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

two World Wars and endured a globally significant climatic catastrophe.

THE ECOLOGY OF TREES AND WOODLAND

      Although there are many tracts of forest in the British Isles that harbour native species and ancient trees, it is important to realise that almost no woodland in Britain and Ireland can be described as truly virgin and untouched. For millennia man has interfered with the forested landscape, cutting down trees for fuel and building materials, and in order to create agricultural land. Some types of woodland are more modified than others and a few exist entirely as a result of human actions. However, when it comes to woodland comprising native species, the history of use does not necessarily detract from its ecological importance and value to wildlife; on the contrary, it often enhances it. Of greater significance than the age of the trees in a given area is a continuity of woodland cover. Many woodlands have had continuous tree cover since before man first settled the land and the diversity of associated wildlife reflects this venerable ancestry. The fact that ecologists refer to most British and Irish woodland as semi-natural is in no way derogatory.

       Almost all the oak trees in Bramley Frith, Hampshire, are just a few hundred years old; much older ones were blown down in the Great Storm of 1703. Nevertheless, the woodland has had continuous tree cover since at least the Domesday Book.

      Even as solitary individuals, native tree species will harbour a good array of wildlife. However, it is when they grow alongside and among other trees, and form woodland, that their true ecological potential becomes apparent. This can be thought of as synergy, if you like: from a wildlife perspective the whole (the woodland) is greater than the sum of the parts (the trees).

      Walk through an area of recently planted woodland and you will usually discover a mixture of tree species, comprising individuals of different ages. However, visit ancient semi-natural woodland and typically you will find that one or two tree species predominate, either because environmental conditions favour them or because they have been encouraged by man. Although these woodlands do not qualify as habitats in the strict sense (ecologists refer to them as vegetation types), some of them are easily recognised and, more significantly, have a classic set of woodland animals, plants and fungi associated with them.

      Professional ecologists recognise a large number of subtly different vegetation types and use them to define the natural history of the British and Irish landscape. However, for most people the differences between many of these types are too subtle to discern and most are happy to make reference to just a handful of easily recognised woodland types. The descriptions that follow cover the more distinctive, widespread and easily recognised of these communities.

      MANAGED PEDUNCULATE OAK STANDARDS WITH HAZEL COPPICE

      The Pedunculate Oak is one of the most common large native tree species across much of central and southern England, and in many woodlands it dominates in terms of stature and tree canopy cover. In some areas, its prevalence may be the result of soil conditions favouring its growth over other species. However, in many instances, an examination of the woodland structure and history will reveal man’s contribution to the equation. If, for example, a particular woodland has oaks all of a similar size, then even if they are old their presence and dominance is likely to be the result of planting, in earlier centuries, and of selective felling of other species. This is hardly surprising because oak has always been considered the construction timber of choice. In such circumstances, mature oaks are referred to as standards.

      In many semi-natural Pedunculate Oak woodlands you will find an understorey of Hazel. Typically this species will have been planted and managed on a regular basis by coppicing (see p.) to produce a constant supply of straight branches, used in hurdle-making and other woodland crafts.

       A managed Pedunculate Oak woodland has near-continuous canopy cover. Only in winter and spring, before the leaves emerge, do significant light levels penetrate to the woodland floor.

      In spring, a sympathetically managed woodland of this type is a floral delight to the eye, with carpets of Bluebells, Wood Anemones and Wood-sorrel intermingling with patches of Dog’s Mercury, Early-purple Orchids and Wild Daffodils. Pedunculate Oaks probably support the greatest diversity of invertebrate life of any of our trees, feeding beetles and moth larvae in abundance. If the occasional Sallow also grows among them, then there is a good chance that Purple Emperor butterflies may be present, assuming the woodland lies within this species’ restricted English range. The larvae feed on Sallow leaves but the adults – males in particular – depend on mature oak standards, using their canopies to define and defend territories. Birdlife is usually as rich as can be expected for a lowland woodland but arguably the star of the show is the Dormouse. Dependent on Hazel nuts in autumn, they occupy the oak canopy for much of spring and summer, feeding on oak flowers and insects.

       A majestic male Purple Emperor surveys his domain from the canopy of a mature Pedunculate Oak.

       Carpets of Bluebells are a stunning feature of managed Pedunculate Oak woodland in lowland Britain.

      SESSILE OAK WOODLAND

      Although Sessile Oak often grows alongside its Pedunculate cousin, its requirements for optimum growth are subtly different and it predominates in upland and western parts of the region where rainfall is highest. Often the best remaining tracts of Sessile Oak woodland are on steep slopes, in part because the trees are less easy to fell there; in such circumstances they are often referred to as ‘hanging oak woodlands’. Try to negotiate the broken ground and slippery roots of one of these woodlands and it is not hard to see why.

      Although the wildlife that Sessile Oak is capable of supporting is broadly similar to that of a Pedunculate Oak, in reality there are subtle differences. In part this may be a reflection of the generally harsher climatic conditions that it favours, although the history of land use by man sometimes plays a part too.

      In lowland oak woods that have an understorey of Hazel, grazing animals were typically excluded in the past, or at the very least discouraged on account of the damage they might do to growing shoots. By contrast, many hanging woods of Sessile Oak are freely grazed by sheep and cattle with the consequence that the shrub layer is considerably reduced. Bluebells and other flowers of the woodland floor are common, but what strikes most visitors is often the abundance of ferns, mosses and liverworts. In part this is a result of an absence of competition from more palatable (in grazing animal terms) flowering plants, but the humidity of the regions where Sessile Oaks grow also plays a part. Hence the abundance of epiphytic mosses and liverworts in particular, often festooning trunks and branches well off the ground. Sessile Oak woodlands are the classic domain of nesting Pied Flycatchers and Redstarts.

       Hanging Sessile Oak woodland.

       Sessile Oak woodland cloaking steep hillsides on Exmoor.

       In the British Isles, Pied Flycatchers reach their highest breeding densities in Sessile Oak woodlands.