Untangling the roles of fire, grazing and rainfall on small mammal communities in grassland ecosystems

Abstract

In grassland systems across the globe, ecologists have been attempting to understand the complex role of fire, grazing and rainfall in creating habitat heterogeneity and the consequences of anthropogenic control of these factors on ecosystem integrity and functioning. Using a South African grassland ecosystem as a model, we investigated the impact of fire and grazing pressure on small mammal communities during three differing periods of a rainfall cycle. Over 2 years, 15,203 trap nights revealed 1598 captures of 11 species (nine rodents, one macroscelid and one insectivore). Results highlighted the importance of the interplay between factors and showed that the role of fire, grazing and rainfall in determining small mammal abundance was species-dependant. While no two species were affected by the same environmental variables, grass cover or height was important to 56% of species. Considered independently, high rainfall had a positive influence on small mammal abundance and diversity, although the lag period in population response was species-specific. High grazing negatively affected overall abundance, but specifically in Mastomys coucha; fire alone had little immediate impact on small mammal diversity. Six months after the fire, vegetation cover had recovered to similar levels as unburned areas, although small mammal diversity and richness were higher in burned areas than unburned areas. Grazing levels influenced the rate of vegetation recovery. In conclusion, low-level grazing and burning can help to maintain small mammal biodiversity, if conducted under appropriate rainfall levels. A too high grazing pressure, combined with fire, and/or fire conducted under drought conditions can have a negative impact on small mammal biodiversity. To maintain small mammal diversity in grassland ecosystems, the combined effects of the previous year's rainfall and existing population level as well as the inhibition of vegetation recovery via grazing pressure need to be taken into consideration before fire management is applied.

The response of bats (Mammalia: Chiroptera) to an incidental fire on a gallery forest at a Neotropical savanna

“…In contrast to the fauna of small non-flying mammals, which normally reach their abundance peak shortly after fire due to an increase in the gramineae of the area (Yarnell et al, 2007), the low abundance and richness of bats during the first sampling may have been influenced by the high mortality of wooded plants that can happen after a fire (Santiago et al 2005), which resulted on an initial decrease of food supply and shelter deficit under foliage.…”

Life on high: the diversity of small mammals at high altitude in South Africa

“…It was essential that each site was at high altitude ([1,700 m) and comprised areas that were large enough to accommodate small mammal trapping. Due to the decline of small mammal diversity and density at sites where grazing pressure by livestock is high (Hoffmann and Zeller 2005;Yarnell et al 2007), study sites were selected where grazing pressure from livestock was minimal (i.e. in conservation areas).…”

Reptile responses to fire and the risk of post-disturbance sampling bias

“…Responses to fire are often measured using a sampling method that depends on animal activity, such as calling by frogs or birds and movement into stationary traps by terrestrial animals (e.g. Cunningham et al 1999;Driscoll 1998;Ford et al 2010;Yarnell et al 2007), including reptiles (Schlesinger 2007). However, if movement rates differ between recently burnt and long-unburnt habitat, abundance estimates based on pitfall trap captures will be confounded with movement (Anderson 2003;Driscoll and Henderson 2008;Schutz and Driscoll 2008).…”