Abstract booklet - gtö – Society for Tropical Ecology

152 PARALLEL SESSION HALL H III THURSDAY ANDEAN BIODIVERSITYPARALLE SESSION THURSDAY H III: ANDEAN BIODIVERSITY HOTSPOT153Session: The Andean biodiversity hotspot and its future: Biodiversity,eco system functioning & ecosystem services under environmentalchangeThursday, 24 February, 15:30, Hall H IIIINFLUENCE OF SHALLOW LANDSLIDES ON FOREST DYNAMICS IN ASOUTH ECUADORIAN TROPICAL MONTANE FORESTClaudia Dislich 1 , Andreas Huth 11UFZ Leipzig, Leipzig, DE, claudia.dislich@ufz.deThe Andean biodiversity hotspot and its future: Biodiversity, eco systemfunctioning & ecosystem services under environmental changeThursday, 24 February, 15:45, Hall H IIIIMPLICATIONS OF LAND-USE CHANGE AND PASTURE-FERTILIZATION ON SOIL MICROBIAL ACTIVITIES ANDCOMMUNITIES IN A MOUNTAIN RAINFOREST REGION OFSOUTHERN ECUADORKarin Potthast 1 , Ute Hamer 1 , Franz Makeschin 1THURSDAY 15:30 Hall H IIIShallow landslides are a major source of natural disturbance in tropical montaneforests. Due to shallow landslides vegetation and often the upper soil areremoved, leaving space for a quasi primary succession and resulting in stronglychanged conditions for forest regeneration. Landslides might therefore affectdifferent processes of forest dynamics: tree growth can be reduced due tonutrient limitation, tree recruitment can be reduced due to a thick vegetationof shrubs and ferns that establishes on young landslide sites and mortality canbe increased due to instability of soils and exposition to wind. We utilize anindividual based model of forest growth to investigate how changes in theseprocesses affect the temporal and spatial succession process and to estimatethe effect of landslides on the carbon balance of forest. The forest model wasparameterized for one forest type of the Reserva Biológica San Francisco inthe Andes of South Ecuador, where approximately 4% of the area is coveredwith visible traces of landslides. The terrain is characterized by deeply incisedvalleys and steep slopes. We developed different scenarios of forest successionafter landslides, where different processes (tree growth, recruitment, mortality)are changed compared to processes in undisturbed forest. For the differentscenarios we find distinct patterns of spatial variation of tree biomass within thefirst fifty years of succession. For all scenarios, overall tree biomass recovers afterapproximately 100 years but species composition takes longer time to recover(> 200 years). On the landscape level landslides reduce standing biomass andproduce a high spatial heterogeneity.1TU Dresden/Soil Science, Dresden, DE, kpotthast@web.deIn the South Ecuadorian Andes, vast areas of the mountain rainforest havebeen converted to cattle-pastures by slash and burn practice. Frequently, thesepastures were invaded by the fire-tolerant tropical bracken fern. When thebracken becomes dominant on the pasture sites the productivity decreasesand the sites are abandoned. To assess the implications of land-use changesand pasture-fertilization on ecosystem functioning, a study was conductedin the area of the German research station Estación Científica San Francisco(ECSF) in Ecuador. For comparison of different land-uses three adjacent siteswere selected at 2000 m asl: a mountain rainforest site, an active pasture sitedominated by the grass species Setaria sphacelata and an abandoned pasturesite overgrown by bracken (Pteridium arachnoideum). To investigate theeffect of the fertilization of pastures with urea and/or rock phosphate on soilmicrobial properties, a fertilization experiment was conducted in situ as well.For soil microbial analysis, the amounts of microbial biomass (CFE-method), themicrobial activity (basal respiration; net and gross N mineralization rates) andthe microbial community structure (PLFA-analysis) were determined.17 years after pasture establishment, a threefold higher content of microbialbiomass C and N as well as significantly lower C:N ratios were determinedcompared to the other land-uses. Furthermore, highest C and gross Nmineralization rates (Fig.1) were observed in the pasture soil. An activelymicrobial inorganic N immobilization indicated an easy availability of organicsubstrates partly due to the prolific fine-root system of the pasture grass. Thesedifferences within the land-use gradient were also associated with shifts in themicrobial community structure (MCS). After bracken-invasion the MCS shiftedagain towards the forest whereby a higher relative abundance of actinomyceteswas associated with a higher acidity and exchangeable Al-concentration.THURSDAY 15:45 Hall H IIIgtöSociety for Tropical Ecology | Gesellschaft für Tropenökologie e.V. Status and future of tropical biodiversity | Frankfurt, 21 - 24 February 2011gtö