Trees Trigger Trouble - Landsliding by Biomass Surcharge and Wind Disturbance in Patagonian Rainforests (RETROGRESS)

• Applicant: Dr. Christian Mohr
• Subject Area: Physical Geography ; Ecology and Biodiversity of Plants and Ecosystems
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 493703771

Coastal temperate rainforests are global players in Earth’s carbon cycle. They experience disturbances at different magnitudes and frequencies. In Patagonian rainforests, disturbances comprise volcanic eruptions, rain-, and windstorms; These disturbances result into shallow landslides, thus unleashing massive pulses of C. Coastal Rainforests are subject to shifts in the climate and disturbance regimes. Such changes are proceeding in similar directions but at different rates. Consequently, quantifying disturbance responses in Patagonian forests, for example, can from useful ‘blueprints’ informing research on rainforests of North America.Multiple disturbances can drive C-storage (net sink) or C-depletion (net source) depending on the relative reduction in C during the disturbance, the mean frequency of events, and the recovery time. Areas with high and low disturbance frequencies are maintain in a relatively lower C status due to limited inter-event periods for biomass regrowth or lowered productivity, respectively. Here, we test the hypothesis that areas of moderate disturbance exposure form spots of relative maximum C formation.Biotic processes are recognized as important controls of geomorphic processes. Yet cause and effect are not always unidirectional. For example, the weight of forest biomass may culminate in sliding triggered by wind forces transferred to the soil via trees. At the same time, landslide scars provide new spots for vegetation succession. Hence, landslides control biomass stocks on thus denuded hillslopes, too. Here we go the next step: We develop a modular process-based landslide model by implementing biomass burden and wind forcing. Using our model, we test for thresholds of biomass surcharge and wind forces on landslide triggering via simulating vegetation-dynamics–landslide-feedbacks over several disturbance recurrence intervals.RETROGRESS uses physics-based modelling coupled with field work, environmental seismology and remote sensing. It aims to (1) quantify C stored in biomass and soils along landslide and wind disturbance exposure gradients using LiDAR, forest inventory plots, and statistics, and (2) to simulate the sensitivity of biomass load as a landslide cause, and (3) wind forcing as a landslide trigger. The model of choice is Landlab.RETROGRESS brings together international experts from ecology, modelling, geomorphology, geology and involves local environment conservation authorities. The expected deliverables are (1) unprecedented insights into C-stocks and its spatial relation to disturbances in Patagonian rainforests, (2) a quantitative test for a fundamental disturbance ecology theory, (3) new insights into forest-intrinsic causes for landsliding, and (4) a potentially important landslide trigger in one of the windiest and most biodiverse spots on Earth. It has the potential to push each field individually as well as the synthesis between them, building new knowledge of the Coastal rainforest biome.

• DFG Programme: Research Grants