On some sites of existing wildlife value, the desire to involve people in practical work will be secondary to the desire for maintaining the wildlife value of the site, and the first consideration should always be potential wildlife losses due to intervention. The site must be surveyed, and a realistic evaluation made of the likely results of intervention. Some urban sites have developed interesting communities of ruderal native and naturalised plants, which are adapted to the limitations of the site. Intervention to try and convert this to something which more closely resembles a recognised natural community may not be the best option. Removal of recently established non-native species of soil invertebrates may be impossible.
Glossary of terms used in the following section.
Abiotic: basic elements and compounds of the environment, including air and water, rocks, minerals in soil.
Alien: used to describe a plant or animal which is known to have been introduced by man, either accidentally or deliberately.
Native: used to describe a plant or animal of long residence in Britain, and with no known record of its deliberate or accidental introduction. The subject of native versus alien flora and fauna is complex and open to debate. See below.
Natural community: a natural plant and animal community is one that has established without any direct help from man. However, it may contain many species which are recently established in Britain, and may be on a substrate which has been much altered by man.
Naturalised: species which are known to have been introduced, and which survive and reproduce without help from man.
Ruderal: the first species of plant and animal to establish on recently disturbed ground.
The following section is based on the paper Alien and native – drawing the line (Barker, George, 1996).
The natural climax vegetation throughout Britain is deciduous woodland, and if man’s influence was removed, virtually all areas, including bare rock, ponds and arable farmland would eventually support deciduous woodland. This succession is a continuum during which biomass increases up to the climax community. To stop or reverse succession, energy must be removed from the system. In managing semi-natural areas, the aim of intervention is to alter the succession, normally by going back down the continuum. For example, by removing birch seedlings from heathland, or clearing scrub off downland, or removing silt from a pond. Sometimes it is the opposite, where the habitat has been degraded by too much removal of biomass from the system, for example by over-grazing of heather moorland or coppicing of woodland. Removal of these agents will allow succession to go forward, from grassland to heather, or from coppice to high forest. Planting trees is adding biomass to the system, so moving succession forward. Pond creation involves removing plants and soil, and pushes the succession back.
Britain’s diverse range of habitats is intimately linked with man’s influence on the environment. The lowland heaths, the Norfolk Broads, the chalk downlands and many other areas are direct results of man’s activity. Even if it were possible to turn the clock back to an era before man’s influence became significant, it would not be desirable if the aim is to achieve diversity of habitat.
The diversity of plant and animal species is also constantly changing, partly under the influence of man’s activity. The last glaciation swept Britain clear of most living things, and in the 10,000 years since, plants and animals have continually moved in, by natural means, accidentally by man, and by deliberate introduction. There have been losses from climatic change, man’s influence and other factors. To quote George Barker: “In this process of continuous recruitment where can the line be drawn logically between native and alien? What is the residency qualification for British citizenship? Is it the same for a tree with a lifespan of several hundred years and a fruit-fly with many generations each year?” Sycamore was probably first planted in Britain in the 1400s, and is long naturalised, but may still be described by some as an alien.
Britain’s flora comprises about 2990 species, of which 1737, or 60%, are naturalised aliens. Of these, some are valued and welcomed, others are not, depending largely on whether they are seen to displace more valued and longer-resident natives, and by the invertebrates and other fauna which they support. Similar value-judgements are made about naturalised alien fauna. Britain’s flora is poor in number compared with continental Europe, mainly because of the rapidity with which woodland established after the Ice Age, preventing the northward spread of many herbaceous, shade-intolerant species. Man has cleared and diversified this woodland cover, and now cherishes those open-ground species that flourish in the clearings.
Because of man’s influence, urban areas have a higher proportion of recently established species, both flora and fauna, than rural areas. Abiotic influences, such as disturbed soils and drainage patterns and climatic differences in urban areas, also may help to make restoration of natural rural habitat an inappropriate goal for managing green spaces in towns. Together with the important need, discussed above, for urban green spaces to be used by people, and even to be centres for creative activity, this suggests a future for urban green spaces which is not dependent on trying to recreate an idealised semi-natural habitat based on the past.
Allowing green spaces to develop naturally with no intervention may be a good option for wildlife value, and with green auditing now being recognised, this may also be the best environmental solution. However most people want their urban green spaces to be managed and controlled to some degree, to be safe and accessible, but to retain some of the look, feel and wildlife value of a ‘natural’ area. There is a range of management options which can be applied to a habitat, as listed below. nearly all sites contain a range of habitats, with different management options applied to different parts of the same site.
Management options
Non-intervention
Doing nothing to a habitat does not usually result in it staying the same. Non-intervention in any community other than a climax community will allow the succession to proceed towards the climax, unless other factors prevent it. Many urban habitats show an interesting natural development from a bare site, through colonisation by pioneer species, into a complex community. This natural succession, with its initial dominance of herbaceous species, and the slow development through to scrub and woodland, is of intrinsic ecological interest. Many of the sites are useful for informal recreation, field study, and as a green lung which absorbs pollutants, improves air quality and raises humidity.
Minimal intervention
Minimal intervention allows natural succession to continue, whilst doing sufficient management to keep any paths cleared, and to keep within any legal imperatives such as dealing with dangerous trees or other public liabilities, or preventing flooding on neighbouring properties. Maintaining the edge of the site so that it looks tidy and attractive may be part of this type of management.
Habitat maintenance
This regime aims to keep the habitat as it is, by preventing succession moving forward. This type of management fits in with many people’s desires to keep familiar things as they are, maintains existing ecological value, and appears simple to do. It may include cutting grassy areas to prevent shrubs and trees becoming established, maintaining coppice and keeping ponds clear of silt. However, this type of balance is not easy to achieve in semi-natural habitats, where the mix of species depends strongly on natural factors. It is particularly difficult early in the succession, when dealing with annuals or perennial herbaceous plant species, where the system is still very dynamic, and the outcome of any management action is by no means certain. Controlled, managed communities such as parks and gardens are straightforward to maintain, but expensive in resources, and forsake the chance of the unexpected which make semi-natural habitats interesting.
Habitat development
This involves guiding natural succession or modifying natural processes. Techniques may include selective removal or reduction of certain species, for example by preventing unwanted plants from setting seed.
Chesham Woods, Bury
Chesham Woods, near Bury, Lancashire, is an ornamental plantation dating back to the last century. The woods have been fenced against grazing, resulting in good regeneration of many species, but dominated by turkey oak, sycamore and beech, none of which are native to the area. There is some regeneration of ash and oak. Local TCV groups have undertaken to remove all non-native regeneration every two years, to encourage the growth of native ash and oak. A successful trial was done to enrich the habitat by introducing several species of common woodland flowering plants, which were absent from the wood. Several thousand individual plants were then planted, and are spreading well.
Habitat restoration
Reversing the succession to a previous state is a common management aim. Management techniques might include clearing a silted overgrown pond or removing scrub to return an area to grass or heath.
Black Lane, Bury
Black Lane, Bury, Lancashire, is a cluster of ponds now surrounded by housing estates, but retaining significant local importance for wildlife, including a population of the great crested newt. Natural succession was proceeding, with open water declining as yellow flag, Typha, willow and other plants took over. A detailed survey was carried out on the flora and fauna, and after consultation with interested parties, a management plan was drawn up. To prevent the pond habitat becoming lost through natural succession, rotational clearance of marginal plants and coppicing of willow has been started.
Habitat diversification
This type of management introduces new habitats, or modifies existing ones, but without having any overall effect on the state of the habitat, or any natural succession which is occurring. Examples include planting a hedge or building a dry stone wall.
Habitat enrichment
This involves introducing or reintroducing species suited to the habitat. Examples include planting wildflowers in grassland or woodland clearings, pond and marginal plants in wetland habitats, and shrub and tree species in existing woodland.
Habitat creation
Constructing or initiating plant and animal communities. These may or may not mimic recognised natural communities. Creation or replication of semi-natural habitats is not easy, especially further along the succession as habitats become more complex. The simplest and most reliable habitat creation projects are new ponds. Creation of herb-rich grassland is difficult (Chapter 7 – Grasslands). Tree planting creates the basic structure from which a woodland can develop, but should not be equated with creating a woodland, which will take many years to develop. Creating artificial habitats such as gardens, either of native, introduced or mixed plantings, can be very successful.
Habitat translocation
Some habitats, which are going to be destroyed due to building or other development, can be moved to a new site. However, even if the new site has a similar substrate, drainage pattern and microclimate, and a similar management regime, long-term success is not guaranteed. Translocation should not be seen as an alternative to conserving the habitat on its original site. Areas of grassland and heathland are relatively simple to translocate, by using a digger to excavate and move large clods of plants and soil, together with soil invertebrates. Threatened animal communities including reptiles, amphibians and invertebrates have been successfully moved, with or without translocating the habitat.
Any intervention should do one or more of the following. The balance depends on the relative importance of each of the following to the community involved. Often, all of these criteria can be satisfied.
- improve the site for wildlife, or for natural features such as rock outcrops.
- improve the value of the site for conservation of heritage.
- improve the appearance of the site
- improve the accessibility of the site
- itself provide an activity in which the community participates.
Drinkfield Marsh, Darlington
Drinkfield Marsh is an 8ha site on the urban fringe of Darlington, owned by Darlington Borough Council and managed by the TCV Darlington Project. The main feature of the site is a 2ha lake, which has been formed by the construction of a series of timber weirs in the ditches leading from a previously seasonally flooded area. Extensive emergent vegetation has been established, to provide wildlife habitat, and to screen sections of the lake from the many dogs which are exercised on the site. This has encouraged breeding wildfowl, including swans, and feeding the ducks has become a daily activity for some local residents.
Work objectives of the site are to replace the existing stand of reedmace (Typha latifolia) with reed (Phragmites australis), which has a greater value for wildlife. The reedmace is removed by hand pulling and by herbicide, cleared in advance of the spreading reed, so that the two species don’t mix. No management work is carried out during the bird breeding season. Three dykes, 2m wide, are kept clear of emergent vegetation.
The site supports a population of water voles, which have nationally suffered a dramatic decline in recent years. Water voles require an abundance of long grass for shelter and food, and steep banks in which to excavate their burrows. Management involves rotational management of banks, to maintain long grass habitats, and sufficient clearance of ditches to prevent them getting choked with vegetation. It is thought that the frequent presence of dogs at Drinkfield Marsh has deterred mink, a predator of water voles, from colonising the area.
