The modern pollen-vegetation relationship of a tropical forest-savannah mosaic landscape, Ghana, West Africa

Transitions between forest and savannah vegetation types in fossil pollen records are often poorly understood due to over-production by taxa such as Poaceae and a lack of modern pollen-vegetation studies. Here, modern pollen assemblages from within a forest-savannah transition in West Africa are presented and compared, their characteristic taxa discussed, and implications for the fossil record considered. Fifteen artificial pollen traps were deployed for 1 year, to collect pollen rain from three vegetation plots within the forest-savannah transition in Ghana. High percentages of Poaceae and Melastomataceae/Combretaceae were recorded in all three plots. Erythrophleum suaveolens characterised the forest plot, Manilkara obovata the transition plot and Terminalia the savannah plot. The results indicate that Poaceae pollen influx rates provide the best representation of the forest-savannah gradient, and that a Poaceae abundance of >40% should be considered as indicative of savannah-type vegetation in the fossil record

Forest fire incidence, damage and control measures in Ghana

This study was conducted in the Afram Headwaters, Tain Tributaries Block II and Worobong South Forest Reserves. Satellite record of fire incidence for the country over 11 years (1997 to 2007) was modelled via binary logistic regression analysis, and correlations between fire incidence and the correlates of fire used to explain the observed trends. Fire incidence was found to be correlated with multiple variables which probably covary. Rainfall, vegetation type and geology showed the strongest correlations with fire incidence. Recurrent fire has impacted negatively on forest structure, ground cover biomass and species composition in two forest reserves, but more marked in the wetter Worobong South Forest Reserve than the drier Tain II Forest Reserve. Basal area has reduced from 40 m2ha-1 in least-degraded to <1 m2ha-1 in heavily-degraded stand in Worobong South Forest Reserve, along with tree density, whereas canopy openness has increased from 6% in least-degraded to 83% in heavily-degraded forest. In Tain II Forest Reserve, however, the heavily-degraded forest has lost close to 50% of its maximum value in terms of basal area, tree density and canopy cover, all in approximately 20 years. Early-burning, with maximum seedling height growth rates of 130 cm yr-1 and 40 cm yr-1 for Worobong South and Tain II Forest Reserves respectively, might help control the fires, and restore forest canopy in about 10 to 20 years if regularly maintained, but must be accompanied by green firebreaks. Complete protection from fire (during convalescence), on the other hand, would take between five and 15 years to restore forest canopy, but at huge resource cost. Implications for sustainable forest management are discussed.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Data from: Fine-root exploitation strategies differ in tropical old-growth and logged-over forests in Ghana

Understanding the changes in root exploitation strategies during post-logging recovery is important for predicting forest productivity and carbon dynamics in tropical forests. We sampled fine (diameter < 2 mm) roots using the soil-core method to quantify fine-root biomass, and architectural and morphological traits to determine root exploitation strategies in an old-growth forest and in a 54-year-old logged-over forest influenced by similar parent material and climate. Seven root traits were considered: four associated with resource exploitation potential or an ‘extensive’ strategy (fine-root biomass, length, surface area and volume); and three traits which reflect exploitation efficiency or an ‘intensive’ strategy (specific root area, specific root length and root tissue density). We found that total fine-root biomass, length, surface area, volume, and fine-root tissue density were higher in the logged-over forest, whereas the old-growth forest had higher total specific root length and specific root surface area than the logged-over forest. The results suggest different root exploitation strategies between the forests. Plants in the old-growth forest invest root biomass more efficiently to maximize soil volume explored, whereas plants in the logged-over forest increase the spatial distribution of roots resulting in the expansion of the rhizosphere

Forest biomass, productivity and carbon cycling along a rainfall gradient in West Africa

© 2017 John Wiley & Sons Ltd Net Primary Productivity (NPP) is one of the most important parameters in describing the functioning of any ecosystem and yet it arguably remains a poorly quantified and understood component of carbon cycling in tropical forests, especially outside of the Americas. We provide the first comprehensive analysis of NPP and its carbon allocation to woody, canopy and root growth components at contrasting lowland West African forests spanning a rainfall gradient. Using a standardized methodology to study evergreen (EF), semi-deciduous (SDF), dry forests (DF) and woody savanna (WS), we find that (i) climate is more closely related with above and belowground C stocks than with NPP (ii) total NPP is highest in the SDF site, then the EF followed by the DF and WS and that (iii) different forest types have distinct carbon allocation patterns whereby SDF allocate in excess of 50% to canopy production and the DF and WS sites allocate 40%–50% to woody production. Furthermore, we find that (iv) compared with canopy and root growth rates the woody growth rate of these forests is a poor proxy for their overall productivity and that (v) residence time is the primary driver in the productivity-allocation-turnover chain for the observed spatial differences in woody, leaf and root biomass across the rainfall gradient. Through a systematic assessment of forest productivity we demonstrate the importance of directly measuring the main components of above and belowground NPP and encourage the establishment of more permanent carbon intensive monitoring plots across the tropics

Contrasting carbon cycle along tropical forest aridity gradients in West Africa and Amazonia

Tropical forests cover large areas of equatorial Africa and play a substantial role in the global carbon cycle. However, there has been a lack of biometric measurements to understand the forests’ gross and net primary productivity (GPP, NPP) and their allocation. Here we present a detailed field assessment of the carbon budget of multiple forest sites in Africa, by monitoring 14 one-hectare plots along an aridity gradient in Ghana, West Africa. When compared with an equivalent aridity gradient in Amazonia, the studied West African forests generally had higher productivity and lower carbon use efficiency (CUE). The West African aridity gradient consistently shows the highest NPP, CUE, GPP, and autotrophic respiration at a medium-aridity site, Bobiri. Notably, NPP and GPP of the site are the highest yet reported anywhere for intact forests. Widely used data products substantially underestimate productivity when compared to biometric measurements in Amazonia and Africa. Our analysis suggests that the high productivity of the African forests is linked to their large GPP allocation to canopy and semi-deciduous characteristics.</p

Fine-root traits in tropical old-growth and logged-over forests

This data file contains mean fine-root (< 2 mm in diameter) biomass, architectural and morphological traits measured in a tropical old-growth forest, and in a 54-year-old logged-over forest in Ghana

Forest biomass, productivity and carbon cycling along a rainfall gradient in West Africa

© 2017 John Wiley & Sons Ltd Net Primary Productivity (NPP) is one of the most important parameters in describing the functioning of any ecosystem and yet it arguably remains a poorly quantified and understood component of carbon cycling in tropical forests, especially outside of the Americas. We provide the first comprehensive analysis of NPP and its carbon allocation to woody, canopy and root growth components at contrasting lowland West African forests spanning a rainfall gradient. Using a standardized methodology to study evergreen (EF), semi-deciduous (SDF), dry forests (DF) and woody savanna (WS), we find that (i) climate is more closely related with above and belowground C stocks than with NPP (ii) total NPP is highest in the SDF site, then the EF followed by the DF and WS and that (iii) different forest types have distinct carbon allocation patterns whereby SDF allocate in excess of 50% to canopy production and the DF and WS sites allocate 40%–50% to woody production. Furthermore, we find that (iv) compared with canopy and root growth rates the woody growth rate of these forests is a poor proxy for their overall productivity and that (v) residence time is the primary driver in the productivity-allocation-turnover chain for the observed spatial differences in woody, leaf and root biomass across the rainfall gradient. Through a systematic assessment of forest productivity we demonstrate the importance of directly measuring the main components of above and belowground NPP and encourage the establishment of more permanent carbon intensive monitoring plots across the tropics

Contrasting carbon cycle along tropical forest aridity gradients in West Africa and Amazonia

International audienceTropical forests cover large areas of equatorial Africa and play a substantial role in the global carbon cycle. However, there has been a lack of biometric measurements to understand the forests’ gross and net primary productivity (GPP, NPP) and their allocation. Here we present a detailed field assessment of the carbon budget of multiple forest sites in Africa, by monitoring 14 one-hectare plots along an aridity gradient in Ghana, West Africa. When compared with an equivalent aridity gradient in Amazonia, the studied West African forests generally had higher productivity and lower carbon use efficiency (CUE). The West African aridity gradient consistently shows the highest NPP, CUE, GPP, and autotrophic respiration at a medium-aridity site, Bobiri. Notably, NPP and GPP of the site are the highest yet reported anywhere for intact forests. Widely used data products substantially underestimate productivity when compared to biometric measurements in Amazonia and Africa. Our analysis suggests that the high productivity of the African forests is linked to their large GPP allocation to canopy and semi-deciduous characteristics