Fire and grazing effects on herbaceous structure, composition and diversity, and plant functional responses to management regimes in Mkomazi, Tanzania

Abstract

Fire is one among the major ecological factors that determine the biotic structure and function of savanna and grassland ecosystems. Together with grazing, fire affects herbaceous vegetation through its effects on floristic composition and diversity, biomass production and the distribution of wildlife population depending upon the interacting elements such as the fire regime (i.e. intensity, frequency, and season). Fire is a natural phenomenon of many savanna ecosystems and has been widely employed by conservation managers to improve the conditions of rangelands and fulfil several other management objectives in protected areas. In many cases this has been done out of usual practice without the actual knowledge of its effects on the biotic and biotic components of the ecosystems, and how these components respond toward fire. For example, while fire may increase species diversity, it may also kills the matrix species results increasing dominance of certain species, thereby altering the structure and composition of the community. In the Mkomazi N. Park and surrounding areas, fire has been regarded to have a critical role on herbivores and their forage production. Thus, burning has been a management tool of the park and a common practice of range management by pastoralists and farmers. In both past and current management regimes (WD and TANAPA), vegetation burning has been conducted by the Ecological department without a clear/proper burning plan and clear understanding of the responses of grass species to prescribed burns.

The perceived importance of fire to the management and conservation Mkomazi N. Park has been the major driver for my thesis to focus on the effects of treatments (i.e. fire gazing, fire no grazing) on species composition and diversity and their relationship with biomass production and functional strategies of plants. To accomplish that, this thesis examines the effects of treatments on 1. Species composition in particular species abundance, vegetation cover, perennial abundance and standing biomass (chapter II), 2. Species diversity and biomass production and the relationships between the two (Chapter III), 3) and 4. The functional diversity of plants in response to management strategies.

The results shows that fire and grazing influences species abundances, a positively responses of plants towards FG treatment. Similarly, the occurrence of functional group of rhizomatous and stoloniferous species ascertain the absences of grazing species in FNG site. Variation in in terms of species identity and number of dominant species in a site indicates individual/species characteristics i.e. the ability to withstand or even take advantage of a particular treatment.

Different levels of disturbance have effects on diversity as result of equal species evenness among the three sites but different species richness and diversity. So if we need to protect the biodiversity then we need to understand how species diversity is impacted by the management strategies. Likewise, how management strategies impacts the function diversity and its implication to the ecosystems process and functioning. The species richness-biomass model showed a positive relationships between species and biomass and not the unimodal shaped curve.