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Accueil du site → Doctorat → Espagne → 1999 → Patrones observados y factores que determinan la variabilidad espacio-temporal de la regeneración del pino carrasco (Pinus halepensis Mill.) después de un incendio

Universitat Autònoma de Barcelona (1999)

Patrones observados y factores que determinan la variabilidad espacio-temporal de la regeneración del pino carrasco (Pinus halepensis Mill.) después de un incendio

Broncano Atencia, M. José

Titre : Patrones observados y factores que determinan la variabilidad espacio-temporal de la regeneración del pino carrasco (Pinus halepensis Mill.) después de un incendio

Auteur : Broncano Atencia, M. José

Université de soutenance : Universitat Autònoma de Barcelona (Espagne)

Grade : Doctora en Biologia 1999

Résumé
Forest fires are the most frequent type of natural disturbance in Mediterranean-type ecosystems (Naveh 1975 ; Gill et al. 1981 ; Trabaud 1991). As a consequence of different climatic and social factors, the effect of large wildfires (i.e., fires larger than ca. 1000 ha) has increased in the last years (Greenpeace, 1995 ; Piñol et al., 1998). Thus, 99.7% of the 5279 wildfires that burned in Catalonia (NE Iberian Peninsula) between 1987 and 1994, were smaller than 1000 ha, but only affected 30% of the total surface. The remainder 16 wildfires (0.3% of the total) were large wildfires which burned 70% of the total surface (Terradas et al., 1996). wildfires are fires of high intensity (Huston, 1994), because they are associated with a continuous and extensive forest cover (Huston, 1994 ; Turner et al., 1994 ; Piñol et al., 1998), and environmental conditions characterized by large drought periods and strong winds (Terradas and Piñol, 1996 ; Turner et al., 1997). These large wildfires may have a double effect on the landscape. On the one hand, large fires are so extensive and so severe in some areas that they destroy forest vegetation independently of its density, age and composition (Christensen et al., 1989 ; Bessie and Johnson, 1995). The result is that the burned lanscape appears more homogeneous than it has been before the fire, because the heterogeneous vegetation patterns generated by the different succesion pathways are syncronized in large areas (Connell and Slatyer, 1980 ; Huston, 1994). On the other hand, large fires often result in a heterogeneous mosaic of burn severities as well of islands of unburned vegetation across the landscape (Turner et al., 1994, 1997). In their study on the effects of large fires on landscape heterogeneity in Yellowstone National Park, Turner et al. (1994) show that this pattern depends on fire size. The main factors responsible of this pattern are wind velocity and direction (Eberhart and Woodward, 1987 ; Fryer and Johnson, 1988). At a smaller spatial scale, several controlling environmental variables, such as air moisture, fuel type and topography, determine the mosaic of fire severities within the burned area (Christensen et al., 1989 ; Turner et al., 1994 ; Glitzenstein et al., 1995). At an even smaller scale, that of individual, fire intensity affects the number and characteristics of plants that are partially or totally burnt, and frequently originates a high degree of spatial heterogeneity in plant survival (Christensen et al., 1989 ; Schullery, 1989). This mortality risk decreases with plant size (Huston, 1994 ; Johnson, 1992), and depends on fire-resistance mechanisms, inflamability and regenerative strategies of species (McKenzie et al., 1996). Postfire spatial heterogeneity, which is determined by the distribution of burned and unburned areas and by the patterns of fire severity and plant survival, is basic to understand postfire regeneration in the burned areas (Turner, 1998). In this paper, we examine the characteristics and consequences on vegetation of a large wildfire that occurred in Catalonia (NE Spain) in 1994. The main objectives of this study are (1) to relate the spacial heterogeneity generated by fire behaviour with topography and prefire vegetation composition, and (2) to analyze the main survival patterns shown by the dominant tree species of the area, Aleppo pine (Pinus halepensis Mill.) and holm oak (Quercus ilex L.).

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