Three centuries of land cover changes in the largest French Atlantic wetland provide new insights for wetland conservation

doi:10.1016/j.apgeog.2013.05.011

Applied Geography

Volume 42, August 2013, Pages 133-139

https://doi.org/10.1016/j.apgeog.2013.05.011 Get rights and content

Highlights

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We assess land cover changes in the largest French Atlantic wetland since 1705.
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Grassland to cropland conversion is a recent phenomenon of the last decades.
•
Marshes, salt-marshes and other marine habitats sharply decreased since 1705.
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Long-term studies reveal new implications for wetland conservation.

Abstract

Grassland to cropland conversion has been a major land cover change in wetlands during recent decades. Many conservation strategies have therefore focused on the protection or restoration of grasslands considered the remnant fragments of nature in wetlands before agricultural development. Through the example of the largest French Atlantic wetland (the Marais Poitevin) and using high-resolution historical records documenting landscape changes since the beginning of the 18th century, we propose the first long-term analysis of a wetland conversion at a large spatial scale. We demonstrate that, although the last land cover changes corresponded to significant grassland to cropland conversions, the mid-20th century was characterized by an exceptional grassland cover (90% of the area). We also show that current surface areas covered by grasslands are similar to those of the 18th and 19th centuries, and that grassland to cropland conversion followed a massive decline in the most natural habitats of the wetland such as marshes, salt-marshes and other marine habitats. From a long-term perspective, grassland to cropland conversion is rather a recent change and grasslands can be viewed as the result of agricultural development in this wetland rather than pristine habitats. In contrast, marshes, salt-marshes and other marine habitats can be considered the remnant fragments of nature of conservation interest, although they are neglected in current conservation plans. We discuss the problem of the time-span and the reference state to be considered when analyzing land cover changes and assessing wetland conservation issues at large spatial scales.

Introduction

Coastal wetlands are sometimes considered the last remaining areas to maintain littoral biodiversity (Wolanski, Brinson, Cahoon & Perillo, 2009). In these ecosystems, the conversion of grasslands to croplands has been a worldwide phenomenon during recent decades (Liu et al., 2005; Rashford, Walker & Bastian, 2010; Rounsevell, Ewert, Reginster, Leemans & Carter, 2005; Schleupner & Link, 2008; Stephens et al., 2008) even though many protected species are considered dependent on grasslands. For instance, they are habitats of importance for 81 of the 278 bird species designated as being Species of European Conservation Concern while for 79 of them, grasslands are considered their preferred habitats (Tucker & Evans, 1997). Consequently, the conservation, restoration and management of grasslands have been at the forefront of many conservation programs (see Cramer & Hobbs, 2007; Török, Vida, Deák, Lengyel & Tóthmérész, 2011).

However, focusing on these recent land cover changes in wetlands may hide other conservation issues that would be revealed by long-term analyses. In fact, many land cover change studies have concentrated on either very long-term periods (e.g. the Holocene) using paleoecological methods or rather short-term periods (e.g. recent decades) using remote-sensing methods. In Europe, a few studies have assessed land cover changes over the last centuries, during historical times, but these have often concerned areas of rather small spatial extent (e.g. Cousins, 2001; Gustavsson, Lenartsson & Emanuelsson, 2007; Johansson et al., 2008; Petit & Lambin, 2002; Skaloš et al., 2011 studied areas of ca. 616 ha; 800 ha; 2250 ha; 1600 ha; and 11,300 ha, respectively) or patchy habitats over larger areas (e.g. wet heathland complexes over 79,700 ha for Cristofoli, Monty & Mahy, 2010). Other studies have modeled land cover or land use changes at continental scale and over several centuries, but with a coarse spatial resolution (e.g. Ramankutty & Foley, 1999). To our knowledge, there have been no land cover change studies of large European wetlands, over several centuries and at a high spatial resolution.

In this study, we selected the Marais Poitevin (MP), which is the largest French Atlantic wetland and among the largest in Western Europe, as a study site. In this area, 34% of the grasslands were converted into arable fields from 1973 to 1990 (Duncan et al., 1999). In 1996, these ecological degradations were estimated to be so serious that the MP was the only area in France to lose its label of Regional Natural Park. In 1999, France was convicted by the European Court of Justice for failure “to adopt special measures necessary for the conservation of bird habitats in the Marais Poitevin” and “to take the appropriate steps to avoid deterioration of those habitats” (Case C-96/98, Commission v. France). To date, the MP is also one of the only European wetlands of such a spatial extent to be excluded from the RAMSAR network (despite there being a large spatial concentration of RAMSAR sites in Western Europe – see Frazier, 1999). Consequently, one of the challenges of local conservationists was to cope with intensive agriculture achieved through drainage and to promote the conservation or restoration of grasslands. In 1976, the first National Natural Reserve of the MP was created in 207 ha of grassland in Saint-Denis-du-Payré (see Fig. 1 for the location of this village). In 1992, subsidies for drainage were stopped (CIEPP, 1994) and new ones were proposed to farmers to maintain semi-natural grasslands through the Structural Funds of the European Union (Duncan et al., 1999). Today, most of the grasslands of the MP are included in a Natura 2000 site of more than 68,000 ha, while 26,000 ha of grasslands benefit from agri-environmental measures (Giret, 2011). The subsidies to farmers implementing agri-environmental measures on grasslands range from 150 to 279 €/ha/year, while subsidies to convert croplands into grasslands reach 340 €/ha/year (Giret, 2011). Through the action of a new structure replacing the former Regional Natural Park (the “Parc Interrégional du Marais Poitevin” (PIMP)), and with subsidies from the State, Regions, Departments, and Europe, the restoration of ca. 600 ha of grasslands has been achieved since the end of the 1990s (Giret, 2011). Nowadays, grasslands are viewed by conservationists as the remaining natural fragments of the MP before its disturbance, and conservation measures aim to recover a “reference state” preceding agricultural intensification. The aim of this work was to assess if the analysis of long-term land cover changes of wetlands may highlight new conservation issues in comparison with studies focusing only on recent decades. To do so, we selected the MP because it is an archetype of the recent agricultural changes affecting wetlands. In this paper, we present an analysis of land cover change from the year 1705–2008 based on high-resolution historical documents and covering the whole area.

Section snippets

Study area

The Marais Poitevin (MP) is the largest Atlantic wetland in France. It overlaps three administrative departments (Vendée (66.5% of the area), Charente-Maritime (25.5%), and Deux-Sèvres (8.0%) – Fig. 1). In this paper, an official perimeter of the MP was used (Forum des Marais Atlantiques & Conservatoire du Forum des Marais atlantiques Conservatoire du Littoral, 1999), to which the whole Baie de l'Aiguillon was added (Fig. 1). The total area considered in this work thus encompasses 102,234 ha.

Image data

Results

There were two major land cover changes from 1705 to 1820 (Fig. 3). The first was the marked decrease in marsh areas which fell from 24.8% to 7.4% (Fig. 4). The second was a massive land reclamation that led to a reconversion of salt-marshes and marine areas into croplands or grasslands. The area covered by salt-marshes fell from 4.2 to 1.9% of the total while marine areas dropped from 10.6 to 5.6% (Fig. 4).

From 1820 to 1950, almost the only phenomenon was a huge increase in grasslands which

Grasslands cannot be considered the remnant fragments of a pristine landscape

The first main result of this study is that grassland to cropland conversion is important but is a very recent phenomenon of the second half of the 20th century. 1950 was an exceptional period during the last three centuries, when grasslands dominated the area: before and after this date, the extent of grasslands was much lower. The second main result is that some of the most natural habitats of the MP almost disappeared (marshes) or sharply decreased (salt-marshes, marine areas).

The

Conclusions

Though very important in the Marais Poitevin, grassland to cropland conversion is a very recent phenomenon of the second half of the 20th century. This major land cover change led to a clear focus of conservation strategies on grasslands, considered the remnant fragments of nature of the area. However, over the last three centuries, we have found that grasslands dominated the area only in 1950, so that conserving or restoring grasslands corresponds to a restoration of a landscape of the end of

Acknowledgements

We thank Loïc Ménanteau for providing the maps of Claude Masse. Special thanks to the Parc Interregional du Marais Poitevin (Pierre Guillermin, Alain Texier) for providing the 2008 land cover map. The authors also thank Vincent Devictor and Jérôme Fournier for helpful comments on a previous draft of this manuscript.

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Three centuries of land cover changes in the largest French Atlantic wetland provide new insights for wetland conservation

Highlights

Abstract

Introduction

Section snippets

Study area

Image data

Results

Grasslands cannot be considered the remnant fragments of a pristine landscape

Conclusions

Acknowledgements

Landscape and Urban Planning

Catena

Biological Conservation

Landscape and Urban Planning

Applied Geography

Remote Sensing of Environment

Agriculture, Ecosystems and Environment

Applied Geography

Applied Geography

Marais poitevin – rencontres de la terre et de l'eau

Les Zones Humides – rapport d'évaluation

Évolution des surfaces boisées en France: proposition de reconstitution depuis le début du XIXe siècle

Revue forestière française

Les Marais de la Sèvre Niortaise et du Lay du Xe à la fin du XVIe siècle

Old fields: dynamics and restoration of abandoned farmland

Long-term changes in agricultural practices and wildfowling in an internationally important wetland, and their effects on the guild of wintering ducks

Journal of Applied Ecology

Analysis of land-cover transitions based on 17th and 18th century cadastral maps and aerial photographs

Landscape Ecology

Le plein rural en France

Espaces, Populations, Sociétés

Vers la réalisation d'une carte géoréférencée des forêts anciennes de France

Le Mondes des Cartes