If human activity over the last 5,000 years has transformed our countryside to the point nothing is actually 'natural' it follows no habitat that we seek to protect by designating it as a nature reserve is a natural environment so why do we do it? And why do we not only designate areas as 'nature reserves' but also spend time, effort and money to 'manage' them?
Succession:
If left to its own devices the natural process for nature is to recolonise a cleared area to the point it returns to woodland. Successions of stages occur on this journey which can take many, many years. An open area will first be colonised by grasses and flowering plants. Over time shrubs will appear and the area will become scrubby. Amongst the scrub trees will start to develop and so the final stage to woodland will be well underway.
Although the places we see now may appear to be always the same they are changing all the time as plants grow. As taller, stronger plants emerge so the smaller, more vulnerable ones perish. We may not realise it but this succession of stages from cleared area to woodland is happening all the time.
Climax Habitat:
Eventually, an area will reach a point where no further succession is possible. This is often woodland but there will be places where trees cannot grow due to climatic or soil conditions. For example, in a boggy area it may be far too wet for trees to grow. Once this situation is reached it is known as climax habitat.
Intervention:
If the succession towards climax habitat is happening all of the time then why is the countryside not covered with trees? It is because the natural succession process is subject to interventions, both natural and unnatural, which reverse, halt or at least, slow down succession. Natural events such as a storm that may bring down trees or a lightning strike that may start a fire that destroys heather and scrub intervene in succession. The human intervention of felling trees for fuel, for building materials and for stock grazing resulted in many areas staying as grassland and unchanged for centuries. This almost permanent cessation of the succession process enables many plants and animals to find a niche that suits them and for them to prosper.
Restoration and Management:
Today, in an attempt to recover lost ground, there is a move towards habitat restoration and on the Dorset heaths, for example, many acres of conifer plantation is being removed to allow the underlying heath to regenerate to the way it was for centuries before post war tree planting took place. Many of our nature reserves are actively managed to ensure the succession process is kept at bay so that unique ancient habitats are maintained. Casual observers are often confused by what can be perceived as habitat destruction but it is not, it is the attempt to stall, or reverse, the succession process.
Habitat Stages:
It depends on where in stages of succession that the suspension of the natural process by intervention creates a more stable set of conditions and thereby forms a long standing ancient habitat type that is rich in wildlife. We see this if broadleaf woodland is not felled and cleared with spring flowers thriving before the canopy opens and ferns and mosses colonising the woodland floor, birds feed in the trees on insect larvae and fungi works its way through the leaf litter enhancing the decaying process and enriching the soil from which trees are extracting nourishment.
If intervention occurs before the trees grow to any real height we find a scrub habitat where open areas are intermingled with shrubs such as hawthorn or bramble. These shrubs are home to countless insects and they, in turn, feed birds and mammals.
Intervention very early in the succession cycle by stock grazing will result in grassland rich in herbs and grasses or, on poorer soils, covered in heathers and gorse.
Transitions and Mosaics:
Sometimes there are quite clear boundaries where one habitat type ends and the next starts. This is not always the case and there can be a gradual transition from one to the other. In these situations it might be difficult to establish exactly which habitat type applies especially as it is quite common for species from both types of habitat to occur in the transition zone. Occasionally one can actually get a mix of habitats in the same area; this is known as a mosaic. This can often be seen on heath where areas of acid grassland can also occur.
We may look at ancient woodland, scrub, chalk grassland and heath and think of them as natural habitat but they are not. What they are are ancient, stable habitats that have a rich biodiversity but they only remain that way if the intervention that brought them about is maintained. If it is not they will, in time, revert to woodland
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