What is the special value of woodlands and why don't we just let them grow?
Because most of Britain was wooded before agricultural clearing, woodlands are home to much of our native wildlife. Decreasing numbers of native plants and animals, as well as species extinctions, are the result of the loss of woodland habitat - only 10 percent of the UK is still wooded. Native UK plants and animals can, therefore, be protected by conserving natural woodland - woodland similar in vegetation and structure to the original woods.
Woodlands with native plants, well developed vertical layers and links with plant and animal breeding populations support the highest numbers of plants and animal species.
Unfortunately, remaining woodland is often not natural. Newly planted woods are of a single age and height and thus lack vertical layers ; they may be occupied by non-native species introduced from abroad ; they may be isolated from other wooded areas by vast uninterrupted acres of farmland. Modern agricultural practices and land development make the replacement and continued existence of natural woodlands possible only through intensive management.
Where biodiversity is a management goal, therefore, woodlands cannot simply be "left to grow" but must be manipulated to simulate the lost woodland habitat as closely as possible.
Lincolnshire Woodland in Autumn
Woodland managers' work includes:
-
classifying each site's soil, water, and climate conditions and understanding which original woodland type(s) will grow there successfully
-
planting native trees and protecting them from grazing during early growth
-
excluding and removing non-native species
-
imposing seasonal disturbances – such as flooding in a swamp or carr
What guidelines and manipulations increase biodiversity in woodlands?
The guiding maxims of woodland management for biodiversity are:
Native, Diverse and Connected
- Retain existing woods and hedgerows wherever possible. Mature woodlands take a century or more to develop. Many woodland plant and animal species are not mobile and do not colonise new sites easily.
- Plant or favour growth of native trees and shrubs. These normally support more wildlife species because their food and breeding habits co-evolved with the native plants.
- Maintain or enhance a multi-layered forest structure. Deciduous woods, the dominant ancient forest type in the UK, have four distinct vertical layers: ground, field, shrub, and canopy. Some plant and animal species complete their entire life cycles in a single layer while others require four healthy layers to find food and shelter and to reproduce.
- Aim for a diversity of native tree and shrub species. This ensures that the food cover and breeding habitat requirements are met for the widest possible range of species, both seasonally and over entire life cycles.
- Plan for forest or hedgerow corridors to connect separate interiors. Allowing movement and interbreeding maximises plant and animal population vigour.
Mature, Stable woods develop over a long period of time.
A stable woodland develops after many years because woodlands are dynamic, changing in resident plants and animals which in turn alter the site soil and water characteristics. Each successive group of organisms provides conditions suitable for the next group until the final stable 'climax' woodland is established. This process is called succession - easy to remember because there are a succession of plant associations which come and go over time.
Woodland succession on moderate sites in Britain is predictable, generally following a pattern of birch to oak dominance. Birch is the woodland coloniser on open land because its seeds are profuse, windborne and not inhibited by the high light levels characteristic of treeless land.
While pioneering birch trees mature, other woodland creatures arrive to use the new woods often bringing with them seeds and nuts, including oak acorns, from the older woods they left. These seeds and acorns establish seedlings of the oak wood community which can persist as small saplings until the short lived birch trees die, allowing an oak community to take their place. Oak trees and oak woodlands are long lived, regenerating young oaks in place of fallen old oaks.
Within this broad example of woodland succession are variations: willow or alder tend to colonise wetter soils whilst beech or ash woods form the climax forest on chalky soils.
Since each successional community is composed of distinct plant/animal associations, overall biodiversity is highest in an area with a variety of woodland types and ages. Furthermore, woodlands situated near quality grasslands and wetlands can be especially valuable, serving as cover, feeding and breeding habitat for animals we normally see active elsewhere - waterfowl, wetland invertebrates, butterflies, and mammals. Whisby Nature Park is fortunate to possess this wetland/woodland combination.
