Assessing the Roles of Fire Frequency and Precipitation in Determining Woody Plant Expansion in Central U.S. Grasslands

Abstract

Woody plant expansion into grasslands and savannas is occurring and accelerating worldwide and often impacts ecosystem processes. Understanding and predicting the environmental and ecological impacts of encroachment has led to a variety of methodologies for assessing its onset, transition, and stability, generally relying on dynamical systems approaches. Here we continue this general line of investigation to facilitate the understanding of the roles of precipitation frequency and intensity and fire frequency on the conversion of grasslands to woody‐dominated systems focusing on the central United States. A low‐dimensional model with stochastic precipitation and fire disturbance is introduced to examine the complex interactions between precipitation and fire as mechanisms that may suppress or facilitate increases in woody cover. By using Lyapunov exponents, we are able to ascertain the relative control exerted on woody encroachment through these mechanisms. Our results indicate that precipitation frequency is a more important control on woody encroachment than the intensity of individual precipitation events. Fire, however, exerts a much more dominant impact on the limitation of encroachment over the range of precipitation variability considered here. These results indicate that fire management may be an effective strategy to slow the onset of woody species into grasslands. While climate change might predict a reduced potential for woody encroachment in the near future, these results indicate a reduction in woody fraction may be unlikely when considering anthropogenic fire suppression.

Bridging the Flux Gap: Sap Flow Measurements Reveal Species‐Specific Patterns of Water Use in a Tallgrass Prairie

“…Despite these simplifications, we provided reasonable estimates of water flux across a range of herbaceous and woody species. For example, we estimated that daily maximum E C varied between approximately 0.5 and 3.0 mm day −1 (Figure ), which is comparable to eddy flux data that estimated maximum daily ET as 6 mm day −1 for this same watershed in 2014 (Brunsell et al, ). We also estimated that cumulative growing season E C for these species was 732.5 and 171.5 mm during the day and at night, respectively.…”

Management of remnant tallgrass prairie by grazing or fire: effects on plant communities and soil properties

“…Historically, tallgrass prairie experienced burning and grazing in a shifting mosaic of disturbance (Anderson 2006, McGranahan et al 2012). Lacking disturbances such as these, tallgrass prairie may transition to woodland (Brunsell et al 2017) or be overrun by non‐native invasive cool‐season grasses (DeKeyser et al 2013), fates that alter ecosystem function and reduce habitat quality for a variety of prairie‐dependent species, including many pollinators. Due to their small size, modern prairies rarely experience both burning and grazing by large ungulates.…”

Woody encroachment happens via intensification, not extensification, of species ranges in an African savanna

“…Woody species with certain common functional traits (e.g., root suckering, fire resistance) may be maximally responsive to the complex interaction of multiple drivers and may therefore be likelier to encroach (Case et al 2020). However, we know little about species-level variation in woody encroachment with respect to prevailing management history and environmental change (Archer et al 1995, Oesterheld et al 1999, Swetnam et al 1999, Brunsell et al 2017, suggesting a need for more systematic study to inform the debate about whether local management has leverage in controlling woody encroachment in the face of global change.…”

“…1999, Brunsell et al. 2017), suggesting a need for more systematic study to inform the debate about whether local management has leverage in controlling woody encroachment in the face of global change.…”