Resolving the current and future carbon dynamics of the dry tropics

Lead Research Organisation: University of Exeter
Department Name: Geography


The ecosystems of the dry tropics are in flux: the savannas, woodlands and dry forests that together cover a greater area of the globe than rainforests are both a source of carbon emissions due to deforestation and forest degradation, and also a sink due to the enhanced growth of trees. However, both of these processes are poorly understood, in terms of their magnitude and causes, and the net carbon balance and its future remain unclear. This gap in knowledge arises because we do not have a systematic network of observations of vegetation change in the dry tropics, and thus have not, until now, been able to use observations of how things are changing to understand the processes involved and to test key theories.

Satellite remote sensing, combined with ground measurements, offers the ideal way to overcome these challenges, as it can provide regular, consistent monitoring at relatively low cost. However, most ecosystems in the dry tropics, especially savannas, comprise a mixture of grass and trees, and many optical remote sensing approaches (akin to enhanced versions of the sensors on digital cameras) struggle to distinguish changes between the two. Long wavelength radar remote sensing avoids this problem as it is insensitive to the presence of leaves or grass, and also is not affected by clouds, smoke or the angle of the sun, all of which complicate optical remote sensing. Radar remote sensing is therefore ideal to monitor tree biomass in the dry tropics. We have successfully demonstrated that such data can be used to accurately map woody biomass change for all 5 million sq km of southern Africa.

In SECO we will create a network of over 600 field plots to understand how the vegetation of the dry tropics is changing. and complement this with radar remote sensing to quantify how the carbon cycle of the dry tropics has changed over the last 15 years. This will provide the first estimates of key carbon fluxes across all of the dry tropics, including the amount of carbon being released by forest degradation and deforestation and how much carbon is being taken up by the intact vegetation in the region. By understanding where these processes are happening, we will improve our knowledge of the processes involved.

W will use these new data to improve the way we model the carbon cycle of the dry tropics, and test key theories. The improved understanding, formalised into a model, will be used to examine how the dry tropics will respond to climate change, land use change and the effects of increasing atmospheric CO2. We will then be able to understand whether the vegetation of the dry tropics will mitigate or exacerbate climate change, and we will learn what we need to do to maintain the structure of the dry tropics and preserve its biodiversity.

Overall, SECO will allow us to understand how the vegetation of the dry tropics is changing, and the implications of this for the global carbon cycle, the ecology of savannas and dry forests, and efforts to reduce climate change. The data we create, and the analyses we conduct will be useful to other researchers developing methods to monitor vegetation from satellites, and also to those who model the response of different ecosystems to climate and other changes. Forest managers, ecologists and development practitioners can use the data to understand which parts of the world's savannas and dry forests are changing most, and how these changes might be managed to avoid negative impacts that threaten biodiversity and the livelihoods of the 1 billion, mostly poor, rural people who live in this region.

Planned Impact

There are many non-academic beneficiaries from the provision of high quality, high resolution data on woody biomass, biomass change, the occurrence of deforestation, degradation and forest growth, and related carbon fluxes. Many land managers in the dry tropics will be able to utilise the SECO data to inform their work, for example:

* Protected area managers can use these data to assess the effectiveness of their procedures for avoiding timber poaching and encroachment
* Government forest departments can use the data to map the extent of forest resources, and their change over time
* Community-based resource management projects can use these data as a measure of the effectiveness of different types of project interventions and tenure regimes
* National governments will be able to improve the quality of the data they submit to the UN climate processes on land use emissions, to the FAO on forest extent and quality, and also to monitor the sustainable development goals. The use of the SECO data for these purposes will reduce costs and improve data quality, as currently many key processes e.g. forest degradation, are not reported by most of the countries in the dry tropics. This will be the focus of our pathways to impact work.

When aggregated to provincial or national scale, the SECO data are useful for policy makers prioritising investments in forest management or seeking to reduce deforestation and degradation as part of international commitments under the Paris Agreement. Bi-lateral (e.g. UK DfID) and multi-lateral (e.g. the World Bank) development donors also need such information to help prioritise their multi-billion dollar investments in sustainable forestry and land management.

Nearly all national forest / land management agencies report data to the FAO on forest resources and to the UN and related bodies on land use emissions. Particularly in resource-poor, developing, countries, these reports often use outdated or inconsistent data. Our Pathways to Impact work will focus on this issue, supporting six national agencies in southern and central Africa to utilise the SECO data for their needs. This will involve a bespoke programme of training, mentoring and opportunities for collaboration, aimed at utilising the SECO data in their work. This will benefit these agencies by:

1) Reducing the effort needed to gain an accurate estimate of land use change emissions and forest resource changes at national and subnational scales, and
2) Improving the quality of such estimates based on state-of-the-art remote sensing and modelling, tailored to the conditions of the dry tropics.

To achieve these benefits, we will produce new training materials, examples of using the SECO data for common tasks, and make the data accessible in a variety of formats and resolutions. This will be combined with face-to-face meetings and webinars throughout the duration of SECO.


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