An assessment of woody vegetation structure in Maasai Mara conservancies of Narok county, Kenya

Abstract

Vegetation structure is a result of adaptation of plants to the environment. Itis important because it can be used as indications of measuring changes in habitats. Vegetation structure mapping and monitoring is however not adequately done in most habitats of East Africa mainly because of cost reasons. Furthermore, protection of habitats especially national parks and reserve prioritize on animal conservation and not woody plants. It has been observed that the woody vegetation formations of the Maasai Mara have been deteriorating hence affecting negatively habitat quality. This has prompted management interventions such as reforestation programmes by the conservancies. These interventions are however done without much scientific information on the woody vegetation structure of the study area which can provide focused solutions. This study examined the woody vegetation vertical, composition, horizontal and temporal structure of six conservancies (Ol Chorro, Lemek, Mara North, Olare Orok, Motorogi and Naboisho) of the Maasai Mara ecosystem. Primary data was collected from 108 sample variable transects and 250 sample car transects. In addition, 9 focus group discussions were held with local groups to get their views on the subject. The study observed that the conservancies’ landscape could be delineated by use of the woody vegetation physiognomy into Acacia bushland, bushed grassland, evergreen bushland, evergreen woodland, grassland, impeded drainage grassland, riverine vegetation, shrubland and Tarchonanthus bushland vegetation formations using canopy height, cover and indicator species. An analysis of similarities showed the different vegetation formation as statistically different in terms of species composition though some overlap exists in the species composition. Mapping procedures using GIS software Quantum GIS and Google Earth images were used to develop a vegetation map of the Maasai Mara Conservancies. A total of 7094 woody tree species were sampled using the variable transects. The results were as follows: Croton dichogamus was the most dominant species while diversity indices showed riverine vegetation and Tarchonanthus bushland formations as the most diverse with impeded drainage grassland being least diverse in respect to woody vegetation. The effect of browsing was evident in 54% of the sampled woody plants while breakages and human use evidence were 13% and 1% respectively. The disturbances were height specific; browsing was prevalent in lower height classes of regeneration while knock over and human use were more prevalent in higher height classes of recruitment and mature trees. Analysis using Chi-square test showed the occurrence of browsing to be statistically different at different height classes. The disturbances were also species specific, for instance, breakages were more pronounced in Acacia species while browsing was prevalent in Grewia, Maytenus and Phyllanthus species. The population structure of some species such as Diospyros abyssinica showed decline while others such as Olea africana and Warburgia ugandensis showed flat structures indicating unhealthy populations. Although comparisons of the current vegetation map and a map done 40 years ago showed the general trend of vegetation formation in the study area has not changed, results from focus group discussions and the absence and/or low frequency of key indicator species show changes in vegetation composition and some woody vegetation formations especially evergreen woodlands as generally decreasing in the study area. The study concluded that browsers and breakages prevent the study area to be woodier and the big tree natured species of the study area as reducing. It is recommended that more efforts be done to conserve the big trees especially those of evergreen woodland vegetation formation in areas with lesser extent of browse, human and breakages disturbances.