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

Abstract

Burning 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.

Effects of burning and mowing on the soil microbiome of restored tallgrass prairie

“…Burning is a dramatic factor affecting the tallgrass prairie ecosystem through increases in the soil temperature and pH, decreases in soil moisture and the loss of nitrogen (Hulbert, 1986; Kennard & Gholz, 2001; Mitros, Mcintyre, & Moscato‐Goodpaster, 2002; Switzer, Hope, Grayston, & Prescott, 2012). Burning treatment increases plant production (burn, ~789 g m −2 ; mow, ~656 g m −2 ) compared to mowing treatment in our study region (Dickson, 2019). Here, based on data collected from two sampling seasons, the pattern of relatively higher maximum soil temperature and pH in burn plots and higher total nitrogen in mow plots was consistent from March to June.…”

“…Soil temperatures at a depth of 2.5 cm were measured every 155 min from every plot from January to June 2015 using a Thermochron® iButtons® model DS1921G‐F5(Maxim Integrated, San Jose, CA, USA). We determined the maximum temperature recorded from each plot in March and June as in the reference (Dickson, 2019). Within each sampling time, a non‐parametric t‐ test was used to compare the significant difference between burn and mow treatments for each variable.…”

“…For example, substantial amounts of carbon (C), nitrogen (N), sulphur (S) and phosphorus (P) can be lost to the atmosphere by volatilization during the combustion of litter, duff (a layer found beneath the litter layer and above the mineral soil) and soil organic matter (DeBano, 1991). In tallgrass prairie land in the Glacier Creek Preserve (GCP), burning also increased average daily maximum soil temperature at 2.5‐cm depth by 6.4°C in the month after burning (Dickson, 2019). The frequency and season of burning also strongly affects the plant community composition (Dickson, 2019; Towne & Craine, 2014).…”

“…In tallgrass prairie land in the Glacier Creek Preserve (GCP), burning also increased average daily maximum soil temperature at 2.5‐cm depth by 6.4°C in the month after burning (Dickson, 2019). The frequency and season of burning also strongly affects the plant community composition (Dickson, 2019; Towne & Craine, 2014). For example, burning in autumn or winter in the Kansas Flint Hills grassland promoted cool‐season graminoids without a concomitant decrease in warm‐season grasses, and widened the seasonal window of high‐quality forage (Towne & Craine, 2014).…”

“…For example, burning in autumn or winter in the Kansas Flint Hills grassland promoted cool‐season graminoids without a concomitant decrease in warm‐season grasses, and widened the seasonal window of high‐quality forage (Towne & Craine, 2014). Plant productivity was significantly higher in a burn treatment compared to a mow treatment after summer disturbance, and total plant production was only significantly influenced by the burn vs. mow treatment in the GCP (Dickson, 2019). Compared with mowing, burning eliminates the litter layer and creates warmer and drier soil, which favours N mineralization and increased plant productivity (Tix, Hebberger, Vaughan, & Charvat, 2003).…”