The inspiration behind the Ghost Ponds Project begins with the story of Manor Farm, and the realisation of just how good farmland ponds can be. For this we have Richard Waddingham to thank. His dedication to protecting wildlife while running a successful farming business, showed us, not only that agricultural ponds can be fantastic conservation opportunities, but that when approached in the right way such conservation need not interfere overly with farming practices.
Manor Farm is located in north Norfolk, and covers an area of 243 hectares. The farm contains around 40 ponds, most of which are abandoned marl pits. Many of these ponds are located in arable fields, and initially seem unlikely candidates for diversity hotspots – they are relatively isolated from each other (no connecting ditches or streams), are surrounded by active farmland which is ploughed, sprayed and cropped regularly, and they are often rather small in size.
Despite this, surveys have shown the ponds to contain 20 species of submerged aquatic plant, 12 species of mollusc, 37 species of water beetle, and 19 species of dragonfly. In addition, over half the ponds support populations of great crested newt (Triturus cristatus), a UK Biodiversity Action Plan (BAP) species. This really is surprising diversity for any collection of ponds, let alone ones located in farmland – so what is the secret to their success?
Firstly, all of the ponds on Manor Farm are surrounded by buffer strips, of at least 5m width. The buffer strips consist of wild grasses and scrub vegetation, and have three main functions;
– The buffer ensures that spray from the field does not drift onto the pond.
– The uneven ground and fast growing vegetation found in the buffer strip provides an intercept, that reduces nutrient rich run-off from the fields entering the pond.
– The vegetation in the buffer strip provides cover for visiting wildlife, especially amphibians and birds.
This however is not the answer to why the ponds on Manor Farm are so diverse. Many farm ponds have buffer strips around them, but few are in as good shape as those on Manor Farm. What makes the real difference on this farm is that the ponds are managed.
Richard employs a heavy-handed approach to pond management. Every 4 years or so, 3-4 of the ponds are managed, to produce a mosaic of ponds at different stages of succession. Each pond is completely cleared of surrounding trees to the south and west sides, allowing all-important light penetration and wind mixing of the pond surface. In addition, large quantities of the old pond sediment are removed and spread on the fields.
This is a somewhat controversial management technique – many pond conservation advisors would warn against large scale tree removal, and sediment removal, for fear of the heavy disturbance it causes. However, one look at the ponds on Manor Farm shows quite clearly that this is not a problem. Trees soon return, and removal of some of the sediment helps break the anoxic conditions which can quickly build up in an overgrown pond, while also exposing the old seed bank from which pond plants can quickly regenerate.
Comparing the diversity of plants and animals found in the managed ponds at Manor Farm, with other non-managed ponds in the surrounding area, gives a clear message;
Plant, invertebrate, and beetle diversity were all significantly lower in unmanaged ponds compared to managed ones, and the significant decrease in diversity of pond communities related to increased pond shading. There was a tendency for pond diversity to peak 3-5 years after management, suggesting the importance of regularly clearing trees and removing silt build-up from ponds.
The managed ponds at Manor Farm are quick to recolonise; whilst active dispersers, especially dragonflies and water beetles, are the first to arrive at a newly managed pond (often within a few hours), aquatic plants are also quick to re-establish in large numbers. Considering the speed and scale to which aquatic plants re-establish in newly managed ponds, it is improbable that this colonisation should be due to seed dispersal alone, but is more likely to be due to the exposure of the old seed bank during sediment removal.
This poses an interesting question; it seems that the seed bank in an overgrown pond, which may have been completely tree-covered and devoid of aquatic plants for decades, can be stirred back into life and re-populate the pond. In this case, what about the seed bank found in the sediment of ghost ponds? This would have been buried when the pond was filled, and for all intensive purposes could be expected to be in a similar dormant state to the seed bank of an overgrown pond.
This forms the starting point for the Ghost Ponds Project – can the buried seed bank of in-filled ponds be brought back to life, and by doing so resurrect a more diverse plant community, in a shorter time span, than that created by digging a new pond from scratch?