MAN-MADE habitats vary enormously in type and interest. They include derelict building sites, gasworks, markets, river banks, car parks, and road verges. Marshalling yards and docks are rather different. Best of all, from the variety of wild life to be found there, are dumps and sewage works, and best for birds are waterworks and reservoirs near towns. Once permission to study in these areas has been obtained, the way is clear for absorbing and valuable work.
DERELICT SITES AND WASTE GROUND
Plants and seeds reach derelict areas in strange ways. Nearly a hundred years ago a survey was made by a botanist of five waste sites in London, all of them in or near the city. Seventy-eight species of plants were found, and thirty-four of them – the biggest single group – were thought to have been distributed from horses’ nosebags. Seeds were dropped from them and then grasses and cereals developed. The wind brought many other seeds, such as willow herbs, coltsfoot, dandelion, groundsel, ragwort, sow thistles, and fleabane. The seeds of five common weeds were brought by birds – shepherd’s purse, swine’s cress, mouse-eared chickweed, common chickweed, and knotgrass. And then there were twenty-four plants apparently escapes from flower gardens or vegetable plots, ranging from opium poppies to cabbages.
Widespread interest in derelict sites was aroused during the Second World War, by the spectacular invasion of London’s bombed sites by plants and animals. Within a year of the first German bombs on the city, some of the devastated areas had turned almost into gardens, and by 1952 the list of wild flowers, grasses and ferns had risen to 269 varieties. It has been said that the Irishman’s dream of London as paved with silver and gold came true, for the bombed sites were covered with silver (Canadian flea bane) and gold (Oxford ragwort).
First of the plants to appear were algae, mosses and ferns, because the spores of these plants are always in the air, ready to colonize whenever an opportunity occurs. The wind brought many light seeds, especially those of the colourful rosebay willow herb. Sandbags brought for defence purposes contained the seeds of grasses and even seaside plants. Horses’ fodder still contributed some kinds, but more came from discarded bird seed and pet food. Office workers in the city started having their sandwich lunches on these sites, as they grew attractive, and so an odd assortment of edible plants began to grow, from apples, tomatoes, plums, dates, cherries, and even figs. Many of these lunch-time visitors scattered packets of garden seeds over the areas. Generally it is a mistake to do this, as alien seed in wild areas may thrive at the expense of other native plants and may even become run-away invaders. But on the London sites they did no harm. Stranger seeds were brought by passing cars. Some species from America seem to have come on the tracks and tyres of military vehicles and tanks. Butterflies and moths soon followed the plants. The caterpillars of the red and black cinnabar moth fed on the leaves of ragwort, and those of the elephant hawkmoth on rosebay willow herb. Rats, mice, cats and stray dogs were numerous, and other animals included hedgehogs, tortoises, lizards, snakes, and lost or discarded pets. It was at this time that the black redstart became noticed as a breeding species in London. A well-known garden shrub, the buddleia, only introduced into this country less than a hundred years ago, became a very common sight on derelict areas.
Today building sites may be less rich in flora and fauna because they are not usually left undisturbed for long periods. But there are some new factors that make investigations into waste land just as interesting. It is known that trains carry seeds from one area to another -the Oxford ragwort appears to have been spread in this way – but what is not certain is how the replacement of steam trains by electrically driven ones will affect the plant life of railway embankments. Hot ash thrown on to the embankments, in the days of steam, burnt off much of the scrub and allowed flowers such as primroses and cowslips to thrive. Nowadays this may not be the case. Nor do we know just how important is traffic as a method of seed dispersal. In June 1968, an investigator tried to test this. He used a car the tyres of which had been scrubbed clean, and then drove it 65 miles after heavy rain along roads in the South Midlands, and finally hosed it down and collected the sediment from the wash. Then he used sterilized horticultural compost to see what would grow. He obtained seedlings from 13 different flowering plants, including 387 seedlings of annual meadow grass, 274 of chickweed, and 220 of rayless mayweed or pineapple weed. Ships are well known to carry cargoes of unexpected seeds and insects. What about aeroplanes? Will they bring plant stowaways? It seems we are unlikely to take or get accidental plants from the moon, but if space ships ever visit Mars or any planet where there may be life, strict precautions will have to be taken, in both directions. All this needs watching.
NEW HOMES FOR WILD LIFE
Rubbish tips are extraordinarily interesting as a habitat for wild life. Grapes, melons, tomatoes – these plants were found growing on a tip near London fifty years ago. In a survey of five of the biggest London tips, two hundred and fifty different plants were found. Many of them were native British species, but 170 of them were aliens, brought from all sorts of places. There was a forest eight feet tall of giant hogweed and great docks. There were many different cereals, probably from chicken food, and garden flowers such as delphiniums, hollyhocks, mignonette, and night-scented stock. Escapes from vegetable gardens then included lettuce, beetroot, spinach, and artichokes. There were surprising plants from Africa and India. This was many years ago, but more recently very detailed work has been done on rubbish tips in many parts of the country. This shows that although conditions vary enormously, as there are different methods of dealing with the material brought, and the refuse itself varies so much, many forms of life can be studied on tips, whether you are interested in algae and mosses, fungi, British native plants, alien plants, insects, birds, or soil animals. There is more diversity on a refuse tip than on any other area of the same size anywhere in the country.
Apart from the interest of finding and identifying various forms of life, these refuse dumps give opportunities for working on many interesting ideas. As an example, we can take the question of plant dispersal and establishment. The succession of plants on a dump is interesting – the first plants to colonize, the changing conditions and how they affect subsequent plant life, and the final result. The ways in which plants exploit themselves to adapt to what are really very artificial conditions of life for them are fascinating. In any other form of life we should consider them very clever. For instance, creeping thistle is a troublesome weed, in many areas, especially in ploughed land. But the roots of the thistle are of such a kind that they really like being cut up and dispersed, so that ploughing, and other hard work intended to get rid of weeds, actually increases their possibilities of survival and increase. This might happen on rubbish tips – the more disturbance on the tips, and the more the plant roots are chopped up, the more plants you would get. Similarly, couch grass spreads by rhizomes bearing buds at the nodes, so that breaking up these slender parts leads to more, not fewer, plants. The more effort you put into trying to get rid of them, the more likely it would be that they were able to spread. An even better example of what one would like to call applied intelligence is seen in the common weed known as fat hen, or goosefoot. It is an annual plant, and produces many seeds. But these seeds are not all alike in their behaviour. Some of them germinate immediately after harvesting – that is, they do not show dormancy. But other seeds from the same plant do show dormancy. They may lie buried, and then when disturbed they may react to the cold; they may germinate in response to the cold. Some of the seeds are brown, some black; some smooth, some reticulated, and they may all have different times and conditions for their germination. In this way fat hen is sure to go on living, as a species, because it is not restricted to one set of conditions before it can reproduce itself. Few animals (except man) can do this. It is as if a jungle animal, such as a lion, could produce twins, one able to thrive in the tropics, and the other in the Arctic.
Visits to refuse clumps would be very useful if you intended to become a chir opt exist – that is, a student of bats. Your first reaction might be to go to church, to find your bats; but in practice a refuse dump might provide better chances of your seeing them. Insects are plentiful there, because of the refuse and garbage, and these insects in their turn will attract bats. The pipistrelle bat is by far the most common species in Britain, but other kinds found on dumps include the noctule (common in southern England and Wales, less so further north, and nowhere common in Scotland), the serotine, also mainly in parts of southern England, Daube?iton’s bat, fairly common everywhere, and Leisler’s bat, locally common throughout Britain. Brown rats are everywhere and will eat amost anything. Mice may also be very numerous. On one site of seven acres in Essex, it was thought that the population of mice was about 30 in winter and between 700 and a thousand in autumn. Lizards may also be found, sunning themselves on warm surfaces, as well as frogs and newts, and natterjack toads may be more frequent than has been realized. Regrettably, abandoned pet dogs often appear on tips, famished and neglected, as they do round litter bins on motorways.
The effect of tips on bird life has been to provide many of them with a new and favourable habitat. It seems that certain species need open surroundings in which to establish breeding territories, and in default of more ordinary sites some of them have moved on or near to tips. Examples given are wheatear, whinchat, skylark, tree-pipit, corn-bunting, and reed-bunting. Insects will attract other birds, weeds and plant garbage still others. Scavenging birds include all members of the crow family, including rooks, jackdaws, and carrion crows. Starlings are nearly always present in hundreds if not thousands, and the availability of food on the refuse tips appears to have had a marked effect on both the numbers and the behaviour of gulls. The great black-backed gull, at one time almost entirely a maritime bird, now is a regular winter visitor inland, and both the black-headed gull and the herring gull have greatly increased in numbers. The common gull also appears in large numbers, especially in passage between February and April in parts of eastern England. These four species are nearly always present on the larger dumps in the east and south. The remarkable feature of their presence is not so much their numbers as the immense journeys they make every day from their distant evening roosts on the north London reservoirs or on the coast of east and southern England, to refuse clumps as far away as Cambridge and Bishop’s Stortford. In other parts of England they make similar journeys.
On the whole it is probably true that the refuse dumps regularly attract large numbers of fairly common birds, but the rarities and the shyer birds with more specialized requirements are not usually to be found on them. This is not true of that other great artificial man-made habitat, the inland waters and especially the reservoirs near London (elsewhere in the country to a lesser extent), and also sewage farms and gravel pits. The pick of the year for Londoners would certainly include visits to some of these areas. Man is often thought of as the great enemy of wild life. It is true he is busily destroying many natural habitats, but his activities are not all damaging. When he destroys homes for wild life he often creates new ones.