Including Tree Diversity In Predictions Of Tropical Forest Drought Responses

Lead Research Organisation: University of Exeter
Department Name: Geography


Tropical forests are one of the world's most important ecosystems; they are a biodiversity hot spot, store vast quantities of carbon, mitigate climate change, and influence global weather patterns. Predicting how these tropical forests will respond to climate change is a priority for making global policy decisions. Prolonged reductions in soil moisture and acute drought events are predicted to be a key threat to tropical forest in the coming century. The fate of tropical forests if exposed to drought in the future will depend on which types of trees die and which can survive from seedling to adult. Understanding this requires knowledge of which properties trees possess that alter their risk of dying or their survivorship during drought, as well as how these properties change between trees of different types, ages or heights. Currently most vegetation models used to predict the responses of tropical forest responses to future climate change only consider there to be one or two fixed types of tropical tree. They only account for very limited differences in how trees of different canopy heights and positions respond to drought. Therefore these models are currently unlikely to capture the variations in drought responses from real-world diversity in tree properties and which will ultimately determine the resilience of tropical forests to drought stress.
Representing the dependency of tropical forest drought responses on the diversity of tree properties in vegetation models is complex. It requires new data on how trees of different functional types and developmental stages respond to prolonged exposure to drought stress. My aim is to collect the data necessary to understand how drought survivorship of tropical trees is related to tree properties and their variation throughout a trees development in drought conditions. I will use this data to develop vegetation models and provide a step change in how they represent tropical forest drought responses. I have the exciting opportunity to use the longest running tropical forest drought experiment in the world, a site where 50% of incoming rainfall has been excluded for the last 15 years. Here I will test if tropical trees at different developmental stages and with different properties respond differently to long-term drought stress and how this influences mortality risk. I will make detailed physiological measurements of properties associated with a trees ability to survive in drought, on important tree taxa of different size classes; these taxa will include species found to be highly sensitive and resistant to drought stress. To accompany this study, seedlings from the focal taxa will be grown in a seedling drought experiment which will be used to test if drought resistance in seedlings increases following prior exposure to drought. Finally seedlings from mother trees which have been exposed to 15 years of experimental drought and seedlings from those which have not been exposed to drought will be grown in lab conditions and subjected to various soil drought conditions. This will test if prior exposure to drought in mother trees induces production of seedling which are more drought-resistant.
My research will create the only data-set which is able to test how functional properties, developmental stage and drought exposure control the risk of drought-induced mortality and which types of tree are most likely to survive from seedling to adult to sustain tropical forests under future drought conditions. This will provide a unique opportunity for my model development work, using a hierarchy of models from the scale of a single tree model to a dynamic global vegetation model. My ultimate goal is to represent the important differences in drought responses, based on a trees canopy position and the properties it possesses, to enable more accurate predictions of how tropical forests will respond to future climate change.

Planned Impact

This research project will have global societal and economic benefits which will reach far beyond the important scientific developments it will achieve.

Tropical forests are a important global resource and therefore predicting and preparing for how they may be altered by climate change is a global issue. I envisage the results of this project having a direct impact on climate change policy, and therefore influencing global decisions on climate change mitigation and adaptation. Consequently world governments, NGOs and companies involved in climate change mitigation and adaptation will directly benefit from the improved capacity to predict the response of tropical forest to environmental change, that this project will create. Firstly I envisage institutions such as the Met Office gaining substantially from this project which will provide the opportunity for them to test their key vegetation model, the Joint UK land environment simulator, against unique experimental data. This will provide the opportunity for them to collaborate on making a step-change in the way this model simulates tropical forests. The results of this collaboration will directly benefit policy makers who are reliant on the predictions from model simulations to create targeted climate change mitigation and adaptation policy. In particular, the Brazilian government is likely to be interested in the results of this study, as the Amazon forest represents a important national resource, which Brazil stands to benefit most from. Within Brazil the Amazon forest is vital for securing local food and water availability, regulating local climate, contributing to the growing tourist industry and as a resource to numerous local communities. However, on a global scale the Amazon and other global tropical forests are central to controlling global climate patterns and therefore governments across the world stand to benefit the greater understanding this project will produce concerning how vulnerable tropical forests are to predicted long-term drought and other climate changes. Furthermore this information will also directly benefit NGOs concerned with the conservation of tropical forests and their biodiversity. Lastly the development of the UN REDD+ initiative is increasingly enabling an economic value to be placed on the ecosystem services tropical forests provide. However the economic value of a tropical forests to local and global businesses is dependent on how these forests will be affected by climate change and on what time-scales. Therefore the results of model predictions made within projects such as this are likely to have important consequences for the economic value of tropical forests and businesses which rely on these values.

During this project I will extend my existing public engagement project both within the UK and Brazil. Currently my public engagement targets teaching pupils about the interactions of people, tropical forest and climate change, from the ages of 5-17 years, and connects pupils in schools across Edinburgh to those in remote locations in Brazil. Such initiatives provide direct benefits to pupils and teachers through providing access to expertise and novel teaching resources, which actively encourage pupils to learn about the important global role of tropical forests. I have also found that regular outreach activities, in schools, such as those that will be undertaken in this project, directly encourage pupils to pursue further education in science related subjects, particularly female pupils. Furthermore I will aim to make contact with the Eden Project in Cornwall, where colleagues in the University of Exeter already have good connections. The Eden project will therefore benefit through collaborating to display presentations of important scientific findings related to tropical forests, which constitute one of the most popular biomes in the project.


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Description Two new papers have been published concerning stem CO2 release from tropical trees increasing substantially as a result of drought (paper 1) and litterfall in a tropical forest undergoing a shock decline and then a re-stabilisation over a 16 year period of drought (paper 2). New data collected at the end of 2017 is also revealing that there is a strong effect on the light availability to trees influencing their drought responses.
Exploitation Route These finding will be valuable to inform future research trajectories, they are being used to develop a NERC large grant also these finding are also being used to scale fluxes to tropical forest regions to estimate the effects of drought at large ecological scales.
Sectors Environment

Description Collaboration with the University of Campinas 
Organisation State University of Campinas
Country Brazil 
Sector Academic/University 
PI Contribution I am collaborating to co-supervise a PhD student in Brazil at the University of Campinas to study the effects of drought on tropical forest seed production. This arose as a spin off project from a field campaign conducted for this project in Sep-Nov 2016.
Collaborator Contribution Dr. Rafael Oliveira is the main supervisor for this student in Campinas and together with him we have jointly created the PhD project.
Impact The production of a PhD project for a Brazilian student Andre Giles.
Start Year 2016