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

Abstract

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.

Drier tropical forests are susceptible to functional changes in response to a long‐term drought

“…Our analysis includes vegetation plots distributed across a climatic gradient, which also encompasses different soil characteristics (Moore et al . ). The focus of this study was to investigate the extent to which climatic factors by their own determine shifts in plant trait composition.…”

“…), soil (Moore et al . ), baseline climate conditions (Malhi et al . ) and El Niño impacts (e.g., Rifai et al .…”

“…Further site details and description of the carbon cycle are given in Moore et al . () and in full details of trait data collection are given in the extended methods section in the Supplementary Information. The GEM‐traits database forms the main trait input data and when needed was complemented with data from the BIEN (Enquist et al .…”

“…The sites sampled were Ankasa (two plots) in the humid forest zone (latitude: 5.26, longitude: À2.69), Bobiri (two plots) in the semi-deciduous forest zone (lat: 6.69, long: À1.33) and Kogyae (3 plots) on the dry forest zone (lat: 7.26, long: À1.15). Further site details and description of the carbon cycle are given in Moore et al (2018) and in full details of trait data collection are given in the extended methods section in the Supplementary Information. The GEM-traits database forms the main trait input data and when needed was complemented with data from the BIEN (Enquist et al 2009) and the TRY (Kattge et al 2011) databases.…”

Greater stem growth, woody allocation, and aboveground biomass in Paleotropical forests than in Neotropical forests

“…We deemed it insufficient to include these few sites in our assessment of large-scale, regional differences, and thus excluded African sites from the analyses. Since the database was assembled and analyzed, at least one new analyses of forest dynamics in Africa has been published (Moore et al 2017), but few of those data are publicly accessible. Thus, for the purposes of this analysis, Neotropical forests include those found in Central and South America (and include the Caribbean and Hawaii), and Paleotropical forests include those in Asia and Australasia.…”