The reproductive response of an endemic bunchgrass indicates historical timing of a keystone process

Jennifer M Fill,Timothy A Mousseau,Shane M Welch,Jayme L Waldron

doi:10.1890/es12-00044.1

Abstract

Restoration of the Pinus palustris (longleaf pine)‐wiregrass ecosystem of the southeastern United States requires information on reference conditions such as the historical fire regime. Aristida beyrichiana (wiregrass), a keystone perennial bunchgrass, was historically widespread throughout the southeast, but its dependence upon growing season fires for sexual reproduction hastened its decline in the face of decades of human fire suppression. The reproductive response of wiregrass is described by patterns of meristem allocation between competing life history strategies (i.e., vegetative growth vs. sexual reproduction). The temporal link between fire and flowering indicates this allocation was optimized to the historical fire regime through selection. In this study, we used the observed allocation of wiregrass reproductive effort to sexual reproduction as the response variable to examine reproductive response to fire season, using plant size as a covariate. Sexual reproduction was positively associated with plant size. Plants burned during early summer (May–June) produced a greater proportion of inflorescences than did those burned in early spring (March–April) or in late summer (August). Using state records of natural (lightning‐ignited) and anthropogenic (human‐ignited) fires from historical (1933–1946) and contemporary (1998–2010) periods we found that the distribution of maximum wiregrass reproductive output most closely reflected the distribution of historical fires with natural ignition sources. Moreover, while the monthly distributions of historical and contemporary fires were different for anthropogenic ignitions, they did not differ for fires with natural ignitions. Our predictions of peak allocation based upon the biology of wiregrass provide strong support for the use of wiregrass as an indicator of the historical fire season (early summer). Efforts to restore the longleaf pine ecosystem should therefore consider the biological response of wiregrass in planning prescribed fires.

Highlights

A central goal of ecological restoration is to assist in the recovery of a natural system that has been damaged by human activities
Contemporary and historical distributions of anthropogenic fires, which were more common during the dormant season, were dissimilar to wiregrass reproductive response (Fig. 3)
Our application of life history theory to wiregrass reproductive allocation patterns demonstrated that the fitness advantage of sexual reproduction was greatest after growing season fires

Summary

Introduction

A central goal of ecological restoration is to assist in the recovery of a natural system that has been damaged by human activities. Within this context, ‘recovery’ is relative to a pre-degraded reference condition, and restoration is based on re-establishing historical trajectories defined by structural and functional interactions that encompass native species and ecological processes (Society for Ecological Restoration 2004). The natural fire regime required a high degree of landscape connectivity that resulted from interactions among regional topography (van Lear et al 2005) and firefacilitating vegetation (Beckage et al 2005) that encouraged fires to burn for extended periods of time and, under favorable climatic conditions, to spread over vast areas (Slocum et al 2010a). An emergent property of this landscape dynamic was a fire feedback that increased the frequency an area burned by allowing ignition sources to occur at great distances (Beckage et al 2005, 2011, van Lear et al 2005)

Objectives

Methods

Results

Conclusion