Abstract booklet - gtö – Society for Tropical Ecology

156 PARALLEL SESSION HALL H III THURSDAY ANDEAN BIODIVERSITYPARALLE SESSION THURSDAY H III: ANDEAN BIODIVERSITY HOTSPOT157Session: The Andean biodiversity hotspot and its future: Biodiversity,eco system functioning & ecosystem services under environmentalchangeThursday, 24 February, 16:45, Hall H IIISession: The Andean biodiversity hotspot and its future: Biodiversity,eco system functioning & ecosystem services under environmentalchangeThursday, 24 February, 17:00, Hall H IIITHURSDAY 16:45 Hall H IIISIMULATION OF NET PHOTOSYNTHESIS OF TWO COMPETINGSPECIES, THE SOUTHERN BRACKEN AND THE PASTURE GRASSSETARIA SPHACELATA, IN A TROPICAL MOUNTAIN ECOSYSTEM.Brenner Silva 1 , Jörg Bendix 11LCRS - Marburg University, Marburg, not U, DE, brenner.silva@students.unimarburg.deThe tropical mountain forest in the Andes of Ecuador is the second hottestbiodiversity hotspot of the world and suffers from a high deforestation rate,mainly to gain pastures. However, the planted pasture grass (Setaria spacelata)is frequently overgrown by an aggressive weed (southern bracken), probablydue to recurrent burning and competition for light. As a result, pastures areabandoned and natural succession is affected. To understand the growthefficiency of bracken and its competitive strength an experimental site wasestablished in the Rio San Francisco Valley. A numerical model (The SouthernBracken Competition Model SoBraCoMo) was developed to simulate the growthof both competing species which will be presented in the talk. Validation wasconducted by means of independent measurements of daily courses. Following,the model was initialized with meteorological data for 2008 in 10 minutes steps.It will be shown that the grass Setaria was more productive, assimilating up to40% more atmospheric CO2 than the southern bracken. It contrasts with fieldobservations and points out that other factors like cattle browsing might beresponsible for the competitive strength of bracken.NEOTROPICAL C3/C4 GRASS DISTRIBUTION - PRESENT PAST ANDFUTURELaurent Bremond 1 , Charly Favier 2 , Arnoud Boom 31CBAE - UMR5059, Montpellier, FR, laurent.bremond@univ-montp2.fr, 2 ISE-mUMR5554, Montpellier, Fr, 3 Dpt Geography - University Leicester, Leicester, GBThe main environmental factors controlling C3 and C4 grass distribution in theintertropical zone are not well known. Some C3/C4 distribution models basedon photosynthetic grass physiologies have been developed but not easilyvalidated with field measurements. Nonetheless, these models are quite usefulbecause they are able to estimate the response of grasslands to past and futureCO2 atmospheric concentration changes.The aim of our study is to establish a schematic of the present altitudinal C3/C4 grass distribution in tropical South America and to then compare it witha simple photosynthetic model and with a dynamic global vegetation model(DGVM) for present, past and future climate.Grass species richness distribution data were compiled from literature andinterpreted in term of species altitudinal distribution and of C3/C4 proportions.A regression was established between mean annual temperatures and C4grasses. This relationship was then compared to simulations of the LPJ-GUESSmodel for the present climate. Finally, the photosynthetic model and the DGVMwere compared with the IPCC climate projections for 2100, and the simulationsof the PMIP2 models at 6k and 18k yrs BP.THURSDAY 17:00 Hall H IIIgtöSociety for Tropical Ecology | Gesellschaft für Tropenökologie e.V. Status and future of tropical biodiversity | Frankfurt, 21 - 24 February 2011gtö