Date Published: May 2, 2013
Publisher: Public Library of Science
Author(s): Lluís Brotons, Núria Aquilué, Miquel de Cáceres, Marie-Josée Fortin, Andrew Fall, Gil Bohrer. http://doi.org/10.1371/journal.pone.0062392
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.
Fire is a key disturbance in many terrestrial ecosystems . Current available data show that future trends in fire drivers, such as climate warming or land use changes, may lead to an increasing impact of fires on ecosystems worldwide with unknown effects on biodiversity patterns and ecosystem services , . Changes in fire regimes associated with new land use for human activities may lead to large scale shifts in vegetation types , . Understanding the role and the relative weight of different factors leading to changes in fire regimes is thus of critical importance to anticipate the fate of biodiversity or to implement management strategies aiming at mitigating or modulating the impact of fires arising from such changes.
The study area was Catalonia a region located in the north-eastern corner of Spain). Catalonia is extensively covered with shrubland and forests (about 60%) but human presence since pre-historical times has led to large-scale changes in species composition and distribution of dominant species in historical and recent times. The majority of the study area has a Mediterranean climate, with winter precipitation and summer drought . According to the Catalan land-cover map, shrublands cover 36.7% of the total wild-land area of 1,950,326 ha, with a diverse specific and mainly evergreen composition . Forest composition as described by the First Ecological Forest Inventory of Catalonia  shows that conifers occur in 60.3% of the total forested area (20% Pinus halepensis, 18.4% Pinus sylvestris, 11.7% Pinus nigra), while sclerophilous and deciduous species cover the remaining 39.7% (15.4 Quercus ilex, 7% Quercus faginea, 5.3% Quercus suber).
The MEDFIRE model is a novel spatially explicit stochastic model that simulates landscape composition changes derived from vegetation dynamics and wildfire disturbances in a Mediterranean context. The model simulates the primary processes of a landscape fire-succession model (Figure 2) : vegetation maturation and succession, fire ignition, fire spread and post-fire effects (vegetation transitions after fire). In addition, the model allows mimicking fire suppression actions that directly affect the simulated fire regime. The MEDFIRE model shares many characteristics with other landscape simulation tools accounting for spatial interactions, such as the LANDIS model , because multiple processes are simulated iteratively in a spatial raster framework for fixed time discrete steps. Similar to other landscape models (e.g., the Mauricie Model  and the Vermillion Landscape Model ), the MEDFIRE model was implemented using the spatio-temporal modeling tool SELES . We follow the updated Overview, Design concepts, and Details (ODD) protocol of  to describe the MEDFIRE model in further detail.
Large-scale changes in fire regimes are expected in a world in which climate change and human activities are on the rise. Recent reviews ,  on the determinants of fire size distributions suggested that insights into the factors behind fire regimes would come from studies that combine empirical observations of past fires with the results of simulation models that use process-based mechanistic knowledge of fire occurrence and behaviour. Our model and methodology fitted this combined approach and allowed us to disentangle the relative effects of different determinants of fire regime in a Mediterranean region. In particular, we introduced the “opportunity” concept allowing us to constrain potential fire sizes by the use of opportunities related to either historical fire scars or to general firefighting efficiency. This allowed us to test and evaluate the impact of particular processes on shaping fire regimes. Our results support the view that active fire suppression is a key factor in determining short-term fire impacts. Furthermore, they also indicate that recent fire history has the potential to play a role in firefighting by offering suppression opportunities. Hence, we suggest that, if one aims at capturing critical drivers of fire regimes at the landscape scale, fire suppression should be explicitly integrated with climate change in the definition of future scenarios.