Effects of fire on belowground biomass in Chihuahuan desert grassland

Shayla A Burnett,Jeffory A Hattey,Scott L Collins,Jennifer E Johnson,Douglas I Moore,Amaris L Swann

doi:10.1890/es12-00248.1

Abstract

Grasslands occupy large areas in the northern Chihuahaun Desert. These grasslands, dominated by Bouteloua eriopoda, are subjected to periodic drought, infrequent fire and grazing by herbivores. Previous work shows that B. eriopoda is sensitive to disturbance but much work has been based on aboveground responses. We evaluated seasonal and annual recovery of belowground production and biomass following fire at two sites in ungrazed B. eriopoda‐dominated grassland in Central New Mexico, USA. At one site, we quantified belowground standing crop and net primary production in burned and unburned areas during the first full growing season following wildfire the previous summer. At a second site, we measured annual below‐ and aboveground net primary production in burned and unburned grassland from 2005 through 2010 following a fire in 2003. At the first site, belowground standing crop did not change seasonally nor differ between burned/unburned areas. Patch types were different in that belowground standing crop was higher in soils under clumps of B. eriopoda than patches of unvegetated soil. Patterns of belowground biomass and daily production differed between patch types and over time in burned/unburned areas. Biomass was higher in soils below clumps of B. eriopoda than beneath unvegetated soil patches throughout the monsoon season. Patterns of belowground biomass and daily production differed in burned and unburned areas. Earlier in the growing season, biomass in the burned area was greater than in the unburned area. By early August, biomass increased rapidly in the unburned area and was higher than in the burned area. Daily rates of belowground production generally declined throughout the growing season with a large increase in rate of production in the unburned site in early August. At the second site's measured inter‐annual responses, annual belowground production did not differ consistently between burned/unburned grasslands nor over time, nor was belowground production correlated with aboveground production. Our results demonstrate that despite the years required for aboveground production to recover following fire in B. eriopoda‐dominated grassland, belowground standing crop and production was unchanged the year following fire. These results emphasize that aboveground production is not a reliable proxy for belowground production in this grassland.

Highlights

Net primary production (NPP) is a key integrating variable in terrestrial ecosystems (McNaughton et al 1989)
We found that belowground standing crop did not differ between burned and unburned areas of B. eriopoda grassland during the first full monsoon season following fire, nor did it change significantly over the growing season (Fig. 1)
Within-season belowground root biomass and daily production were initially higher in burned compared to unburned areas (Fig. 2)

Summary

Introduction

Net primary production (NPP) is a key integrating variable in terrestrial ecosystems (McNaughton et al 1989). Arid and semiarid ecosystems occupy approximately 40% of terrestrial lands (Reynolds et al 2007, Schimel 2010). These ecosystems are undergoing rapid transformations in response to climate change and land use management, especially desert grasslands that are experiencing changes in both fire frequency and grazing regimes. Aboveground production of B. eriopoda grasslands is strongly driven by seasonal (monsoon) precipitation and temperature (Gosz and Gosz 1996, Muldavin et al 2008, Collins et al 2010), but unlike aboveground responses the relationship between belowground production, climate and disturbance remains poorly understood (Ladwig et al 2012)

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