Improving resilience of an old-growth urban forest in Southern Italy: Lesson(s) from a stand-replacing windstorm

There is a current concern that the capacity of urban forests to recover from the effects of climate change may be diminishing. New management options are needed so that they can continue to provide ecosystem services to local communities. After a windstorm occurred on June 2014 pre- and post-disturbance stand conditions (years 2010 and 2015, respectively) of the historical old-growth holm oak forest of Parco Gussone were analysed by combining ground- and satellite-based methodologies. Results highlighted that Parco Gussone was primarily valued for its historical importance and, despite the phytosanitary conditions of the trees, no silvicultural treatments were made since 1986, most probably due to conflicts arisen between different stakeholders. Therefore in 2014, the windstorm damaged 406 trees (8.1% of the total aboveground forest dry biomass) and it was stand-replacing on 1.53 ha (9.3 % of the total forest area). Windthrows, heterogeneously distributed and unequally sized (103 canopy gap ranging between ∼6 to 1632 m2), caused, overall, a significant reduction of LAI (∼19%). The presence of large gaps promoted the invasion of non-native herbaceous species whereas native species of the shrubs and herbaceous layers were favoured when felled trees were left on the ground or removed mechanically during harvest, respectively. In this context, urban forests should be considered as ‘complex adaptive systems’, therefore natural processes can be simulated by applying a ‘close-to-nature’ silviculture (e.g. by opening small gaps), vulnerability assessed (e.g. using a tree-by-tree VTA), biodiversity and ecological resilience improved and short- and long term disturbance effects evaluated (e.g. analysis of disturbance attributes and stand dynamics) so that specific conservation goals can be adapted to a specific landscape and biotic community. By implementing and applying the proposed guidelines in urban forest planning, we are confident that the resilience of those Mediterranean urban forest ecosystems could be effectively restored and improved