P. Mark S. Ashton

The effects of selective logging on forest structure and tree species composition in a Central African forest: implications for management of conservation areas

Abstract The forests of Central Africa enjoy world-wide recognition for their spectacular wildlife and also harbor an abundance of high quality timber. With mismanagement and the conversion of large tracts of West African forest to agricultural production, Central African forests are experiencing increased harvesting pressures. This is particularly true for species of African mahogany ( Entandrophragma spp.). In the tri-national region of Cameroon, Central African Republic, and Republic of Congo, a widely applied version of the Integrated Conservation and Development Model attributes the dual management objectives of biodiversity conservation and timber production to the same zones. Many conservationists working in the region believe that highly selective timber extraction is the best management scenario to meet these objectives. Conventional wisdom holds that if selective logging does not adequately regenerate Entandrophragma spp., loggers will quit the region after having mined the forest. A comparison between unlogged, 6-month and 18-year post-harvest forest stands indicates lasting effects of highly selective, high grade logging. While there was little difference in tree species composition and diversity between treatments, stem densities of both saplings and trees in unlogged forest were significantly higher than those in forest sampled 18 years after logging. Evidence suggests inadequate recruitment of Entandrophragma cylindricum and E. utile , the principal timber species, to justify continued timber extraction. Data indicate a significant shift in canopy dominance from shade intolerant to shade bearing species due to insufficient canopy disturbance. Nevertheless, an abundance of other top quality timber species remains after selective removal of African mahogany and these forests will remain attractive to loggers long after the elimination of Entandrophragma spp. A better approach to manage timber zones for timber production and conservation would be an adaptive management approach based on increased species selection and canopy disturbance. Zones targeting the conservation of closed forest obligate species should not be logged.

Seedling survival and growth of four Shorea species in a Sri Lankan rainforest

In this study four species of the genus Shorea section Doom were investigated. All occur together as canopy trees in the Sinaraja rainforest of south-west Sri Lanka. Partitioning of the regeneration niche can be one explanation for the co-existence of ecologically similar canopy tree species within a forest. Seedlings were planted in plots located in five zones that represent a range of forest groundstorey microenvironments found adjacent to and across canopy openings of three sites – valley, midslope, ridgetop. Experiments were designed to monitor survival and growth of planted seedlings for two years. At the end of two years percentage survival was calculated, height increment recorded and destructive samples taken to measure dry mass gain of root, stem and leaves. Comparisons were made of establishment and growth performance of seedlings planted in the different plots and sites. Results demonstrated clear differences in survival and growth among species. These differences appeared related to availability of soil moisture and groundstorey radiation regimes. Disturbance patterns that determine species co-existence are suggested.

A self-perpetuating bamboo disturbance cycle in a neotropical forest

We investigate a hypothesis for explaining maintenance of forest canopy dominance: bamboo (Guadua weberbaueri and Guadua sarcocarpa) loads and crushes trees, resulting in a self-perpetuating disturbance cycle. Forest inventory data revealed a peculiar pattern of tree form and size class distribution in bamboo-dominated plots within the Tambopata River watershed, Madre de Dios, Peru. Bamboo disproportionately loaded trees 5-29 cm in diameter, and this size class had over seven times more canopy damage than trees in control plots without bamboo. These differences were accompanied by reduced tree basal area and tree density in the 5-29-cm-diameter size class in the presence of bamboo. Elevated tree canopy damage was not apparent for trees ≥30 cm dbh, which are beyond the reach of bamboo. Additional evidence for the impact of bamboo was revealed by an experiment using artificial metal trees. Artificial trees in bamboo-dominated forest plots had nine times higher frequency of physical damage and nine times more plant mass loading as compared with control plots. Our results support the hypothesis that bamboo loading causes elevated physical damage to trees and suppresses tree recruitment, particularly for trees 5-29 cm in diameter.

Habitat characterizations underestimate the role of edaphic factors controlling the distribution of Entandrophragma

Numerous theories have been developed and tested to explain the high botanical diversity in tropical forests, ranging from nonequilibrium theories emphasizing the importance of chance to equilibrium theories depicting highly specialized species occupying narrow ecological niches. Niche-based theories have most often evaluated species adaptation to different light environments, but some studies have evaluated the importance of edaphic attributes in controlling species distributions. We evaluated the role of edaphic factors in controlling the distribution of African mahogany in the genus Entandrophragma on a 100-ha plot in the Dzanga-Sangha Dense Forest Reserve, Central African Republic. This study went beyond simple characterization of edaphic conditions in topographic or other classes to test for specific associations with chemical and physical soil parameters known to be important to plant growth. Trees ≥30 cm dbh of the four species of Entandrophragma evaluated were nonrandomly distributed in the forest. Torus translation tests indicated that none of the species exhibited any topographic preferences. However, three of the four species had significant associations with at least two soil chemical attributes. Randomization tests evaluating links between soil chemical and physical properties and topographic position underscored the complexity of the relationship and suggest that inferring edaphic attributes from broadly and simply defined habitat classes may significantly underestimate the importance of soil heterogeneity in contributing to species coexistence.

Harvesting impact and economic value of Geonoma deversa, Arecaceae, an understory palm used for roof thatching in the Peruvian Amazon.

We evaluated the impact of two leaf harvesting methods on the clonal understory palm Geonoma deversa. In the first method only the leaves are cut, in the second the complete crown is severed. Stands representative for each method are compared with unharvested stands. Both methods of harvesting reduce clone size and reproductive output (inflorescence and infructescence per clone), and lower the number of ramets available for the next harvest. Cutting only the leaves represents a better method of harvest because of a lower impact on the residual stock. Economic analysis reveals that the value of this resource (standing leaf value) is low (2 to 26 U.S.

Effect of fire intensity on understory composition and diversity in aKalmia-dominated oak forest, New England, USA

/ha) compared with labor costs that can be between 55 to 86% of palm thatch revenues. Harvesting Geonoma leaves generates a net present value (NPV) that ranges from 3 to 191 U.S.

Seedling growth of three co-occurring Entandrophragma species (Meliaceae) under simulated light environments: implications for forest management in central Africa

/ha depending on the stand location, the wage, and the interest rate employed for the calculation.ResumenSe evaluó el impacto de dos metodos para cosechar hojas de Geonoma deversa. El primer método consiste en la corta de las hojas mientras que en el segundo, se corta la copa antes de la remoción de las hojas. Se compara rodales representativos de coda metodo de corta con rodales no cosechados. Los resultados muestran que la cosecha reduce el tamaño de los clones, la producción de inflorecencias e infructecencias pero afecta sobre todo las ramas aptas para la cosecha. El método de cortar sólo las hojas es más ventajoso porque afecta menos las ramas cosechables por clon. La evaluatión económica muestra que el valor del recurso en el bosque (valor de ho ja en pie) es relativamente bajo (2 a 26 U.S.

Seedling performance of four sympatric Entandrophragma species (Meliaceae) under simulated fertility and moisture regimes of a Central African rain forest

/ha), comparado con el costo de la mano de obra necesaria para esta actividad. La mano de obra representa entre 55 y 86 por ciento de los ingresos brutos por la venta de paños tejidos. La cosecha de hojas genera un valor presente neto (VPN) que varia entre 3 y 191 U.S.

A protocol for measuring abundance and size of a neotropical liana,Desmoncus polyacanthos (Palmae), in relation to forest structure

/ha, lo cual depende de la localizatión del rodai, el valor del jornal y la tasa de interés empleada.

Method for the evaluation of advanced regeneration in forest types of south and southeast Asia

This study investigates the understory dynamics of two mixed-oak stands following fire of varying intensity. Composition and diversity of woody and herbaceous species in the understory were measured in two stands 7–8 years after a prescribed burn. On both sites, unburned areas, low-intensity fire areas, and areas where the overstory had been severely damaged were measured. Patterns of species presence and absence following fire were consistent with an initial-floristics model. Most species increased in density and frequency following fire; onlyAralia nudicaulis andQuercus alba showed statistically significant decreases in density. Overall, 29 species increased in density following fire, while 8 declined; 29 species increased in frequency, while 6 declined. However, diversity and equitability measures were depressed on the moderately burned sites, due to rapid regrowth ofKalmia latifolia. Ordination using binary discriminant analysis suggested species responded individualistically to both burning and site variation.