Long-Term Forest Dynamic After Land Abandonment in a Fire Prone

Landscape Ecology (2005) 20: 101–112 Ó Springer 2005 DOI 10.1007/s10980-004-1297-5 -1 Research article Long-term forest dynamic after land abandonment in a fire prone Mediterranean landscape (central Corsica, France) Florent Mouillot1,*, Jean-Pierre Ratte1, Richard Joffre1, David Mouillot2 and Serge Rambal1 1IRD-UR 060, DREAM CEFE/CNRS, 34293 Montpellier Cedex 05, France; 2UMR CNRS-UM2 5119, 34095 Montpellier Cedex 05, France; *Author for correspondence (e-mail: [email protected]) Received 30 December 2003; accepted in revised form 12 July 2004 Key words: Land cover change, Landscape patterns, Mediterranean-type ecosystem, Transition matrix Abstract 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. Introduction In recent times, most Mediterranean landscapes of southern Europe have undergone dramatic land Plant growth rates and life history traits have been abandonment (Debussche et al. 1987; Etienne et al. shown to have strong effects on local processes of 1998; Le Houe´rou 1992; Lepart and Debussche succession in disturbed habitats (Grime 1977; Noble 1992; Moreira et al. 2001; Pausas 2004). Although and Slatyer 1980). However, dispersal ability is a landscape changes in the Mediterranean basin have major spatial process driving landscape dynamics, and been recently studied, most of those studies focussed recent studies have increased understanding of how on quantifying the rate of land abandonment (Deb- the spatial pattern of seed sources and colonizable ussche et al. 1999; Debussche et al. 1987; Garcia- patches, can influence the spatial and temporal course Ruiz et al. 1996), forest expansion (Debussche and of colonization (Gustafson and Gardner 1996; Holt Lepart 1992; Moreira et al. 2001), or fire effects et al. 1995; Lavorel et al. 1995; Turner et al. 1997; (Trabaud and Galtie´ 1996; Vazquez and Moreno With and King 1999). Indeed, in the case of land 2001). The processes driving these dynamics have abandonment, the initial landscape pattern may drive been identified to be controlled by species dispersal the course of succession by determining the compo- abilities (Ne’eman and Izhaki 1996), and locally sition and the spatial distribution of both the seed modified by soil properties (Roche et al. 1998; source and host community (Smith et al. 1993). This Tatoni et al. 1994). More recently, spatially explicit pattern may also influence the occurrence and the studies modeled landscape dynamics based on initial spread of disturbances (Turner et al. 1989). landscape pattern and few biologically relevant 102 variables (Carmel and Kadmon 1999; Carmel et al. 2001; Kadmon and Harari-Kremer 1999; Pausas 2003). However, analysing and understanding the interaction of historical spatial modifications of these landscapes with recurrent fires and environment has rarely been considered because few data are avail- able on both vegetation changes and fire history. Understanding these interactions would clarify the remaining question on the inter-related effects of land abandonment and fire on long-term Mediterra- nean vegetation dynamics. Particularly, our goal is to identify the potential feedbacks of spatial changes in landscape composition on the fire regime itself. In this study, we intend to answer this question i) by reconstructing both the land-cover dynamics and fire history over a period sufficiently long to reflect both land use changes and intrinsic successional processes, and ii) by analysing and simulating the rates and patterns of change in landscape composition after land abandonment, in relation to topography and fire. Study site The study area is located in the Venaco area (43°12¢ N, 9°12¢ E), in the central part of Corsica (a French Mediterranean island covering 8752 km2 Figure 1. (a) Location of Corsica and the Venaco area in the west (Figure 1a). For centuries, the region has been covered Mediterranean basin. (b) The study area (black line) is also reported on the topographical map of the Venaco region (dotted line). by mixed areas of managed forest and agriculture (Diodore of Sicily, ND), to ‘provide food for livestock … on a rude, uneven and difficult terrain’ (Rousseau 1765). The collapse of the agricultural activity at the composed of sandy brown and slightly acid soils (pH beginning of the 20th century, due to the geographical = 6.5) (Mesleárd and Lepart 1991). isolation of the island and new agricultural policies, The climate is Mediterranean (cool moist winters allowed only cow, sheep and goat grazing as major and hot dry summers). Annual rainfalls recorded at activity (Lenclud 1980). The study area covers 3,760 Venaco for the 1960–1982 period range from 668 mm ha in the Parc Naturel Regional, with an elevation to 1709 mm with a mean of 1088 mm. Eighty percent ranging from 200 m to 1100 cm. The area consists of of precipitation occurs between October and April. foothills, with a Mediterranean-type vegetation Mean annual temperature is 13.5 °C; it varies between growing on acidic soils. Patches of Quercus ilex L., Q. 6.2 °C in February and 22 °C in August. pubescens Willd., Q. suber L. or Pinus pinaster Ait. woodlands co-occur with patches of shrublands (called maquis): High shrublands (1-2m height) are Material and methods dominated by Arbutus unedo L. and Erica arborea L. Low shrublands (height < 1m) are dominated by Historical land cover reconstruction Cistus monspeliensis L. (Mesleárd and Lepart 1991). The maquis area is approximately delimited on its The creation of a map (Plan Terrier) was ordered in west side by a 1000m altitude contour line, and on the 1774 by King Louis the fifteenth to inventory the southern and eastern boundary by the Vecchio- natural resources of the island after its acquisition Tavignano river corridor (Figure 1). The substrate is (Caratini 1995). A precise map at 1:10,000 scale was 103 consequently published in 1793 (Albitreccia 1942). tween 75% and 100% of the polygon, ‘open forest’ Land-cover patches are represented by polygons on a between 25% and 75%. The remaining 5 non-forested schematic topographic background. A copy of this types (trees covering 0–25%) were then defined map was scanned and georeferenced using IDRISI according to the percentage cover of high shrubs (Eastman 1987). Confluence and ridge lines were used (>1m, <2m), low shrubs (<1m) and herbaceous, as as base points for georeferencing the map with Lam- described in Table 1. The vegetation types were bert 4 coordinates; twenty-two base points were used aggregated into the 4 ‘generic’ land cover types for on the whole landscape. The polygons were redrawn in some analysis (Table 1). vector format by tracing the lines of the scanned and The three maps (1960, 1975, 1990) were digitized georeferenced image. Each polygon was assigned to and converted to 20m resolution raster format in a GIS one of eight land cover types (Figure 2a). Since species database (Figure 2b, 2c, 2d). The aspects map was are not mentioned in the initial legend, we considered derived from a 20m Digital Elevation Model (DEM). that ‘Chestnut forests’ were dense forests containing not only Castanea sativa but also Quercus ilex and Fire maps Quercus pubescens, and that ‘woodlands’ were exclusively Quercus ilex. Pinus pinaster forests are not Major fires have been mapped yearly on the study mentioned in the legend, but they may have been area since 1970 based on police and fire reports, and sporadically present in the shrublands. We aggregated registered on a GIS database in vector format (source olive trees, vineyards and crop cultivations into a ODARC-Bastia: Agricultural Office of Corsica). This ‘cultivated areas’ generic land cover type. The map database was validated and updated using local was converted to raster format with 20 m resolution. reports (Joffre 1981) and aerial photograph surveys Two additional surveys were carried out on the from 1975 and 1990. Additional fire boundaries territory by the French fiscal services (Source: Ar- (Barry and Maniere 1975; Joffre et al. 1982) were chives departementales de Haute-Corse). These sur- added on a topographical map at 1:25,000 scale, veys provide landscape composition for the years digitized and converted to 20 m resolution raster 1848 and 1913, but in a non-spatial format. We used format. This work led to a complete database for the them as intermediate updates of landscape composi- 1957–1997 period (Mouillot et al. 1998) (Figure 2e). tion in Figure 3. They consider the four ‘generic’ land cover typesÀforested, shrublands-grasslands, culti- Land cover change analysis vated and urban areas – that we used as the common classification for long-term translation across time. Temporal analyses were performed in 1960, 1975 and 1990, using transition matrices. We limited this approach to these three dates because those maps have Present land-cover maps and additional data a common legend, and the time interval between two consecutive maps is long enough for changes in Joffre (1981) and Amandier et al. (1984) established vegetation types to be detected. This interval was not precise land cover maps for 1960 and 1975 respec- so long as to hide trends due to changes in land use or tively.

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