The effects of human disturbances on diversity and dynamics of eastern Tanzania miombo arborescent species
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Date
2000
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University of the Witwatersrand, Johannesburg
Abstract
This interdisciplinary study makes comparisons between patterns of woody resource
abundance (stocks) under contrasting management regimes and describes the effects
of human disturbance on plant diversity and population dynamics of miombo
woodlands. Socio-economic data were collected from two sampled villages
surrounding the Kitulanghalo Forest Reserve in eastern Tanzania, about 150 km west
of Dar-es-Salaam. Biophysical data were collected from sixty-four modified-
Whittaker nested plots in the reserve and surrounding public lands. Use was also
made of the data from permanent sample plots and aerial photographs & landsat
images.
The ethnobotanical and utilisation survey indicated that major uses of woody
species were for charcoal production (the main commercial activity in the area),
firewood, medicine and poles. Commercial production of charcoal results in local
wood consumption of 6.01 nf capita'1 year'1 compared to subsistence firewood
consumption of only 1.5 m3 capita'1 year'1. Shifting cultivation is practiced by 68%
of the population. The present level and pattern of harvesting are changing the
structure and composition of the vegetation, especially in public lands and are not
sustainable. However, the heavy wood utilisation in public lands has minimal effect
on floristic composition as indicated by a high Sorensen’s similarity of 87.7%
between the reserve and public lands.
Multivariate analysis indicated that the linear combinations of physiographic
variables (most of which are associated with human disturbance) significantly
influence the pattern of tree harvesting, and species composition at the community level. The decrease in plant density through harvesting or self-thinning (natural
mortality) in public lands is accompanied by enhanced wood productivity, hence
growth rates were higher in public lands compared to the reserve. Ninety percent of
harvested woody species in public lands resprouted hence management under coppice
rotation as a silvicultural system is recommended.
Common property regimes and local institutional capacities are weak and need
to be strengthened before local people are given the full responsibility of managing
the public lands and assisting in policing the forest reserve. This calls for government
institutions to provide and motivate for an enabling environment in order to ensure
equity and sustainable development of natural resources.
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Keywords
Kitulanghalo Forest Reserve, Miombo woodlands-Eastern Tanzania, Wood products, Miombo woodlands