Burning and mowing similarly increase prairie plant production in the spring, but not due to increased soil temperatures

Timothy L Dickson

doi:10.1002/ecs2.2606

Abstract

AbstractBurning and mowing are two of the most common grassland disturbances across millions of hectares worldwide, but uncertainty remains about when and why these disturbances increase plant production. One of the main hypotheses for increased plant production is that disturbances increase soil temperature in the early growing season and thereby increase plant growth. I tested this hypothesis using a multi‐decade study of the frequency (annual or quadrennial) and season (spring, summer, or autumn) of reconstructed tallgrass prairie burning and mowing. To determine plant production, I measured aboveground biomass during three periods of the 2015 growing season: (1) prior to mid‐May; (2) mid‐May to early July; and (3) early July to the end of the growing season in late September. I also measured soil temperatures from May 2014 to January 2016. This unique dataset allows a detailed picture of when burning and mowing are increasing plant production and whether these increases are likely caused by soil temperatures. I found that, compared to other treatments, autumn burning and mowing similarly increased plant production from the beginning of the growing season to mid‐May (autumn disturbances increased production from 37 to 77 g/m2) and, compared to other treatments, both autumn and spring burning and mowing similarly increased plant production from mid‐May to early July (autumn and spring disturbances increased production from 363 to 439 g/m2). Mowing had little effect on soil temperature but burning increased average daily maximum soil temperature at 2.5 cm depth by 6.4°C in the month after burning. Overall, these results suggest that burning did not increase early growing season plant production due to increased soil temperature, given that mowing similarly affected plant production but did not similarly affect soil temperature. I explore alternate explanations for changes in plant production, including increased light and nutrient availability, and decreased detritus.

Highlights

Grasslands require disturbance to prevent woody plant encroachment (Bragg and Hulbert 1976), and burning and mowing are two of the most common grassland management techniques
Annual burning in the spring has been shown to increase prairie plant production relative to unburnt prairie (Anderson et al 1970, Launchbaugh and Owensby 1978), and a more recent study suggests that annual autumn and winter burning increase prairie plant production the same amount as spring burning (Towne and Craine 2014, but see Towne and Owensby 1984)
The increased plant production that occurs after spring and autumn burning and mowing has been hypothesized to be caused by the increased soil temperatures in the early growing season (Rice and Parenti 1978)

Summary

Introduction

Grasslands require disturbance to prevent woody plant encroachment (Bragg and Hulbert 1976), and burning and mowing are two of the most common grassland management techniques. Millions of hectares of prairie are burned every year in central North America, primarily to prevent woody plant encroachment and improve cattle forage (Mohler and Goodin 2012) As another example, approximately 7 million hectares of federally managed roadsides in the USA are mowed to prevent woody plant encroachment, improve visibility, and reduce the likelihood of fires from discarded cigarettes and other ignition sources (Ament et al 2014). Approximately 7 million hectares of federally managed roadsides in the USA are mowed to prevent woody plant encroachment, improve visibility, and reduce the likelihood of fires from discarded cigarettes and other ignition sources (Ament et al 2014) Both burning and mowing can increase plant production, depending on the. The increased plant production that occurs after spring and autumn burning and mowing has been hypothesized to be caused by the increased soil temperatures in the early growing season (Rice and Parenti 1978)

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