The field layer of woodlands consists of plants which are adapted to the conditions of shade, shelter and high humidity. The flowering plants have to seize the opportunity in early spring when rising temperatures allow insect pollination to take place, but before the canopy is in full leaf. Primroses, wood sorrel and wood anemones are amongst the earliest to flower. As the canopy begins to close, there is a second burst of flowering of the more shade tolerant species, with dog’s mercury, bluebell, bugle and ground ivy typical of southern lowland oakwoods. In damp northern woods on limestone soils, ramsoms, bellflower and yellow archangel are found. Less common and easily overlooked are several species which are now more associated with gardens, including violets, yellow star-of-Bethlehem, lily-of-the-valley, columbine and monk’s hood. Orchids and helleborines are amongst the rarest woodland flowers. Many woodland plants grow from bulbs or rhizomes, storing food during the long periods of shade, and allowing a rapid burst of growth in spring. The woodland field flora of ancient woodlands is very specialised, and cannot be replicated.
The variable conditions of woodland edges, rides and glades allow a much greater range of generally more common plants to flourish. Woodland edge habitats vary from sunny, dry banks to shady, damp ditches, and are affected by grazing, mowing and other management. Plants vary from those that are able to take advantage of recent clearance, to those that are adapted to stable, undisturbed conditions. Large grassy glades and clearings may have a flora more typical of old meadow or pasture, depending on how the clearing is managed.
Ferns are adapted to the damp, shady conditions of the deciduous woodland floor. They die back in winter, the dead fronds protecting the crown, and then in late spring the new fronds uncurl. Typical species include hart’s-tongue, male, soft shield and broad buckler fern. The size and appearance of the fronds can vary considerably between different individuals of the same species, and many different varieties of most species have been identified. Some species of ferns can grow in the humus that accumulates on the spreading branches of mature trees, particularly oak, giving an almost tropical appearance to some ancient deciduous woods in the damp mild parts of Britain. Bracken is the most adaptable fern, and can grow not only in woodlands but in pastures and other open areas, where it can become an invasive weed.
Mosses are a primitive type of plant, many species of which are adapted to growing in woodland. They have no true leaves, stems or roots, but instead absorb water and nutrients over their entire surface, and so every moss cell must be within reach of the growing surface to obtain its water supply. Some of the most spectacular mosses are found in very damp places, near springs and upland streams, where the water is rich in oxygen and minerals. Mosses are sensitive to soil acidity and alkalinity, to light and shade, and to moisture conditions. They grow actively when it’s cool and damp, and are at their most luxuriant in late winter. In spring they produce their spore capsules, and then gradually wither and die as summer progresses.
Mosses also grow on tree trunks, especially on the shady, lee side of leaning trunks where moisture can accumulate. The water-trapping ability of mosses enables them to grow on rocks and other exposed places, where they can play a significant role in succession, by providing a suitable substrate for seeds of other plants to germinate. Tree trunks are also host to other epiphytic plants, including lichens and liverworts, which absorb their nutrients from the air around them. Lichens are either crustose and pressed to the branch, or foliose, forming festoons of branching, trailing growth. They are particularly abundant in damp, western areas as they require moisture-laden air and are sensitive to pollution. Epiphytes grow most abundantly on fissured bark of old trees, which grows only slowly.
Where wood is decaying there is often a distinctive epiphyte flora due to the nitrogen being exuded from the tree.
Fungi that appear on living trees, decaying branches and on the woodland floor are the visible signs of the complex breakdown process which is an essential part of the woodland ecosystem. The visible toadstool, mushroom or other fruiting body is only a short-lived part of the intricate thread-like mycelium which penetrates wood, leaf litter and soil. Fungi lack the ability to make food, but instead break down living and dead plants into simple substances on which they can feed and grow. There are many hundred species of fungi in Britain that require wood for their survival, and most are host-specific, living on only one species or group of species. Standing trees can become infected by spores which settle on them and develop in damp conditions. Fallen trees and branches are infected by the mycelium that is abundant but invisible in the leaf litter on the woodland floor.
