I’m a third year PhD student at the University of Edinburgh, primarily supervised by Casey Ryan as part of the LANDTeam research group. Broadly, my research will focus on using remote sensing of vegetation structure to delimit and understand dry tropical biomes – namely savannas and dry forests. I’m part of the SENSE CDT, which aims to train PhD students to use satellite data to work on a wide range of environmental problems. My other supervisors are Kyle Dexter, Toby Pennington, Oliver Phillips and Tim Baker.
What are the Dry Tropics?
Although famous for tropical rainforest ecosystems, 40 – 50% of the global tropics have a seasonally dry climate, which supports dry forest and savanna biomes (Miles et al., 2006; Murphy and Lugo, 1986; Pennington et al., 2018; Riggio et al., 2020).
The dry tropical biomes are roughly found between 30°N and 30°S, reaching higher latitudes than tropical rainforest. The dry tropics are predominantly found in Latin America and Africa, and additionally across parts of Asia and Australia. Both dry forest and savanna biomes exist within similar climatic space, but are not controlled by climate alone. Variation in edaphic factors, climate, and most importantly, disturbance agents, define the balance between savanna and dry forest. Here’s some examples of savanna and dry forest from my fieldwork in Brazil earlier in 2022:
The dry tropics are vital from both an ecological and human perspective. They are important in terms of biodiversity, with high levels of endemism (Portillo-Quintero et al., 2015), functional diversity, and variation in floristic composition (Dexter et al., 2015) in tropical dry forests, and high biodiversity in savanna ecosystems (Bond and Parr, 2010). They are inextricably linked to the livelihoods of millions of people across the world, with a third of the human population living in the dry tropics, and many more depending on the services they provide (Pennington et al., 2018). The dry tropics are particularly vital for supporting vulnerable households and individuals across the world (Blackie et al 2014), with roughly 70% of the world’s drylands occurring in developing countries (Reid 2005). Furthermore, research suggests the dry tropics are important in global carbon cycling, having a particular impact on interannual variability (Ahlstrom et al., 2015).
What are Biomes and why are they important?
Biomes are a key concept in ecology and biogeography, and are generally understood as large-scale ecosystems, which occupy a large geographical area, at the continental scale, often recognisable by characteristic vegetation types and animal communities (Mucina, 2019; Woodward et al., 2004). Accurate biome delineation is important for appropriate management, conservation planning, and modelling the response of vegetation to climate and other global changes.
Traditionally they are described using climatic data, for example tropical rainforests have higher rainfall than dry tropical biomes. However, some biomes are climatically similar, and are different in different ways, which makes delimiting them a challenge, according to traditional climatic descriptions. Dry tropical forests and savannas are like this.
What’s my research?
Savannas and dry forests are fundamentally different ecosystems, but its not yet fully understood why, which means delimiting them is difficult. For example, they are different in terms of:
- Which species are present, and their evolutionary lineages
- Traits of different species, for example the presence of thick bark in savnna trees
- Savannas generally have a grassy understory, whereas dry forest does not. This is as a result of differences in disturbance dynamics
- Structural differences, such as differences in number of layers in the canopy
- Differences in soil composition and structure
Differences between biomes means that they are likely to react differently to different situations, for example changes in climate. We’re not sure how these reactions will differ, and what that means both ecologically and for the people living in these ecosystems.
This confusion leads to problems defining appropriate management, and for climate change adaptation. For example, managing CO2 fertilisation and the resultant bush encroachment in savannas, or prescribing appropriate fire regimes to support biodiversity.
Here we address this problem by using the differences that we do know about between savanna and dry forest. In this case, we have used structural differences between savanna and dry forest and savanna, measured using remote sensing, to delimit them. Vegetation structure is a good measure because it can be remotely sensed over large geographical areas, for example using variables such as NDVI and biomass.
Chapter 1 uses the case study of North-East Brazil in order to address these questions.
Contact me
Email: L.H.Wells@sms.ed.ac.uk
Past work
- MSci Conservation Biology and Ecology, University of Exeter, Penryn Campus (2015 – 2020)
- Full time volunteer Nature Reserves Assistant, Devon Wildlife Trust (2018 – 2019)
- Team Leader, Expedition Cloudbridge 2017, Costa Rica
References
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Blackie, R., Baldauf, C., Gautier, D., Gumbo, D., Kassa, H., Parthasarathy, N., Paumgarten, F., Sola, P., Pulla, S., Waeber, P., Sunderland, T., 2014. Tropical dry forests: The state of global knowledge and recommendations for future research. CIFOR
Bond, W.J., Parr, C.L., 2010. Beyond the forest edge: Ecology, diversity and conservation of the grassy biomes. Biol. Conserv., Conserving complexity: Global change and community-scale interactions 143, 2395–2404. https://doi.org/10.1016/j.biocon.2009.12.012
Dexter, K.G., Smart, B., Baldauf, C., Baker, T.R., Balinga, M.P.B., Brienen, R.J.W., Fauset, S., Feldpausch, T.R., Silva, L.F.-D., Muledi, J.I., Lewis, S.L., Lopez-Gonzalez, G., Marimon-Junior, B.H., Marimon, B.S., Meerts, P., Page, N., Parthasarathy, N., Phillips, O.L., Sunderland, T.C.H., Theilade, I., Weintritt, J., Affum-Baffoe, K., Araujo, A., Arroyo, L., Begne, S.K., Neves, E.C.-D., Collins, M., Cuni-Sanchez, A., Djuikouo, M.N.K., Elias, F., Foli, E.G., Jeffery, K.J., Killeen, T.J., Malhi, Y., Maracahipes, L., Mendoza, C., Monteagudo-Mendoza, A., Morandi, P., Santos, C.O.-D., Parada, A.G., Pardo, G., Peh, K.S.-H., Salomão, R.P., Silveira, M., Sinatora–Miranda, H., Slik, J.W.F., Sonke, B., Taedoumg, H.E., Toledo, M., Umetsu, R.K., Villaroel, R.G., Vos, V.A., White, L.J.T., Pennington, R.T., 2015. Floristics and biogeography of vegetation in seasonally dry tropical regions. Int. For. Rev. 17, 10–32. https://doi.org/10.1505/146554815815834859
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Mucina, L., 2019. Biome: evolution of a crucial ecological and biogeographical concept. New Phytol. 222, 97–114. https://doi.org/10.1111/nph.15609
Murphy, P.G., Lugo, A.E., 1986. Ecology of Tropical Dry Forest. Annu. Rev. Ecol. Syst. 17, 67–88. https://doi.org/10.1146/annurev.es.17.110186.000435
Pennington, R.T., Lehmann, C.E.R., Rowland, L.M., 2018. Tropical savannas and dry forests. Curr. Biol. 28, R541–R545. https://doi.org/10.1016/j.cub.2018.03.014
Portillo-Quintero, C., Sanchez-Azofeifa, A., Calvo-Alvarado, J., Quesada, M., do Espirito Santo, M.M., 2015. The role of tropical dry forests for biodiversity, carbon and water conservation in the neotropics: lessons learned and opportunities for its sustainable management. Reg. Environ. Change 15, 1039–1049. https://doi.org/10.1007/s10113-014-0689-6
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Riggio, J., Baillie, J.E.M., Brumby, S., Ellis, E., Kennedy, C.M., Oakleaf, J.R., Tait, A., Tepe, T., Theobald, D.M., Venter, O., Watson, J.E.M., Jacobson, A.P., 2020. Global human influence maps reveal clear opportunities in conserving Earth’s remaining intact terrestrial ecosystems. Glob. Change Biol. 26, 4344–4356. https://doi.org/10.1111/gcb.15109
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