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Longleaf pines & fire in the growing season

Prescribed fire every two years had no impact on the growth or survival of mature longleaf pines – even when prescribed fire was conducted in the growing season, finds long-term experiment. USDA Forest Service scientist John Willis led a study comparing stands of Pinus palustris burned in winter, spring, and summer.

escambia-national-forest
In mature longleaf pine stands, prescribed fire in the growing season can reduce hardwood encroachment and promote wire grass. USDA Forest Service photo by John Willis.

Summer lightning often ignites fires in the South between May and August. However, prescribed fires have historically been set in winter, for fear that fire during the growing season would damage mature trees.

Bill Boyer established the study on the Escambia Experimental Forest in southern Alabama in 1973, when these trees were 15 years old, to show how biennial burning in different seasons affected longleaf pine growth and survival.

Boyer reported in 1987 that the season of burn had no significant effect on the growth of longleaf pine, but there was a productivity decline in trees that had been burned compared to those that had not.

Willis and collaborators continued Boyer’s work and examined the effect of seasonal, biennial burning in the same stands with trees from 37 to 60 years old. Their results indicate that season of burning has minimal impact on mature longleaf pine height, diameter, volume growth, or survival.

Smaller longleaf pines (2-inch diameter) were 40 percent more likely to die than larger longleaf pines (12-inch diameter), regardless of burn season.

This research has important implications for the maintenance of restored southeastern woodlands, as interest in burning – both during and outside of the dormant season – continues to grow.

Read the article in Frontiers in Forests and Global Change. For more information, email John Willis at john.willis@usda.gov.

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