Effects of a fire on the vegetation of a mountainside of the Orobic pre-Alps (Bergamo, Italy)

Fire is one of the main factors that shape the landscape as well as a fundamental component of some ecosystems. In Italy, several studies have been conducted in order to understand the effects of fires on vegetation but most refer to the Mediterranean environment. Few data exist concerning the plant communities presenting after fires in the Alpine and pre-Alpine area. This study aims to identify the main effects of a fire on the vegetation of a mountainside of the Orobic Alps located in the municipality of San Pellegrino Terme (Brembana Valley, Bergamo, Italy) in which there was a mixed wood of Quercus pubescens, Ostrya carpinifolia and Fraxinus ornus, typical of the sub-montane and hilly areas of the pre-Alps of Lombardy (1, 2). The fire, caused accidentally by human intervention, spread from 2nd to 4th April 2012, and involved approximately 6 ha of forest (Fig. 1). Climate data for the area studied revealed a particularly dry period during the first three months of 2012, which could have helped to facilitate the start and the spread of the fire. Data on the flora and vegetation were collected by performing two phytosociological relevés, one in an area of the mountainside not affected by fire (wood), the other within the burnt area (Fig. 2) adjacent to the first. Relevés were conducted from April to July 2013 (one year after the fire) according to the criteria of the sigmatist school of Zurich-Montpellier (3). Life-form and chorological spectra were elaborated for each community. The ecological indices of Landolt (4) were used to analyze the response of vegetation to the disturbance; the Index of Maturity (IM) was calculated (5) and an analysis was performed according to Grime’s CSR model (6). Results showed that the post-fire plant community is de-structured and depleted in nemoral and shrub species of Carpino-Fagetea which are replaced by others, mostly belonging to Elyno-Seslerietea caeruleae and Festuca-Brometea, which were not present before the fire. Some of this species are rare or endemic including Carex baldensis which showed moderate coverage. Ecological analysis showed that the post-fire vegetation has many more heliophilous species that grown on dry soils poor in nutrients compared to the wood. The post-fire vegetation also has a lower IM value and a greater number of ruderal and stress-tolerant species which indicate the start of a regressive series.