Relationships between Plant Biomass and Species Richness under Different Farming Systems and Grazing Land Management in Montane Grasslands of Kokosa District, Southern Ethiopia
The study was conducted in a montane grassland of Kokosa District, West Arsi Zone of Oromia Region, southern Ethiopia. The objective of the study was to investigate the relationships between aboveground plant biomass and species richness in three farming systems and four grazing management systems. A total of 180 quadrats (each 1 m x 1 m) were sampled in the three farming systems (dominant livestock-enset, enset-livestock and enset-livestock-cereal) and four grazing management systems (communal, enclosure, stream bank and benchmark). All the farming system and grazing management have different management practices. Plant species composition and aboveground plant biomass at different sites were quantified. Altogether 50 plant species (34 grasses, 4 legumes, 3 sedges and 9 forbs) were recorded in the montane grassland of Kokosa District. Even though the majority of the plant species share the different farming systems and grazing management practices, the highest number of species (39) was recorded in the enset-livestock farming system, whereas the lowest (33) species were recorded in the enset- livestock-cereal farming system when all the grazing management and farming systems were combined. Significantly, the highest species richness (4.9 species m-2) was recorded in the enclosure grazing management site whereas the lowest (3.4 species m-2) was recorded in the benchmark grazing site when all grazing sites and farming systems were combined. The relationship between species richness and biomass was detected in the montane grassland. There was significant difference (P ≤ 0.05) in species richness for a combination analysis of farming system by grazing management system of the montane grassland. The highest biomass was recorded in the benchmark grazing management sites while the lowest was recorded in the communal grazing sites. On the contrary, maximum species richness was found in the enclosure grazing management sites which had intermediate biomass yield and the lowest species richness was recorded in the benchmark grazing areas with the maximum biomass records. Thus, species richness was observed first to ascend along with biomass increment up to 1932 kg ha-1 and then declined at constant increase of biomass. An increase in biomass in the benchmark grazing sites was not accompanied by an increase in species richness suggesting the dominance of few species in these sites. The rationale behind this might be due to the competitive exclusion of the less competent species from the community at peak biomass production.
Keywords: Biomass; Farming System; Grazing Management; Montane Grassland; Species Richness