ORIGINAL PAPER Provision of ecosystem services by large scale corridors and ecological networks M. J. Samways ��� C. S. Bazelet ��� J. S. Pryke Received: 23 January 2009 / Accepted: 22 September 2009 / Published online: 10 October 2009 �� Springer Science+Business Media B.V. 2009 Abstract Large scale landscape transformation and contingent habitat loss are among the greatest threats to ecological integrity and ecosystem health. One of the mitigation approaches used to deal with these pressures is to leave interconnected corridors and nodes as remnant ecological networks (ENs) within the transformed landscape. The South African forestry industry has already allocated 500,000 ha, one-third of the plantation holdings, consisting predominantly of natural grassland, as ENs among and within timber plantations. These ENs are intended to maintain structural, compositional and functional biodiversity. However, little scientific research is available on the effectiveness of these huge ENs for biodiversity conservation and maintenance of natural ecosystem function, although initial findings are encouraging. While the local adverse effect of alien plantation trees on functional biodiversity is not in dispute, it is at the scale of the whole landscape where there is much interest in determining how effective these ENs are in maintaining the untransformed portion of the transformed landscape in a close-to-natural state. As these ENs are extensive, species beta diversity is a consideration in addition to alpha diversity. Initial findings reveal diminished ecological integrity in narrow corridors due in part to the adverse edge effect from the alien trees into the margin of the EN. Quality of the ENs is of great importance for maintaining functional diversity, with human disturbance reducing their effectiveness. First findings, and their application to the Framework for Ecosystem Service Provision, suggest that these ENs are significant for biodiversity conservation and for provision of ecosystem services. Nevertheless, still much more research is required on a greater range of taxa, and their interactions, to improve the design of these ENs for ecological and evolutionary processes. Keywords Ecosystem services Corridors Ecological networks Function Grassland Plantation forestry South Africa Mitigation M. J. Samways (&) C. S. Bazelet J. S. Pryke Department of Conservation Ecology and Entomology, Stellenbosch University, P/Bag X1, Matieland 7602, South Africa e-mail: Samways@sun.ac.za 123 Biodivers Conserv (2010) 19:2949���2962 DOI 10.1007/s10531-009-9715-2

Introduction Creative management approaches are required to avert further loss of biodiversity and to maintain the functional integrity of ecosystems (MA 2005). Ensuring connectivity between habitat patches for organism dispersal is important for mitigating loss of habitat and for reducing the effects of isolation of remnant habitat patches (Fahrig 2003). Connectivity may be in the form of a physical linkage, or corridor (Bennett 1999). Such corridors are now being built into landscape design for biodiversity conservation in urban and agri- cultural contexts (Smith and Hellmund 1993 Burel and Baudry 1995 Rosenberg et al. 1997 Jongman and Pungetti 2004 Nasi et al. 2008). This approach is based on consid- erable theoretical discussion of the value of corridors (Forman 1995 Bennett 1999 Chetkiewicz et al. 2006 Hilty et al. 2006), and their practical value (Jongman 1995 Boitani et al. 2007). A corridor has several functions for a species, which may vary from one species, and even morph, to another. A conduit for one may be a barrier for another, which may vary seasonally or according to a disturbance factor such as fire. In turn, different corridors in any one geographical area may have slightly different functions for the same suite of species. Corridors may be relatively simple to define, say, as movement corridors for a focal species (Hilty et al. 2006). However, when overall biodiversity is being conserved, inherent biological complexity of whole ecosystems becomes a major consideration. In short, no one corridor will necessarily benefit all ecological integrity, nor all natural ecosystem functions. Corridors may also have ���negative��� effects, by providing pathways for predators or pathogens. Conceptually, it is useful to know to what extent corridors within a transformed matrix can maintain biodiversity and whether they are sustaining the properties of dynamic ecosystems (i.e. durable, robust, stable and resilient Dawson et al. 2009). Furthermore, with increasing demand for understanding the function and dynamics of socio-ecological systems (Rounsevell et al. 2009), we can apply conceptual frameworks which help define and structure those variables which are important for the sustainable management of corridors. Two conceptual guidelines can serve as starting points in deciding what a corridor should accomplish: Firstly, the landscape can be envisaged as a large continuous piece of land. The ideal, and perhaps theoretical, outcome from instigating a corridor within the transformed matrix (i.e. an alien timber plantation) would be where the corridor contains the same biodiversity and provides the same functions as a similar-dimensioned array of land in an untrans- formed matrix such as a neighbouring reserve (Fig. 1). Secondly, Hess and Fisher (2001) provide a very useful conceptual framework for corridors based on six ���functions��� or attributes: (1) conduit (2) habitat (3) filter (4) barrier (5) source, and (6) sink. These functions may not be mutually exclusive, and depend on which species, even which morph or ecotype, is being considered, on the spatial scale being stipulated, and over a particular time scale. A focal corridor should be defined in terms of these functions, in relation to the focal species, or community. Generally, the aim of a functioning corridor is to promote the attributes of conduit, habitat and source, and not the other attributes. Improving connectivity for all species in an area, and their interactions under varying weather and climatic conditions, as well as maintaining long term evolutionary advantage, is a challenging task. One way to tackle this complexity and its variation over time is to establish a network of corridors, with the addition of nodes where they interconnect and 2950 Biodivers Conserv (2010) 19:2949���2962 123