Collins Complete Guide to British Trees: A Photographic Guide to every common species. Paul Sterry

       The damp environment with which Alder carr is associated allows ferns and mosses to thrive in abundance.

      NATIVE SCOTS PINE FOREST

      Visit the Highlands of Scotland and you will discover remnants of the ancient Scots Pine forests that once cloaked the region; these areas are often referred to as Caledonian Pine forests. In contrast to the relative paucity of wildlife found in most regimented conifer plantations, there is plenty of wildlife to find here. In Britain, Crested Tits are found only in these forests and the Scottish Crossbill occurs nowhere else in the world. Pine Martens and Red Squirrels also occur in good numbers.

      Native Caledonian Pine forests are typically rather open, comprising trees of varying ages, including many dead and dying individuals of course. Typically there is a lush ground cover of Bilberry and mosses, with botanical highlights that include several wintergreen species, Twinflower and Creeping Lady’s-tresses, the latter a charming if diminutive orchid.

       Native Scots Pine forests are typically light and airy, with an understorey of Juniper and Bilberry.

       Twinflower is a scarce but enchanting botanical highlight of a few Scottish forests.

      ALIEN CONIFER FORESTS

      If you encounter conifers in Britain outside the native range of the Scots Pine in central Scotland, then (with the exception of a very few Yew woods) their occurrence will not be natural. Regimented plantations are easy enough to spot, with trees of uniform age planted a standard distance from one another. But even isolated clumps of Scots Pine found on a southern heathland are at best going to be naturalised trees, their seeds having spread from nearby plantations.

      Does the fact that most conifers in Britain are introduced matter? In the case of isolated trees or small clumps, perhaps not. But, when it comes to the impact upon native habitats and wildlife, then plantations are a different matter. The dense manner in which they are planted effectively destroys the natural vegetation that once existed there – just think of the scandalous destruction of areas of Scotland’s Flow Country if you are in any doubt. But even naturalising conifers can be a threat, endangering already diminishing areas of heath-land.

      The benefits of conifer plantations to a select band of birds – Crossbills in particular – is often cited in favour of tolerance, although of course not all planted conifer species produce cones that are accessible to these birds. However, anyone willing to take an overall ecological view of the process, rather than trying simply to look on the bright side of things, will realise that the losses, in wildlife terms, heavily outweigh the gains.

FUNGI, TREES AND WOODLAND

      Most naturalists recognise the significance of the role played by fungi in decay and the recycling of nutrients from dead organic matter back into the environment. But beyond that, for many, fungi are little more than colourful curiosities in autumn woodland. Worse still, people whose interest is primarily in trees often view fungi with suspicion, concerned about the threat of disease. True, a few fungal species are capable of destroying a precious specimen tree. However, the real relationship between trees and most fungal species (indeed between fungi and almost all plants) is entirely positive and profound, and illustrates the dangers of generalisation. It involves an intimately close, and mutually beneficial, relationship called symbiosis. That between birches and the Fly Agaric Amanita muscaria is often quoted, but in reality almost every trees species found in Britain depends for its survival upon a unique relationship between its roots and specific soil fungi.

      Gardeners occasionally come across networks of fine threads in the soil. Essentially these are the body of a fungus, the mycorrhiza, a term that means ‘fungus root’. Several different types of mycorrhizal relationship exist between fungi and plants but ectomycorrhizal ties are of particular significance to trees. In this relationship the fungus sheaths the tree roots and hyphae (fungal threads) extend into the soil and into the cortical layer of the root cells. The fungus derives almost all of its energy requirements, particularly as sugars, from the photosynthetic reactions of the tree’s leaves. In return the tree obtains nitrogen and phosphorus, otherwise in short supply, via fungal action in the soil. Many of the toadstools that adorn the woodland floor in autumn are the fruiting bodies of these ectomycorrhizal fungi. This explains why, in many cases, certain toadstool species are found only under specific trees. For further information about the subject, and about fungi in general, see the excellent Fungi in the Collins New Naturalist series (see p.).

       Honey Fungus may be dreaded in a garden context, but its role in the decomposition and recycling of nutrients from dead timber is profound.

      In the case of a few fungal species, their relationship with trees is less benign and parasitism is well documented, as are instances where fungi invade an already diseased or damaged tree, hastening its end. It is a short step from this strategy to that found in the Honey Fungus Armillaria mellea, which is capable of penetrating seemingly healthy trees and ultimately causing their demise.

      Arguably the most important environmental role played by fungi, of course, is in decomposition. Without the process of decay, nutrients locked up inside dead organic matter would remain there and the cycle of life would grind to a halt. Although fungi are not the only agents of decomposition (bacteria obviously have a significant part to play and the mechanical action of many insects is important too), their role is vital. In the context of trees and woodland, they ensure that fallen leaves are recycled and that nutrients contained within fallen timber enter the woodland soil.

       Woodland fungi come in all shapes, sizes, colours and growing habits. Among the more intriguing are the Pinecone Cap Strobilurus tenacellus

       which grows on decaying pine cones; the Sulphur Tuft Hypholoma fasciculare

       which lives in decaying stumps; the Collared Earthstar Geastrum triplex

       which appears in leaf litter, often under Beech or pines; the Blusher Amanita rubescens

       which is associated with oaks; King Alfred’s Cakes Daldinia concentrica

       found on dead wood, often that of Ash; the Jelly Ear Auricularia auricula-judae

       which grows on Elder branches; the Blue Roundhead Stropharia caerulea

       found among fallen pine needles; and