cycling and total site carbon.


The calculated average above ground woody biomass for recently burned stands was 7.4±2.9 kg.m-2, and for stands from older burns was 11.0±3.5 kg.m-2, and were both significantly less than the above ground living woody biomass in the undisturbed stands with 13.7±2.6 kg.m-2 (P<0.05). The average regional biomass accumulation rate following a non-stand replacing fire was assessed to be approximately 0.1 kg.m-2.yr-1. Vegetation community succession study showed that recently disturbed stands have slightly higher densities of juniper with values of 290 stem.ha-1 compared with oak species of 180 stem.ha-1. Undisturbed stands and stands from older fires had higher densities of oak (350 stem.ha-1) compared with juniper (300 stem.ha-1). Juniper appears to dominate sites faster after fires relative to oaks.  However, recruitment favors oaks as more oak seedlings are likely to grow into mature trees.

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