Max Debussche

Rural depopulation and recent landscape changes in a Mediterranean region: Consequences to the breeding avifauna

We studied the vegetational and avifaunistic changes following rural depopulation in an area covering 2,600 ha north of Montpellier (Southern France). The study area is covered by a mosaic of Mediterranean habitats that includes cultivation, grasslands, shrublands, and woodlands and is representative of the natural features present and of the human usage practiced so far in this part of the Mediterranean.We sampled the vegetation and the bird fauna in the same 193 census plots in 1978 and in 1992. At both the habitat and landscape scales the cover of woody plants increased significantly. Open habitats tend to disappear. As a consequence the abundance of open-habitat bird species decreased significantly whereas the abundance of forest birds increased significantly. These changes favor a pool of forest species widespread in western Europe and reduce habitat availability for open habitat and shrubland species. Many of the latter are Mediterranean species whose distribution in Western Europe could become reduced under current landscape dynamics. Our observation of more woodlands and their typical birds and of less open habitats and their associated avifauna is not consistent with the traditional worry shown by the public and the managers about the regression of forests and woodlands in the Northern Mediterranean as a consequence of fire.

Fleshy fruit characters and the choices of bird and mammal seed dispersers in a Mediterranean region

An eight-year study in a Mediterranean area near Montpellier allows us to document and discuss the relationships between morphological and chemical characteristics of fleshy fruits of the native plant species and the choices made by their bird and mammal seed disperses. This study is based on qualitative (presence-absence) data

Ornithochory and plant succession in mediterranean abandoned orchards

Data on the occurrence of species with fleshy diaspores and on breeding birds were collected in three abandoned orchards, resp. 8, 11 and 24 years after abandonment. Most of the 41 phanerophytes and vines with fleshy diaspores are also found in the borders of the orchards, the more so if the number of years since abandonment increases. Most species have small seeds and red or black coloured diaspores, most of which ripen in autumn. The frequent species show a characteristic distribution pattern in relation to the distance of the fruit trees: high densities near the trunk and uniform decrease with distance. This is explained by the behaviour of frugivorous birds. No correlation was found between distribution patterns and soil conditions. Age structure of colonizing species shows a distribution conforming an inversed J curve in the more recently abandoned orchard. The main conclusions are: 1. Pioncor trees are attractive for frugivorous birds and may act as nuclei. This supports the facilitation model. 2. The distribution of diaspores by birds helps to homogenize the species distribution on the regional level but at the site level individual differences in nucleation cause a heterogeneity. Pioncor trees are attractive for frugivorous birds and may act as nuclei. This supports the facilitation model. The distribution of diaspores by birds helps to homogenize the species distribution on the regional level but at the site level individual differences in nucleation cause a heterogeneity.

Changes in Mediterranean plant succession: old‐fields revisited

. Old-field plots used for a study of succession in Mediterranean France were revisited after 12–14 yr. Our aims were: (1) to verify if predicted patterns of species richness, turnover and composition are confirmed; (2) to compare the development in disturbed plots with that in undisturbed ones; (3) to discuss the impact of management changes. In undisturbed plots species richness and turnover decreased with successional age. Floristic composition changed in a way consistent with the predicted successional development in most plots. Therophytes decreased and phanerophytes increased; anemochorous species decreased and endozoochorous species increased, as expected. In plots disturbed since the first analysis richness decreased with successional age, but generally remained higher than in undisturbed plots. Floristic composition, species turnover and an increase in therophytes indicated changes towards younger successional stages. Thus, disturbance changed succession but not much. This is probably linked with the regeneration abilities typical of mediterranean species, e.g. resprouting. At the landscape scale, richness did not change and species turnover was low. The plots studied were situated in two distinct locations. One had not been disturbed between the two observation periods, while the other is a mosaic of undisturbed and disturbed sites. Observations fitted predictions much more closely at the undisturbed location. We conclude that permanent plot studies are powerful in identifying successional trends and can also provide additional insights into the effects of disturbance some of the mechanisms underlying the dynamics of diversity.

Rapid invasion of Fraxinus ornus L. along the Herault River system in southern France: the importance of seed dispersal by water

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Small scale disturbances and the maintenance of species diversity in Mediterranean old fields

In three Mediterranean old fields, one, seven, and fifteen years after the last ploughing, small scale disturbances (0.25 m 2 ) by contact herbicide associated or not with litter removal and scratching of the top 3 cm of the soil were generated in October 1988, December 1988, and March 1989. Subsequent changes in cover, species richness and composition were observed over the two following vegetation cycles (until May 1990), and compared to the dynamics in undisturbed samples. The identity of the colonizers for each disturbance date were compared to the soil readily-germinable seed content, sampled simultaneously to the disturbances. The species richness of the samples within the fields increased the first year after disturbance. Within-field heterogeneity for taxonomic composition was unchanged, but species turnover was increased by disturbances

Establishment of woody plants in Mediterranean old fields: opportunity in space and time

The establishment of woody plants following agricultural abandonment in the Mediterranean region is a very widespread process which underlines the extent of the rural exodus. The installation windows in space and time were studied in the French Mediterranean region for two common woody plants, Buxus sempervirens and Fraxinus angustifolia and for a group of common woody fleshy-fruited species. These plants differ in their principal modes of dispersal which are respectively, barochory, anemochory and ornithochory. Their installation was analyzed in relation to the seed shadows, the spatial patterns and the age structures of the seedlings. The majority of the seeds were dispersed over short distances, although some animal vectors may promote a limited amount of long distance dispersal. Hence, whatever the mode of dispersal, a few seeds are often dispersed far from the maternal plant. The combination of several dispersal types in one plant species is a frequently observed feature, one being dominant at a small scale, and related to successional processes, the other being dominant at a larger scale and related to invasive processes. In the old fields the spatial pattern of seedlings closely follow the observed seed shadows. However, competition with the maternal plants may lead to, in some cases, a recruitment deficit close to the seed-bearers. Age structures show that woody plants often install very early after the abandonment of cultivation and that the installation window in time is shortened by the development of a dense herbaceous cover. It is concluded that the installation of woody plants in Mediterranean old fields cannot be reduced to a general rule. The rate and extent of installation depends mainly on the spatial distribution of the seed-bearers, therefore of the spatial patterns of the landscape.

Human Impact on Landscape Patterning: Mediterranean Examples

Humans have modified large areas of landscape throughout the world. At a local level, humans may change dominant plant species, vegetation structure, and characteristics of ecotones between vegetation patches. At a regional level, humans may alter land use, arrangement of tessera in the landscape mosaic, and characteristics of ecotones between mosaics. Analysis of past and present human activities is essential in many locations for understanding landscape patterns. In this chapter, we analyze and discuss the importance of anthropic disturbances over approximately the past 8000 years in the Mediterranean region, and more specifically the Languedoc (southern France). We address the following questions: How does natural landscape structure influence human settlement patterns? How is human action distributed in time and space? Do anthropic disturbances differ from natural disturbances in kind or only in scale? Do human actions typically lead to more homogeneous landscapes? What are the long-term consequences of human activity patterns? To what extent do social and economic factors drive human land use and, in turn, landscape patterning? All these questions are interrelated. We perform the analysis with reference to a hierarchy of time and space scales, as is often done for natural disturbances (Pickett and White 1985, Urban et al. 1987).

Ants as seed dispersers in a Mediterranean old-field succession

Seed dispersal by ants was studied in three Mediterranean old-fields (6, 15 and 43 years after abandonment) and a Quercus pubescens forest that represented the last successional stage. In each plant community, we investigated I) the occurrence of both seed dispersal strategies involving ants, namely myrmecochory and dyszoochory, relatively to plant species frequency and cover, 2) the abundance of disperser species likely to perform one dispersal type or the other 3) the relative effectiveness of myrmecochory and dyszoochory, by experimentally offering elaiosome-bearing seeds of Viola alba and Euphorbia nicaeensis, and seeds of the same species deprived of their elaiosome. The proportion of dyszoochorous plants and the abundance of granivorous ants followed the same trend along the successional gradient. The youngest stage had the highest proportion of dyszoochorous plants and the highest abundance of granivorous ants, including the harvester ant Messor structor, whereas the oak forest showed the lowest proportion of dyszoochorous plants and held no granivorous ants. In contrast, there was no coincidence during the succession between the number of myrmecochorous plants and the number and abundance of ant species collecting elaiosomes. More generally, myrmecochorous plants were rare while ant species collecting elaiosomes were present from old-field to forest. Seed removal experiments showed an overall significant increase in the removal rate of elaiosome-bearing seeds over that of seeds without elaiosome, but in the youngest old-field the difference was not significant for V. alba and was attenuated for E. nicaeensis seeds, due to high harvester ant activity. We suggest that dyszoochory by ants could be a major mechanism influencing plant dynamics in open and grassy vegetation in the Mediterranean region. We also suggest that, though apparently efficient, myrmecochory is underrepresented because of biogeographical features (rarity of the medio-European flora) and lack of strong selective pressure. We emphasize that dispersal strategies involving animals, be it ants, birds or mammals, all share the same dichotomous pattern that shows the evolutionary strength of two mechanisms, one directly derived from predation (dyszoochory), the other generally more deeply shaped by mutualistic processes (e.g. myrmecochory).

Genetic structure of continental and island populations of the Mediterranean endemic Cyclamen balearicum (Primulaceae).

Cyclamen balearicum is a self-compatible perennial herb endemic to the western Mediterranean Basin. This species occurs in five geographically isolated terrestrial islands in southern France and on four Balearic islands. In this study, we compare genetic variability and differentiation within and among 11 terrestrial island populations and 17 true island populations. Of nine readable enzyme loci, five were polymorphic in both terrestrial and true islands. F statistics showed a significant heterozygote deficiency in all populations, probably due to high levels of autonomous selfing, restricted gene flow, and subsequent genetic drift. Genetic diversity was higher in terrestrial islands than on the Balearic islands, suggesting that the Balearic islands were colonized when they were in contact with the continent. Population differentiation was greater among terrestrial islands (Fst = 0.417 and Gst = 0.344) than among true islands (Fst = 0.112 and Gst = 0.093). Furthermore, differentiation among populations on the Basses Cévennes terrestrial island was greater (Fst = 0.254) than among populations on the true island of Mallorca (Fst = 0.163). The greater genetic differentiation among terrestrial islands could have been caused by genetic bottlenecks associated with changes in climate and human land use that may have reduced population sizes more severely in terrestrial islands in southern France than on the Balearic islands.