In the search for common ground it would also be helpful if we could agree that the timber trade in the UK is not actually a rapacious, insensitive group of people intent on plundering the world's forests as rapidly as possible, without scruple or thought for tomorrow. I suspect they are generally somewhat bewildered by the onslaught from campaigning lobbies and would say that they spend time answering allegations which could more usefully be spent putting forward constructive plans to the producers, both at home and abroad.

Ladies and gentlemen - talking about trees, talking round trees, talking up, at, with, or even to trees is, I have discovered, a risky business. Nevertheless, on this occasion, it seems to me to be a risk worth taking - firstly because the question of sustainable forestry is an important one and, secondly, because I wanted to show my support for the process of communication which is taking place between the timber trade, environmentalists and other interested parties.

It may be worth starting by reminding ourselves that behind all the rhetoric (of which there is certainly no shortage!) there is much common ground. When all is said and done, I suspect most of us are thoroughly committed to the straightforward aim of achieving sustainable timber production from well-managed forests, even though there are bound to be differing perspectives on what constitutes an acceptable level of production, what systems of extraction should be used and what other criteria should be used in assessing good management.

In the search for common ground it would also be helpful if we could agree that the timber trade in the UK is not actually a rapacious, insensitive group of people intent on plundering the world's forests as rapidly as possible, without scruple or thought for tomorrow. I suspect they are generally somewhat bewildered by the onslaught from campaigning lobbies and would say that they spend time answering allegations which could more usefully be spent putting forward constructive plans to the producers, both at home and abroad.

Nor is it true, or sensible, to dismiss the environmental groups as irresponsible, ignorant, unelected 'green police', intent on wrecking a vital component of international trade. On the contrary, they represent an enormously significant trend in public opinion and carry out a good deal of high quality, professional and scientific research to back up their campaigns.

Perhaps we might also agree that wood is a simply wonderful natural material - strong, light, beautiful, easily worked and, ultimately, biodegradable. Forests can absorb carbon dioxide from the atmosphere, stabilise soils and regulate climate; they also provide a habitat for a high proportion of the world's animal and plant species, and can also strike an emotional chord in the human heart. It is, therefore, all the more depressing to be told that only a tiny percentage of the world's hardwood timber production can be described as sustainable.

I last spoke about forestry in a lecture at Kew, just over four years ago. I said then that I wanted to do what little I could to draw further attention to the precarious state of tropical forests, and to the unimaginable loss to mankind in general if we were unable, or unwilling, to reach agreement on a series of reasonable measures to halt the inexorable destruction which was taking place.

Since then the picture in the tropics has changed only slightly. In addition, concern is now being expressed about the fate of forests worldwide - not just in the tropics. This is partly because supplies of timber from the tropics are dwindling. To give just one example, the once vast forests of West Africa have been decimated. Nigeria, until recently the most important exporter of tropical hardwoods in the region, is now a net importer to meet its own needs. As a result, timber-hungry countries are increasingly turning to temperate and boreal forests for their needs and are finding a ready supply. This is particularly the case where the collapse of communist regimes in Eastern Europe and the former Soviet Union has resulted in a distressing scramble to convert the remaining old-growth forests into much-needed foreign exchange.

It is certainly true that the total forest area in many temperate countries is stable or actually increasing, but this is matched by a depressing decline in forest quality. Natural, old-growth forests are being cleared and replaced with the plantation monocultures known by the Canadian logging industry as 'tree farms'. Anyone who has driven through Caithness and Sutherland will know exactly what that expression means - even if the circumstances are different and the term itself is outdated!

This is not to say that I am necessarily opposed to the crucial commercial enterprise of plantation forestry. But it is the question of where and how those plantations are established that matters.

When I spoke at Kew I said that, with the tropical forests at such risk, it would seem to be eminently sensible to work towards the restriction of timber extraction to secondary forests - to those forests which have already been logged over in order to protect what little pristine forest we have left. I suggested that we could then look towards future timber needs being met from plantations established on the vast area of already degraded land.

It is, of course, just as desirable to operate on this basis where temperate forests are concerned. A short walk in the old-growth forest of New Zealand's West Coast, or in the tiny remnants of Scotland's Caledonian Pine Forest, followed by a brief visit to a plantation of 30-year-old sitka spruce will quickly demonstrate the reason - with or without a scientific survey of biodiversity! (And for the benefit of professional foresters and sitka-lovers I will add here that, in my opinion, an 80-year-old sitka spruce is a wonderful thing. But how many of us ever have the chance of seeing such a tree?)

Any form of plantation will always be a good deal less attractive, for wildlife and for people, than an old-growth forest, but as the Forestry Commission demonstrated to me last year at their vast Kielder Forest, a commitment to sustained good management can produce a degree of diversity and wildlife value, as well as productivity, even in a plantation forest which was developed with none of these things in mind.

Ladies and gentlemen, the environmental movement has been highly effective in raising public awareness of these issues. An increasing number of people do now ask themselves whether their purchase of wood or wood products is contributing to forest destruction and the loss of biological diversity. And they do ask whether or not they can rely on any of the wide range of assurances given by producers and manufacturers. And this doesn't just apply to individual consumers. It applies just as much to architects, planners and local authorities - many of whom are doing their best to respond to public concerns on these issues.

As a result of this public concern, various organisations set a variety of target dates by which certain categories of wood would be supplied entirely from sustainable sources. The most challenging and all-embracing (as far as I am aware) was set by the World Wide Fund for Nature in 1991 when it called for all wood and wood products from all forests to be based on sustainable sources by the end of 1995.

In this country the challenge has been taken up, so far, by 24 companies which sell and use wood and wood products. The 1995 group covers a wide range of companies operating in different sectors and I was pleased to be able to meet many of their representatives just now. It isn't easy to get out in front in the way that these companies have, and they are all encountering difficulties in working towards a challenging target, but they clearly believe there will be a commercial advantage in being ahead of the game, as well as recognition of their efforts by their customers and workforce - and I do commend them for taking a courageous decision.

In seeking to ensure that their supplies come only from sustainably managed sources, the 1995 group of companies are encountering a difficulty which I referred to in my speech at Kew in 1990. I said then that many people wished to be satisfied that tropical hardwood products came from sustainably managed forests - but that I couldn't imagine how we could be satisfied on that score without a proper labelling scheme. Well, I'm sorry, but four years later I still can't imagine how it can be done and I regard the creation of a credible, independent certification and labelling scheme for wood from sustainably managed forests to be a priority. Of course such a scheme is difficult to achieve; it will require an unprecedented degree of cooperation between the various interests to overcome a range of technical and communication problems, and it will need to take account of a wide range of regional differences. But the principle of such a scheme is not, I believe, in question.

I am quite convinced that this is one of those situations in which boycotts and bans will generally be ineffective and probably counter-productive. What is needed at the moment is a voluntary system which operates through market forces by adding value to timber which can be certified as being from a sustainable source.

I do believe such a system must be international in its application if it is to have any credibility. It really isn't good enough to suggest that it's probably right to have a scheme that operates 'over there', but not 'over here', on the grounds that we think we do these things rather well. Perhaps we do, but if so then we have nothing to fear from independent scrutiny.

Any such scheme is bound to have its detractors, from those who genuinely believe it is 'too difficult' to those who would much rather continue as they are, thank you very much. But I think the example of the Soil Association in certifying organic farming is quite instructive. This relatively small organisation recognised the need to certify the produce of organic farms in 1973. The symbol scheme was established to the kind of scepticism and muted hostility which brave people who try to do something new usually encounter. Less than 20 years later it was the Soil Association to whom the UK Government, and even the European Union, turned to draw up their own certification schemes.

It was therefore no surprise to me to find that the Soil Association is taking a leading role in timber certification and labelling. They have received substantial assistance from the UK Government's Overseas Development Administration for their work in developing countries and have already certified two woodlands in this country. The Soil Association's scheme operates under the auspices of the newly-formed Forest Stewardship Council, about which I know you will be hearing more later today.

As you will by now have deduced, I believe strongly in the principle of independent certification. Far from likening such a process to the attentions of the 'green police', I prefer an altogether milder comparison - with the work of the British Standards Institute. BS 5750 and, more recently, 7750 are now well known and widely sought after marks of excellence. No one is compelled to apply for them, but those who do are professionally assessed and, if successful, recognised as achieving a meaningful standard which gives them credibility in a competitive market. Indeed, I understand that the Canadian Standards Association is looking to develop such a scheme for sustainable forestry.

For the sake of completeness, I should also tell you that I have asked the Soil Association to inspect and, hopefully, certify The Duchy of Cornwall's woodlands near Liskeard, and that the Royal Household's timber suppliers have been asked to supply only timber which comes from independently certified sustainable sources after the 1995 deadline. So there!

In conclusion, perhaps you will allow me to reiterate that there is a worldwide, long-term need for sustainable forestry, but we are a very long way indeed from achieving such a thing. I believe we will only get there if two things happen. Firstly, governments, business and environmental organisations will have to adopt an approach based not just on cooperation but on partnership.

Secondly, consumer pressure will have to be enlisted to ensure that sustainably grown timber is worth more than the alternatives. And to achieve that we need voluntary certification schemes which are both independent and respected. It may take a long time to get there, but the time to start is now, and I hope that today's seminar will make a useful contribution to the process.

Sometimes, just sometimes, ladies and gentlemen, I have to confess to feeling an overwhelming sense of despair when confronted by the starkly terrifying statistics of forest loss throughout the world. I know all the reasons for it, as I'm sure you do; all the perfectly understandable excuses given for the apparently unstoppable destruction. The trouble is that the statistics seem so remote from our lives - a veritable case of 'out of sight, out of mind'. But what concerns me most about this whole business is how on earth are we going to explain what has happened - and the precious things we have lost from this unique world - to our children or our grandchildren? What are they going to say to us, or of what are they going to accuse us in years to come? I shall be able to say that I attended a few seminars and made a few speeches; got into a spot of trouble and controversy occasionally; was accused of being a crank of various sorts, but can't claim to have done much more. What about all of you, ladies and gentlemen? What are you going to say to your grandchildren who, by then, will have discovered that you can't recreate old growth forest or re-invent the extinct species that could possibly have provided great benefits for mankind?

Some of you here today I know, are doing a great deal to address these problems, but I am sure there are others who could still make a difference - even at this late stage. I wonder who will have the courage, or the temerity, or the far-sightedness, or the wisdom to do so?"