Reversing ecological succession to conserve ponds

Posted on June 30, 2013

Ponds are key aquatic habitats, especially in cleared agricultural areas where they act as important high-biodiversity ”islands”.  However, pond habitats are increasingly threatened by  agricultural and urban development, pollution and invasions by non-native species.  Also relevant to conservation is the fact that ponds are not permanent habitats and are gradually transformed to swamp or wet woodland by the processes of ecological succession. In the face of these threats and changes, new ponds can be created to maintain biodiversity.  Alternatively, the terrestrialisation process can in principle be reversed by periodically removing accumulated sediment and cutting back fringing trees and bushes.  Although this option  hasn’t received much scientific attention, it’s been validated by the results of a study in Norfolk, U.K. , where environmental variables, aquatic plants and invertebrates were sampled in 28 managed and unmanaged ponds in an agricultural landscape.  Aquatic plant and animal diversity was significantly lower in ponds that had been left unmanaged over the period 1999-2009.  There was a tendency for diversity, especially that of aquatic plants, to peak three to five years after management, and then gradually decline.  In  unmanaged ponds, overhanging vegetation shaded out aquatic macrophytes, which reduced habitat opportunities for pond animals.  At the same time, the decomposition of fallen leaves and branches from the surrounding trees reduced the supply of oxygen and thus the faunal diversity of a pond.  

Reference:  Sayer, C. et al.  2012.  The role of pond management for biodiversity conservation in an agricultural landscape.  Aquatic Conservation: Marine and Freshwater Ecosystems 22,  626–638.