Las tijeretas (Dermaptera, Forficulidae) en el control del pulgón en cítricos.

Cañellas N, Piñol J, Espadaler X (2005) Las tijeretas (Dermaptera, Forficulidae) en el control del pulgón en cítricos. Boletín de Sanidad Vegetal – Plagas 31: 161-169.

Modelling the effect of fire-exclusion and prescribed fire on wildfire size in Mediterranean ecosystems

Piñol J., Beven K., Viegas D.X. (2005) Modelling the effect of fire-exclusion and prescribed fire on wildfire size in Mediterranean ecosystems. Ecological Modelling. 183: 397-409.
Enllaç
Doi: 10.1016/j.ecolmodel.2004.09.001

Resum:

There is a debate on which factor, fuel accumulation or meteorological variability, is the fundamental control of the occurrence of large fires in Mediterranean-type ecosystems. Its resolution has important management implications, because if the fuel hypothesis proves to be right, then fire-exclusion would enhance the occurrence of large wildfires, and prescribed-fires would be a useful tool to fight them. On the other hand, if large fires were just a direct consequence of some extreme weather situations, neither fire-exclusion nor prescribed fire would have any influence on the size of wildfires. Here we present a simple model of vegetation dynamics and fire spread over homogeneous areas intended to treat quantitatively this issue. In particular, we wanted to address the following questions: (1) What is the effect that different fire fighting capacities have on the total area burnt and, especially, on large fires? (2) What is the effect that different levels of prescribed fire have on the area burnt in wildfires and, especially, in large fires? The model incorporates meteorological variability, different rates of fuel accumulation, number of ignitions per year, fire-fighting capacity, and prescribed burning. The model was calibrated with fire regime data (mean fire size, annual area burnt, and fire size distribution) of Tarragona (NE Spain) and Coimbra (Central Portugal), and it accurately reproduced both data sets, while allowing for multiple behavioural models and prediction uncertainties within the GLUE methodology. Results showed that for a given region, with its particular characteristics of climate, number of ignitions, and vegetation flammability, there was a fairly constant annual area burnt for different fire-fighting capacities. However, higher fire-fighting capacities resulted in a slightly higher proportion of large fires. There was also a quite constant annual area burnt (prescribed and wild fires together) for different prescribed fire intensities in each region. However, the total amount and proportion of large fires decreased as the prescribed burning intensity increased. So, according to the model, it seems that the total area burnt will be more or less the same despite any effort to reduce it by extinguishing fires or by using prescribed burning. Nevertheless, the effect of the fire exclusion policy slightly enhances the dominance of large fires, whereas the use of prescribed fires greatly reduces the importance of large fires. © 2004 Elsevier B.V. All rights reserved.

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Does fire occurrence modify the probability of being burned again? A null hypothesis test from Mediterranean ecosystems in NE Spain

Salvador R., Lloret F., Pons X., Piñol J. (2005) Does fire occurrence modify the probability of being burned again? A null hypothesis test from Mediterranean ecosystems in NE Spain. Ecological Modelling. 188: 461-469.
Enllaç
Doi: 10.1016/j.ecolmodel.2004.12.017

Resum:

Two main causes have been proposed as drivers of fire regime in Mediterranean-type ecosystems: fuel build-up and weather conditions. If fuel build-up is the main cause, then areas recently burned will not burn again until some years later. Contrarily, if weather is the main cause, then all areas will burn irrespective of their age. We have devised a statistical test aimed to distinguish between these two hypotheses. To use the test is necessary to know the spatial distribution of fires during a period of time as long as possible. Then, a percolation algorithm procedure is applied to mimic the location, extent, and perimeter/area ratio of the real fires, independently of previous fire occurrence. This model is run many times and each run is considered a realization under the null hypothesis that a pixel burns irrespectively of whether it was burnt in the previous years. The actual number of pixels burned twice is then compared to the histogram of the probability density function of pixels burned twice, which is obtained from the simulations. Actual values falling in the right tail of the distribution point to a clumped pattern (fires tend to be more abundant in some locations), while falling in the left tail will indicate a segregated pattern (burning reduces the probability of further fires in the same site). The method was applied to three different areas of Catalonia (NE Spain) by comparing the actual fires from 1975 to 1998 to the pattern obtained from random fire simulations. An aggregated pattern was obtained in two of the studied areas when the origin of the simulated fires was located randomly, indicating that fires were not uniformly distributed in the territory. When the simulations were started at the centroids of the real fires, the null hypothesis of independence from previous fires was not rejected, and the fuel-driven assumption was not supported. In the third area, results were inconclusive because two large fires, occurred in 1994, totally changed the results obtained until then. © 2005 Elsevier B.V. All rights reserved.

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