Some of the best places for the naturalist are those that, on the face of it, seem the least promising or prepossessing.
The Holywell industrial estate, on the borders of Watford and Croxley Green, is an example. Until the recent redevelopment of Dickinson’s Mill and the expansion of the rest of the estate, it was always worth a visit, especially in the evenings and at weekends when not too many people were about.
The expanse of mown grass, in season, sometimes produced passage wheatears. The thistles and burdocks attracted many cardueline finches – mainly goldfinches and linnets, but also redpolls. The streams, ditches, and wet thickets provided breeding for blackcaps and sedge warblers, with woodpeckers in the older timber.
A sizable birchwood at the end of Greenhill Crescent – good for fungi in the autumn – has now vanished and its site is buried under factories. The area of woodland and scrub between the Sun Printers and the canal has been razed, destroying a number of notable botanical sites.
Not far from the old Sun Printers clock tower, for instance, among the concrete foundations of a derelict building, was a good variety of grasses, some common and others less so, but all growing untrampled and undisturbed. The surrounding scrub, neglected for years, was, thanks to the buddleias, sallows, and other shrubs that had established themselves there, one of the richest places in the district for butterflies and moths. The waste ground yielded many interesting exotic and alien plants, notably a colony of cypress spurge and, not quite so unusual, but colourful in the late summer, a mass of purple toadflax along the wire fence of the Post Office compound in Ascot Road.
The uses to which man puts the land are often, if not usually, detrimental to other living things. But, immediately his intervention stops, nature begins to take over again. Within a week of its opening in 1973, a new section of the Watford road system had been invaded by several species of weed, growing in cracks between the brand-new concrete blocks.
The new factories, once they have served their purpose, will eventually fall down. Whether it lakes fifty years or five hundred, nature will get the land back.
At the edge of the Holywell Estate this process can already be seen in action. The old railway line from Oxhey to Rickmansworth was dismantled in the seventies. No longer sprayed or weeded by the track crews, the shingle bed, running beside Croxley Moor for much of its length, quickly became home to a great variety of beautiful wild flowers. Among these were Pyrenean and long-stalked cranesbills, fumitory, moon- daisy, valerian, and two species of poppy – nothing especially rare, but all plants which are less and less easily found these days.
A little further along, the course of the railway runs between a small marsh on one side and the river moor on the other. Part of the moor has been dug for gravel, leaving a network of flooded pits. The water vegetation has encroached on the embankment and the track itself, and a yard or two from the shingle is a reedbed with nesting reed warblers. When the air is momentarily quiet, the breeze in the stems generates exactly the same magical rustling that can be heard in the vast, wild marshes of the Danube or the Camargue. If the warblers are singing the illusion is complete.
The track has also been invaded by trees. The young alders and willows form a corridor lined in spring with catkins. Elsewhere there are birch saplings, lots of them, providing shelter for insects and winter food for birds. The birch is a pioneer species, always ready to colonize vacant ground. It is tough, hardy, but short-lived, and provides shelter for more durable trees that come in its wake. Already there are several small oak trees among the birches; if left to themselves they will continue to grow for centuries.
The absence of maintenance has allowed a hawthorn bush to develop into a huge, densely thorned mass, ideal for nesting blackbirds and long-tailed tits.
If you squat on your haunches, or better, kneel down with a lens, there is another, miniature flora to be seen on the thin soil that has already accumulated on the surface of the roadbed. By the end of February the tiny white flowers of whitlow-grass are in bloom, supported on threadlike stems no more than an inch or two high. Later come other dwarf flowers, all adapted to exposed conditions or thin soil. Among these are both our native species of sandwort, with minute flowers which can only be dissected by means of the finest needles.
Where the line used to cross a small stream there is a little bridge in grey engineering brick, which now supports a microscopic flora of its own. Besides the velvety cushions of moss there are grey lichens, strange organisms which share the characteristics of both fungi and algae. And then, yet further along, the mortar of the bridge over the canal is home to a colony of a curious little fern called wall-rue. Swallows nest under the bridge, swooping in and out through the echoing space above the water.
Or at least they used to. There are new earthworks going on now, and lorries rumble back and forth over the bridge. This spring the swallows will probably choose another site. But, so soon as the lorries have gone – next year, the year after, or even the year after that – we can hope and reasonably expect the swallows to come back.