Assessing stability of topographic impacts on northern boreal forest carbon allocation across the Tundra-Taiga Ecotone amid climate crisis

• Applicant: Dr. Stefan Kruse
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems ; Forestry
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 563037533

A significant portion of carbon in the Tundra-Taiga Ecotone (TTE) is stored as above-ground biomass (AGB) in trees and shrubs through photosynthesis, where carbon dioxide is extracted from the atmosphere during the brief growing season in high latitudes. This results in low carbon sequestration in the TTE. Climate change may influence low productivity, reorganizing vegetation patterns. However, the role of abiotic factors in carbon sequestration capacity of boreal forests is poorly understood. An evaluation of vegetation organization must be conducted concerning static modulators. Topography, a significant determinant of water and nutrient availability, is a static abiotic factor that profoundly influences local growing conditions. As temperatures rise, precipitation is expected to become more intense and frequent, potentially leading to waterlogging or nutrient leaching at specific topographic positions, which may cause the decline of certain tree species. Thus, climate change could alter local responses to topographic position and change interactions with weather patterns. Topography could mitigate climate change impacts, benefiting adaptable species while others suffer from altered conditions. Understanding the relationship between topography and biomass accumulation is essential for assessing boreal forests' future role in global carbon balances. The BToBE project aims to address knowledge gaps regarding topography's mechanistic influence on biomass accumulation in the TTE and evaluate its impact through forward simulation with a process-based vegetation model. The central hypothesis is that vegetation responses to topographic conditions in the TTE have transformed due to significant global warming. Recently, drone-derived 3D point clouds processed to yield forest biomass were collected at AWI. This high-resolution reference data captures the extensive bioclimatic gradient of the TTE, with the northern treeline situated in permafrost lowlands and across mountainous terrain. The drone-derived AGB data will be used to develop an AGB model for upscaling with Landsat and Sentinel-2 multispectral satellite sensors. The objective is threefold: first, to elucidate relationships between AGB and topography using generalized additive modeling; second, to ascertain the stability of these dependencies by reconstructing long-term AGB data from past decades. This will enhance and allow implementing the individual-based and spatially explicit boreal forest vegetation model LAVESI, to estimate AGB trajectories in the TTE over coming decades.

• DFG Programme: Research Grants