The variety of different habitats on Mitcham Common are home to many species of wildflowers and animals. It provides a diverse distraction from busy urban life, full of colours, sights, sounds and scents, in an area close to the heart of London. These habitats however require management to ensure that they do not degrade and lose their species diversity.
Acid Grassland Restoration
Lowland Acid Grassland is a priority habitat type in London where it is estimated there is 4% of the total national resource. It develops on low-nutrient, free-draining acid soils overlying gravels and sands and supports a distinctive community of insects and spiders – many of which are scarce. Unfortunately the vast majority of acid grassland has been lost to sports pitches and other amenity grassland, or has been neglected and allowed to develop into scrub and woodland. However it still survives in substantial parcels on Mitcham Common.
In 2009 the Common’s acid grassland parcels were entered into an Environmental Stewardship agreement with Natural England whereby the Conservators receive an annual payment in return for undertaking specific management tasks. These include clearing scrub and developing woodland together with rotational cutting of grassland. A more recent problem is nutrient build-up from dog fouling and atmospheric pollution which degrades acid grassland by favouring more vigorous species of grasses. To reverse this trend the top layer of soil is scraped away allowing the desired grassland species to re-colonise the nutrient-poor subsoil. There are several areas where these scrapes have already been created and it is a technique that will be used more often in the years to come.
Heathland was once widespread across London, but now little more that 80 hectares remain. Accordingly, as with acid grassland, it is now idenfitied as a regional priority habitat with targets to maintain what is left and create new areas. In London heathland usually comprises of heather with varying amounts of gorse. The latter, although a valuable component of heathland, can become dominate and shade-out the other species. Well managed heathland should not be unifrom in structure, but rather made up of a mosaic of mature and leggy heather bushes interspersed with carpets of young heather and bare ground.
Most of the heathland areas on the Common are on the golf course where it is under pressure from gorse and scrub shading. Here it is managed by cutting back allowing more light to reach the heather. The use of scrapes to reduce the nutrient content, as described above, is also used for heathland restoration. In 2007 a large scrape was dug and subsequently seeded with heather on the Mill House Sub-Site of the Common.
The three main ponds on the Common, Seven Islands, One Island and Bidder’s, all contain a variety of wildlife including amphibians, birds, dragonflies and varying numbers of fish. However, this balance can sometimes be lost as fish are illegally added to ponds.This affects other animals whose young become vulnerable as prey for fish. In addition, the increase in angling that large numbers of fish attracts can cause conflict with other users of the ponds. It can also generate litter and problems for birds becoming entangled in line and hooks. To reduce these problems the ponds are periodically destocked of fish.
Over time ponds fill with silt which reduces the area of open water and detracts from their appearance. To combat this the Conservators have a rolling programme of pond desilting. In 2008 Seven Islands Pond was drained, the silt removed and the islands re-shaped.
Apart from the obvious ponds, there are various seasonal ponds around the Common which dry up over the summer months. Here fish are unable to survive, meaning they are excellent for amphibians and invertebrates, and the fluctuating water level also provides opportunties for uncommon plants to exploit.
A good way of preserving the openness of the Common is to harvest grassland areas for hay, so tree species cannot colonise. Late every summer areas are designated for cutting, and the arisings are allowed to dry and be collected as hay. Whilst this operation is carried out, it is important to leave suitable adjacent areas uncut, to allow refuge for animals. This practice also removes nutrients from the system, which over a period of time will encourage more revered nutrient poor species to colonise, including acid grassland species.
There are some 35 hectares of woodland on the Common. Much of this is relatively recent in origin; although some of the boundary trees on the Gunsite are probably over 200 years old. The woodland parcels are very much valued by local users and without doubt hold considerable wildlife value. However in places the woodland and scrub has expanded at the expense of acid grassland and where this has happened future managment will seek to redress the balance by prevent further encroachment and in some parcels pushing the woodland boundary back. Elsewhere management will be largely non-interventional, apart for regular tree safefy inspections and the maintenance of existing glades.