The Warden’s Report in the Winter 2020 Magpie, mentioned that the final phase of the Acid Grassland Restoration Project would occur shortly. The article referred to a map showing the location of the work, but unfortunately the map was omitted. Many of you will now know the location without needing a map, as the trees have been felled, though not yet removed.
Snow covered acid-grassland restoration area. In the foreground there are felled silver birch. Small oaks were also cut down.
The purpose of the project is to restore areas that were for a long time acid-grassland but that have gradually become overgrown.
The ‘acid’ in acid-grassland refers to the soils, which are acidic (as opposed to alkaline, chalky soils) and lacking in nutrients. Such soils, along with grazing, result in grassland that supports many rare species of insects and plants. Mitcham Common is designated as a Site of Metropolitan Interest largely because of the biological diversity found in its acid grasslands. Without grazing, such grasslands gradually return to forest and this has been the progression on the Common.
In the Sixties, the houses on Commonside East were easily visible from the Seven Islands Pond, but in the meantime the woods have grown, firstly as low scrub, brambles and gorse, then hawthorne and then oaks, which as they grow with the protection of the hawthorn, overshadow and smother the rest. The woods expand into the remaining grasslands, their seeds spreading gradually and the woodland edge advancing.
The end state of this progression, if uninterrupted, is an oak woodland with bramble, yew and holly (and little else) underneath. Oak woodland can be lovely, of course, in as much as it is accessible. But so are grasses, smaller plants and flowers. Many birds feed among the grassy areas, for example on the insects that thrive there. Kestrels may nest in trees but they hover over grasslands and feed on small mammals found there; green woodpeckers feed not on trees but on grassland anthills (which rely on sunshine); rabbits eat grass; hedgehogs eat snails and slugs on the grasslands and inhabit the edge of the woodland; foxes eat the rabbits. Without grasslands, much is lost.
Would anyone really want a Common that lacked a variety of habitats, such as a common covered in oak woods? I doubt that many would. So what do we do to maintain variety, to preserve the Common’s special scientific status? This management dilemma has existed for decades, but the acid grasslands and all their biodiversity will disappear under gorse, brambles and trees within the next decade if nothing is done. Look closely and you will see a multitude of saplings, brambles and gorse sprouting among the grasses. The existing woods advance continually towards the pond each year.
Hopefully this helps to put the recent clearance in context for readers. Though it looks unpleasant now, it will in due course recover and help to preserve the diversity of life on the Common. Readers are welcome to comment below. Comments will appear after a delay for moderation, so please be patient.
- Mitcham Common is not an SSSI but a Site of Metropolitan Importance – one grade down.
- Added a link to a booklet about acid grasslands from the London Biodiversity Partnership.
- Removed reference to hedgehog predation.