Saturday, 15 February 2014

A changing urban landscape

Whilst preparing a short article on spring hoverflies for the UK Hoverflies Facebook group it struck me just how much spring has changed in London over the past 40 years. That thought process took me on to other changes in that urban environment that are equally striking.

I grew up in Mitcham (south London) and was extreley fortunate to have Mitcham Common on my doorstep. From a very early age My friends and I built camps (on the ground and up the bigger trees), searched for caterpillars and messed about in the pond. At the time, there were vast acres of open grassland. I now realise this grassland was actually pretty important; it was a last vestige of the grass heaths that once populated many of the Thames terrace gravels that made up the commons of south London. So, although I lived in what might be assumed to be an urban environment, it was in effect quite rural and I was introduced to many interesting facets of natural history.

What I remember best is the ease with which I found the caterpillars of many moths – lots of lime, poplar and elephant hawk moths, and even the occasional puss-moth. The other abiding memory is the sound of a singing skylark over Mill Hill, the kestrels nesting in an old crows nest and the stone chats singing from the top of gorse bushes. Reed buntings bred there too, as did plenty of linnets and goldfinches. During the winter we would occasionally be blessed with the wonderful sight of a short-eared owl hunting over rough grassland, and I remember great excitement when a long-eared owl was discovered (I failed to see this).

Those days are long-past. The skylarks, stone chats and reed buntings are simply ancient records in reports on the ecology of the common. Occasionally, a kestrel hunts on the common, but I cannot recall the last time I saw one. I suspect a list of the losses would actually be considerably longer, as I have made no real attempt to log birds or to make a special effort to look for the unusual visitors such as willow or marsh tits.

The most striking aspect of change is how the traditional birds of the British countryside have disappeared and have been replaced by an assortment of opportunists and recent colonisers. Forty years ago, magpies were pretty scarce and it was a point of interest to find a nest; today I've seen as many as a dozen on the roofs of houses and trees around my mother's house. I well-remember first encountering ring-necked parakeets at Hersham whilst fishing a favoured stretch of the River Mole. That was a huge surprise. Today, there is a very large flock of a couple of thousand parakeets that roost on the common! They have replaced the millions of starlings that once streamed out of London and roosted on the common, but use very different trees. The starlings favoured the hawthorns in dense woodland whereas the parakeets like the tall poplars.

Others in the ascendancy include Canada geese, which now breed in considerable numbers on the pond; much to the detriment of the native mallard that struggle to bring up a spring brood. I think the geese are a definite problem from an ecological perspective. They range quite considerable distances from the pond, grazing the adjacent grassland to a few millimetres high and covering it with droppings. The phorbs in the grassland seem to me to have substantially declined within a radius of 50 metres of the pond – so several hectares of grassland has been affected.

Meanwhile, the fantastic acid grasslands are invaded by scrub and especially a very vigorous bramble that I think can only be a hybrid of a vigorous cultivar. Turkey oak is also springing up all over the place. It is quite a revellation because at one time there was just a single Turkey oak on the common, and it was felled a long while ago – well before the recent seedlings could have been propagated. So, where do the seed sources come from? It suggests that birds (presumably jays) must fly considerable distances before hiding their stash of winter supplies. Interestingly, the grasslands are also invaded by honeysuckle. To my untrained eye it looks like the native Lonicera periclymenium but it has escaped the woodland and is now invading vast patches of grassland.I don't recall seeing this problem anywhere else but perhaps other observers know of similar problems.

This is almost something out of a horror movie as the march of the aliens threatens to overwhelm a fantastic oasis of nature. The other amazing invader is spindle – normally a species associated with Chalk downland, but in recent years clumps have been springing up in the acid grasslands. This too is a potentially troubling addition to the army of invaders. On a more positive note, the majority of the Japanese knotweed has been eradicated!

I've studied the ecology of the common for most of my life and have published several accounts of its invertebrate fauna. It was, and still is (in places) a very special place that I think probably should have been designated as a SSSI. Certainly I think there was a strong case in the context of the ecology of London and the degree to which the site had been documented (as far back as a flora in 1911). Whether that case can be maintained today is a matter of debate. It probably still ranks as one of the most important grasslands in south London but it is under siege from a variety of forces. The Warden and his team battle valiently, but it is a huge job.

So, what is the lesson that can be drawn from this musing? Well, what really strikes me is how the study of the Common has changed. In the 1950s, 60s and 70s there were several local natural historians who regularly recorded the plants and animals of the common. The great, late, J.E. Lousley published an account of the flora in the 1970s; my late father published an account of the birds around the same time; various notes on the entomology of the common were published by the late Len Parmenter; and I know that Alan Stubbs recorded there on several occasions. The common was also a 'constant effort site' monitored by two local ringers (Mike Netherwood and Mick Cook). In the 1980s there was a comprehensive ecological survey (that I led and edited) and in the early 1990s both David Lees and I recorded Diptera, Hymenoptera and Lepidoptera from the common. It has a long history of recording. Who studies the common today? I cannot recall the last time I saw somebody out birding and it is noticeable that there are rarely any posts on iSpot of plants and animals anywhere near Mitcham. It almost seems as though that fantastic wild asset has been abandoned by natural historians.

I feel sure the invertebrate fauna is still interesting. There are numerous interesting plants to see (e.g. petty whin, spiny restharrow and dwarf gorse). There is also plenty of scope for the inquisitive natural historian to start to record what currently exists, so as to provide a baseline for future analysis. We know the botanical interest in 1911, the 1950's to 1970s and 1983-4. Modern digital technology could make it possible to make much more accurate analyses of the flora; and digital photography allows us to compile very accurate pictures of the changing ecology of a site. What seems to be lacking is anybody to pick up the opportunity.

There seems to be no lack of people interested in wildlife, but instead of taking on a local patch, many of them seem to pursue lists of what they have seen purely as an end in itself. If we are going to make a better job of conserving the country's wildlife we need a renaissance of interest in the study and recording of a local patch. Mitcham Common is just one of several south London Commons that would benefit from renewed interest by local natural historians. I expect there are sites across the country just crying out for their own recorder and champion!

also see

Syrphing Time

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