Does shifting Carbon Use Efficiency determine the growth rates of intact and disturbed tropical forests? Gathering new evidence from African forests

Lead Research Organisation: University of Oxford
Department Name: Geography - SoGE

Abstract

Why do trees in different tropical forests grow at different rates? Why do some trees within a site grow faster than others? At first impression, It seems a reasonable assumption that the 'visible productivity' (e.g. wood production and canopy litterfall) is somehow related to how much carbon and energy the forest or the individual tree captures from photosynthesis, the Gross Primary Productivity (GPP); this assumption is implicit in much of the forest ecology literature, as well as in many biosphere models. When we see explanations as why forests are increasing growth rates in response to global change, or increased productivity after disturbance, we tend to frame these explanations in the context of increased photosynthesis (either because of increased abiotic drivers - e.g. increased light or carbon dioxide, or because of increased photosyntheric capacity, e.g leaf nitrogen content) However, our recent work in Amazonia has indicated that the site-to-site variability in net primary productivity (NPP) in lowland rainforests is not related to how much carbon and energy the forest captures through photosynthesis, but much more determined by how much of that captured carbon used by plants for their internal metabolism (Malhi et al., submitted to Nature), the autotrophic respiration, Ra. This tentative finding has consequences for much of tropical forest research, and global change vegetation models. Moreover, our early results suggest that disturbance is the main determinant of how much an ecosystem allocates to autotrophic respiration, with less autotrophic respiration in disturbed systems. We would now like to explore this topic further in five ways: (i) by exploring in greater detail the spatial and temporal variation of autotrophic respiration; (ii) by greatly increasing the number of sites investigated; (iii) by assessing the extent to which results from Amazonia are generalisable in another biogeographical realm, namely equatorial Africa; (iv) by explicitly exploring how disturbance affects carbon use and allocation by tracking these before and after selective logging; (v) by exploring how much interspecific variation in NPP is determined by autotrophic respiration. The underlying hypotheses we are exploring are that (i) there is no significant site-to-site variation in the GPP of moist tropical lowland forests (within Africa and in comparison to Amazonia), despite variation is soil properties, climate and tree species composition; (ii) there is substantial site-to-site variation in net primary productivity (NPP), and this is mainly driven by shifts in carbon use efficiency (CUE, the proportion of photosynthetic carbon converted to biomass), and (iii) forest CUE increases substantially after disturbance (logging) and subsequently declines over time, and (iv) this shift is driven by differing plastic variation in CUE within surviving individuals, rather than by community replacement. In the process, we will pioneer comprehensive carbon cycle assessment in intact and disturbed African tropical forests, replicated across two contrasting countries, Ghana (West Africa) and Gabon (Central Africa). Our sampling strategy will encompass plots in (i) wet primary forests (2 countries x 2 plots), (ii) moist primary forests (2 countries x 2 plots),(iii) tracking sites before, during and after logging disturbance (2 countries x 2 plots), and (iv) plots recovering from logging disturbance 10, 15 and 20 years ago (2 countries x 2 plots). At all sites we will collect 2.0-2.5 years of data. Our project will provide substantial scientific capacity building in Ghana and Gabon,we will train and utilise 6 student field researchers (3 full time, 3 part-time) in each country, and hold wider-reach training workshops in carbon cycle science in each country at the start and end of the project. this event.

Publications


10 25 50
Bastin JF (2015) Seeing Central African forests through their largest trees. in Scientific reports
Fisher JB (2013) African tropical rainforest net carbon dioxide fluxes in the twentieth century. in Philosophical transactions of the Royal Society of London. Series B, Biological sciences
Lewis SL (2013) Above-ground biomass and structure of 260 African tropical forests. in Philosophical transactions of the Royal Society of London. Series B, Biological sciences
Malhi Y (2013) African rainforests: past, present and future. in Philosophical transactions of the Royal Society of London. Series B, Biological sciences
 
Description We have provided the first descriptions of productivity of African forests, and found that forests in Ghana are the most productive yet described in the tropics.
Exploitation Route N/A
Sectors Environment
 
Description The data gathered in this project (still in the process of being published) has contributed to 3 PhD student projects in Ghana, and 3 MSc dissertations in Ghana (the scholarships funded from other sources)
First Year Of Impact 2015
Sector Education,Environment
Impact Types Societal
 
Description GEM-TRAITS ERC Advanced Investigator Award
Amount € 2,500,000 (EUR)
Organisation European Research Council (ERC) 
Sector Public
Country European Union (EU)
Start 05/2013 
End 04/2018
 
Description Royal Society Africa Award
Amount £160,000 (GBP)
Organisation The Royal Society 
Sector Academic/University
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 01/2014 
End 12/2017
 
Title Global Ecosystems Monitoring database 
Description This database standardises and archives all of the forest growth and respiration data from multiple sites all around the world in the GEM network. 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact Accessing data from other plots around the world is significantly easier when all the datasets are standardised. 
 
Description Ecosystems Lab Blog 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact The Ecosystems Lab Blog enables all our researchers to report on their fieldtrips as well as other interesting stories related to their research.
Year(s) Of Engagement Activity 2016,2017
URL http://oxfordecosystems.weebly.com/blog
 
Description Global Ecosystems Monitoring TV 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Study participants or study members
Results and Impact This on-going engagement activity was devised as a new way in communicating our science to other parties around the world who would like to join the Global Ecosystems Monitoring network. We are in the process of making a series of short video clips which demonstrate our field methods accompanied by visual and audio narrative to facilitate growth of the network primarily in tropical regions around the world.
Year(s) Of Engagement Activity 2016,2017