How far from naturalness. Effects of anthropogenic landforms on spontaneous woodland vegetation in an urban ecosystem (Capital City of Rome, Italy)

Urban landscapes in historical cities often result from long-standing stratification of human activities, which also affected natural morphology and, in turn, ecological settings and ecosystem dynamics. However, the specific impact of geomorphological alterations on woodland successional stages has remained poorly explored. This study aims at filling this gap, concomitantly providing useful knowledge for practical ecological restoration. Moving from the identification and mapping of anthropogenic landforms in Rome, the intensity of eventual disruption in spontaneous woodland dynamics was assessed across a disturbance gradient with respect to Potential Natural Vegetation (PNV) types, adopted as local reference systems. Vegetation was surveyed both inside (altered) and outside (low and high naturalness controls) anthropogenic landforms, and site-level shifts due to geomorphological alteration and/or alternative human disturbances were qualified and quantified. Woodlands on anthropogenic landforms resulted to be significantly divergent in species composition from PNV, being characterised by invasive, nitrophilous, and light-demanding species, and the Redundancy Analysis showed this type of disturbance alters woodland composition much more than other impacts from the urban context. Differences between woodland types were thus quantified, in terms of ecological distances from PNV, modelled and mapped across the city by a Generalised Additive Model (GAM). The identification and spatialisation of areas that shifted furthest from reference systems, with an unlikely reversible deviation from PNV, represent useful tools to inform ecological restoration in cities.