Pine savanna overstorey influences on ground‐cover biodiversity

Abstract

Question: Does the overstorey of pine savannas influence plant species biodiversity in the ground cover? Location: Camp Whispering Pines (30°41' N; 90°29' W), eastern Louisiana (USA). Methods: We used ecologically sensitive restoration logging to remove patches of Pinus palustris (longleaf pine) in a second-growth loess plain Pinus palustris savanna managed using frequent lightning season fires. Five years later, we measured numbers of vascular plant species and transmitted light in replicated 100-m 2 plots. Treatments involved three different overstorey conditions: no overstorey for 5 years, no overstorey for several decades, and overstorey pines present for decades. Results: Both recent and long-term openings contained, on average, about 100 vascular plant species per 100 m 2 , 20% more than in similar-sized areas beneath overstorey trees. Responses varied with life form; more herbaceous species occurred in recent and older overstorey openings than beneath overstorey trees. Total numbers of all species and of less abundant forb species were positively and linearly related to light transmitted to ground level. Those species responding to openings in the overstorey and positively associated with increased transmitted light levels were monocarpic and shortlived perennial forb and grass species with a seed bank in the soil. In addition, community structure, as reflected in species composition and abundances, appeared to vary with canopy condition. Conclusions: Restoration involving ecologically sensitive removal of patches of overstorey pines in frequently burned pine savannas should benefit the ground cover and increase plant species biodiversity as a result of increased abundance of seed bank species.

Pyrogenic fuels produced by savanna trees can engineer humid savannas

“…Since 1990, management has included prescribed fires that mimic the 1-2 yr frequency and timing (fire season) of natural lightning-ignited fires in pine savannas (Platt 1999. A more detailed history of Camp Whispering Pines, its restoration and prescribed fire management, is presented in Platt et al (2006) and updated in Appendix S1.…”

“…Second, spatial variation in fire regimes generated by pyrogenic shed leaves should affect plant community dynamics. Pyrogenic fuels should increase understory light levels (e.g., Platt et al 2006), as well as generate and maintain conditions facilitating fire-resistant plant species when fires occur frequently. Small-scale heterogeneity in biodiversity has been noted in savannas (e.g., Stott 1988, Schmitz et al 2002, Uys et al 2004, Myers and Harms 2009, Sankaran 2009, Ratnam et al 2011, Veldman et al 2013.…”

The role of herbicide in savanna restoration: Effects of shrub reduction treatments on the understory and overstory of a longleaf pine flatwoods

“…The understory communities historically associated with longleaf pine are dominated by herbaceous plants adapted to frequent ground layer disturbance in the form of fire, and regular overstory disturbance by lightning, windthrow, and hurricanes (Platt and Rathbun, 1993;Platt et al, 2002). Native herbaceous species respond positively to the increased light levels in newly opened canopy gaps (Keddy et al, 2006;Platt et al, 2006), and it has been hypothesized that many of these species are such weak competitors for light that they could be considered fugitive or ephemeral (Keddy et al, 2006). Wiregrass (Aristida stricta Michx.…”

Drivers of plant functional group richness and beta diversity in fire‐dependent pine savannas

“…The reintroduction of fire has yielded a regional landscape dotted with fire-maintained savanna fragments. Many studies have provided valuable information about the factors affecting within-preserve plant species diversity and composition (i.e., fire frequency, land use history, hydrologic and soil gradients, and overstory-understory relationships) (Glitzenstein, Streng, Masters, Robertson, & Hermann, 2012;Kirkman, Mitchell, Helton, & Drew, 2001;Platt, Carr, Reilly, & Fahr, 2006;Veldman et al, 2014), but data on plant diversity patterns at the regional metacommunity level are lacking. With so many savanna preserves in the NACP now returned to a fire-maintained grass-tree structure, expanding to metacommunity-level biodiversity questions is timely.…”