Forest biomass distribution and its loss between 1985 and 2010 in the Western Carpathians

Kurzfassung

The ability to monitor and quantify forest change is a prerequisite for better understanding human-induced environmental changes and their impact on forest ecosystems. Moreover, the questions relating to the spatial (where) and temporal (when) dimensions, and its magnitude (how much) remain fundamental to forest services concerns. Here, we assessed changes in forest aboveground biomass associated with forest disturbances and recovery between 1985 and 2010 in the Western Carpathians. First, yearly maps of aboveground biomass based on Landsat time series and field data were created. Second, we applied a trajectory-based change detection to reconstruct forest disturbances and recovery. Then, we distinguished and investigated abrupt and gradual disturbances in respect to topographic factors and dominant stand age. Finally, we quantified biomass losses and gains associated with abrupt and gradual disturbances, and forest recovery. Overall, 55% (~30,700 ha) of the total coniferous forest experienced a loss of biomass over the observation period, while ~30% showed severe or complete removal of forest biomass. At the same time, 11.2% of the area was reforested or regenerated on previously damaged forest stands. The total coniferous biomass dropped by 15% between 1985 and 2010, indicating negative balance between the losses and the gains. Comparing abrupt and gradual disturbances, results indicated more chronic and long-term than acute biomass losses at every altitude and slope. The distribution of the relative magnitude of biomass loss (low, moderate, and severe loss) by elevation and slope zones revealed significantly higher fraction of severe losses caused by abrupt than gradual disturbances. Both disturbances occurred predominantly on S, SW, and SE facing slopes, where severe biomass losses were dominating. Severe biomass loss affected by gradual disturbances lasted up to ten years, and its proportion increased with altitude. Finally, abrupt disturbances were predominant within older coniferous stands (between 90 and 120 years). The synergistic effect of unsustainable forest management in the past, catalyzed by high levels of pollution loads during communist times caused a significant damage to the coniferous forests in the Western Carpathians. Since the early 1990s spruce-dominated stands have shown low resistance against biotic and abiotic factors. They have thus been susceptible to fungal diseases and insects outbreaks on the one hand, and adverse climate condition with subsequent extreme weather events on the other. Since 2005, widespread and severe biomass loss has taken place. Monitoring and quantifying forest changes are of prime scientific and economic interest. Our study provided an example of spatially and temporally explicit quantification of forest biomass. Such knowledge is prerequisite for sustainable forest management and the provision of ecosystem services.