High Resilience of Mediterranean Land Snail Communities to Wildfires
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Biodiversity and Conservation (2006) 15:2925–2944 Ó Springer 2006 DOI 10.1007/s10531-005-3430-4 -1 High resilience of Mediterranean land snail communities to wildfires LAURENCE KISS* and FRE´ DE´ RIC MAGNIN Institut Me´diterrane´en d’Ecologie et de Pale´oe´cologie, U.M.R. 6116 du C.N.R.S., Baˆtiment Villemin, Domaine du Petit Arbois, Avenue Louis Philibert, BP 80, Cerege 13545, Aix-en-Provence Cedex 04; *Author for correspondence(e-mail: [email protected]; phone: (+0)-33-04-42-90-84-42; fax: (+0)-33-04-42-90-84-48) Received 6 May 2004; accepted in revised form 28 February 2005 Key words: Biodiversity, Land snails, Mediterranean ecosystems, Resilience, Wildfires Abstract. In the Mediterranean region, wildfires have devastating effects on animals with limited mobility. With their poor dispersal abilities, their habitats on vegetation and in litter, and their sensitivity to humidity and shade, we expected land snails to be an interesting model to assess short, medium and long-term impact of fires on fauna biodiversity and their resilience. Stratified sampling was carried out on 12 sampling sites in garrigues and forests of Provence (southeastern France), according to fire regime (number of fires, fire intervals and age of the last fire) over the past 30 years. Data were investigated using diversity indexes, Kruskal–Wallis test, dendrogram of affinities and Correspondence Analysis (CA). We found, however, that Mediterranean land snail communities are particularly resilient to fires. Although abundance is drastically reduced in the short-term, species richness and community diversity are preserved provided that the time lapse between two successive fires is longer than the time required for recovery (i.e. around 5 years). This high community resilience in the short-term may be partly due to ecological and ethological aptitudes of land snails. However, these astonishing results, which have implications for conser- vation biology, are mainly due to the presence, within burned areas, of cryptic refuges that allow initial land snail survival, malacofauna persistence after successive fires and consistent biogeo- graphical patterns in the long-term. Introduction Wildfires are major disturbances within the Mediterranean basin, particularly within ecosystems of Provence (southeastern France) owing to climatic conditions (drought during summer and a strong wind called Mistral) and flammability of vegetation (Sousa 1984; Le Houe´ rou 1987; Trabaud 1987; Whelan 1995). Over recent decades, wildfires have been reinforced by build-up of fuel due to increasing garrigue (calcareous mattoral) and forest subsequent to land-abandonment since the beginning of the 20th century (Barbero et al. 1987; Le Houe´ rou 1987). Over the last decades, consequences of wildfires on Mediterranean fauna have been broadly studied (Athias-Binche et al. 1987; Hetier 1993; Whelan 1995; Hailey 2000; Haim 2002; Santalla et al. 2002). Both direct and short-term impacts of fire generally have devastating effects on fauna with an immediate reduction in abundance (Athias-Binche 2926 et al. 1987; Arnold et al. 1993; Hetier 1993; Whelan 1995; Lyon et al. 2000). Animals, with limited mobility living above ground on vegetation or in litter, which are not able to escape approaching front flame, are most vul- nerable to fire-caused mortality and injury (Hetier 1993; Whelan 1995; Hailey 2000; Lyon et al. 2000; Vernes 2000; Tooker and Hanks 2003). In addition, the resulting habitat loss influences communities much more dra- matically than does smoke, heat or flames (Whelan 1995; Hailey 2000; Lyon et al. 2000). Burned areas are more open, illuminated and desiccated than pre-fire areas, and generally favour a more xerophilous fauna (Athias-Binche et al. 1987; Arnold et al. 1993; Fons et al. 1993; Whelan 1995; Santalla et al. 2002; Kiss and Magnin 2003). Habitat structure, vegetation stands and fauna generally respond to disturbance by secondary successions, i.e. post-fire changes (Sousa 1984; Athias-Binche et al. 1987; Fons et al. 1993; Haim 1993). During the one or two decades following fire, ecosystems reach more or less rapidly a stable state comparable to the pre-fire state (Trabaud and Lepart 1980): initially dominant herbaceous layers decrease, while shrub and tree layers become dominant over time (Barbero et al. 1987; Trabaud 1987). Species with high dispersal ability, which are able to use post-fire resources under rough habitat conditions, are favoured during the first post-fire years and replace pre-fire species (Sousa 1984; Athias-Binche et al. 1987; Blondel 1995; Whelan 1995). However, when frequent fires occur with fire interval of under 10 years, vegetation structure tends to be very simple, with only low shrubs and grass, (Barbero et al. 1987) and fire regime may also induce change in fauna biodiversity (Gill and McCarthy 1998). Although numerous studies treat the effects of fire on fauna and on their patterns of post-fire recovery, our studies (Kiss 1999, 2002; Kiss and Magnin 2002, 2003; Kiss et al. 2004) are among the few which have dealt with the impact of wildfire on Mediterranean land snail communities and with their habitat destruction. Land snails live for the most part on vegetation and in litter (Kerney et al. 1999; Heller 2001), and they have little or no ability to escape and poor active dispersal aptitudes (Cameron et al. 1980; Baur and Baur 1990; Pfenninger 2002). Moreover, gastropods are very sensitive to desiccation (Bonavita 1961; Lazaridou-Dimitriadou and Daguzan 1978; Godan 1983) and they probably do not survive the high temperatures reached during a fire. In consequence, they are highly vulnerable to fire and then to destruction of their habitats. In addition, land snails are particularly sensitive to the structure, humidity and shade of their micro-habitats (Boycott 1934; Cameron and Redfern 1976; Bishop 1977; Kerney et al. 1999). Thus, malacofaunas are expected to have low ability to respond to disturbances. They would appear to be an interesting model to reliably assess the short, medium and long-term impact of wildfires on fauna bio- diversity, and to analyse their patterns of recovery and their resilience after one or successive fires. Understanding such patterns may be important in conservation. 2927 Figure 1. Location map of study area and of sampling sites. The 12 sampling sites are named after the dates of the various wildfires over the sampling period (i.e. 1973–2001). Materials and methods Study area The study area is located in the ‘‘de´ partement des Bouches-du-Rhoˆ ne’’ (Provence, southeastern France) (Figure 1; Table 1) where fire is a frequent disturbance, with an average of 26 wildfires of over 100 ha per year between 1973 and 2001 (Centre informatique de la Pre´ fecture des Bouches-du-Rhoˆ ne 2002). A true Mediterranean climate (three dry summer months and two cold winter months) characterises the study area with annual rain averaging be- tween 543 and 680 mm and annual temperatures averaging between 14 and 11 °C (C.N.R.S. 1975). Sampling sites, with calcareous substrates, range from 140 to 660 m in altitude and are composed of grassland, of garrigue (calcareous mattoral), and of pine and oak woods (Molinier 1974). Sampling strategy Stratified sampling, based on synchronic study, was carried out according to number of fires, fire intervals and age of the last fire over the past 30 years, i.e. fire regime (Sousa 1984; Whelan 1995; Lloret and Marı´ 2001). Twelve sites of various fire regimes were selected. Six sites which have burned once over the period studied (i.e. 1973–2001) were sampled during Spring 2000. Five sites 2928 Table 1. Sampling sites. Fire dates Name of mountainous areas 1998 Regagnas 1997 Chaıˆ ne de l’Etoile 1979–1997 Chaıˆ ne de l’Etoile 1973–1979–1997 Chaıˆ ne de l’Etoile 1979–1989–1997 Chaıˆ ne de l’Etoile 1995 Chaıˆ ne des Coˆ tes 1989–1995 Chaıˆ ne des Coˆ tes 1993 Sainte Baume 1991 Chaıˆ ne des Coˆ tes 1989 Regagnas 1979–1989 Chaıˆ ne des Coˆ tes 1971 Chaıˆ ne des Coˆ tes Each sampling site is named after the dates of the various wildfires over the sampling period (i.e. 1973–2001). The mountainous areas for each sampling site are also indicated. which have burned twice or three times and one last burned in 1971 were sampled during Spring 2001. This latter site was chosen to act as a reference site since post-fire recovery of forest in the French Mediterranean region is around 30 years (Barbero et al. 1987; Hetier 1993). For each site, 10 sampling points were plotted in various post-fire vegetation stands: grassland (Brachypodium retusum Beauvais), garrigue (Quercus coccifera Linnaeus, Quercus ilex Linnaeus, Ulex parviflorus Pourret, Rosmarinus officinalis Linnaeus and Cistus albidus Linnaeus), oak stand (Quercus pubescens Willdenow) and pine stand (Pinus halepensis Miller). For the sites which have burned more than once, sampling was performed at the intersection of the burned areas. A total of 120 sampling points were performed in order to ensure a proper representation of land snail communities from various post-fire vegetation stands within each sampling site. Floristic variables, environmental variables (Godron et al. 1968) and malacofauna were recorded at each sampling point consisting of a square of 5 · 5m. Sampling of land snails At each sampling point, two different samples of land snails were taken (Kiss et al. 2004). All land snails over 5 mm in diameter were collected during a standard interval of 30 min within the square of 5 · 5 m. Minute species (i.e. under 5 mm in diameter) were collected in four squares of 25 · 25 cm including litter and the five upper centimetres of soil. Soil sample treatment (sieved on series of meshes graded from 5 to 0.5 mm), snail count and snail identification were performed in the laboratory.