I heard the other day (November 2010) that one of our British universities has set up a "DNA archive of endangered species". The plan as I understand it's to store the DNA in a freezer until, at some time in the future, clones can be created to replace animals that have become extinct.

Although this is a new technical twist, the concept is quite long in the tooth. There have been numerous attempts to re-introduce extinct species into our landscape - wolves to Scotland, and specific birds and butterflies to various localities. Sometimes they have succeeded in the short term, sometimes they have got out of hand and sometimes they have had to be constantly tinkered with to keep them working.

But the basic premise that most of these exercises seem to ignore is that all the living creatures in a given environment - from microbes to mammals - form a complex network of interdependences which either works or doesn't as a whole. Incomplete networks fail, and extinctions (other than by arbitrary extermination on the lines of the 19th century American bison shoots) usually indicate that the overall network is failing - in the sense that it has changed so it no longer provides the necessary niche for the species in question.

But that there's practically nowhere on Earth where something alive cannot be found - indeed it's recently been established that specialised bacteria live hundreds of feet down in the ocean floor sediments. So when a species becomes extinct another will almost certainly move in and take over the space. The grey squirrel - widely accused in Britain of evicting the red from its niche - is actually more successful than the red in the often highly unnatural woodland environment we have created. In reality, the red squirrel was declining in numbers - partly also due to disease - before the grey took over a largely vacated niche. But the red squirrel has cute ear tufts and the grey squirrel is "vermin" so we struggle to reverse what is in fact a perfectly natural adaptation of the woodland community to a changing environment.

I absolutely accept that the way we manipulate our surroundings - it often hardly merits the word "manage" - is probably triggering extinctions that would otherwise not occur so soon, and that's not something we should be complacent about. But maybe changing the way we interact with the environment at local level could be more useful overall than grandiose plans - ultimately rather reminiscent of "Jurassic Park" - for the piecemeal re-introduction of creatures that have become extinct for valid reasons. Not making such a mess in one's own back yard is less exciting as a "conservation activity", but it's at least as effective - and it can start small.

Wild bees are declining in numbers, which means fewer pollinators and thus fewer viable seeds, fruits and berries - less food for other creatures. Many other invertebrates are also becoming less common, in part due to the loss of wild plants on which they feed. So there's less food for insectivorous birds as well. A cascade of decline in diversity sets in - and current land management practices that often utterly ignore their effects on the wild are much to blame.

Hedgerows continue to disappear, and where they remain they're usually maintained using a tractor-mounted flail at whatever time of year seems convenient. But this can be disastrous. Not far from where I live is a roadside blackthorn hedge that used to yield masses of sloes - useful both for my wine making and as winter feed for many animals. But for the last few years it has been flail-trimmed in Summer between flowering and fruiting. The result is a thin hedge bearing no sloes. If it's trimmed in winter, a blackthorn hedge will gradually thicken with fresh growth and produce masses of flowers, and if these are left to bear fruit a huge number of creatures will make use of the hedge for cover and food, including around twenty moths and butterflies, shield bugs, small birds and rodents. But a Summer-cut blackthorn hedge is almost completely barren, and flail trimming leaves bruised, crushed and split twigs that facilitate attack by fungus. The problem is of course that hedge-laying is an almost forgotten and thus expensive art, and, unless laid properly, field hedges cease to be stock proof. Wire is cheaper, so the hedgerow has ceased to be a benefit to the stock farmer - it's become a drain on resources to maintain it for little direct advantage. So the quickest, cheapest way to keep the largely redundant hedge in bounds is used. It's an understandable change of attitude. But, sadly, improperly managed hedgerows may have little more habitat value than the wire that now fulfils their previous purpose for the farmer.

Excess use of agricultural herbicides and pesticides has - in some cases quite rightly - received a lot of publicity, but a much greater contributor to the decline in wild flowers has been the loss of traditional field margins. In many parts of Britain, a border some nine feet (3 metres) wide used to be left round the edges of arable fields. This was where the horse-drawn plough was turned at the end of the furrow, and, later, where the steam ploughing engine was placed. But with the advent of the diesel tractor these field margins were mostly reclaimed for planting, so a substantial niche for wild flowers was eliminated. It has been argued that field margins are a waste of good arable land, but as fields become ever larger the loss is proportionally reduced, so I for one am not convinced that re-instating field margins would seriously affect the balance sheet.

The loss of ancient pastures has made many once-common wild plant species rare. During the second World War huge areas of ancient natural pasture were ploughed up for crops. Such pasture as was later recovered by re-seeding is largely devoid of wild flowers both because the seed bank was disrupted by more than five years of ploughing and because the re-seeding grasses are more aggressive than their wild predecessors, reducing the opportunity for pasture flower species to re-establish themselves.

In any case, the way pasture is used has changed out of all recognition in the last century. Cattle are kept indoors for much of the time and fed on a staple diet instead of browsing freely, so when they do get turned out into pasture their changed eating habits may well have a different effect on the pasture plant community.

But the "countryside" is by no means the sole potential habitat for wild plants and animals, and farmers are by no means the most culpable in the continued loss of habitats. Between ten and 30 per cent of most urban areas is designated as public open space, and well over half of this is grassland not used as sports fields. Then there are the road verges. The total area is in the thousands of hectares per UK county. That's an awful lot of land that could contribute significantly to the wild flower population and support invertebrates, birds and other creatures. Sadly, it often doesn't - primarily due to the way it's typically managed by county and local councils. Typically, the grass is scalped almost to ground level by a gang mower every six weeks or so, whatever the time of year or the weather. I've done a local survey of the results in West Hertfordshire and discovered that, of over 60 grassland wild flower species found locally in places that are not mowed to the ground, only eight are significantly present in the open spaces mowed under this regime. Of those eight only four or five get to flower, and two or three to reliably set seed. This could be largely corrected by the very simple expedient of raising the height of cut on the mowers so the grass is never shorter than a couple of inches (50 mm). The mowing schedule could be maintained much the same. In a few years, low-growing wild flowers would arise from the seed bank and flourish, as they would no longer be regularly decapitated.

There's also quite a lot we can do ourselves, and if enough people make small individual contributions, they can lead to great changes - I suspect, greater than the odd high-profile re-introduction of some arbitrarily chosen creature into a habitat no longer fitted for it as a result of our activities. It's a good idea to plant wild flowers in one's garden to attract "wildlife". But if it forms no more than an island in the midst of a wild flower wilderness, it's not going to be enough to halt the decline. Most wild creatures prefer to move along corridors of congenial habitat - as we do (I guess we call them "roads") - and need a very good reason to make the leap across the open between isolated pockets of shelter and resources. Nevertheless, a garden with a good depth of grass and packed with wild and nectar-rich flowers is a good start, and if you can persuade most of your neighbours to do the same, the total difference can be significant.

Putting up bird feeders is really worthwhile, provided you also have enough dense shrubs nearby for the birds to use as a refuge. But it only really supports seed-eating birds. None of the packaged dried insect products from the pet shop are ideal for carnivorous wild birds, but a pile of decaying logs is invaluable. The fungi, insects and vertebrates that inhabit this are an integral part of the wild food web. If you use wood for fuel, you can also leave your fuel store partly open at ground level so it can serve as a wild life refuge while it's waiting to be used. I've had toads, frogs, hedgehogs and field mice living in my wood pile, and the insects bring robins and other birds down to feed.

So adjust your mower to leave the grass no shorter than two inches (5 cm) and pile the cuttings in a heap in a shady corner. And even if you don't use fire wood, a couple of dozen hardwood (deciduous) logs some 10 inches (250 cm) in diameter and about two feet (60 cm) long, loosely stacked directly on the ground under or near shrubs or trees and left to decay gracefully, will rapidly become populated with a huge range of wild creatures.

Plants need to be selected with care if they are to contribute usefully to the wild garden. Most highly cultivated garden ornamentals are pretty useless to bees, as scent, pollen and nectar have been sacrificed in favour of large bright coloured flowers that don't interest the bee at all. Cottage garden flowers such as single hollyhocks, lavender, rosemary and old fashioned roses are excellent bee plants, and also provide food for other creatures - squirrels love rose hips and hollyhock seed heads. Shrubs and trees are also necessary, both as refuges for birds and sources of berries and buds as food (thank you Bullfinch, for stripping one of my gooseberry bushes of buds!). A rowan or mountain ash tree (Sorbus aucuparia) is a good source of bird food when in fruit, and will fit in quite a small garden. It's not a big tree - maybe 15 feet (3 metres) in height and 10 feet (3 metres) in spread - and doesn't cast deep shade. If you have the space, an elder (Sambucus nigra) is excellent shelter and food for birds, but it does get large, dense and invasive. Both support quite a range of invertebrates too. Blackberry - wild bramble - (Rubus fruticosus) is also an excellent food source for bees, birds and rodents, but you need a lot of space for it, and the energy to keep it in bounds, as it spreads inexorably. If you don't have the space or the energy, a black currant bush is a good substitute. A bonus is that all these shrubs will feed you too if you get in first. But bear in mind that the ideal garden for wild creatures is probably more chaotic and crowded than elegant - just like the natural world, which is never neat and tidy. But it's vibrantly alive, and ultimately that's what matters.

So much for what can be done in a garden. But even if you live in the middle of town and have only a patio or a window box, you can feed bees and birds by judicious choice of herbs and wild flowers and by hanging up bird feeders.

Birds will cross barren wasteland to feed if we provide these facilities for them, but we're lucky if they nest in our gardens, as they're usually deterred by our close proximity. So we need as much as possible of the intervening - public - spaces managed properly too, to provide a larger congenial habitat. But I've seen publicly-owned grass being mown while larks were rising above it - strongly suggesting the presence of occupied nests - and in my locality the grass banks and greens under trees are regularly strimmed to bare soil. Such generalised wanton destruction is very common, and may indeed be perpetrated by the very same public bodies that fund or promote expensive "conservation projects" in designated areas. So as well as planting our gardens with wild flowers and providing food and shelter we must also be prepared to agitate strongly against negligent damage to the rest of the landscape by its appointed custodians.