Notes from an award winning Farm – Ponds
On many farms ponds have been drained and filled in. We have kept most of ours for their wildlife and scenic value, and still have nearly the same number of ponds as fields. There are four kinds of pond on the farm.
1. Mediaeval fish ponds, associated with a deserted mediaeval village.
2. Brick clay pits of the C17 and C18, usually close to buildings.
3. Marl pits of the C19.
4. Modern ponds dug for shooting or conservation.
The first and last types, the very old and the very new, are in low lying places where they are readily replenished by natural drainage, usually channelled into them through field drains or ditches. The opposite is true of the other two kinds. These were dug in places where they did not fill easily or quickly, to allow the maximum period of use. The old marl pits in particular are in the dry parts of the fields, sometims in the centre of flat fields, sometimes at the high point of sloping fields. They are difficult to keep filled during times of low rainfall and falling water table.
We owe most of our ponds to the clay subsoil. This was useful raw material in earlier centuries, and gave an impermeable surface to the resulting hole. This clay provided the material for baking bricks and tiles on site during the C17, C18 and early C19, until the railways and improved roads made transport easier in the mid C19. Similarly in the C19 clay was dug from marl pits and spread on the fields to replenish minerals used up by cropping. Both types, puddled by the feet of men and horses, subsequently filled with water and provided drinking pools for livestock.
Their method of excavation made them particularly suitable for this purpose. They were dug by hand with three sides nearly vertical, and the fourth providing a gradual slope up which loaded carts were pulled by horses. When subsequently filled by rain or rising water table, even a small amount of water would collect at the bottom of the slope and provide a useful drinking depth in periods of summer drought; the same effect gave useful water to the very end, and also provided a refuge for aquatic life.
All types of pond gradually fill with silt. Over the years in dry autumn weather after dry summers we have cleaned out most of them, removing up to 7ft of silt from the deepest. It is easy to trace the original slope and depth, black silt suddenly gives way to red clay. This was particularly interesting for the mediaeval fish ponds, now back to their original size and shape. We even found the old outlet, a hollowed out old tree trunk, and brought it back into use.
Cleaned out ponds hold a lot more water, and seldom dry out completely. Even in recent dry summers there has been some water at the bottom of the slope in most of them. To help top them up in winter, we channel field drainage into every pond we can. The run off from even a couple of acres helps significantly.
After cleaning out we restock with aquatics. Hornwort, bogbean, fringed water lily, pond weed and duck weed are our usual mixture. They spread rapidly from small beginnings. The following spring we put in toad and frog spawn, or their tadpoles. Many an overcrowded garden pond has supplied us with its surplus, and we get adult newts from the same source.
The pond edges get enriched too . Severat kinds of reed, rush and sedge go into the shallows, with yellow flag and watermint. Along the banks we plant teazle, purple loosestrife, yellow loosestrife, water aven, figwort, yellow fleabane, lesser spearwort, brooklime, ragged robin, and others wherever conditions seem appropriate.
Old marl pits provide the majority of our ponds. They are usually out in the field well away from any hedge, and cannot be connected to wildlife corridors. To enhance the appeal of these isolated ponds, we fence off a small area up to quarter of an acre on the North side, and plant with trees and shrubs. Our usual scheme is a clump of oak with a few deodar and Norway spruce, surrounded by smaller flowering trees and shrubs. Wildlife quickly moves in. By the second spring mallard, pheasant and partridge may be nesting in the dead herbage, and once we had a brood of tufted duck. Moorhen tend to wait until the clumps of rush or yellow flag are big enough to hide a nest.
Herons are a menace. Our resident heronry warmly approves our pond programme, and herons descend by the dozen when toads and frogs are gathering for mating. This seems to happen over a period of 24-48 hours, but on different days for each pond. We find it necessary to loop string round bamboos about a foot above the edge of the water. This effectively deters the herons, which otherwise clean out the breeding stock of amphibians.
None of our ponds are of the irregular shape, with little bays and inlets, recommended as best for wildlife. They are nearly all too small, and even when we enlarge or dig a new one, we find the low water level a problem. Modern field drains are usually laid 3 feet deep, and the pond outlet has to be a few inches lower, to keep the inlet drains running freely. With the water level at least 3 feet 6 inches below ground level, a little inlet with sloping sides become a major excavation, and quickly dries out in summer if left shallow. This is a problem we have yet to solve.
Improving ponds is probably our most expensive form of conservation. The post and rail fencing around the planted area costs hundreds of pounds. We find barbed wire unreliable against stock, particularly in dry summers when the grass on the other side is really greener. Cleaning out ponds requires contractors’ plant, rarely used for less than two days. Even if nothing is charged for the cost of farm labour to erect fencing or to clear and spread silt, the cost is over £1,000. Digging new ponds is even more expensive. However, the effect on wildlife makes all the cost and effort worthwhile. Each pond becomes a focus of interest in fields with nothing else but grass or crops. Wildfowl provide interest throughout the year, and amphibians in spring and summer. The wild flowers are a delight after so many years without them. Moreover, in sheltered locations, they attract a wide range of insects, with dragonflies, hoverflies and butterflies particularly noticeable.
The most dramatic effect was with a small pond dug six yearsago in the SW corner of a sloping field, fed by new field drainsrunning into it. We left a strip about 5 yards wide all around it, a total lengt of about 100 yards, and sowed a mixture of perennial grasses and wild flowers. Sheltered by tall hedges from the prevailing SW wind, this small area now has the healthiest butterfly population seen on the farm since the war. Eight species breed, another ten visit, and large and small Skippers fly in scores. The Small Skipper did not flourish until we stopped cutting the hedge each autumn. Then its number soared. We had clearly been destrying the tiny hibernating caterpillars inside their tall grass stems of Yorkshire Fog.
Plans are to repeat this process on a bigger scale in an adjacent field next to a new small wood. We hope the combination of habitats will prove attractive to a wider range of species.