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Vegetation structures, dominance patterns and height growth in an Afromontane forest, Southern Africa

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Abstract

Information on forest structures are fundamentally important to keep track of successional vegetation dynamics for efficient forest management. This study reports on vegetation characteristics, dominance patterns and species height growth in a Northern Mistbelt forest type in South Africa. Common alpha-diversity indices (species richness and Shannon diversity), structural vegetation parameters (tree density and basal area) and species importance value index were used. Size class distribution and height-diameter allometries were further examined for the overall stand and dominant species. Stem densities (472±43.46 and 605.33±28.10 treesha-1 for 5–10 cm and ≥10 cm dbh classes, respectively) and basal area values (1.99±0.19 and 48.07±3.46 m2ha-1, respectively) are comparable to other Afromontane forests in East Africa. The overall stand showed an inverted-J shaped distribution pattern which is typical feature of stand size class distribution in most natural forests. Most ecologically important species also exhibited an inverted-J shaped distribution pattern, suggesting good regeneration and recruitment potential. There were significant effects of species on tree height, reflecting species-specific patterns in height growth, probably a result of intrinsic growth potential and competitive interactions. The present study suggests that conservation and management policies, including protection of surrounding land uses against fire, contributed to maintain a successful recovery of these forests. However, it should be taken into account that these forests may be experiencing relatively slow dynamic flux as a result of the over-mature state of some trees with several years under relatively strict protection.

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Wof-Washa forest is one of the few remaining dry Afromontane forests in the central plateau of Ethiopia. Woody species composition, structure and regeneration patterns of this forest were studied to generate information essential for formulating feasible management options for the forest. Vegetation data were collected from 64 quadrats of size 20 m × 20 m, 10 m × 10 m and 5 m × 5 m for tree/shrub, sapling and seedling, respectively, laid systematically along transects. A total of 62 woody species belonging to 54 genera and 40 families were recorded. Rosaceae was the most diverse family with five (12.5%) species followed by Anacardiaceae, Euphorbiaceae and Myrsinaceae with three (7.5%) species each. Tree/shrub, sapling and seedling densities were 699, 1178 and 7618.7 individuals/ha. About 56.7% of the importance value index was contributed by Juniperus procera, Maytenus arbutifolia, Podocarpus falcatus and Ilex mitis. Vegetation classification resulted in five plant communities: Ilex mitis - Maytenus obscura, Galiniera saxifraga - Maesa lanceolata, Juniperus procera - Erica arborea, Podocapus falcatus - Allophylus abyssinicus and Pittosporum viridiflorum - Polycias fulva community types. Regeneration status of all the woody plant species was categorized as 'Good' (28%), 'Fair' (19%), 'Poor' (8%), 'None' (40%) and 'New' (5%).
Article
An investigation of the small-scale floristic structure and composition of Chirinda forest, Zimbabwe was carried out to show the effects of historical logging activities done in the northern section of the forest. Abundance and diameter-at-breast height were measured in different size classes from 26 circular plots, 15 and 11 in south and north respectively. The southern section had 81 woody species belonging to 43 families while the northern section had 73 belonging to 32 families, with a total of 111 for the forest. Considerable species overlap was apparent. Plant species richness and diversity were not significantly different (P > 0.05) in the two sections. The combined size class distribution was however significantly different (P =0.005) with the south section having more small diameters than the north. Despite the high proportion of species shared by the two sections, they differed consistently in terms of density of the most abundant species. Classification and ordination consistently grouped the north and south plots indicating similarity of species. Size class distribution showed neither coarse nor fine grain indicating that individual species population could be declining. Management options should focus on maintaining an inverse J-shaped structure through enrichment planting of important species thus maintaining recruitment.
Article
Commercial plantations in South Africa have been established mainly in grasslands adjacent to native forest which occur as small, scattered patches, restricted to valleys and scarps by regular fires in the adjacent fire-prone grasslands. Understorey vegetation was sampled in plantation stands of different age of Pinus patula, and old stands of P. elliottii, P. taeda and Eucalyptus saligna, growing on the forest margin. The study was done in two areas in Northern Province, South Africa (23°S to 25°S, and 30°E to 31°E): Woodbush-De Hoek along the Eastern Escarpment, and Entabeni on Soutpansberg mountains. The area receives 1200 to 1900 mm rain per annum, mainly during summer. Two hypotheses were tested: understorey colonisation by native plant species is strongly influenced by the overhead plantation species; and abundance and diversity of indigenous woody and herbaceous species increase with increasing stand age. A total of 170 species were recorded on 62 plots of 78.5 m2 each, and included all major growth forms present in the surrounding forest, except epiphytes. Trees were represented by 62 species, but only 18% of these occurred in more than 10% of the plots. Seventy-two percent of the 95 tree, shrub and climber species are animal-dispersed but only 22% of the animal-dispersed species occur in more than 10% of the plots. Mean clean bole length of the plantation stand gave the best regression coefficients with species richness, stem density, mean DBH and mean height of the woody regeneration, all of which increased with stand age. There was no clear pattern in understorey species composition among the different plantation species. Site factors such as substrate (geology) and temperature (altitude and radiation index) had a strong correlation with species composition and density of understorey vegetation. The results do demonstrate a useful successional process which could be used to achieve specific management objectives at relatively low costs. Potential applications of this succession process are manipulation of tree stands (commercial plantations or invader plants) to restore native forest biodiversity, control of understorey weeds in commercial plantations, and growing of useful crops under tree canopies.
Article
6 The Amazon Basin is one of the world's most important bioregions, harboring a rich array of plant and animal species and offering a wealth of goods and services to society. For years, ecological science has shown how large- scale forest clearings cause declines in biodiversity and the availability of forest products. Yet some important changes in the rainforests, and in the ecosystem services they provide, have been underappreciated until recently. Emerging research indicates that land use in the Amazon goes far beyond clearing large areas of forest; selective logging and other canopy damage is much more pervasive than once believed. Deforestation causes collateral damage to the surrounding forests - through enhanced drying of the forest floor, increased frequency of fires, and lowered productivity. The loss of healthy forests can degrade key ecosystem services, such as carbon storage in biomass and soils, the regulation of water balance and river flow, the modulation of regional climate patterns, and the amelioration of infectious diseases. We review these newly revealed changes in the Amazon rainforests and the ecosystem services that they provide.
The use of diameter distributions in sustaineduse management of forests: examples from Southern Africa
  • C J Geldenhuys
Geldenhuys CJ (1993) The use of diameter distributions in sustaineduse management of forests: examples from Southern Africa. In: Piearce GD, Gumbo DJ (eds) The ecology and management of indigenous forests in Southern Africa. Proceedings of an international symposium. Zimbabwe Forestry Commission and SAREC, Harare, pp 154-167
Towards sustainable management based on scientific understanding of natural forests and woodlands. Proceedings of natural forests and savanna woodlands symposium II. Department of Water Affairs and Forestry, Indigenous Forest Management
  • C J Geldenhuys
Geldenhuys CJ (2000) The need for monitoring recruitment, growth and mortality in the indigenous forests: examples from northern province. In: Seydack AHW, Vermeulen WJ, Vermeulen C (eds) Towards sustainable management based on scientific understanding of natural forests and woodlands. Proceedings of natural forests and savanna woodlands symposium II. Department of Water Affairs and Forestry, Indigenous Forest Management, Knysna, pp 17-28
Multiple use management of natural forests and savanna woodlands: policy refinements and scientific progress. Proceedings of natural forests and savanna woodlands symposium III. Department of Water Affairs and Forestry
  • C J Geldenhuys
  • S M Venter
Geldenhuys CJ, Venter SM (2002) Plant communities and biodiversity of the Limpopo province forests: relevance and management options. In: Seydack AHW, Vorster T, Vermeulen WJ, van der Merwe I (eds) Multiple use management of natural forests and savanna woodlands: policy refinements and scientific progress. Proceedings of natural forests and savanna woodlands symposium III. Department of Water Affairs and Forestry, Indigenous Forest Management, Pretoria, pp 23-37
The vegetation of South Africa
  • L Mucina
  • M Rutherford
Mucina L, Rutherford M (2006) The vegetation of South Africa, Lesotho and Swaziland, vol 19. Strelitzia. South African National Biodiversity Institute, Pretoria