Towards an Austrian Glacier Foreland Inventory: Multi-decadal Greening Trajectories Linked to Terrain-based Disturbance Potential

Glacier forelands are hotspots of accelerated environmental change in high mountain environments. As landscapes transition from glacial to non-glacial conditions, they undergo pronounced geomorphic and ecological disequilibrium driven by paraglacial adjustment and primary succession. These coupled dynamics control sediment redistribution, disturbance regimes, and emerging ecosystem functions. Yet, despite extensive local-scale research, there is still a lack of integrated, comparative datasets that quantify foreland development trajectories across sites and environmental gradients.

We build on the Austrian Glacier Inventory outline series (GI LIA ~1850; GI1 1969; GI2 1998; GI3 2006; GI4 2015; GI5 2023, forthcoming) to reconstruct retreat-derived surface-age domains across 582 Austrian glacier forelands exposed since the Little Ice Age maximum. Surface-age domains are derived from successive inventory differences, providing discrete deglaciation-stage units for chronosequence-based comparisons across contrasting geomorphic and climatic settings.

For the remote sensing component, we use Google Earth Engine–derived Landsat NDVI time series (1985-2025) to quantify vegetation development across glacier forelands, with Sentinel-2 integrated for recent high-resolution trajectories. Annual NDVI layers are generated as cloud-masked August 90th-percentile composites to represent near-peak seasonal vegetation conditions while minimising snow and cloud contamination. We extract annual mean NDVI and fractional vegetation cover (NDVI > 0.2) for each surface-age domain.

To link vegetation stabilisation with geomorphic forcing, we derive DEM-based predictors (e.g., slope, curvature, roughness, topographic wetness, and flow concentration) to delineate surface-process domains and terrain-based disturbance potential. This enables evaluation of how terrain setting and hydrologic controls modulate vegetation establishment, persistence, and disturbance-driven setbacks.

First results show pronounced heterogeneity in greening and stabilisation signals among Austrian glacier forelands. A pixel-based comparison of multi-year NDVI medians (2020-2024 minus 1985-1989) yields ΔNDVI values from −0.37 to +0.84. Classifying ΔNDVI into four greening/stability classes indicates that no–minor change dominates at the foreland scale (median ~70%), while moderate greening is widespread (median ~21%) and negative/unstable trends typically remain limited (median ~5%) but locally concentrate into persistent disturbance corridors, particularly in high-disturbance process domains.

Field validation in summer 2026 will combine stratified vegetation and geomorphic plot surveys with UAV-based orthomosaics and surface models across 15 representative forelands. This effort will be complemented by existing high-resolution datasets from Austria’s two largest forelands (Pasterze and Gepatschferner), supporting calibration of vegetation fractions and attribution of stabilisation trajectories to process-domain characteristics and surface mobility indicators. Together, these components form an integrated national baseline for cross-site analysis and long-term monitoring of glacier-driven surface-process and ecosystem trajectories. This contribution provides the basis for a public Austrian glacier-foreland vegetation change inventory and invites collaboration on validation, process interpretation, and cross-regional comparisons.