Browsing by Author "Possacos, Anabela"
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- Como é que os bosques de azinheira sobrevivem em áreas de fogos frequentes?Publication . Azevedo, João; Possacos, Anabela; Fernandes, P.; Dias, Rui; Saraiva, Ângelo; Loureiro, CarlosApesar da azinheira (Quercus rotundifolia) ser uma árvore muito comum em Portugal os bosques desta espécie são raros no nosso país. Muitos dos actuais azinhais ocorrem em áreas de elevada ou muito elevada frequência de fogos florestais. Foi recentemente observado que determinados fogos se extinguem ao contacto com azinhais.
- Exploring the potential of vegetation corridors in forest fire hazard reduction at the landscape level: examples from PortugalPublication . Azevedo, João; Possacos, Anabela; Dias, Rui; Marrão, Rosalina; Loureiro, Carlos; Fernandes, Paulo M.In north-eastern Portugal, holm oak (Quercus rotundifolia) woodlands have persisted in the landscape despite the occurrence of frequent fires. The hypothesis that these elements have a role in fire related processes has been proposed by foresters and scientists but only recently it has been addressed. In this research we analysed the current distribution of holm oak remnants in the region in terms of features such as slope, aspect, distance to streams, and position in the slope. We also compared their distribution in relation to the distribution of areas burned in the last decades. We found that holm oak woodlands are often adjacent to burned areas suggesting a barrier effect of these vegetation structures. Also, the woodlands are often located towards the bottom of very steep slopes. Additionally, we tested the hypothesis that these patches arrest wildfires based on a modeling and simulation approach using field data collected in edges of holm oak woodlands. Computer simulated fire behaviour provided evidence that variations in intensity and velocity across holm oak edges make it possible for these woodlands to affect significantly fire spread. Founded on these results we explored the potential for holm oak corridors to be used in fire hazard reduction planning.
- Herbaceous plant diversity across fire created edges in continental holm oak woodlandsPublication . Azevedo, João; Fernández-Núñez, Esther; Miguel, Luis; Amado, Anabela; Possacos, Anabela; Aguiar, CarlosWe analyzed herbaceous plants distribution across edges of holm oak (Quercus rotundifolia) woodlands created and maintained by fire in order to describe plant community structure across edges and to evaluate the role of fire in the patterning of plant diversity at the patch scale. We recorded abundance in twelve 60 m long sampling lines placed perpendicularly to the woodlands boundary at 1, 5, 10, and 20m outside and 0, 1, 5, 10, 20, and 40m inside the woodlands, using the line intercept method (2 x 10 m line parallel to the boundary). In the same locations, we measured tree and shrub cover, height and density and recorded time since last fire disturbance. Data was analysed graphically and statistically using multivariate ordination analysis techniques, namely CCA. Results indicated that, on average, herbaceous species richness was higher outside than inside the woodlands and peaked 1m outside the boundary. Time since last fire in adjacent shrublands affected richness patterns across edges. Richness was higher outside than inside in young adjacent shurblands, higher inside than outside in old shrublands and peaked 1m outside in intermediate age shrublands, interior, exterior and edge (1m outside the boundary) species and locations were well correlated with explanatory variables reflecting the interior exterior woodland gradient sampled and shrub recovery after fire.
- Influência de manchas de azinhal na dinâmica espacial de fogos florestaisPublication . Possacos, Anabela; Azevedo, JoãoO presente trabalho pretende testar a hipótese de que a resistência dos azinhais ao fogo depende da distribuição de combustíveis ao longo do gradiente exterior – interior dos azinhais (orlas). Com base na descrição quantitativa do complexo combustível, pretende ainda criar modelos de combustível para o azinhal e analisar o comportamento do fogo potencial, de acordo com os parâmetros do modelo de propagação do fogo de Rothermel (1972) que integra o Software BehavePlus (Andrews et al., 2004). Este trabalho iniciou-se em Abril 2007 e foi realizado na região Este do Parque Natural de Montesinho (Distrito e Concelho de Bragança), onde foi feita a identificação e descrição de todas as manchas de azinhal envolvendo os incêndios ocorridos nesta área com base em cartografia de azinhais e de fogos florestais. Ao longo das orlas de doze manchas seleccionadas quantificaram-se parâmetros estruturais dos vários estratos do complexo combustível (herbáceo, arbustivo e arbóreo), e ainda parâmetros ambientais e de relevo, necessários para a criação dos modelos de combustível para utilização com o modelo de propagação do fogo de Rothermel. Desenvolvidos os modelos e para podermos comparar inflamabilidades entre complexos de combustíveis, simulamos o comportamento do fogo em BehavePlus para os modelos de combustível de acordo com a sua distribuição ao longo do gradiente exterior – interior dos azinhais. Os modelos específicos desenvolvidos reflectem o conjunto de condições, no que diz respeito ao combustível, que é possível encontrar nos bosques de azinhal, ao longo do gradiente exterior – interior dos bosques e ainda no exterior do mesmo. Como resultados, observou-se que o fogo simulado tem uma tendência para decrescer em termos de velocidade de propagação, intensidade da frente das chamas, e comprimento da chama ao passar de áreas dominadas por matos para o azinhal. Esta alteração do comportamento do fogo nas orlas parece indicar a possibilidade de o fogo se extinguir naturalmente quando entra em contacto com os azinhais. Estas alterações do comportamento do fogo parecem estar associadas a alterações da estrutura destas orlas, não obstante outros factores poderão igualmente contribuir para este fenómeno.
- Survival of holm oak woodlands in fire prone landscapes in Northeastern PortugalPublication . Azevedo, João; Possacos, Anabela; Dias, Rui; Saraiva, Ângelo; Loureiro, Carlos; Fernandes, P.It has been observed that holm oak (Quercus rotundifo/ia) woodlands survive wildfires in Northeastern Portugal which sell-extinguish in contact with these woodlands. The mechanisms underlying this phenomenon are unknown. As part 01 an effort to understand the role of holm oak woodlands in landscape fire hazard, we have tested the hypothesis that holm oak woodlands are lire resistant and that this is due to fire behavior modification at the shrubland-woodland interface.
- The role of holm oak edges in the control of disturbance and conservation of plant diversity in fire-prone landscapesPublication . Azevedo, João; Possacos, Anabela; Aguiar, Carlos; Amado, Anabela; Miguel, Luis; Dias, Rui; Loureiro, Carlos; Fernandes, Paulo M.Holm oak (Quercus rotundifolia) woodlands have been able to persist in fire-prone landscapes in northern Portugal where they seem to play a relevant role in community and landscape level patterns and processes, namely in the control of disturbance events and in the maintenance of biodiversity. In this research we tested the following hypotheses: (i) holm oak woodlands affect fire behavior, mainly by disrupting and delaying fire spread; (ii) disruption and delaying of fire spread is due to fire extinction at the edge of woodlands; and (iii) plant diversity is favored by frequent low-intensity fires as a result of the control of fire spread by holm oak woodland edges. We sampled herbaceous, shrub and tree structure and herbaceous plant composition across edges of holm oak woodlands with known recent contact with fire. Using BehavePlus we converted structural data into fuel models and simulated fire behavior for the locations sampled along the exterior–interior gradient of the woodlands. Our results indicate that holm oak woodlands play a relevant role in the control of fire spread and in the maintenance of plant diversity. We found differences in simulated maximum rate of fire spread (ROS) and fireline intensity (FLI) between outside and inside woodlands as well as a 100% probability of fire extinction when fuel moisture was >12% and wind speed at 10 m aboveground was <40 km h 1, supporting the self-extinction hypothesis. We found also that richness and abundance of herbaceous plants varied between the interior and exterior of the woodland, with higher values outside the woodland, and that plant composition along the interior–exterior gradient had distinct patterns. These variables and the pattern of plant distribution were also significantly affected by time since last fire event. We conclude that holm oak woodlands affect fire behavior by interrupting fire spread at the edge zone and that fire-created edges affect herbaceous plant species richness, abundance and distribution by maintaining habitat diversity, which increased plant diversity at patch and landscape levels. Based on our results and other evidence, we developed a conceptual model of the dynamics of fire, landscape structure, and plant diversity in fire-prone landscapes where holm oak patches persist.