Department für Geographie




Seminar on vegetation and climate by Stephen Sitch & Lina Mercado on June 1

27.05.2022  Pongratz, J.

Please join us for a double-feature seminar at our Department on June 1 at 9:15-10:30, Luisenstr. 37, C 006

Stephen Sitch is Professor of Physical Geography at the University of Exeter, UK. He is involved in a range of international projects that cover divers fields from biogeography and carbon, water nutrient cycling in tropical and high latitude ecosystems, climate-chemistry-ecosystem interactions, land-use and land cover changes and implications for the global carbon cycle to air pollution impacts on vegetation. He is one of the few vegetation modelers I know who is equally successful coding - Stephen is the developer of the world’s most cited dynamic global vegetation model - as taking observations out in the field. He is also coordinating the estimates of the terrestrial sink in the annual Global Carbon Budgets.

Lina Mercado is Associate Professor in Ecosystems and Environmental Change at the University of Exeter. Her work, too, very successfully combines observations and computer models. She currently leads projects using manipulation and observational studies to (i) determine thermal acclimation of tropical montane forest species (ii) model the effects of soil fertility on tropical forest carbon cycling iii) quantify non-temperature control mechanisms of nocturnal plant respiration. The modelers among us will know Lina from her landmark study in Nature on showing that the 'global dimming’ period associated with anthropogenic emissions of aerosol precursors increased the land carbon sink.


Lina Mercado: Response of tropical montane forest tree to warming: insights from a field transplant experiment in the Colombian Andes

The tropics have experienced the largest recent increases in heat extremes over the globe, with mean temperatures predicted to continuously exceed bounds of historical variability in the next two decades in concert with more intense and frequent heatwaves. Recent warming has been associated with i) widespread reduction of growth and biomass carbon stocks in the warmest locations in lowland tropical forests in all continents and ii) increased mortality of cold-affiliated species in the warm extreme of their thermal ranges in the Andes, triggering a compositional change towards warm-affiliated species across all elevations. However, the specific mechanisms behind such compositional changes remain unknown.

We use a 3-year field transplant experiment on an elevation gradient in the Colombian Andes to investigate the impact of warming on survival, growth and gas exchange of dominant Andean tree species ( We planted 24 x 2-year old saplings of 15 of the most dominant tree species of intermediate succession from the Colombian Andes at three experimental locations with mean annual temperatures of 14°C, 22°C, 26°C under common irrigated soils. Specifically, we expose cold affiliated species to a range of temperatures within and outside the warm edges of their thermal niche and warm affiliated species were exposed to temperatures on their cold edges. We obtain differential responses of warm and cold affiliated species to warming which will be outlined during the presentation.

Stephen Sitch: The role of the terrestrial biosphere in the Earth System and for achieving Paris climate targets

In this presentation I will first give a broad overview of the role of the terrestrial ecosystems in the contemporary global carbon cycle, and ecosystems mitigate climate change already today. A key question relates to the efficiency of land ecosystems to sequester CO2 and how it will change in the near-term future, e.g. can it help us achieve the Paris agreement to avoid dangerous climate change. To begin to answer this question we first need to understand processes and regional attribution of the contemporary land carbon sink, e.g. the relative contribution of changing atmospheric composition, climate and land-use change to the land sink dynamics. I will draw upon research conducted using the TRENDY ensemble of land models which supports the annual Global Carbon Budget. I will highlight recent work in tropical forests and dryland ecosystems, and the role of cascading effects of deforestation on the land sink. Finally, I present work on how land-use emissions play a critical role in land-based mitigation for Paris climate targets.