Allometry of the pyrophyticAristidain fire‐maintained longleaf pine–wiregrass ecosystems

Abstract

Premise of the Study Aboveground biomass (AGB) of herbaceous vegetation is a primary source of fuel in frequent surface fires that maintain grasslands, savannas, and woodlands. Methods for nondestructively estimating AGB are required to understand the mechanisms by which fuels affect fire behavior and the effects of time since the last burn. We developed allometric equations to estimate AGB in wiregrass (Aristida beyrichiana/A. stricta), a dominant bunchgrass in Pinus palustris ecosystems and a key species for ecological restoration. Methods We collected wiregrass from North Carolina to Florida, across a range of time‐since‐last burn and site types. We tested 32 mixed effect models to see which predictors were best at predicting live, dead, and total AGB. We also examined how time since burn (TSB) affected the live‐to‐dead ratio (LDR) using regression. Key Results Wiregrass AGB was found to increase with increasing latitude (relative to tussock volume), possibly due to an increase in precipitation, and was greater on more fertile clay soils and flatwoods than on sandy soils. The LDR decreased as a power function with TSB, resulting in rapid accumulation of dead, highly flammable, biomass in the fire‐free period. Conclusions Greater biomass will support fires of higher intensity. Our models can be useful in the parameterization of future physics‐based models to predict fire behavior. Understanding the environmental variables that influence the allometry of wiregrass should help increase the precision of AGB estimates and the subsequent effects on fire behavior and effects on neighboring vegetation.

Coupling Terrestrial Laser Scanning with 3D Fuel Biomass Sampling for Advancing Wildland Fuels Characterization

“…The primary grass species at Pebble Hill is wiregrass (Aristida stricta), as opposed to a broader mix of grasses at Eglin. Shearman et al (2019) reported that basal volume of the grass tussock was a strong predictor of total aboveground biomass of wiregrass clumps, also describing a local range of biomass at fine scales (both live and dead) at approximately ±200 g. From our results, we hypothesize that biomass density is more variable than suggested by occupied volume estimates.…”

Pyrogenic flowering of Aristida beyrichiana following 50 years of fire exclusion

“…, Crone and Rapp ). Increased fire‐free periods have been shown to have a negative effect on live aboveground biomass for a given sized wiregrass tussock (Shearman et al., ). Presumably, long fire‐free periods would also reduce belowground biomass such as nonstructural carbohydrates.…”

“…Resource budget models are hypothesized to be a mechanism for synchronized masting in plants and assume that individual plants will only flower when they reach a certain threshold of stored nonstructural carbohydrate reserves (Crone et al 2009, Crone andRapp 2014). Increased fire-free periods have been shown to have a negative effect on live aboveground biomass for a given sized wiregrass tussock (Shearman et al, 2019). Presumably, long fire-free periods would also reduce belowground biomass such as nonstructural carbohydrates.…”

Non-Destructive Fuel Volume Measurements Can Estimate Fine-Scale Biomass across Surface Fuel Types in a Frequently Burned Ecosystem

“…Wiregrass, the dominant herbaceous component in this ecosystem, has a dense crown closer to the forest floor and accumulates senesced material around the crown [40][41][42]. Given that these plots had two years of growth since the last fire and a long history of frequent fire (40 years) [39], our results corroborated that the crown was dense enough to have a different bulk density than the upper portions of the plant [42]. As such, applying a height metric for herbaceous fuel estimates is required to accurately represent the vertical distribution of a major component of the fuelbed.…”