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Brotons L.,Ctfc Center Tecnologic Forestal Of Catalonia | Aquilue N.,Ctfc Center Tecnologic Forestal Of Catalonia | de Caceres M.,Ctfc Center Tecnologic Forestal Of Catalonia | Fortin M.-J.,University of Toronto | Fall A.,Simon Fraser University
PLoS ONE | Year: 2013

Available data show that future changes in global change drivers may lead to an increasing impact of fires on terrestrial ecosystems worldwide. Yet, fire regime changes in highly humanised fire-prone regions are difficult to predict because fire effects may be heavily mediated by human activities We investigated the role of fire suppression strategies in synergy with climate change on the resulting fire regimes in Catalonia (north-eastern Spain). We used a spatially-explicit fire-succession model at the landscape level to test whether the use of different firefighting opportunities related to observed reductions in fire spread rates and effective fire sizes, and hence changes in the fire regime. We calibrated this model with data from a period with weak firefighting and later assess the potential for suppression strategies to modify fire regimes expected under different levels of climate change. When comparing simulations with observed fire statistics from an eleven-year period with firefighting strategies in place, our results showed that, at least in two of the three sub-regions analysed, the observed fire regime could not be reproduced unless taking into account the effects of fire suppression. Fire regime descriptors were highly dependent on climate change scenarios, with a general trend, under baseline scenarios without fire suppression, to large-scale increases in area burnt. Fire suppression strategies had a strong capacity to compensate for climate change effects. However, strong active fire suppression was necessary to accomplish such compensation, while more opportunistic fire suppression strategies derived from recent fire history only had a variable, but generally weak, potential for compensation of enhanced fire impacts under climate change. The concept of fire regime in the Mediterranean is probably better interpreted as a highly dynamic process in which the main determinants of fire are rapidly modified by changes in landscape, climate and socioeconomic factors such as fire suppression strategies. © 2013 Brotons et al.

Capinha C.,University of Evora | Brotons L.,Ctfc Center Tecnologic Forestal Of Catalonia | Anastacio P.,University of Evora
Journal of Biogeography | Year: 2013

Aim: We assess the relative contribution of human, biological and climatic factors in explaining the colonization success of two highly invasive freshwater decapods: the signal crayfish (Pacifastacus leniusculus) and the red swamp crayfish (Procambarus clarkii). Location: Europe. Methods: We used boosted regression trees to evaluate the relative influence of, and relationship between, the invader's current pattern of distribution and a set of spatially explicit variables considered important to their colonization success. These variables are related to four well-known invasion hypotheses, namely the role of propagule pressure, climate matching, biotic resistance from known competitors, and human disturbance. Results: Model predictions attained a high accuracy for the two invaders (mean AUC ≥ 0.91). Propagule pressure and climatic suitability were identified as the primary drivers of colonization, but the former had a much higher relative influence on the red swamp crayfish. Climate matching was shown to have limited predictive value and climatic suitability models based on occurrences from other invaded areas had consistently higher relative explanatory power than models based on native range data. Biotic resistance and human disturbance were also shown to be weak predictors of the distribution of the two invaders. Main conclusions: These results contribute to our general understanding of the factors that enable certain species to become notable invaders. Being primarily driven by propagule pressure and climatic suitability, we expect that, given their continued dispersal, the future distribution of these problematic decapods in Europe will increasingly represent their fundamental climatic niche. © 2012 Blackwell Publishing Ltd.

De Caceres M.,Ctfc Center Tecnologic Forestal Of Catalonia | De Caceres M.,Autonomous University of Barcelona | Legendre P.,University of Montreal | Wiser S.K.,Landcare Research | And 2 more authors.
Methods in Ecology and Evolution | Year: 2012

1. Indicator species are often determined using an analysis of the relationship between the species occurrence or abundance values from a set of sites and the classification of the same sites into site groups (habitat types, community types, disturbance states, etc.). It may happen, however, that a particular site group has no indicator species even if its sites have a community composition that is clearly distinct from the sites of other site groups. This motivates an exploration of the indicator value of not only individual species but also species combinations. 2. Here, we present a novel statistical approach to determine indicators of site groups using species data. Unlike traditional indicator value analysis, we allow indicators to be species combinations in addition to single species. We require that all the species forming the combination must occur in the site to use the combination as an indicator. We present a simple algorithm that identifies the set of indicators (each one being either a single species or a species combination) that show high positive predictive value for the target site group. Moreover, we demonstrate the use of the percentage of sites of the site group where at least one of its valid indicators occurs to determine whether the group can be reliably predicted throughout its range. 3. Using a simulation study, we show that if two species are not strongly correlated and their frequency in the data set is larger than the frequency of sites belonging to the site group, the joint occurrence of the two species has higher positive predictive value for the site group than the two species taken independently. 4. We illustrate the proposed method by determining which combinations of vascular plants can be used as indicators for 29 shrubland and forest vegetation types of New Zealand. 5. The proposed methodology extends traditional indicator value analyses and will be useful to develop multispecies ecological or environmental indicators. Further, it will allow newly surveyed sites to be reliably assigned to previously defined vegetation types. © 2012 The Authors. Methods in Ecology and Evolution © 2012 British Ecological Society.

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