The role of exotic conifer plantations in rehabilitating degraded tropical forest lands: A case study from the Kibale Forest in Uganda

The role of exotic conifer plantations in rehabilitating degraded tropical forest lands: A case... Exotic softwood plantations were introduced into the Kibale Forest of western Uganda in the 1960s and early 1970s to convert grassland areas into wood fiber producing sites. Following establishment, few silvicultural activities were initiated within these plantings, and today harvesting operations are planned to remove these over-stocked stands to allow for the development of natural forest communities. During the period May–September, 1994, we inventoried the overstorey and advanced regeneration in plantations of Pinus caribeae and Cupressus lusitanica . Within 92 randomly located 0.01 ha plots per plantation type, we measured the height and diameter of all stems encountered. The pines supported approximately 1.5 times the density and diversity of native woody stems found beneath the cypress (3424 tree and shrub stems ha −1 under the pines), while the pines themselves were characterized by stocking levels, mean heights, and canopy closures which were higher than those of the cypress. We suggest that the greater natural regeneration development observed beneath the pines, when compared with the cypress, is a function of pine development (influence upon competition) and stem characteristics (influence upon seed dispersal mechanisms). We then compared our regeneration observations with those reported for unlogged and logged areas of the surrounding natural forest. Within the sapling class (diameter at breast height (dbh) less than 5 cm), which accounted for the majority of the advanced regeneration under the softwoods, the plantations failed to support the same density of tree-species stems as found in the natural forest (3077 stems ha −1 vs. 2177 and 1111 under the pines and cypress, respectively). The number of stems ha −1 in the pines approximated those in 25-year-old logged-over areas of the natural forest. Species richness beneath the conifers appears to approach the number found in the surrounding forest; however, a closer look at the species composition suggest several deficiencies in the composition of the advanced regeneration beneath the plantations (especially within the commercial class). Following 25 years of development, the advanced regeneration beneath the plantations (especially the cypress stands) is relatively impoverished compared to the levels of tree diversity and stocking characteristic of both unlogged and logged natural forest sites. The conditions beneath the pines however, suggest that a diverse community of native species may eventually exploit this environment through time. The dominance of the fast-growing, light-canopied, N 2 -fixing Albizia and Milletia genera, could help to nurture the further development of a well-structured, well-represented secondary forest through time. With the application of silvicultural treatments, there may be management opportunities to further enrich the quality of the advanced regeneration beneath softwood plantations. We explore future areas of research that could contribute to this end. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Forest Ecology and Management Elsevier

The role of exotic conifer plantations in rehabilitating degraded tropical forest lands: A case study from the Kibale Forest in Uganda

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Publisher
Elsevier
Copyright
Copyright © 1996 Elsevier Ltd
ISSN
0378-1127
eISSN
1872-7042
DOI
10.1016/0378-1127(95)03637-7
Publisher site
See Article on Publisher Site

Abstract

Exotic softwood plantations were introduced into the Kibale Forest of western Uganda in the 1960s and early 1970s to convert grassland areas into wood fiber producing sites. Following establishment, few silvicultural activities were initiated within these plantings, and today harvesting operations are planned to remove these over-stocked stands to allow for the development of natural forest communities. During the period May–September, 1994, we inventoried the overstorey and advanced regeneration in plantations of Pinus caribeae and Cupressus lusitanica . Within 92 randomly located 0.01 ha plots per plantation type, we measured the height and diameter of all stems encountered. The pines supported approximately 1.5 times the density and diversity of native woody stems found beneath the cypress (3424 tree and shrub stems ha −1 under the pines), while the pines themselves were characterized by stocking levels, mean heights, and canopy closures which were higher than those of the cypress. We suggest that the greater natural regeneration development observed beneath the pines, when compared with the cypress, is a function of pine development (influence upon competition) and stem characteristics (influence upon seed dispersal mechanisms). We then compared our regeneration observations with those reported for unlogged and logged areas of the surrounding natural forest. Within the sapling class (diameter at breast height (dbh) less than 5 cm), which accounted for the majority of the advanced regeneration under the softwoods, the plantations failed to support the same density of tree-species stems as found in the natural forest (3077 stems ha −1 vs. 2177 and 1111 under the pines and cypress, respectively). The number of stems ha −1 in the pines approximated those in 25-year-old logged-over areas of the natural forest. Species richness beneath the conifers appears to approach the number found in the surrounding forest; however, a closer look at the species composition suggest several deficiencies in the composition of the advanced regeneration beneath the plantations (especially within the commercial class). Following 25 years of development, the advanced regeneration beneath the plantations (especially the cypress stands) is relatively impoverished compared to the levels of tree diversity and stocking characteristic of both unlogged and logged natural forest sites. The conditions beneath the pines however, suggest that a diverse community of native species may eventually exploit this environment through time. The dominance of the fast-growing, light-canopied, N 2 -fixing Albizia and Milletia genera, could help to nurture the further development of a well-structured, well-represented secondary forest through time. With the application of silvicultural treatments, there may be management opportunities to further enrich the quality of the advanced regeneration beneath softwood plantations. We explore future areas of research that could contribute to this end.

Journal

Forest Ecology and ManagementElsevier

Published: Feb 1, 1996

References

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