Effects of prescribed burning on soil and vegetation
Catalanotti, Ambra Elena (2011) Effects of prescribed burning on soil and vegetation. [Tesi di dottorato] (Inedito)
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Fire has always been a natural ecological factor, affecting evolution, dynamics and distribution of vegetation in the world. Wildfires are favoured by the alternance of a wet season in which fuel (biomass and necromass) accumulates, and a dry season, in which the dried fuel becomes easily flammable. Therefore, the Mediterranean Region, with these climatic conditions, has been strongly interested by wildfires so that vegetation is adapted to this perturbation being able to regenerate either vegetatively or sexually or both. However, recently, wildfires derive mainly by human activities. The first tracks testifying the ability of Homo erectus to control and use fire go back to about one million years ago. Then, fire recurrence has progressively increased during time and in the XX century 95 % of fire was due to human activity. In the Mediterranean Basin fire has been widely used by man permanently shaping the landscape. At present, the abandonment of agricultural land, a less intense forest management and the fire suppression regime have led to the accumulation of large amounts of fuel, so increasing wildfire hazard. Wildfires are becoming a major problem for many European countries, mainly Portugal, Spain, Italy, France and Greece. As a consequence of more frequent and intense fires, in Mediterranean ecosystems loss of biodiversity, soil erosion and desertification can occur, together with large economic losses and threatened human lives. To contrast wildfire occurrence an integrated fire management is needed, that consists in a social, economic, cultural and ecological planning aimed at minimizing damages and maximizing benefits due to fire. In particular, a successful burning programme for wildfire risk reduction must both decrease wildfire propagation and ease its suppression. This requires, in addition to the regulation of traditional fire use, also prevention and suppression actions, for example through technical fire: prescribed fire to reduce fire risk and suppression fire in the active fire fighting. Prescribed fire consists in a deliberate application of fire in a defined area and in specific operative conditions (prescriptions) in order to obtain defined goals established in the planning phase. Fire risk reduction is the main objective of prescribed fire, but other possible objectives can be pasture improvement, agricultural residue reduction or conservation of some natural habitats listed in Annex I of the Directive 92/43/EEC, weed control. This practice was born in the United States in the 1940s, but the first experimentations in Europe began only 40 years later, in Portugal and France. Then, prescribed fire spread in some Regions of Spain (Catalonia and Canary Islands), and some Central-northern countries (England, Germany, Sweden, Norway). In Italy this type of experimentation has started in the last few years. Since fire may have variable impacts on vegetation and soil physical, chemical and biological characteristics depending on fire intensity and frequency as well as on previous land-use practices, monitoring ecological effects of prescribed burning in different ecosystems is a crucial issue to assess the sustainability of this practice on a short, medium and long term perspective. Differently by wildfire, a correctly executed prescribed burning should not have severe and permanent effects on the biotic community. As well as it is important to consider the impact on different key components of an ecosystem, such as vegetation and soil. These components have not been, until now, widely investigated simultaneously after a prescribed fire. Aim of this study was to evaluate the impact of prescribed fire on soil microbial community, some physical and chemical soil properties and vegetation at different times after prescribed burning and in different types of vegetation. Italian and Portuguese study areas were chosen because these countries are, among European countries, characterized by the highest fire incidence. Prescribed-fire experiments were performed in five study sites differing for plant cover, mainly chosen on the basis of their high fire risk: two pine plantations of Cilento e Vallo di Diano National Park (PNCVD), one in a hilly area and one in a coastal area, characterized by different fire risk, a Quercus cerris forest of PNCVD, chosen because this vegetation type has been never treated with this technique until now in Europe, a Spartium junceum shrubland of PNCVD, where the treatment objective was both fire risk reduction and conservation of natural habitat, as it is both a SCI (Sites of Community Importance) and a SPA (Special Protection Area), respectively, after Directives 92/43/EEC and 79/409/CEE, and a Erica sp.pl. shrubland on a mountain area of Portugal, an area at a very high fire risk. Results highlight that prescribed burning in pine and oak woodlands had no effect on plant species composition and a temporary and not very pronounced effect on the fermentation layer, suggesting that prescribed burning can be considered a sustainable practice for fire risk reduction. On the other hand, the fire effects on shrublands were more marked. In fact, a reduction in plant cover and, in the Italian shrubland, also a change in species composition were observed. Moreover, both of them showed marked and lasting effects of fire treatment on the fermentation layer. Therefore, in shrubland a better definition of prescriptions appears necessary.
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