Interactive influence of rainfall manipulation and livestock grazing on species diversity of the herbaceous layer community in a humid savannah in Kenya

Abstract

Changes in rainfall regime and grazing pressure affect vegetation composition and diversity with ecological implications for savannahs. The savannah in East Africa has experienced increased livestock grazing and rainfall variability but the impacts associated with those changes on the herbaceous layer have rarely been documented. We investigated the effect of livestock grazing, rainfall manipulation and their interaction on the composition and diversity of the herbaceous community in the savannah for two years in Lambwe, Kenya. Rainfall manipulation plots were set up for vegetation sampling; these plots received either 50% more or 50% less rainfall than control plots. Simpson's diversity and Berger–Parker indices were used to determine diversity changes and dominance respectively. The frequency of species was used to compute their abundance and their life forms as determined from the literature. Grazing significantly increased species diversity through suppression of dominant species. Rainfall manipulation had no significant impact on plant diversity in fenced plots, but rainfall reduction significantly reduced diversity in grazed plots. In contrast, rainfall manipulation had no impact on dominance in either fenced or grazed plots. The interaction of grazing and rainfall manipulation is complex and will require additional survey campaigns to create a complete picture of the implications for savannah structure and composition.

The changing role of natural and human agencies shaping the ecology of an African savanna ecosystem

“…Grazing pressure reduced proportionately during these years, pointing to an upward reset of plant biomass in an otherwise declining trend. This accords with the finding that in less productive savannah ecosystems it takes extremely high amounts of rainfall, usually above 600 mm, to counter the effect of grazing pressure on grass biomass (Ondier et al 2019). Details of the model fit assessment, predictions, and diagnostics are presented in the Appendix S1: Eq.…”

Rangeland Biodiversity and Climate Variability: Supporting the Need for Flexible Grazing Management

“…The impact of biotic stress, particularly grazing pressure, on plant diversity is quite controversial [32,33]. On one hand, grazing is considered as a key factor to promote diversity [34,35], on the other hand, grazing can reduce plant diversity and lead to the homogenization of rangeland [36,37]. Furthermore, other studies carried out in arid areas have shown that climate variability is more important in affecting plant diversity than grazing, and moderate grazing does not damage vegetation [10,38].…”

Vegetation Response to Removal of Plant Groups and Grass Seeding in a Microphyllous Desert Shrubland: A 4-Year Field Experiment

“…Total forbs had greater relative biomass in protected areas than in grazed areas. Trampling and grazing may explain forb reduction because trampling by cattle is common in xeric ecosystems, and intensely influences plant performance [47,48]. The unchanged diversity in the grazed area stems from the suppression of dominant species by cattle [48] which allow the dissemination of other plants in this ecosystem.…”

“…Trampling and grazing may explain forb reduction because trampling by cattle is common in xeric ecosystems, and intensely influences plant performance [47,48]. The unchanged diversity in the grazed area stems from the suppression of dominant species by cattle [48] which allow the dissemination of other plants in this ecosystem. In our case, a community defined by undesirable plants are defined by the treatments CON, GRAZ, and UND (Figure 2).…”