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.
Organisations
- University of Oxford (Lead Research Organisation)
- Forestry Research Institute of Ghana (Collaboration)
- National Agency for National Parks (Gabon) (Collaboration)
- Tropical Ecology Research Institute IRET (Project Partner)
- Swedish University of Agricultural Sciences (Project Partner)
- Council for Scientific and Industrial Research (Project Partner)
Publications
Malhi Y
(2013)
African rainforests: past, present and future.
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
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
Malhi, Y.
(2015)
Routledge Handbook of Forest ecology
Bastin JF
(2015)
Seeing Central African forests through their largest trees.
in Scientific reports
Chiti T
(2016)
Impact of woody encroachment on soil organic carbon storage in the Lopé National Park, Gabon
in Biotropica
Cardoso AW
(2016)
Winners and losers: tropical forest tree seedling survival across a West African forest-savanna transition.
in Ecology and evolution
Sullivan MJP
(2018)
Field methods for sampling tree height for tropical forest biomass estimation.
in Methods in ecology and evolution
Moore S
(2018)
Forest biomass, productivity and carbon cycling along a rainfall gradient in West Africa.
in Global change biology
Malhi Y
(2018)
New perspectives on the ecology of tree structure and tree communities through terrestrial laser scanning.
in Interface focus
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, whereas our forest plots in Gabon are less fertile and less productive. This has led to development of a general model about predicting tropical forest productivity. |
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 6 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 | Belgium |
Start | 04/2013 |
End | 04/2018 |
Description | Royal Society Africa Award |
Amount | £160,000 (GBP) |
Organisation | The Royal Society |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 01/2014 |
End | 12/2017 |
Description | The multi-year impacts of the 2015/2016 El Nino on the carbon cycle of tropical forests |
Amount | £650,394 (GBP) |
Funding ID | NE/P001092/1 |
Organisation | Natural Environment Research Council |
Sector | Public |
Country | United Kingdom |
Start | 12/2016 |
End | 11/2021 |
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 | ANPN |
Organisation | National Agency for National Parks (Gabon) |
Country | Gabon |
Sector | Public |
PI Contribution | We have trained several of the research staff in advanced field methods and provided them with open access to all of the data collected within the research sites including long-term meteorological monitoring data from our weather stations. |
Collaborator Contribution | They have provided logistical support for our field teams and granted access to research sites as well as helped with export permits for samples. They have also contributed to some of the field assistant salaries. |
Impact | Full report for the ANPN Scientific Committee. |
Start Year | 2011 |
Description | FORIG |
Organisation | Forestry Research Institute of Ghana |
Country | Ghana |
Sector | Public |
PI Contribution | We have organised two technical workshops at FORIG's headquarters that focused on research methods and data analysis/ These were heavily attended by FORIG staff beyond the scope of our research members. We also have provided access to data including soil and weather data. |
Collaborator Contribution | FORIG have helped us by providing personnel to carry out the intensive field campaigns required in this project. |
Impact | Two of FORIG's researchers have now gone on to study PhD's at American and Canadian Universities using this projects ideas as a basis of their research. We are also mentoring a number of other FORIG research staff at PhD and MSc levels, including inviting some for internship opportunities at Oxford. |
Start Year | 2011 |
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 |