In the United States, prior to European settlement, vast areas of the country were associated with frequent fire regimes. However, many long-term studies on fire effects often target ecosystems with extended fire return intervals and succession is often studied. When research targets frequent fire return intervals, evaluation of effects usually spans a few years. A common assumption has been that this is sufficient to evaluate effects of frequent fires in different seasons and/or a range of frequencies however increasingly dependence on short-term studies is being questioned. This is due, in part, to growing awareness that in some frequent-fire ecosystems, many (perhaps most) dominant plant species (not just trees) are long-lived. Recently-developed models support the idea that large areas of the US once burned multiple times a decade and, in some areas, more frequently than every 2 years (on average). This provides an additional reason to improve understanding of effects of frequent fires. Our research is based in a native ecosystem dominated by longleaf pine (Pinus palustris) and once covering more than 37 million ha in the Southeast US.
Results/Conclusions
We present data based on complex treatments in seven different sampling years spanning 25 years. Treatments are six different complex fire regimes: fire every two, three, or five years in either winter or late spring plus a no burn treatment in each of three treatment blocks. The study site is Escambia Experimental Forest (USDA Forest Service) in south-central Alabama. Assessments have been made every 3-5 years and data collected on longleaf pine trees plus all hardwood stems > 2.5cm at breast height.
Evaluation of long-term data spanning 25 years evaluated outcomes related to small one or two-year differences in fire return intervals and four to five months between burn events. Surprisingly results revealed only small-moderate differences among treatments for longleaf pine survivorship and growth over much of the sample period. However, there were significant differences in number and size of hardwood stems. Over 25 years, fire regimes varying by only one or two-year frequencies resulted in ecologically significantly different outcomes. Season also eventually contributed to differences in hardwood stems. These outcomes suggest that long-term studies may be important in understanding many how other ecosystems respond to small differences in frequent disturbances.