Abstract
The diversity, population structure and regeneration status of woody species were studied at Xobe and Shorobe Villages in northern Botswana. A total of 130 and 111 quadrats of 20 × 20 m size were laid down at 50 m intervals along parallel line transects at Xobe and Shorobe, respectively. A total of 46 woody species, 27 from Xobe and 41 from Shorobe were recorded. Of the 46 woody species, only 22 were recorded at both sites. Ten genera and six families were found only in Shorobe while one genus and one family were found only in Xobe. The diversity and evenness of woody species were 1.5 and 0.5 in Xobe, respectively, and 2.18 and 0.6 in Shorobe, respectively. The similarities of woody species in terms of richness of species, genera and families at the two sites were about 50%, 54% and 56%, respectively. The mean densities of woody species were 2745.7 ± 1.35 and 4269.7 ± 36 individuals ha-1 at Xobe and Shorobe, respectively. Despite differences in absolute numbers, the total mean densities of woody species at both sites did not exhibit significant (P = 0.35) differences. At both sites, woody species were dominated by individuals of only a few species, which also exhibited the highest values of important value index. The population structure patterns of the woody species were categorized into five groups. The species in the first group exhibited reverse J-shaped distribution, which indicates stable population structures. The species in the second group showed relatively good recruitment but the regeneration is negatively affected. The species in the other three groups exhibited hampered regeneration as a result of disturbances caused by humans, domestic animals and annual fires. The parameters assessed indicate the need for attention and appropriate management interventions by the relevant national authorities at various levels.
Highlights
Dry forests and woodlands, including those in Botswana, form more than 40% of all tropical forests, and Africa and tropical islands of the world house the largest proportion of dry forest and woodland ecosystems where they account for 70% 80% of the forested area (Murphy & Lugo, 1986)
Tropical dry forests and woodlands have been under exploitation for thousands of years since they have often been preferred for human settlement to wetter forest zones for biological and ecological reasons (Murphy & Lugo, 1986; Janzen, 1988)
The results revealed that Shorobe and Xobe together house 46 different woody species, which provide the local communities with various goods and services
Summary
Dry forests and woodlands, including those in Botswana, form more than 40% of all tropical forests, and Africa and tropical islands of the world house the largest proportion of dry forest and woodland ecosystems where they account for 70% 80% of the forested area (Murphy & Lugo, 1986). Tropical dry forests and woodlands have been under exploitation for thousands of years since they have often been preferred for human settlement to wetter forest zones for biological and ecological reasons (Murphy & Lugo, 1986; Janzen, 1988). As a result, they are either vanishing or being degraded rapidly due to accelerated growth of human and livestock populations, which result in the conversion of forested land to agriculture and excessive exploitation of forests for fuelwood, construction material and timber for export. The loss or degradation of forests results in land degradation in the form of soil erosion and decline of fertility, decline or loss of biodiversity and water bodies, impoverishment of ecosystems and global warming, which affect the welfare of humans, plants, animals and micro-organisms negatively (Teketay, 2004-2005)
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