Fire and grazing in a mesic tallgrass prairie: impacts on plant species and functional traits

Abstract

Abstract. Fire is a globally distributed disturbance that impacts terrestrial ecosystems and has been proposed to be a global ''herbivore.'' Fire, like herbivory, is a top-down driver that converts organic materials into inorganic products, alters community structure, and acts as an evolutionary agent. Though grazing and fire may have some comparable effects in grasslands, they do not have similar impacts on species composition and community structure. However, the concept of fire as a global herbivore implies that fire and herbivory may have similar effects on plant functional traits. Using 22 years of data from a mesic, native tallgrass prairie with a long evolutionary history of fire and grazing, we tested if trait composition between grazed and burned grassland communities would converge, and if the degree of convergence depended on fire frequency. Additionally, we tested if eliminating fire from frequently burned grasslands would result in a state similar to unburned grasslands, and if adding fire into a previously unburned grassland would cause composition to become more similar to that of frequently burned grasslands. We found that grazing and burning once every four years showed the most convergence in traits, suggesting that these communities operate under similar deterministic assembly rules and that fire and herbivory are similar disturbances to grasslands at the trait-group level of organization. Three years after reversal of the fire treatment we found that fire reversal had different effects depending on treatment. The formerly unburned community that was then burned annually became more similar to the annually burned community in trait composition suggesting that function may be rapidly restored if fire is reintroduced. Conversely, after fire was removed from the annually burned community trait composition developed along a unique trajectory indicating hysteresis, or a time lag for structure and function to return following a change in this disturbance regime. We conclude that functional traits and species-based metrics should be considered when determining and evaluating goals for fire management in mesic grassland ecosystems.

Mapping the Dabus Wetlands, Ethiopia, Using Random Forest Classification of Landsat, PALSAR and Topographic Data

“…Expanses of tall emergent meadows covering the lower half of the Dabus wetlands are transformed into barren land by the end of the dry season ( Figure 2c,d), but hydric soil conditions are nevertheless maintained as periods of inundation are sustained for several months each year. These areas present high abundance of annual C4 grasses, which are adapted to fire and grazing [41], but floristic diversity is limited, especially where the most severe impacts have occurred.…”

Long Term Effect of Major Disturbances on the Northern Mixed Grassland Ecosystem—A Review

“…To some extent fire and grazing behave similarly. And fire was proposed as a non-selective, globally-distributed "herbivore" [59] [91]. Though here "non-selective" is clarified as regarding to trait composition instead of species composition [59].…”

“…Spasojevic [91] specifically investigated long-term ) field experiment to compare effects of fire and grazing. They failed to verify whether grazed grass communities and burned communities would converge or not.…”

“…Impact of drought on the grassland ecosystem (adapted from the table by [18]). composition of grassland communities than selective grazing [91]. Also, chronic fires tend to have greater impact on species and trait composition than chronic grazing at light to moderate levels, because these two disturbances are different in their selectivity [94] [95].…”

A Statistical Approach for Predicting Grassland Degradation in Disturbance-Driven Landscapes

“…For example, frequent burning typically results in prairie dominated by C4 grasses, with lower species richness and diversity, and higher average peak-season aboveground biomass. When considered with other factors such as weather and climate, topographic position, grazing and other anthropogenic disturbances, the impact of fire on grassland dynamics is even more complex [16]- [20].…”