Increased drought length and intensity is expected in the Mediterranean basin under anthropogenic increase in atmospheric CO₂, leading to extreme events not yet encountered in the present climate ...variability. Understanding ecosystems responses and capturing peculiar ecophysiological processes related to these events have been investigated in the field by rainfall manipulation experiments. Quantifying the actual drought faced by the ecosystem under control and dry plots, or among experiments remain a key challenge for explaining functional impacts on plant growth. Full-profile soil water content can be tricky to assess in rocky soils, and time-consuming plant water potential measurements remain a discrete information unable to capture short rainfall pulses. We propose here to fully investigate the water budget of a total rainfall interception manipulation on a Mediterranean shrubland, coupled with a plant–soil water balance model. We could accurately simulate the seasonal course of plant water status, including small rainfall pulses. We then derived yearly estimates of water stress integral for each water treatment, leading to an estimate of 66–86 % increase of drought intensity for the dry treatment compared to the control. Comparing actual and expected plant water budget from simulations in the dry plots allowed to identify and quantify the impact of methodological issues related to rainfall interception experiments as side effects for intrusive rain drops and subsurface lateral water flow.
Two hundred years of landscape changes were studied on a 3,760 ha area of central Corsica (France) representing a typical Mediterranean environment. Different historical sources, including an ...accurate land-cover map from 1774 and statistics on land cover from 1848 and 1913, were used. Three additional maps (1960, 1975 and 1990) were drawn, and a complete fire history from 1957 to 1997 was created. Forests expanded slowly by a border effect. Forest expansion was more rapid in unburnt sites (0.59% per year) than in burnt sites (0.23% per year), mostly because the initial amount of forests was greater. Because of the border effect, the combination of past landscape pattern and short distance colonization abilities of forest species may have allowed the shrublands to persist in some places after land abandonment. This persistence may explain the pattern of fire in the landscape, since shrubland burn more readily than forests.PUBLICATION ABSTRACT
Based on recent needs to accurately understand fire regimes and post-fire vegetation resilience at a supra-level for carbon cycle studies, this article focusses on the coupled history of fire and ...vegetation pattern for 40 years on a fire-prone area in central Corsica (France). This area has been submitted since the beginning of the 20^sup th^ century to land abandonment and the remaining land management has been largely controlled by frequent fires. Our objectives were to rebuild vegetation and fire maps in order to determine the factors which have driven the spatial and temporal distribution of fires on the area, what were the feed backs on the vegetation dynamics, and the long-term consequences of this inter-relationship. The results show a stable but high frequency of small fires, coupled with forest expansion over the study period. The results particularly illustrate the spatial distribution of fires according to topography and vegetation, leading to a strong contrast between areas never burnt and areas which have been burnt up to 7 times. Fires, when occuring, affect on average 9 to 12% of the S, SE and SW facing slopes (compared to only 2 to 5% for the N facing slopes), spread recurrently over ridge tops, affect all the vegetation types but reburn preferentially shrublands and grasslands. As these fire-proning parameters have also been shown to decrease the regeneration capacity of forests, this study highlights the needs in spatial studies (both in terms of fire spread and vegetation dynamic) to accurately apprehend vegetation dynamic and functionning in fire-prone areas.PUBLICATION ABSTRACT
Biomass burning impacts vegetation dynamics, biogeochemical cycling, atmospheric chemistry, and climate, with sometimes deleterious socio-economic impacts. Under future climate projections it is ...often expected that the risk of wildfires will increase. Our ability to predict the magnitude and geographic pattern of future fire impacts rests on our ability to model fire regimes, either using well-founded empirical relationships or process-based models with good predictive skill. A large variety of models exist today and it is still unclear which type of model or degree of complexity is required to model fire adequately at regional to global scales. This is the central question underpinning the creation of the Fire Model Intercomparison Project -- FireMIP, an international project to compare and evaluate existing global fire models against benchmark data sets for present-day and historical conditions. In this paper we summarise the current state-of-the-art in fire regime modelling and model evaluation, and outline what lessons may be learned from FireMIP.
Understanding the interrelationship that exists between landscape patterns and fire history requires a great range of case studies to reduce the effects of substrate and climate. The lack of such ...data has led to an increasing need for spatially explicit models dealing with vegetation dynamics. The challenge is to find a compromise between process complexity, realism and landscape applications. In this paper, we describe a simulation approach (SIERRA) focussed on the particular case of Mediterranean-type communities subjected to large recurrent fires. Firstly, disturbance response strategies used in “vital attributes models” are used to simulate the influence of fire on vegetation dynamics, focussing in particular on the integration of specific regeneration abilities of Mediterranean species. Next, the model takes a functional approach towards carbon and water budgets to drive competition and simulate the seasonal vegetation water status to estimate fire risk. Spatial processes of seed dispersal, surface water fluxes depending on topographic convergence, and fire spread are used to accurately simulate landscape heterogeneity. The model offers a spatial representation of the annual course of vertical structure of biomass and carbon fluxes coupled with the weekly soil water budget and evapotranspiration rates. Some simulation and validation exercises are presented to illustrate both the functional properties on a
Quercus ilex stand, and the fire-prone community dynamics of a maquis shrubland. These initial results will form a strong basis for using the model to test hypotheses about fire-prone landscape patterns.
The heterogeneity associated with the spatial distribution of organisms is an awkward problem in ecology because this heterogeneity directly depends on the sampling scale. To specify the scope of the ...influence of sampling scale on the level of species aggregation, we need data sets that entail excessive sampling costs in situ. To find a solution for this problem, we can use models to simulate patterns of organisms. These models are often very complex models that take into account heterogeneity of habitats and displacement or longevity of studied species. In this article, we introduce a new stochastic model to simulate patterns for one taxon and we want this model to be parsimonious, i.e., with few parameters and able to simulate observed patterns. This model is based on an aggregation–repulsion rule. This aggregation–repulsion rule is defined by two parameters. On a large scale, the number of aggregates present on the pattern is the first parameter. On a smaller scale, the level of aggregation–repulsion among individuals is determined by a probability distribution. These two parameters are estimated from field data set in a robust way so that the simulated patterns reflect the observed heterogeneity. We apply this model to entomological data: four Diptera families, namely the Sciaridae, Phoridae, Cecidomyiidae, and Empididae. The field data for the Phoridae family are used to simulate sampling using different trap sizes. We record changes in the coefficient of variation (C) as a function of the sampling scale, and we can suggest to ecologists emergence traps of 0.6 m2, in other words a square 77 × 77 cm trap, to obtain a C value under 20%.
The degree of general applicability across Europe currently achieved with several forest succession models is assessed, data needs and steps for further model development are identified and the role ...physiology based models can play in this process is evaluated. To this end, six forest succession models (DISCFORM, FORCLIM, FORSKA-M, GUESS, PICUS v1.2, SIERRA) are applied to simulate stand structure and species composition at 5 European pristine forest sites in different climatic regions.
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