What have cutting down trees, herds of sheep or putting holes in a sea wall got to do with science? Surprising as it may sound these can all be ways of helping to restore a heathland, grassland, or saltmarsh. Studying restorations is not easy, it can be difficult to find undamaged habitats to use as comparisons, and because the natural world is constantly changing it is hard to say what a habitat should look like and what species it normally contains. In fact some people argue that restoration is as much of an art as a science! However, scientific methodology is important in evaluating different methods for restoration and in monitoring the success of the restoration. Scientific knowledge of ecology and the natural world is also needed to understand the process of restoration.
Understanding the cause, or causes, of the habitat damage is vital if the restoration will succeed. Sometimes the causes will be obvious such as filling in a pond or the conversion of woodland to arable land. But some causes are less obvious. For example, acidification, caused by air pollution, makes the conditions in some rivers and ponds unsuitable for the animals, plants and micro-organisms that live in them.
Starting at the bottom
Having the right substrate, the soil (or the mud and sand of a coastline), is also important for success. The composition, texture, acidity and nutrient content of the substrate will determine what can live there and this often changes when a habitat is damaged or neglected. When heathland is used for growing crops or when scrub and trees invade the site the nutrient content and soil chemistry changes. This can make it less suitable for heathland species. heathland soil is naturally slightly acidic and poor in nutrients. These restoration of the right soil conditions can be helped by removing topsoil, scraping away dead plant material or in some cases adding sulphur make the soil more acidic.
They may not be obvious, but micro-organisms such as bacteria and some types of fungi are also important in the restoration of habitats. Many plants and trees depend on these tiny organisms in the soil, as they help the plant to obtain nutrients or water. Scientists working on replanting species in damaged grasslands have found that identifying the important fungi and growing them with seedlings can significantly increase the survival of plants in the recreated habitat.
To plant or not to plant?
Should the habitat be left to re-grow naturally or should species be re-introduced? If you do re-introduce species then where should they come from?These are just a few of the difficult questions faced by anyone attempting to restore a habitat. Scientists are still learning a lot about how and when species return to restored sites.
Studies have shown that some plant seeds can grow after years in the soil once the right conditions for growth are restored. Poppy (Papaver spp.) seeds have regrown after 100 years and Heather (Calluna vulgaris, L. 1758) seeds can still grow in large numbers after 30 years in the soil. Unfortunately these tend to be exceptions and many habitat have been damaged a long time before they are restored. In these cases species will not recover without some help either by sowing seed or growing and planting seedlings. Once restoration has started natural processes may help, seed can be carried from nearby areas by wind or even in bird droppings.
Preserving genetic diversity is also important. Many species have unique genetic characteristics that vary between different parts of the country. Restoring sites using species from nearby habitats can help to maintain this diversity.
Keeping an eye on things
Unfortunately most restored habitats cannot just be left alone once the restoration has finished. The majority will need to be managed and monitored to ensure that the restored area develops into the intended type of habitat. Alien invasive species such as rhododendron (Rhododendron ponticum, L. 1758) may need to be controlled regularly and there are many native invaders such as birch (Betula Pendula, Roth) and bramble (Rubus fruticosus agg., L. 1758) which naturally colonise some habitats such as heathland. Grazing animals such as cattle and sheep can be important in maintaining the characteristic species of grasslands, heaths and moorlands. Coppicing (the regular cutting of certain trees) in ancient woodlands is a common practice to maintain the diversity of woodland habitats.
Does it work?
Not all restorations are a success, but restorations that fail are often caused by lack of understanding of the ecology of the habitat. Habitat restoration is being attempted for most of Britain’s major threatened habitats and the number of successes is increasing all the time. Wetlands have been recreated in central London, airfields turned back into heathlands and bypasses into chalk downland. The science of restoring habitats is still relatively new but the more we understand about the habitats of the British Isles the better restorations will become.