Forage Nutritive Quality in the Serengeti Ecosystem: The Roles of Fire and Herbivory

Abstract

Fire and herbivory are important determinants of nutrient availability in savanna ecosystems. Fire and herbivory effects on the nutritive quality of savanna vegetation can occur directly, independent of changes in the plant community, or indirectly, via effects on the plant community. Indirect effects can be further subdivided into those occurring because of changes in plant species composition or plant abundance (i.e., quality versus quantity). We studied relationships between fire, herbivory, rainfall, soil fertility, and leaf nitrogen (N), phosphorus (P), and sodium (Na) at 30 sites inside and outside of Serengeti National Park. Using structural equation modeling, we asked whether fire and herbivory influences were largely direct or indirect and how their signs and strengths differed within the context of natural savanna processes. Herbivory was associated with enhanced leaf N and P through changes in plant biomass and community composition. Fire was associated with reduced leaf nutrient concentrations through changes in plant community composition. Additionally, fire had direct positive effects on Na and nonlinear direct effects on P that partially mitigated the indirect negative effects. Key mechanisms by which fire reduced plant nutritive quality were through reductions of Na-rich grasses and increased abundance of Themeda triandra, which had below-average leaf nutrients.

Nitrogen fertilization and fire act independently on foliar stoichiometry in a temperate steppe

“…Britton et al (2008) found that P concentration of current-year shoots of Calluna vulgaris increased in burned plots, though this increase disappeared 5 years later. Increased foliar nutrient concentrations following annual burning would have important consequences for many ecosystem processes, including photosynthesis (Granath et al 2009), plant growth and primary production , herbivory (Anderson et al 2007), and litter decomposition (Kozovits et al 2007).…”

Comparative changes in density and demography of large herbivores in the Masai Mara Reserve and its surrounding human-dominated pastoral ranches in Kenya

“…Grass height influences both forage quality and predation risk. In the wet season less heavily grazed grasses, such as occur in most parts of the Mara reserve, become tall and therefore allocate more energy to developing structural fibers with higher carbon to nitrogen ratios, thereby diluting the concentration of nitrogen and phosphorous available to herbivores (Anderson et al 2007). From an herbivore's perspective, the digestibility of grasses is therefore inversely related to rainfall amount (Hopcraft et al 2011).…”

Comparative study of trophic behaviour and herd structure in wild and feral goats living in a Mediterranean island: Management implications

“…Herbivore large herds, as it is usually the case of livestock, are likely to have severe impacts on vegetation (Orueta, 2003), especially in habitats with no history of intense herbivory; whereas herbivory caused by small herds is usually beneficial (see, e.g., Anderson et al, 2007). However, in an island where herbivore ungulates have been around since before the arrival of man, as it is the case of Majorca (Alcover et al, 1999), endemic plant species have been subjected to browsing and have evolved with the presence of these herbivores.…”