Mike Swaine - Academia.edu (original) (raw)

Papers by Mike Swaine

Research paper thumbnail of An application of ordination to the identification of forest types

Vegetatio, 1976

Summary The problems of allocating new vegetation stands to an existing classification are outlin... more Summary The problems of allocating new vegetation stands to an existing classification are outlined. As one solution, the vegetation samples from an area may be ordinated by reciprocal averaging and classified by dividing the ordination into community-types. The ordination scores for a short list of species present in a new sample may then be averaged to locate that sample on the ordination axes and in one of the community-types. The method is tested by comparing estimates from incomplete species lists with that from a complete list of species in an forest stand in southern Ghana.

Research paper thumbnail of Early Succession on Cleared Forest Land in Ghana

The Journal of Ecology, 1983

Page 1. Journal of Ecology (1983), 71, 601-627 EARLY SUCCESSION ON CLEARED FOREST LAND IN GHANA M... more Page 1. Journal of Ecology (1983), 71, 601-627 EARLY SUCCESSION ON CLEARED FOREST LAND IN GHANA MD SWAINE* AND JOHN B. HALLt Department of Botany, University of Ghana, Legon, Ghana SUMMARY (1 ...

Research paper thumbnail of The odd man out? Might climate explain the lower tree ?-diversity of African rain forests relative to Amazonian rain forests?

Journal of Ecology, 2007

1. Comparative analyses of diversity variation among and between regions allow testing of alterna... more 1. Comparative analyses of diversity variation among and between regions allow testing of alternative explanatory models and ideas. Here, we explore the relationships between the tree α-diversity of small rain forest plots in Africa and in Amazonia and climatic

Research paper thumbnail of Talbotiella gentii: genetic variation and conservation

Research paper thumbnail of Climbing plants in Ghanaian forests

Forest climbing plants of West Africa: diversity, ecology and management, 2005

The total number of forest climbers in Ghana has been recorded as 604 but this number has increas... more The total number of forest climbers in Ghana has been recorded as 604 but this number has increased to 634 following further research and taxonomic revisions as the taxa become better known. The focus of this paper is on woody climbers (lianes), and the variation in liana biology and ecology is described for the commoner Ghanaian species. These features are related to their distribution and the forest environment across the country.

Research paper thumbnail of A sharp floristic discontinuity revealed by the biogeographic regionalization of African savannas

Journal of Biogeography, 2018

Aim: In tropical Africa, savannas cover huge areas, have high plant species richness and are cons... more Aim: In tropical Africa, savannas cover huge areas, have high plant species richness and are considered as a major natural resource for most countries. There is, however, little information available on their floristics and biogeography at the continental scale, despite the importance of such information for our understanding of the drivers of species diversity at various scales and for effective conservation and management. Here, we collated and analysed floristic data from across the continent in order to propose a biogeographical regionalization for African savannas. Location: We collated floristic information (specifically woody species lists) for 298 samples of savanna vegetation across Africa, extending from 18°N to 33°S and from 17°W to 48°E. Taxa: We focused on native woody species. Methods: We used ordination and clustering to identify the floristic discontinuities and gradual transitions across African savannas. Floristic relationships, specificity and turnover, within and between floristic clusters, were analysed using a (dis-)similarity-based approach. Results: We identified eight floristic clusters across African savannas which in turn were grouped into two larger macro-units. Ordinations at species and genus levels showed a clear differentiation in woody species composition between the North/ West macro-unit and the South/East macro-unit. This floristic discontinuity matches to the High (i.e. N&W) and Low (S&E) division of Africa previously proposed by White (1983) and which tracks climatic and topographical variation. In the N&W savannas, the floristic gradient determined by rainfall was partitioned into the Sudanian (drier) and Guinean (wetter) clusters. Within the highly heterogeneous S&E savannas and woodlands, six clusters were identified: Ugandan, Ethiopian, Mozambican, Zambezian, Namibian and South African. Main conclusions: The proposed pan-African classification of savannas and woodlands might assist the development of coordinated management and conservation policies.

Research paper thumbnail of Climate seasonality limits carbon assimilation and storage in tropical forests

Biogeosciences Discussions, 2016

The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, althoug... more The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associate canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is…

Research paper thumbnail of Population genetic structure of Milicia speciescharacterised by using RAPD and nucleotide sequencing L

Milicia species (M. excelsa and M. regia, Moraceae, the irokos) are among the most useful indigen... more Milicia species (M. excelsa and M. regia, Moraceae, the irokos) are among the most useful indigenous rain forest tree species in Africa. They are not grown in plantations but extracted from the natural forest at an unsustainable rate. The major constraint on cultivation and afforestation is the gall-forming insect Phytolyma lata, which destroys seedlings through gall formation, causing dieback of the shoot. Genetic diversity studies should aid the design of conservation and resistance-breeding strategies. This study, therefore, aimed to investigate the genetic variability in Milicia from three West African countries and the power of bulk-family DNA in partitioning of genetic diversity. Genetic variation within and between 5 natural populations of Milicia from Ghana, Cote d'Ivoire and Sierra Leone was investigated using random amplified polymorphic DNA (RAPD) and non-coding chloroplast DNA sequencing. RAPD analysis of 41 DNA samples with 8 primers produced a total of 74 bands with 40 bands (54.1%) being polymorphic. Dendrogram analysis produced 2 major clusters separating dry and moist / wet ecotypes. Sub-clustering further separated accessions by forest type and / or geographic region. A greater proportion of the total genetic variability was attributed to variation between populations (62.2%) than within Leu populations (37.8%). Sequencing of chloroplast tRNA intron (cptrnL) and intergenic spacer (cpIGS) between Phe cptrnL and tRNA (trnF) did not show any variation. The RAPD analysis suggests that trees from wet / moist sites are mostly M. regia, while those from dry sites are mostly M. excelsa. Sequencing results, however, suggest that the two species are closely related. These results are discussed with reference to conservation strategies.

Research paper thumbnail of Natural Regeneration Dynamics of Tree Seedlings on Skid Trails and Tree Gaps Following Selective Logging in a Tropical Moist Semi-Deciduous Forest in Ghana

Open Journal of Forestry, 2014

One of the main threats to the sustainability of timber production in naturally managed forests i... more One of the main threats to the sustainability of timber production in naturally managed forests in Ghana is insufficient regeneration of timber tree species. This study assessed regeneration success of a logged forest by comparing the species composition, diversity, density, recruitment, mortality, and growth of naturally established seedlings in 160 seedling plot samples of 50 m 2 located randomly on main skid trails, secondary skid trails, felled tree gaps and unlogged parts of the same forest. The study was done within a 134-ha compartment in a selectively logged moist semi-deciduous forest in Ghana over a period of 33 months involving four enumerations. Seedlings population was initially dominated by pioneers, but after 33 months, population in all sites was dominated by non-pioneers. Seedling densities showed an increase initially in all the sites after logging, but declined after 10 months. The high seedling densities were driven by four (Albizia zygia, Ceiba pentandra, Celtis mildbraedii and Turreanthus africanus) out of the 37 species that regenerated. All four species exhibited a period of exceptionally high new seedling recruitment in the first 10 months. Diversity differed significantly among disturbance types initially, but after 33 months diversity was lower in the unlogged areas though not significant. Seedling mortality was initially greater in unlogged areas of the forest and growth rates higher in the logged areas. These results show that disturbed areas appear to be suitable sites for the regeneration of timber species following logging, although the long-term fate of trees growing on these areas remains uncertain as growth rates declined with time.

Research paper thumbnail of Low genetic diversity and high genetic differentiation among severely fragmented populations of the critically endangered tree Talbotiella gentii (Fabaceae)

Southern Forests: a Journal of Forest Science, 2011

... 2000; Araucaria, Chile: Bekessy et al. 2002: Cupressaceae, China: Li and Zia 2005). ... The p... more ... 2000; Araucaria, Chile: Bekessy et al. 2002: Cupressaceae, China: Li and Zia 2005). ... The population in the Bandai Hills Forest Reserve (Abiriw), however, is seriously threatened by fire as the surrounding vegetation is grassland derived from forest. ...

Research paper thumbnail of Structure and dynamics of a tropical dry forest in Ghana

Vegetatio, 1990

Forest under low rainfall (averaging 745 mm yr-1) on the Shai Hills in S.E. Ghana has redeveloped... more Forest under low rainfall (averaging 745 mm yr-1) on the Shai Hills in S.E. Ghana has redeveloped following cessation of farming in the 1890s. Forest stature is low, with a canopy at about 11 m, principally of three species, Diospyros abyssinica, D. mespiliformis and Millettia thonningii. Drypetes parvifolia and Vepris heterophylla are common understorey trees. Twelve species of woody liane were recorded. Species of thicket vegetation in the area were also present at low density. Most species are evergreen. Tree mortality averaged 2.3~o yr ~ and exceeded recruitment (1.5~ yr-1). Differences between species in mortality and recruitment were pronounced: canopy species showed a small decline in density; understorey species increased markedly and the thicket species declined. Seed production was very variable, but seedling establishment was very poor for all species. Seedling mortality was high (11 ~o yr-1) especially for small seedlings. These population trends probably represent the latter stages of succession of forest regrowth after farming about 100 years ago. Compared with tropical rain forest, Shai Hills forest has similar relative tree diameter growth (1-3.5 ~o yr-1), mortality and recruitment rates, and small-litter fall (5.52 t ha-1 yr-1). Shai Hills forest differs from rain forest by its short stature, relatively few (evergreen) tree species, poor regeneration from seed, high soil nutrient status and low rainfall. Similar forests have been reported in east Africa and in parts of New Guinea.

Research paper thumbnail of On the definition of ecological species groups in tropical rain forests

Vegetatio, 1988

The species richness of tropical rain forests creates difficulties for ecological analysis. It ma... more The species richness of tropical rain forests creates difficulties for ecological analysis. It may usefully be simplified by defining ecological species groups whose members share characteristics of importance for determining forest structure and composition. Many such classifications have been published, but few are properly explained. The terminology is confused from lack of precise definitions. We propose a simple division of tree species into two groups or guilds, pioneer and non-pioneer (or climax), based on seed germination and seedling establishment. Within each guild there is continuous variation and we recommend arbitrary subdivision by height at maturity. We believe this classification to be applicable in all tropical rain forests.

Research paper thumbnail of Explosive Seed Dispersal in Hura Crepitans L. (Euphorbiaceae)

New Phytologist, 1977

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, a... more JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Blackwell Publishing and New Phytologist Trust are collaborating with JSTOR to digitize, preserve and extend access to New Phytologist.

Research paper thumbnail of Root hemiparasitism in a West African rainforest tree Okoubaka aubrevillei (Santalaceae)

New Phytologist, 1996

We studied hemiparasitism in Okoubaka aubrevillei Pellegr. & Normand (Santalaceae), an uncommon W... more We studied hemiparasitism in Okoubaka aubrevillei Pellegr. & Normand (Santalaceae), an uncommon West African rainforest tree of widespread distribution (Ivory Coast to Zaire) which attains heights of up to 40 m. It has a very large seed (mean fresh mass of 101 g), and slow accumulation of biomass characteristic of seedlings of shadetolerant rainforest trees. 0. aubrevillei seedlings became hemiparasitic within 6 months when grown next to seedlings of the tree species Entandrophragma angolense (Wel.) DC., Pericopsis elata (Harms) Van Meeuwen, Pterygota macrocarpa K. Schum., and Tieghemella heckelii Pierre ex Chev. P. macrocarpa, and the nitrogenfixing legume, P. elata were most infected. Characteristically for hemiparasites, midday leaf water potentials in 0. aubrevillei were at-2 MPa lower than those of the host seedlings. Stomatal conductance, however, was low, with a maximum of 111 mmol m2 s-1. After 1 yr, no significant effects of the hemiparasitism were observed on the growth of 0. aubrevillei or on its nutrient status as measured by foliar element concentrations. By contrast, the two most infected host species showed increased mortality and/or reduced growth. Foliar element concentrations were not, however, affected in host plants of the surviving species. Although the resources of a large seed might enable seedlings of 0. aubrevillei to grow independently from hosts for prolonged periods, their simultaneous strong effect on the mortality and growth of host seedlings might point to an alternative competitive function of hemiparasitism.

Research paper thumbnail of Increasing carbon storage in intact African tropical forests

Research paper thumbnail of Characteristics of dry forest in West Africa and the influence of fire

Journal of Vegetation Science, 1992

The climate, soil, structure and floristics of dry forests in West Africa are summarised. Data fr... more The climate, soil, structure and floristics of dry forests in West Africa are summarised. Data from Ghana show that these forests have two-peak annual rainfall between 850 and 1350 mm, with 6-10 dry months (< 100 mm rain) each year; by relatively nutrient-rich soils developed over a variety of rock types; by short stature (tallest trees 10-40 m) relatively high deciduousness in the upper canopy and evergreenness in the understorey; and by a distinctive flora which changes gradually towards areas of higher rainfall but abruptly at the forest-savanna boundary. Dry forests near the forest-savanna boundary form a distinctive sub-type as a result of occasional encroachment by litter fires which have become more common in the 1980's. Evidence is presented to suggest that many parts of the forest zone in West Africa may have been subject to fires most often in the dry forest types. Past fires are likely to have had a profound influence on the composition of the present forest canopy. Fire mortality is greatest in small trees, whilst drought (without fire) kills more large trees. This thinning process allows rapid recolonisation especially by Marantaceous and Zingiberaceous forbs and by pioneer trees. Seedlings of canopy trees grow beneath these colonising plants. Recurrent fires seriously impede the recovery of burnt forest and are a principal concern for the rehabilitation of dry forests.

Research paper thumbnail of The dynamics of tree populations in tropical forest: a review

Journal of Tropical Ecology, 1987

ABSTRACTPublished work on the dynamics of forest tree recruitment, growth and mortality in natura... more ABSTRACTPublished work on the dynamics of forest tree recruitment, growth and mortality in natural tropical forest is reviewed. In most forests studied, annual mortality is between 1% and 2% and is independent of size class in trees >10 cm dbh; mortality is negatively correlated with growth rate and crown illumination; growth rate is highly variable between individual trees, but shows strong autocorrelation between successive measurements on the same tree.Differences in the rate of dynamic processes can be detected between some species at a site, but data are presently insufficient to determine whether these differences are preserved at other sites where the species occur. None of the studies discussed are of sufficient duration to permit us to draw any conclusions about the equilibrium or non-equilibrium of floristic composition.

Research paper thumbnail of The mosaic theory of forest regeneration and the determination of forest composition in Ghana

Journal of Tropical Ecology, 1988

ABSTRACTEarly studies comparing adult and juvenile tree populations in West Africa described a co... more ABSTRACTEarly studies comparing adult and juvenile tree populations in West Africa described a contrast in flonstic composition between the two age classes. These studies have been mis-represented in more recent literature, and confusion has arisen over their interpretation.Similar comparisons are reported here for six forest sites in Ghana. At any one site, clear differences in composition were recognized between adult and juvenile samples, but in terms of the variation in flonstic composition over the whole of the forest zone, they are slight and forest types appear to ‘breed true’.At one site, Kade, compositional differences between size classes are fully described for all canopy species on a 0.25 ha plot. There was an abrupt change in composition at about 30 cm gbh. At this site, mortality rates for trees >30 cm gbh were greater amongst species with a high proportion of juveniles in the population. At other sites, changes in composition were sometimes abrupt, occurring at var...

Research paper thumbnail of Effect of light on the germination of forest trees in Ghana

Journal of Ecology, 1999

ABSTRACT 1 Seed germination in light and dark, and responses to irradiance and light quality, wer... more ABSTRACT 1 Seed germination in light and dark, and responses to irradiance and light quality, were tested in shadehouse experiments for 19 West African tropical forest tree species representing a wide range of ecological types. Germination in forest gaps of different size was tested for 11 species. 2 Percentage germination was reduced in the dark only for three small-seeded species that are common in forest soil seed banks: Musanga cecropioides, Nauclea diderrichii and Milicia excelsa. Percentage germination of the other 16 species, including four widely regarded as ‘pioneers’, was unaffected. 3 Effects of different irradiances in shadehouses, where the seeds were watered, were significant for some species, but there was no consistent pattern. Irradiance effects in forest gaps, where the seeds received only natural wet season rainfall, were more widespread and substantial, and were most commonly shown as a depression of percentage germination at high irradiance. 4 Effects of light quality (neutral vs. green shade; red : far-red = 0.43) were insignificant at 5% irradiance in shadehouses for all species except Nauclea diderrichii. In growth chamber experiments, the low energy response was only evident at 1.0 µmol m–2 s–1 (&lt; 1% of unshaded forest irradiance) in Musanga and Nauclea. 5 The speed of germination was affected by irradiance in many species, but the effect was small compared with differences between species, in which time to complete germination varied between 3 weeks and over 6 months. 6 Seeds of Ceiba pentandra and Pericopsis elata planted in deep forest shade (2% irradiance) and in a small gap (30% irradiance) germinated well in both sites, showed exponential biomass growth in the gap but a linear decline in mean seedling biomass and subsequent death in deep shade. 7 Light-mediated germination is relatively rare among these forest trees, even among pioneers, so that the working definition of a pioneer should be seen to depend more on a species’ ability to survive in forest shade. The effects of canopy opening on seed germination are small except in the largest openings, which severely depress germination in a number of species, including some species with strongly light-demanding seedlings.

Research paper thumbnail of Responses of tropical forest tree seedlings to irradiance and the derivation of a light response index

Journal of Ecology, 1999

... important differences both within and between species, leading to oversimplified 'paradi... more ... important differences both within and between species, leading to oversimplified 'paradigms' (Grubb 1996). ... & Poorter (1998) have used to model the carbon balance in three categories of ... While this work demonstrates the pan-tropical equivalence of species' responses, it does ...

Research paper thumbnail of An application of ordination to the identification of forest types

Vegetatio, 1976

Summary The problems of allocating new vegetation stands to an existing classification are outlin... more Summary The problems of allocating new vegetation stands to an existing classification are outlined. As one solution, the vegetation samples from an area may be ordinated by reciprocal averaging and classified by dividing the ordination into community-types. The ordination scores for a short list of species present in a new sample may then be averaged to locate that sample on the ordination axes and in one of the community-types. The method is tested by comparing estimates from incomplete species lists with that from a complete list of species in an forest stand in southern Ghana.

Research paper thumbnail of Early Succession on Cleared Forest Land in Ghana

The Journal of Ecology, 1983

Page 1. Journal of Ecology (1983), 71, 601-627 EARLY SUCCESSION ON CLEARED FOREST LAND IN GHANA M... more Page 1. Journal of Ecology (1983), 71, 601-627 EARLY SUCCESSION ON CLEARED FOREST LAND IN GHANA MD SWAINE* AND JOHN B. HALLt Department of Botany, University of Ghana, Legon, Ghana SUMMARY (1 ...

Research paper thumbnail of The odd man out? Might climate explain the lower tree ?-diversity of African rain forests relative to Amazonian rain forests?

Journal of Ecology, 2007

1. Comparative analyses of diversity variation among and between regions allow testing of alterna... more 1. Comparative analyses of diversity variation among and between regions allow testing of alternative explanatory models and ideas. Here, we explore the relationships between the tree α-diversity of small rain forest plots in Africa and in Amazonia and climatic

Research paper thumbnail of Talbotiella gentii: genetic variation and conservation

Research paper thumbnail of Climbing plants in Ghanaian forests

Forest climbing plants of West Africa: diversity, ecology and management, 2005

The total number of forest climbers in Ghana has been recorded as 604 but this number has increas... more The total number of forest climbers in Ghana has been recorded as 604 but this number has increased to 634 following further research and taxonomic revisions as the taxa become better known. The focus of this paper is on woody climbers (lianes), and the variation in liana biology and ecology is described for the commoner Ghanaian species. These features are related to their distribution and the forest environment across the country.

Research paper thumbnail of A sharp floristic discontinuity revealed by the biogeographic regionalization of African savannas

Journal of Biogeography, 2018

Aim: In tropical Africa, savannas cover huge areas, have high plant species richness and are cons... more Aim: In tropical Africa, savannas cover huge areas, have high plant species richness and are considered as a major natural resource for most countries. There is, however, little information available on their floristics and biogeography at the continental scale, despite the importance of such information for our understanding of the drivers of species diversity at various scales and for effective conservation and management. Here, we collated and analysed floristic data from across the continent in order to propose a biogeographical regionalization for African savannas. Location: We collated floristic information (specifically woody species lists) for 298 samples of savanna vegetation across Africa, extending from 18°N to 33°S and from 17°W to 48°E. Taxa: We focused on native woody species. Methods: We used ordination and clustering to identify the floristic discontinuities and gradual transitions across African savannas. Floristic relationships, specificity and turnover, within and between floristic clusters, were analysed using a (dis-)similarity-based approach. Results: We identified eight floristic clusters across African savannas which in turn were grouped into two larger macro-units. Ordinations at species and genus levels showed a clear differentiation in woody species composition between the North/ West macro-unit and the South/East macro-unit. This floristic discontinuity matches to the High (i.e. N&W) and Low (S&E) division of Africa previously proposed by White (1983) and which tracks climatic and topographical variation. In the N&W savannas, the floristic gradient determined by rainfall was partitioned into the Sudanian (drier) and Guinean (wetter) clusters. Within the highly heterogeneous S&E savannas and woodlands, six clusters were identified: Ugandan, Ethiopian, Mozambican, Zambezian, Namibian and South African. Main conclusions: The proposed pan-African classification of savannas and woodlands might assist the development of coordinated management and conservation policies.

Research paper thumbnail of Climate seasonality limits carbon assimilation and storage in tropical forests

Biogeosciences Discussions, 2016

The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, althoug... more The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associate canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is…

Research paper thumbnail of Population genetic structure of Milicia speciescharacterised by using RAPD and nucleotide sequencing L

Milicia species (M. excelsa and M. regia, Moraceae, the irokos) are among the most useful indigen... more Milicia species (M. excelsa and M. regia, Moraceae, the irokos) are among the most useful indigenous rain forest tree species in Africa. They are not grown in plantations but extracted from the natural forest at an unsustainable rate. The major constraint on cultivation and afforestation is the gall-forming insect Phytolyma lata, which destroys seedlings through gall formation, causing dieback of the shoot. Genetic diversity studies should aid the design of conservation and resistance-breeding strategies. This study, therefore, aimed to investigate the genetic variability in Milicia from three West African countries and the power of bulk-family DNA in partitioning of genetic diversity. Genetic variation within and between 5 natural populations of Milicia from Ghana, Cote d'Ivoire and Sierra Leone was investigated using random amplified polymorphic DNA (RAPD) and non-coding chloroplast DNA sequencing. RAPD analysis of 41 DNA samples with 8 primers produced a total of 74 bands with 40 bands (54.1%) being polymorphic. Dendrogram analysis produced 2 major clusters separating dry and moist / wet ecotypes. Sub-clustering further separated accessions by forest type and / or geographic region. A greater proportion of the total genetic variability was attributed to variation between populations (62.2%) than within Leu populations (37.8%). Sequencing of chloroplast tRNA intron (cptrnL) and intergenic spacer (cpIGS) between Phe cptrnL and tRNA (trnF) did not show any variation. The RAPD analysis suggests that trees from wet / moist sites are mostly M. regia, while those from dry sites are mostly M. excelsa. Sequencing results, however, suggest that the two species are closely related. These results are discussed with reference to conservation strategies.

Research paper thumbnail of Natural Regeneration Dynamics of Tree Seedlings on Skid Trails and Tree Gaps Following Selective Logging in a Tropical Moist Semi-Deciduous Forest in Ghana

Open Journal of Forestry, 2014

One of the main threats to the sustainability of timber production in naturally managed forests i... more One of the main threats to the sustainability of timber production in naturally managed forests in Ghana is insufficient regeneration of timber tree species. This study assessed regeneration success of a logged forest by comparing the species composition, diversity, density, recruitment, mortality, and growth of naturally established seedlings in 160 seedling plot samples of 50 m 2 located randomly on main skid trails, secondary skid trails, felled tree gaps and unlogged parts of the same forest. The study was done within a 134-ha compartment in a selectively logged moist semi-deciduous forest in Ghana over a period of 33 months involving four enumerations. Seedlings population was initially dominated by pioneers, but after 33 months, population in all sites was dominated by non-pioneers. Seedling densities showed an increase initially in all the sites after logging, but declined after 10 months. The high seedling densities were driven by four (Albizia zygia, Ceiba pentandra, Celtis mildbraedii and Turreanthus africanus) out of the 37 species that regenerated. All four species exhibited a period of exceptionally high new seedling recruitment in the first 10 months. Diversity differed significantly among disturbance types initially, but after 33 months diversity was lower in the unlogged areas though not significant. Seedling mortality was initially greater in unlogged areas of the forest and growth rates higher in the logged areas. These results show that disturbed areas appear to be suitable sites for the regeneration of timber species following logging, although the long-term fate of trees growing on these areas remains uncertain as growth rates declined with time.

Research paper thumbnail of Low genetic diversity and high genetic differentiation among severely fragmented populations of the critically endangered tree Talbotiella gentii (Fabaceae)

Southern Forests: a Journal of Forest Science, 2011

... 2000; Araucaria, Chile: Bekessy et al. 2002: Cupressaceae, China: Li and Zia 2005). ... The p... more ... 2000; Araucaria, Chile: Bekessy et al. 2002: Cupressaceae, China: Li and Zia 2005). ... The population in the Bandai Hills Forest Reserve (Abiriw), however, is seriously threatened by fire as the surrounding vegetation is grassland derived from forest. ...

Research paper thumbnail of Structure and dynamics of a tropical dry forest in Ghana

Vegetatio, 1990

Forest under low rainfall (averaging 745 mm yr-1) on the Shai Hills in S.E. Ghana has redeveloped... more Forest under low rainfall (averaging 745 mm yr-1) on the Shai Hills in S.E. Ghana has redeveloped following cessation of farming in the 1890s. Forest stature is low, with a canopy at about 11 m, principally of three species, Diospyros abyssinica, D. mespiliformis and Millettia thonningii. Drypetes parvifolia and Vepris heterophylla are common understorey trees. Twelve species of woody liane were recorded. Species of thicket vegetation in the area were also present at low density. Most species are evergreen. Tree mortality averaged 2.3~o yr ~ and exceeded recruitment (1.5~ yr-1). Differences between species in mortality and recruitment were pronounced: canopy species showed a small decline in density; understorey species increased markedly and the thicket species declined. Seed production was very variable, but seedling establishment was very poor for all species. Seedling mortality was high (11 ~o yr-1) especially for small seedlings. These population trends probably represent the latter stages of succession of forest regrowth after farming about 100 years ago. Compared with tropical rain forest, Shai Hills forest has similar relative tree diameter growth (1-3.5 ~o yr-1), mortality and recruitment rates, and small-litter fall (5.52 t ha-1 yr-1). Shai Hills forest differs from rain forest by its short stature, relatively few (evergreen) tree species, poor regeneration from seed, high soil nutrient status and low rainfall. Similar forests have been reported in east Africa and in parts of New Guinea.

Research paper thumbnail of On the definition of ecological species groups in tropical rain forests

Vegetatio, 1988

The species richness of tropical rain forests creates difficulties for ecological analysis. It ma... more The species richness of tropical rain forests creates difficulties for ecological analysis. It may usefully be simplified by defining ecological species groups whose members share characteristics of importance for determining forest structure and composition. Many such classifications have been published, but few are properly explained. The terminology is confused from lack of precise definitions. We propose a simple division of tree species into two groups or guilds, pioneer and non-pioneer (or climax), based on seed germination and seedling establishment. Within each guild there is continuous variation and we recommend arbitrary subdivision by height at maturity. We believe this classification to be applicable in all tropical rain forests.

Research paper thumbnail of Explosive Seed Dispersal in Hura Crepitans L. (Euphorbiaceae)

New Phytologist, 1977

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, a... more JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Blackwell Publishing and New Phytologist Trust are collaborating with JSTOR to digitize, preserve and extend access to New Phytologist.

Research paper thumbnail of Root hemiparasitism in a West African rainforest tree Okoubaka aubrevillei (Santalaceae)

New Phytologist, 1996

We studied hemiparasitism in Okoubaka aubrevillei Pellegr. & Normand (Santalaceae), an uncommon W... more We studied hemiparasitism in Okoubaka aubrevillei Pellegr. & Normand (Santalaceae), an uncommon West African rainforest tree of widespread distribution (Ivory Coast to Zaire) which attains heights of up to 40 m. It has a very large seed (mean fresh mass of 101 g), and slow accumulation of biomass characteristic of seedlings of shadetolerant rainforest trees. 0. aubrevillei seedlings became hemiparasitic within 6 months when grown next to seedlings of the tree species Entandrophragma angolense (Wel.) DC., Pericopsis elata (Harms) Van Meeuwen, Pterygota macrocarpa K. Schum., and Tieghemella heckelii Pierre ex Chev. P. macrocarpa, and the nitrogenfixing legume, P. elata were most infected. Characteristically for hemiparasites, midday leaf water potentials in 0. aubrevillei were at-2 MPa lower than those of the host seedlings. Stomatal conductance, however, was low, with a maximum of 111 mmol m2 s-1. After 1 yr, no significant effects of the hemiparasitism were observed on the growth of 0. aubrevillei or on its nutrient status as measured by foliar element concentrations. By contrast, the two most infected host species showed increased mortality and/or reduced growth. Foliar element concentrations were not, however, affected in host plants of the surviving species. Although the resources of a large seed might enable seedlings of 0. aubrevillei to grow independently from hosts for prolonged periods, their simultaneous strong effect on the mortality and growth of host seedlings might point to an alternative competitive function of hemiparasitism.

Research paper thumbnail of Increasing carbon storage in intact African tropical forests

Research paper thumbnail of Characteristics of dry forest in West Africa and the influence of fire

Journal of Vegetation Science, 1992

The climate, soil, structure and floristics of dry forests in West Africa are summarised. Data fr... more The climate, soil, structure and floristics of dry forests in West Africa are summarised. Data from Ghana show that these forests have two-peak annual rainfall between 850 and 1350 mm, with 6-10 dry months (< 100 mm rain) each year; by relatively nutrient-rich soils developed over a variety of rock types; by short stature (tallest trees 10-40 m) relatively high deciduousness in the upper canopy and evergreenness in the understorey; and by a distinctive flora which changes gradually towards areas of higher rainfall but abruptly at the forest-savanna boundary. Dry forests near the forest-savanna boundary form a distinctive sub-type as a result of occasional encroachment by litter fires which have become more common in the 1980's. Evidence is presented to suggest that many parts of the forest zone in West Africa may have been subject to fires most often in the dry forest types. Past fires are likely to have had a profound influence on the composition of the present forest canopy. Fire mortality is greatest in small trees, whilst drought (without fire) kills more large trees. This thinning process allows rapid recolonisation especially by Marantaceous and Zingiberaceous forbs and by pioneer trees. Seedlings of canopy trees grow beneath these colonising plants. Recurrent fires seriously impede the recovery of burnt forest and are a principal concern for the rehabilitation of dry forests.

Research paper thumbnail of The dynamics of tree populations in tropical forest: a review

Journal of Tropical Ecology, 1987

ABSTRACTPublished work on the dynamics of forest tree recruitment, growth and mortality in natura... more ABSTRACTPublished work on the dynamics of forest tree recruitment, growth and mortality in natural tropical forest is reviewed. In most forests studied, annual mortality is between 1% and 2% and is independent of size class in trees >10 cm dbh; mortality is negatively correlated with growth rate and crown illumination; growth rate is highly variable between individual trees, but shows strong autocorrelation between successive measurements on the same tree.Differences in the rate of dynamic processes can be detected between some species at a site, but data are presently insufficient to determine whether these differences are preserved at other sites where the species occur. None of the studies discussed are of sufficient duration to permit us to draw any conclusions about the equilibrium or non-equilibrium of floristic composition.

Research paper thumbnail of The mosaic theory of forest regeneration and the determination of forest composition in Ghana

Journal of Tropical Ecology, 1988

ABSTRACTEarly studies comparing adult and juvenile tree populations in West Africa described a co... more ABSTRACTEarly studies comparing adult and juvenile tree populations in West Africa described a contrast in flonstic composition between the two age classes. These studies have been mis-represented in more recent literature, and confusion has arisen over their interpretation.Similar comparisons are reported here for six forest sites in Ghana. At any one site, clear differences in composition were recognized between adult and juvenile samples, but in terms of the variation in flonstic composition over the whole of the forest zone, they are slight and forest types appear to ‘breed true’.At one site, Kade, compositional differences between size classes are fully described for all canopy species on a 0.25 ha plot. There was an abrupt change in composition at about 30 cm gbh. At this site, mortality rates for trees >30 cm gbh were greater amongst species with a high proportion of juveniles in the population. At other sites, changes in composition were sometimes abrupt, occurring at var...

Research paper thumbnail of Effect of light on the germination of forest trees in Ghana

Journal of Ecology, 1999

ABSTRACT 1 Seed germination in light and dark, and responses to irradiance and light quality, wer... more ABSTRACT 1 Seed germination in light and dark, and responses to irradiance and light quality, were tested in shadehouse experiments for 19 West African tropical forest tree species representing a wide range of ecological types. Germination in forest gaps of different size was tested for 11 species. 2 Percentage germination was reduced in the dark only for three small-seeded species that are common in forest soil seed banks: Musanga cecropioides, Nauclea diderrichii and Milicia excelsa. Percentage germination of the other 16 species, including four widely regarded as ‘pioneers’, was unaffected. 3 Effects of different irradiances in shadehouses, where the seeds were watered, were significant for some species, but there was no consistent pattern. Irradiance effects in forest gaps, where the seeds received only natural wet season rainfall, were more widespread and substantial, and were most commonly shown as a depression of percentage germination at high irradiance. 4 Effects of light quality (neutral vs. green shade; red : far-red = 0.43) were insignificant at 5% irradiance in shadehouses for all species except Nauclea diderrichii. In growth chamber experiments, the low energy response was only evident at 1.0 µmol m–2 s–1 (&lt; 1% of unshaded forest irradiance) in Musanga and Nauclea. 5 The speed of germination was affected by irradiance in many species, but the effect was small compared with differences between species, in which time to complete germination varied between 3 weeks and over 6 months. 6 Seeds of Ceiba pentandra and Pericopsis elata planted in deep forest shade (2% irradiance) and in a small gap (30% irradiance) germinated well in both sites, showed exponential biomass growth in the gap but a linear decline in mean seedling biomass and subsequent death in deep shade. 7 Light-mediated germination is relatively rare among these forest trees, even among pioneers, so that the working definition of a pioneer should be seen to depend more on a species’ ability to survive in forest shade. The effects of canopy opening on seed germination are small except in the largest openings, which severely depress germination in a number of species, including some species with strongly light-demanding seedlings.

Research paper thumbnail of Responses of tropical forest tree seedlings to irradiance and the derivation of a light response index

Journal of Ecology, 1999

... important differences both within and between species, leading to oversimplified 'paradi... more ... important differences both within and between species, leading to oversimplified 'paradigms' (Grubb 1996). ... & Poorter (1998) have used to model the carbon balance in three categories of ... While this work demonstrates the pan-tropical equivalence of species' responses, it does ...