NERC-FAPESP PhenoChange: Towards a Dry Tropics Global Phenological Monitoring Network

Phenology is a term used to describe the seasonal timing of animal and plant behaviour. Examples of phenological events are when plants first flower in the spring or when birds migrate to the tropics for the winter. In the dry regions of the tropics, phenological behaviour of plants seems to be primarily linked to water availability, rather than to changes in temperature as for example in temperate areas like the UK, but determinants of tropical phenology are poorly understood. Yet, elucidating the phenological behaviour of plants, including in the dry tropics, is essential to measure the flow of carbon into and out of ecosystems. This contributes in turn to understanding the links between plants and the atmosphere and ultimately to predicting the potential impact of climate change on vegetation and vegetation impacts on the climate.

Recent reports from the Intergovernmental Panel on Climate Change and the United Nations Environment Programme have made it clear that more data are needed on the phenological patterns of vegetation in the tropics, in order to improve predictions on the future of the climate, both in the tropics and globally. To do that, we need to study the phenology of tropical vegetation over broad geographic areas. Hypothetically this can be accomplished using satellite observations, but in fact, the data available from satellites are inadequate: clouds often block a space-based view of the vegetation and the spatial resolution of the images is too coarse (imagine a very fuzzy photograph). The latter means that it can be very difficult to distinguish between trees leafing out versus grasses, with important implications for the amount of carbon flowing into or out of an ecosystem. This is particularly relevant in dry tropical regions where mixed ecosystems with trees and grass are widespread. We also have a poor idea of how phenological timing varies over geographic regions with different patterns of rainfall.

Ground-based observations of phenology are therefore needed to complement satellite observations and provide a more accurate picture of vegetation behaviour. Historically, ground-based observations have been difficult to implement at a broad geographic scale in a consistent way, because they are labour intensive and difficult to do in a consistent manner. However, new technologies point a way forward to overcome these issues and advance multi-site and multi-layer (tree and grass) observations across tropical regions. Specifically, cameras can be installed that take photographs every day of the same patch of vegetation over the course of months and years. Such images can be efficiently processed using new computational techniques to quantify when a given patch of vegetation, or ecosystem, flushes new leaves, and whether those leaves are on trees or the ground layer.

The proposed project, PhenoChange, will link up global experts on camera-based phenological monitoring in Brazil and the USA with a team of British and African scientists that are leading pioneering, ground-based studies of tropical dry vegetation across sub-Saharan Africa. The project team will install and monitor cameras at six representative sites across dry tropical areas in Brazil and sub-Saharan Africa. This will result in the first comparable, ground-based dataset of vegetation phenology in the dry tropics across multiple continents. The research team will analyse these data to address some key unanswered questions around the timing of tree versus grass phenology in tropical dry vegetation and how this varies over gradients of rainfall. The results will have important implications for models that predict future climate change and its interaction with vegetation change. Finally, the results will lay the groundwork for future grant applications that will deepen and expand UK expertise on vegetation in tropical dry ecosystems.