Natural Canopy Damage and the Ecological Restoration of Fire-Indicative Groundcover Vegetation in an Oak-Pine Forest

J Stephen Brewer

doi:10.4996/fireecology.1202105

Abstract

An important goal of restoring fire to upland oak-dominated communities that have experienced fire exclusion is restoring groundcover plant species diversity and composition indicative of fire-maintained habitats. Several studies have shown that fire alone, however, may not be sufficient to accomplish this goal. Furthermore, treatment-driven declines in rare forest specialists could negate the benefits of ecological restoration in these ecosystems. I present the results of an experiment examining effects of tornado-generated canopy openings and biennial spring burning on groundcover vegetation at an oak-pine forest in north Mississippi, USA. Results from four years of monitoring showed that species richness and abundance of species indicative of fire-maintained open habitats were greater at sites with canopy damage than at sites with undamaged canopies, especially in years without drought. Annual ruderals increased initially following canopy damage but then decreased. Few forest indicator species changed in abundance, and the few that did increased. Canopy openings appeared to have a greater effect than fire on groundcover vegetation, although some legumes and panicgrasses appeared to benefit directly from fire. Results suggest that fire restoration treatments must include both canopy openings and fire to effectively increase the diversity and distinctiveness of groundcover vegetation in mixed oak-pine forests. Prescribed burning after years of fire exclusion, by itself, does not constitute effective restoration of fire (at least in the short term), but it also does not appear to reduce the abundance of rare, forest-specialist groundcover species.

Highlights

Throughout much of eastern North America, modern fire exclusion efforts have converted plant communities that previously were open habitats dominated by fire-tolerant tree species to more or less closed-canopy upland forests containing a mix of fire-tolerant and mesophytic tree species (Nowacki and Abrams 2008)
In contrast to what was observed before the tornado in 2006, after the tornado in 2009 but before the 2010 fires, groundcover plant species richness in severely disturbed subplots was significantly greater than in subplots that were not severely disturbed (F1,6 = 8.14; P = 0.014; Figure 2)
The weighted summed abundance of open habitat indicators and ruderals was greater in severely damaged subplots than in undamaged subplots (F1,6 = 6.02, P = 0.049, and F1,6 = 12.59, P = 0.012, respectively; Figure 3)

Summary

Introduction

Throughout much of eastern North America, modern fire exclusion efforts have converted plant communities that previously were open habitats dominated by fire-tolerant tree species to more or less closed-canopy upland forests containing a mix of fire-tolerant and mesophytic tree species (Nowacki and Abrams 2008). During the periods of early European settlement and before in the eastern and southern United States, fire frequency in many oak-dominated portions of the upland landscape was greater than observed following modern fire suppression in the twentieth century (Van Lear and Waldrop 1989, Delcourt and Delcourt 1998, Guyette and Spetich 2003, Hart et al 2008, Fesenmeyer and Christensen 2010, Spetich et al 2011). Modern fire exclusion (in addition to other land use changes) likely resulted in dramatic losses of groundcover plant production and diversity in these ecosystems (Smith 1994, Heikens and Robertson 1995, Taft 1997, Bowles and McBride 1998, Hutchinson et al 2005, Phillips and Waldrop 2008, Surrette and Brewer 2008, Brewer and Menzel 2009, McCord et al 2014, Brewer et al 2015). Like fire-maintained open habitats, forests dominated by fire-sensitive, mesophytic species have been dramatically altered, but would most likely benefit from protection from frequent or intense fires (Mola et al 2014). Both community types warrant serious consideration for protection and ecological restoration to maintain biodiversity

Methods

Results

Conclusion