Illustrated Encyclopedia of Trees

North American readers come to this European book from a privileged position and a different viewpoint. In the first place, the native tree flora of the North American continent is immensely rich and varied where that of Europe is small and reduced. Natural woodlands across temperate America regularly exhibit a fine array of different trees all growing together. In Europe they tend to be dominated by a few or sometimes monotonously only a single species. The reason for this difference lies in the last Ice Ages and in the different conformation of our mountains and valleys. In North America, the principal mountain ranges run north-south. As the ice descended from the north, plants were able to retreat before its advance, and then repopulate their old territories once the ice retreated. In Europe the major physical barriers lie east-west: the Alps, Pyrenees, most other ranges and the northern shore of the Mediterranean all barred the way to plants' retreat before the ice, condemning the majority of warmth-needing species to extinction. When the ice retreated, far fewer plants had survived to advance northwards again. Of those that did, the trees most adaptable to different soils and conditions were able to form dominant colonies with less competition. For the time being, the post-Ice Age botanical landscapes were established - wonderful variety in North American woods and forests, not in the European. And away from parks and gardens, this is still the situation today. But in compensation, the Europeans have been active for centuries in collecting trees from other parts of the world and bringing home the seeds of unfamiliar species - to Germany, France and Holland but most of all to Britain. From the late seventeenth century onwards a passion for new trees provided commercial impetus for collecting expeditions launched by individuals, botanic gardens or the tree nurseries themselves such as Veitch. As a result, warmed by the Gulf Stream and favoured by a moist maritime climate without extremes of heat or cold, more tree species can be found growing today in Britain and Ireland - and usually growing better - than in any comparable area of the temperate world. The vast majority of tree species growing in the great British and Irish gardens, both public and private, are therefore exotic species, or cultivars of them. They include by far the widest coverage of American trees in the world outside North America itself, but also trees originally from all other parts of the temperate world. The British Isles have thus come to form over the centuries something of a 'warehouse' of the world's cool-climate trees, and a Mecca for tree-enthusiasts everywhere. Note that throughout this book, we exclude of course the tropics, where over three-quarters of the world's flowering plants are to be found - but see page 15. Flowering plants (Angiospermae) began to appear about 120 million years ago. They completely dominated the earth's vegetation in the following 30 million years. There are reckoned to be now over 250,000 species, three quarters of which are tropical. All trees are classified as flowering plants. Even conifers have primitive structures that resemble flowers and serve the same reproductive purpose. Many garden trees are 'cultivars'. This means in broad terms that they have been first produced by human selection from chance seedlings and have ever after been propagated vegetatively so that their individual characteristics are perpetuated rather than lost again in a genetic 'soup'. They may be grafted, layered, grown from cuttings or replicated from their tissues in a laboratory. It is as if a red-headed Scotsman could be selected and conveniently reproduced, a process now less distant if not yet imminent. A new vegetatively produced plant will furthermore begin flowering at an early age, unlike many seedlings whicWhite, John, Jr. is the author of 'Illustrated Encyclopedia of Trees' with ISBN 9780881927511 and ISBN 0881927511.