Speaker: Dr Imma Oliveras, Departmental Research Lecturer in Ecosystems Science and Deputy Programme Leader on Ecosystems, Environmental Change Institute, University of Oxford
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Vegetation transitions are characterised by a shift –either gradual or sharp- between different vegetation types with different plant functional types, often also associated with different climatic and edaphic conditions. They are often characterised by a fire-adapted vegetation adjacent to a fire-sensitive vegetation. This contrasting shift creates a zone of tension between ecosystems, thus these transitions are thought to be especially sensitive to changes in disturbance regime and climate change, with potential for one vegetation type expanding over the other. In this talk we will visit different types of vegetation transitions in South America and Africa: from the tropical montane tropical forest and grasslands treelines in the Andes to different types of forest-grassy environments transitions in Bolivia, Brazil, Ghana and Gabon. Each place has its own ecological particularities associated with the ecological processes and mechanisms of the transition, as well as with the local drivers of change. Nonetheless, we will see how different places share common processes, and their vulnerability to regional to global change drivers. In the Andes, increasing temperatures are increasing the cloud base in elevation. While forests are tending to migrate upwards due to the increasing cloud base elevation, they are facing a ceiling posed by fire, grazing and highly productive grasses. Forest-grassy environment transitions share many ecological mechanisms, with forests being more fire and drought sensitive and grassland fire and drought tolerant. However, each place is ecologically different because of different abiotic drivers (e.g. soil, climate) and disturbances (e.g. megafauna, fire, deforestation). This results in different shifts along each transition, but all share a common axis of change: woody encroachment in grassy environments, and forest degradation with grass invasion in forested areas.
Imma Oliveras returned to ECI in 2015 from Wageningen University where she held a Marie Curie Fellowship and led the research project TipTropTrans: Tipping Points of Tropical Forest-Savanna Transitions. The project aimed to gather a detailed ecological and ecophysiological understanding of the dynamic process of tropical forest-savanna transitions from a functional trait perspectives, at a number of sites in South America and Africa.
At ECI she currently conducts research on the functional traits along forest-savanna and rainfall gradients, and leads the GEM Traits campaigns conducted in Ghana (Kwaeemma) and Brazil (BACABA). In a previous position (2009-2013) she conducted research about fire regimes in the Tropical Andes, looking at the key factors that determine fire ignition and spread in cloud forests of the Peruvian Andes, the resilience to fire of the main tree species and the carbon losses due to forest fires in those traditional non-burning, cool ecosystems.