5th Symposium on Fire and Forest Meteorology and the 2nd International Wildland Fire Ecology and Fire Management Congress

Tuesday, 18 November 2003: 11:00 AM
Fine fuel characteristics: differences among grass species and significance for prescribe fire management in longleaf pine forests
Sharon M. Hermann, Auburn University, Auburn, AL
When ground cover vegetation is considered as fuel for fire, components are often categorized based on growth form (grasses, forbs, shrubs, etc.), in large part because the relative abundance of the various growth forms is often correlated with characteristics of the associated fuels. Across the geographic range of longleaf pine forests in the southeast United States, there are regional differences in ground cover species composition, especially as it relates to the presence/absence of species of grass. Wiregrass (Aristida stricta and A. beyrichiana) is usually dominate in the lower coastal plain from North Carolina through Alabama but is absent from Mississippi to east Texas as well as in the entire inland portion of the range of longleaf pine. In the non-wiregrass region, various species of Andropogon (bluestem) and other grasses make up a large part of the fine fuel. This is also true in lower coastal plain sites where past land use has eliminated wiregrass.

There is documentation of variation of growth and flowering responses of wiregrass compared to other grasses in response to fire, especially season/month of burn. However, there has been little consideration of possible differences among grass species in regards to their contribution to the quality of a site’s fine fuel. Variation in relative moisture content of live and dead above ground vegetation is one of many factors that may be related to differences fire effects. Data from various grasses reveal differences among species and within live and dead material of a species. During May and June, at sites where species co-occur and during periods of no drought stress (Keetch-Byram Drought Index < 300), wiregrass tissue contained ~ 75% of moisture content compared to bluestem species (Andropogon virginicus and A. gerardii). This difference holds for both green and brown material. The relative moisture content found in fronds of bracken fern (Pteridium aquilinum) is similar to that of wiregrass leaves.

Differences in species’ relative moisture content should translate into differences in effectiveness of prescribed fire. Variation in relative moisture content among dominate grasses suggests that ground cover species composition may be an important consideration for the development of the specifics of a site’s burn plan. Under similar burn conditions, the presence of wiregrass should result in at least a small increase in fire severity compared to non-wiregrass sites. Burn regimes applied in wiregrass habitat are not expected to produce identical outcomes when applied to non-wiregrass sites. Such differences should be considered when planning management for conservation of species of special concern such as the federally-listed red-cockaded woodpecker. To enhance restoration of open-canopied forest structure in non-wiregrass areas, it may be necessary to modify prescribed fire plans designed for wiregrass sites. Possible alterations include creating slightly more extreme burn conditions and/or increasing fire frequency.

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