Prescribed fire effects in a longleaf pine (Pinus palustris) ecosystem: Are winter fires working?

Background/Question/Methods

Longleaf pine (Pinus palustris) ecosystems once dominated 60-90 million acres and it is suggested that some remnant stands continue to support one of the most diverse floras in North America.  It is well-known that longleaf pine ecosystems must burn frequently to maintain natural structure and function.  This vegetation type ranks as one of the most fire-dependent ones in the country and must burn frequently (multiple times a decade) for natural structure and function to be maintained.  Frequent fires maintain relatively low fuel loads and so many burns do not directly affect adult longleaf trees.  However, other species are immediately affected by each fire that burns through a stand.  Because many resident species are perennials that re-sprout after fires, it likely takes multiple burns to change the plant assemblage of the ground layer.  There is a need is for better insight into fire effects on small woody stems in the ground layer.  How and when fire is applied should influence the likelihood as to whether hardwood stems will overtake the ground layer, cast increasing shade over herbaceous species long before the woody species become understory shrubs and trees. 

Results/Conclusions

For decades, most prescribed fires in longleaf pine ecosystems were conducted during the winter months, usually on a 3-year cycle.  In 1974, the US Forest Service established field trials on the Escambia Experimental Forest (EEF) in south-central Alabama to study the impact of biennial prescribed burns in the spring, summer, and winter, as well as a no burn treatment on longleaf pine as well as the woody and herbaceous layer.  As a result of the negative impacts to longleaf pine growth, a study was established in 1984 to follow up the above study.  The summer fire treatment was removed, and the frequency between fires was expanded to include 3-year and 5-year return intervals.  The hardwood species composition from each of the season of burn and fire frequency treatments will be discussed.  Winter burning has not removed what are considered to be fire intolerant species such as water oak (Quercus nigra), and sweetgum (Liquidambar styraciflua), from the landscape.  These species will make future fires more difficult to make and eventually make it difficult to regenerate longleaf pine.  We need to do a better job with our burning or longleaf pine will be lost from the landscape.