Plant species-specific responses and community associations with fire season

Abstract

Many temperate pine forests are characterized by midstory hardwood encroachment that inhibits timber production and limits herbaceous vegetation needed by wildlife. In the southeastern United States, lack of historical fire regimes compounds this problem and may require additional treatments to control woody vegetation. Research on fire season impacts on plant community dynamics exists, but studies often disagree on the most effective fire season for hardwood control. Our study evaluated the role species composition may have in overall plant community response to dormant season (March) and growing season (June) fire and explored associations with fire temperature 2 years post-fire in thinned (x = 22 m2 ha−1) loblolly pine (Pinus taeda) stands in east-central Mississippi. Growing season fire (Growing) reduced midstory stem density (shrubs and trees ≥ 1.37 m in height and ≤ 15 cm diameter at breast height) by 47 % relative to unburned control (Control) stands which did not differ from dormant season fire (Dormant; 1.3 % reduction). Five of 22 species responded to fire season similar to the midstory as a whole, but 77 % of species deviated. We identified 7 fire season response patterns, 3 of which are exemplified by: American beautyberry (Callicarpa americana) stem densities increased 135 % following Dormant, persimmon (Diospyros virginiana) decreased 32 % after Dormant, and mockernut hickory (Carya tomentosa) was unaffected by fire season. We found no influence of fire temperature on stem densities but Growing was hotter than Dormant with average temperatures of 376 (SE = 16) and 321 (SE = 12) C, respectively. In contrast to varied response patterns by midstory species, significant effects relative to Control in the understory include a 76 % increase in forb coverage by Growing and 18 % increase in grass coverage and 34 % increase in woody coverage by Dormant. Indicator species analyses showed non-native species in the midstory and understory were associated with Control and Dormant but not Growing. These results suggest the disparity in midstory community response reported in fire timing studies is partly due to differences in species composition. Managers can use these response patterns to tailor management plans to site conditions for a variety of objectives including timber production and wildlife.