Introduced Trees

In recent years hundreds of thousands of evergreens have been planted by English gardeners, whether for hedging or as specimen conifers. Many of the trees sold here belong to a species called Lawson’s Cypress, which has been bred into a bewildering variety of cultivars and crossed with other cypresses to make such hybrid forms as the Leyland Cypress. The Western Red Cedar or Arbor-vitae is another common kind, and there are several others.

Most of these come from the western seaboard of North America. The climate there is mild and equable and ideal for trees: the giant redwood is one of the most famous inhabitants of the forests at California and Oregon.

Our own climate is also oceanic and in certain ways is even better for the growth of trees. What some people might not guess is that the tiny conifer bought today at a garden centre may – unless it is a specially-bred dwarf form – have the potential to grow to a height of a hundred feet or more.

The suitability of Britain for trees is not reflected in the diversity of the native tree flora. Britain was cut off from the rest of Europe at a fairly early time. This, together with the fact that the ice sheet came as far south as the Thames, combined to deprive us of many sorts of plants, including trees, that are common on the Continent, and our native flora only has about thirty-five species of trees.

However, conditions here are just about perfect for the sustained slow growth which makes the finest specimens, and our introduced tree flora is one of the most varied in the world – containing at least 500 species to be found generally, along roadsides, in parks and gardens, and over 1,200 more in special collections. One such arboretum at Westonbirt, in Gloucestershire, has no fewer than 540 different species.

Once started, tree-watching can become a compulsive hobby. All you need is a good book – trees have the great merit of not running or flying away when you get near them, and can always be revisited with a more knowledgeable friend if you are not sure of your identification.

The charm of trees is not easy to convey in words. Their obvious qualities of permanence, grace and silence lend them nobility. Each species has its own particular style, its own solution to the problem of life, that colours everything it does and every particle of its substance.

When you are examining closely, under a lens, a spray of pungent Incense Cedar, or a shoot of Hornbeam or Silver Maple, you enter another realm where normal scale does not apply. Each leaf is perfection, complete in itself. No matter how many times it is replicated, the quality is maintained, the flavour of the tree remains intact. The flavour extends to the shape the tree makes in the landscape, and here again each species is unique. An expert can tell one kind of poplar from another while passing in the train.

For tree-addicts there is no arboretum locally, and excluding Kew and the London parks, the closest collection of any merit is at the Savill Garden, near Windsor. Nonetheless, you do not have to go far to find unusual trees – probably no further than your nearest street-planting or municipal park.

Cassiobury Park, for example, is the next best thing to Watford’s own arboretum. Especially in the area near the Shepherd’s Road to Stratford Way path, there are many fine specimens of North American oaks – including Red, Pin, and Scarlet Oaks. To the east of this path are specimens of such exotics as Hupeh and Kashmir Rowans, Sweet Gum, Indian Horse Chestnut, and Monterey Pine. Nearby, standing with Cedars of Lebanon, is a young Giant Redwood and, by the croquet lawn, a Japanese Red Cedar.

Further down the hill is a Tulip Tree, and near the paddling pool are many Western Balsam Poplars; by the river, next to the children’s railway, is a single specimen of the Swamp Cypress, a native of the southern U.S.A. and one of the few trees in the world able to thrive with its roots submerged in water. The black, boggy soil by the Gade is perhaps the best place for it but even so it looks ill at ease, like an animal in a zoo cage, and you come to realise that it really has no business there.

However much fascination exotic trees add to the view, there are not many to compete with our own natives in planting schemes, formal or otherwise. The colours of the beech and oak are in complete harmony with the colours of English skies; and to these trees, and to the kind of forest they make, our native animals and lesser plants are completely adapted.

The exotic trees are comparatively lifeless. Some birds, including the Greenfinch, are slowly learning to exploit the sterile conifer hedges, but compare the number of nests to be found in a hedge of hawthorn or yew. Pressure on land is now so intense that there can no longer be much justification for planting alien species.

And, if you are thinking of buying a conifer this weekend, it might be a good idea to leave enough money in your will for your children to buy climbing irons and a pruning saw!

(Introduction to these pieces; see all)