Timber harvesting and wildfires drive long-term modification in forest structure of Nothofagus pumilio: Resilience characterization based on disturbance legacies

Background Forests are intrinsically resilient to natural disturbances but can be vulnerable to anthropogenic impacts (e.g. fires and harvesting), especially in high latitude temperate ecosystems. Changes in the natural dynamic pathways can lead to changes in the ecosystem structure and function, where legacies left after disturbances can play a major role in recovery. The objective was to characterize the resilience of different natural forest types in Tierra del Fuego, Argentina ( Nothofagus pumilio, N. antarctica , and mixed) based on disturbance legacies and long-term natural recovery of the forest structure after human impacts. Results Forest structure values significantly decreased in impacted stands compared to non-impacted areas (F between 13.50 to 25.23). Some woody legacies increased after impacts (e.g. snags, F = 2.12–3.20) while others tend to decrease (e.g. coarse-woody-debris, F = 3.49–3.90) in the long-term. Regeneration values generally decreased, depending on the impact type (e.g. wildfire decrease regeneration occurrence, F = 1.63). The impact severity changed according to impact type (wildfire > harvesting), where negative synergies were found in multivariate analyses for each forest type. Some variables presented greater changes across the impact gradients, where some thresholds can be used to determine points of no return in the forest recovery, e.g. Nothofagus pumilio was less resilient to the combination of impacts (wildfire and harvesting) than N. antarctica forests. Conclusions Natural landscapes have gradients related to forest structure from closed Nothofagus pumilio to open N. antarctica forests and grasslands. The human derived impacts (e.g. harvesting and wildfires) significantly modified the forest structure, but legacies remain after impacts according to the type and magnitude of these impacts. Wildfire and harvesting generate negative synergies, being more severe in N. pumilio forests than in stands with N. antarctica (mixed or pure forests). Indexes based on forest structure, legacies and regeneration values allow us to identify potential ecological thresholds related to these human impacts and the generation of hybrid or novel ecosystems linked to ecological and economic degradation. These findings can be allowed to design more efficient long-term monitoring to implement better adaptive management.