Final Report Summary - T-FORCES (Tropical forests in the changing earth system)
Tropical forests protect at least half of all species on earth as well as hundreds of billions of tons of carbon. They are potentially critically sensitive to climate change, and their fate (extinction or survival, growth or decline) is closely tied to processes that will affect the rate of global climate change this century. T-FORCES aimed to deepen our understanding of the role of these complex forests in the global carbon cycle and climate change. To do this we have been applying identical ecological methods to forests worldwide across four tropical continents (Amazon, Africa, Asia, Australia). The project includes: (1) Measuring ecosystem behaviour throughout tropical forests; (2) Making intensive measurements to measure the sensitivity of the forest carbon cycle to climate; (3) Testing the long-term sensitivity of forest carbon to temperature, using elevation experiments across the tropics; and (4) Starting to scale-up our findings using mapping and modelling approaches.
Our results reveal subtle but important changes in forest behaviour. In parts of South America, Asia and Africa, in spite of some drying, the biomass of mature forests has, surprisingly, been increasing. This demonstrates unexpected resilience in tropical forests to climatic changes, and suggests that the huge diversity of tropical forests helps provide this. We also completed parallel analyses for the other great tropical forests of the world, in Africa and Southeast Asia. In Africa the carbon ‘sink’ (net uptake from the atmosphere into forests) has now continued undiminished for several decades. Similarly, in Asia’s few remaining intact forests the sink has also continued for decades. Growth rates have tended to increase everywhere. This consistent response shows that the factor driving these changes must be acting across all the world’s major tropical forest regions, and the best explanation for such long-term, planet-wide changes is the increase in carbon dioxide concentrations in the atmosphere, and the long-term stimulation to plant growth rates that this provides. Our findings also show how climate changes and threats can at times in some regions overwhelm the benefits provided by CO2, even when partially protected by the high diversity of tropical forests. For example we have now seen real reverses (increased mortality, decreased growth) during the Amazon droughts in 2005 and 2010 and 2015-16. Overall, in the Amazon as a whole, repeated droughts are impacting forests. As a result the magnitude of the net carbon sink into forests – caused by the difference between growth and death and which has been positive since at least the 1980s – is threatened by climate change. In the longer term other processes are also threatening to diminish the sink. Most notably, the acceleration of tree life-cycles means that future gains in biomass may be smaller than most models of the 21st century Earth actually predict. If the tropical carbon sink continues to diminish as we expect, this means that a major 'subsidy from nature' is coming to an end, and therefore even deeper cuts of carbon dioxide emissions will be needed if the whole planet is to chart a course to a stable, liveable climate.
The changes witnessed are not just confined to altered carbon storage and carbon dynamics. Now, for the first time, we also have evidence that the tree species functional composition of Amazon forests is shifting. For example a new paper led by our PhD student from Brazil is showing how drought-adapted species are starting to gain, at the expense of some species which are specialised in less seasonal moist conditions. In fact, a key part of T-FORCES has been to develop scientists worldwide. Our work has been supported by cutting-edge data analysis software which we have custom-built. This allows us to upload, check, share and analyse data from everywhere, and track the contributors of our global team, helping knowledge exchange amongst researchers, whether they are collaborating together locally or across continents. Our approach thus *shares* technology, while ensuring that knowledge and skills are *transferred* to where they are needed most. Our partners in developing countries can benefit greatly, a process which we have started to support with training in the UK & South America. As an example of the impact of this approach in terms of outputs and skills fostered we have more than 130 scientific papers published already by T-FORCES, with more to come, and with a wide variety of authorship beyond just the core project team.
Our results reveal subtle but important changes in forest behaviour. In parts of South America, Asia and Africa, in spite of some drying, the biomass of mature forests has, surprisingly, been increasing. This demonstrates unexpected resilience in tropical forests to climatic changes, and suggests that the huge diversity of tropical forests helps provide this. We also completed parallel analyses for the other great tropical forests of the world, in Africa and Southeast Asia. In Africa the carbon ‘sink’ (net uptake from the atmosphere into forests) has now continued undiminished for several decades. Similarly, in Asia’s few remaining intact forests the sink has also continued for decades. Growth rates have tended to increase everywhere. This consistent response shows that the factor driving these changes must be acting across all the world’s major tropical forest regions, and the best explanation for such long-term, planet-wide changes is the increase in carbon dioxide concentrations in the atmosphere, and the long-term stimulation to plant growth rates that this provides. Our findings also show how climate changes and threats can at times in some regions overwhelm the benefits provided by CO2, even when partially protected by the high diversity of tropical forests. For example we have now seen real reverses (increased mortality, decreased growth) during the Amazon droughts in 2005 and 2010 and 2015-16. Overall, in the Amazon as a whole, repeated droughts are impacting forests. As a result the magnitude of the net carbon sink into forests – caused by the difference between growth and death and which has been positive since at least the 1980s – is threatened by climate change. In the longer term other processes are also threatening to diminish the sink. Most notably, the acceleration of tree life-cycles means that future gains in biomass may be smaller than most models of the 21st century Earth actually predict. If the tropical carbon sink continues to diminish as we expect, this means that a major 'subsidy from nature' is coming to an end, and therefore even deeper cuts of carbon dioxide emissions will be needed if the whole planet is to chart a course to a stable, liveable climate.
The changes witnessed are not just confined to altered carbon storage and carbon dynamics. Now, for the first time, we also have evidence that the tree species functional composition of Amazon forests is shifting. For example a new paper led by our PhD student from Brazil is showing how drought-adapted species are starting to gain, at the expense of some species which are specialised in less seasonal moist conditions. In fact, a key part of T-FORCES has been to develop scientists worldwide. Our work has been supported by cutting-edge data analysis software which we have custom-built. This allows us to upload, check, share and analyse data from everywhere, and track the contributors of our global team, helping knowledge exchange amongst researchers, whether they are collaborating together locally or across continents. Our approach thus *shares* technology, while ensuring that knowledge and skills are *transferred* to where they are needed most. Our partners in developing countries can benefit greatly, a process which we have started to support with training in the UK & South America. As an example of the impact of this approach in terms of outputs and skills fostered we have more than 130 scientific papers published already by T-FORCES, with more to come, and with a wide variety of authorship beyond just the core project team.