Notwithstanding these uncertainties, corridors have been considered seriously in nature conservation since the introduction of island theory and metapopulation theory (Simberloff & Abele 1976; Shrader-Frechette & McCoy 1993; Looijen 2000). In 1980, the International Union for the Conservation of Nature and Natural Resources (IUCN) adopted the idea of ecological corridors into its World Conservation Strategy (IUCN 1980) and in the United States and Europe the concept was soon accepted by governmental and non-governmental organizations (NGOs) (Simberloff et al. 1992; Jongman, Külvik & Kristiansen 2005). Ecologists working within NGOs, centres for applied science and governmental institutions have demonstrated much enthusiasm for the concept (Rientjes & Roumelioti 2003). As Simberloff & Cox (1987) state: ‘corridors have been promoted outside the bounds of mainstream science’; so it seems that the concept of corridors has been a successful societal enterprise. As an example of the role of societal context we will sketch the rise and implementation of the concept in the Netherlands.
development at the national level
For the period 1980–2005, we studied national nature policy documents, reports from Alterra, the research institute for applied ecology and landscape design, and all volumes of the leading Dutch journal Landschap (Landscape) published by the Society for Landscape Ecological Research.
After its introduction in the Netherlands at the end of the 1970s, landscape ecologists discussed the relevance of ecological corridors for Dutch nature conservation (Opdam 1978; Brussaard & van der Weijden 1980; Saris 1984). The 1981 national nature policy document was already suggesting creating corridors between nature reserves as an additional aim in conservation, referring to new ecological insights (CRM & VRO 1981). The situation changed radically in 1989 when the new national nature policy document announced the creation of a National Ecological Network of 750 000 ha by connecting existing and newly developed nature reserves with more than 200 national and 40 transnational ecological corridors (LNV 1989a). The responsible Ministry of Agriculture, Nature Management and Fisheries found it necessary to start an offensive to save nature reserves because of large problems with eutrophication, acidification, parching and fragmentation. Nature reserves had to become more robust; that is, larger and more connected to other reserves. The plan was initiated by ecologists within this ministry and the relevant ecological theories were presented in a background document (LNV 1989b). The Alterra institute or one of its precursors was hardly involved (Visser 2006).
Many provincial authorities and private conservation organizations became enthusiastic because this new national plan could be used to create and plan new nature areas. Accordingly, many proposals for ecological corridors throughout the country were initiated. An evaluation study from 1997 by a precursor of the Alterra institute shows that 30% of the intended corridors had already been created, in line with the planning of the 1989 national nature policy document. However, it also reports that most projects paid no attention to the question of whether the corridors were really effective ecologically and that several provinces were resistant to the plans (Bak & Reijnen 1997).
Because of these problems, the Dutch government decided in 2000 to focus on 27 000 ha of ‘robust corridors’. These robust corridors were regarded as better able to connect nature reserves and to cover multiple functions. In addition to the central objectives of enhancing the migration of animals such as the great bittern and red deer and of improving the cohesion of the National Ecological Network, these corridors also had to improve the historical cultural identity of the landscape, recreation opportunities, water management, and even agriculture (LNV 2000). By introducing this element of multifunctionality the government expected more support from provincial authorities and stakeholders and to reduce the implementation costs for the plans (Visser 2006). It was thought that in the case of large multifunctional corridors the lack of scientific information was less crucial (Opdam, Reijnen & Vos 2003). The government decided to stop subsidizing the implementation of hundreds of planned small corridors, except those which result in strong judicial or administrative problems if they were stopped. Later, the government was forced to ask Alterra for advice, in particular to select the ecologically most valuable small corridors as well (LNV 2004; Visser 2006). The corridor concept was thus transformed to make it socially stronger, but nevertheless ecological corridors were still regarded as an essential element of the National Ecological Network.
What about the scientific development during the same period? After a symposium of the Dutch Landscape Ecology Society in 1983 on ecological infrastructures, Landschap has published some 30 papers on dispersion, fragmentation, metapopulation theory and ecological corridors. Many landscape ecologists were positive about the corridor concept because insights from population ecology could be linked to concepts of landscape structure and to proposals for landscape design. However, some of them echoed international criticism in stressing that the concept of a corridor is rather vague – corridors can simply be hedgerows or narrow side ditches – and that it is risky to use such unsubstantiated concepts in conservation (Dekker & Knaapen 1986).
In 1987, Opdam, one of the leading Dutch corridor experts working at the Alterra Institute, stated that ‘you cannot conclude from metapopulation theory that corridors are the only solution for the survival of populations’ (Opdam 1987). Ever since, there has been an ongoing discussion on ecological corridors in Landschap, based on empirical studies. Some underpin the notion that corridors are useful for several species of fish and large mammals (Lammers 1989) or that models show that connections between nature reserves are necessary for the survival of metapopulations (Verboon, Opdam & Schotsman 1991). Others stress that ecological corridors do not work for many plants (van Dorp 1992) or that several corridors appear to be useless (Bal & Reijnen 1997).
In 2000 the Ministry of Agriculture, Nature Management and Fisheries presented the reports of two working groups consisting of researchers from Alterra and officials from ministries, provinces, water authorities and municipalities. Both reports conclude that ecological corridors are necessary, that there is insufficient knowledge, and that robust corridors may combine ecological and social functions (Beentjes & Koopman 2000; Pelk et al. 2000). These reports could function as the scientific and societal basis for the political shift towards the so-called robust corridors.
Almost immediately, Alterra published the Handboek Robuuste Verbindingen (Handbook for Robust Corridors) (Broekmeyer & Steingröver 2001), offering guidelines for the size and shape of ecological corridors based, as far as possible, on ecological information. The handbook describes detailed corridor conditions for 50 animal species (mainly butterflies, birds and mammals) and for several hundred flowering plants. For instance, for the otter the corridor should be at least 50 m wide and consist of water and rough vegetation. The handbook picks up the political message, providing information on whether, when and how the corridors can be combined with recreation, water management and agriculture. The authors realize that corridors are not a panacea, emphasizing that they should be seen as just one of the strategies to counter the fragmentation of habitats and populations. Other approaches include improving habitat quality and enlarging nature reserves.
To help unravel the specific relationships between landscape structures and dispersion of species, Alterra commenced two studies. In one the institute designed guidelines for monitoring the corridors (Vos & Smulders 2004); the other study consisted of a survey of the literature and three empirical studies. The literature survey reveals that of 18 species (butterflies, mammals and amphibians), nine are strongly dependent on a dispersion corridor and nine either to some or no extent (Vos, Baveco & van der Veen 2005). The empirical studies show that corridors are not necessary per se, but that they can stimulate the dispersion of the wood mouse and the common frog.
Most of the policy-related scientific work was carried out by Alterra researchers familiar with the scientific weaknesses of the concept, but convinced that fragmentation was a problem for many species and that corridors could be helpful for certain species. The idea of a National Ecological Network was a successful political enterprise and to be seen criticizing these concepts was regarded as strategically dangerous (Visser 2006). Thus, for Alterra scientists the ecological corridor was barely acceptable from a scientific viewpoint but desirable from a nature conservation policy viewpoint.
This outline of the rise of the ecological corridor in the Netherlands demonstrates that many parties were involved in its development and determination, including both scientists and non-scientists. The concept and the related National Ecological Network appeared to be binding and stimulating concepts for these parties. From the development of an ecological corridor this led to the development of the multifunctional robust corridor.
implementation on the regional level: the green river
We now review the perception and judgement of the concept of ecological corridors on the regional level through the example of a proposed restoration project of an ecological water corridor in the northern part of the Netherlands during the period 2001–05. This is based on assessment of policy documents, structured interviews with key actors (listed in the Acknowledgements), and by observations gathered during a workshop on this wet corridor.
After the decision to fund a National Ecological Network according to the national nature policy document of 1989 (LNV 1989a), the provincial authorities were charged with its implementation from 1990 onwards. As a result, 900 corridors were planned in provincial schemes for ecological networks instead of the 200 intended in the national policy document (Visser 2006).
In the province of Groningen, most attention was paid to wet corridors because of developments in national water management after 1990, such as the need to combine requirements for flood safety, water transport and nature conservation. Besides the corridors mentioned in the official National Ecological Network plans and Provincial Ecological Network plans, ecologists and nature conservationists, sometimes together with a fishery organization, launched several additional plans. They stressed the importance of these plans for the migration of fish species, the quality of the landscape in relation to recreation and water management (Vegter 1997; IWACO 1999). At the same time, a consortium of large Dutch nature conservation organizations presented a national plan called Veters los (Loosen the Laces), proposing to restore old river and brook systems to enlarge riparian areas (Helmer, Van Beek & Schouten 1997).
Developing from these plans, the Green River plan was proposed by a coalition of nature protection organizations. This plan aimed to restore brook valleys in the northern part of the Netherlands (Het Drentsch Landschap et al. 2001). According to the Green River plan, the rainwater draining from the higher Pleistocene plateau in the province of Drenthe south of the city of Groningen would follow an hourglass-like pattern on its way to the Dutch Wadden Sea, a shallow part of the North Sea. The central part of this pattern would approach the city fairly closely on its western side through an already planned new industrial zone. After this narrow passage, the water would be guided into brooks throughout the countryside of the province of Groningen. The Green River plan won the support of the Algemene Nederlandse Wielrijders Bond (ANWB), the largest recreational organization in the Netherlands, because this plan also aimed to improve recreation facilities and the quality of life in Groningen (Het Drentsch Landschap et al. 2001). In the same year, similar ideas were presented by the Ministry of Agriculture, Nature Management and Fisheries (Geraedts 2001).
Both the province and the city of Groningen considered that restoring riparian habitats to brooks could be the new approach that would also fulfil nature conservation, water management and landscape quality aims. However, farmers and industrial parties wanted guarantees that such plans would not harm their interests. Some provincial and communal politicians were critical of the costs. Last but not least, the regional Water Authority was highly sceptical of the idea of water management through the restoration and construction of wet ecological corridors.
To ensure commitment and create a consensus, the provincial authorities initiated a number of workshops with regional and local authorities and stakeholders, assisted by several consultancies (Kuiper Compagnons 2001; Tauw 2003). Gradually, the Green River ecological corridor became linked to other issues within a rather complicated process of decision-making and different levels of government (community, province, region and state) with different visions and responsibilities becoming involved.
From interviews with the main actors, it appears that the stakeholders involved had different evaluations of nature and water. Conservationists showed a preference for so-called wilderness nature, whereas the authorities and farmers preferred functional nature, i.e. nature that supported human interests such as recreation and transport, or more arcadian nature perspectives (van der Windt, Swart & Keulartz 2007). With respect to water, conservationists focused on restoring the old brook systems, provincial authorities stressed recreational and other functional aspects, while farmers were interested primarily in the safety and irrigation quality of water. However, during the decision-making process, communicative efforts on the part of the provincial authorities contributed to bridging these contrasting viewpoints. Nature conservationists and water authorities became aware that water storage could be combined with the restoration of brook valleys. In some parts of the proposed brook valley system, farmers were willing to manage ecological zones in a nature-friendly way; in other parts they asked for assurances that they could continue to develop rationalized forms of agriculture.
The role of the province was somewhat ambiguous, despite its aim to reach a wide consensus. The Green River plan was not completely in line with its own nature conservation and spatial policy in which little room was left for the development of new riparian systems (Provincie Groningen 1993, 2000). As a compromise, the provincial authorities proposed making a smaller ecological corridor, only 50 m wide instead of the 150 m in the Green River plan. The city of Groningen was also ambivalent, mainly because of the high costs. After intervention by the Green party in the city council, the city was forced to accept the Green River plan for this industrial area, with a width of 150 m in principle for the riparian zone. It is expected that substantial parts of the Green River plan will be implemented within a few years.
During the decision-making process on this regional and provincial level ecological knowledge played a role in legitimizing the concept of corridors, but on the operational level it played only a marginal role. For example, during one workshop towards the end of the decision-making process, the ecological backing of the Green River, particularly the width of the riparian corridor near the city of Groningen, was questioned without receiving convincing answers from ecologists and conservationists. Furthermore, according to usual practice, it is unlikely that monitoring programmes will evaluate the ecological functioning of the corridor (Commissie Beleidsonderzoek Natuur en Landschap 2001).
Thus scientists played only a minor role and it is still uncertain whether this Green River corridor will be adequate for the migration and survival of species. Nevertheless, Green River appeared to be an appealing metaphor that could unite the interests and values of multiple actors because it could fulfil several functions.