The role of pond management for biodiversity conservation in an agricultural landscape

Debate surrounds the best way to deal with pond terrestrialization so as to maximize landscape-scale biodiversity. One way of addressing this issue is to re-set succession via management activities, but the merits of this approach relative to non-intervention and pond creation are little known. Manor Farm in Norfolk, UK, possesses around 40 ponds, and each year three to four ponds are subject to management involving tree (de-shading) and/or sediment removal. To determine the consequences of management for pond biodiversity, macrophyte and invertebrate communities were surveyed for replicate ponds covering four time since management categories: no management, and managed over the periods 19992003, 20042006 and 20072009. Macrophyte diversity was significantly lower in unmanaged ponds compared with ponds managed in 20042006 and 20072009. In addition, with the exception of Mollusca, invertebrate diversity was significantly lower in the unmanaged ponds compared with all the managed ponds. A tendency was evident for diversity to peak 35 years after management and for a subsequent decline in diversity (significant for macrophytes). No distinctive species assemblages were associated with the different pond successional stages, although several species were confined to individual ponds. Although many species were absent from the non-managed ponds, especially in the macrophytes and Coleoptera, few species were unique to these ponds. The principal driver of species turnover in the ponds was shade, which was negatively correlated with macrophyte cover. Shade was substantially higher in the unmanaged ponds, whose species-poor assemblages appeared to be a consequence of low oxygen levels. By arresting succession and restoring macrophyte-dominated early- and mid-successional ponds, management may have an essential role in biodiversity conservation. In pond-rich landscapes, where a high proportion of ponds are heavily terrestrialized, management provides a sustainable means both of preserving heterogeneity in the pond network and preventing the loss of large numbers of species which favour early- and mid-successional ponds. Copyright (c) 2012 John Wiley & Sons, Ltd.