CHOBHAM COMMON NNR - Surrey Wildlife Trust

2.2 SITE MANAGEMENT
2.2.1 Introduction
“Lowland heathland is characterised by the presence of plants such as heather,
dwarf gorses, and cross-leaved heath and is generally found below 300 metres in
altitude. Areas of good quality heathland should consist of an ericaceous layer of
varying heights and structures, some areas of scattered trees and scrub, areas of
bare ground, gorse, wet heaths, bogs and open water.
Lowland heathland is a priority for nature conservation because it is a rare and
threatened habitat. In England only one sixth of the heathland present in 1800 now
remains. The UK has an important proportion (about 20%) of the international total of
this habitat.
In the past heathland was lost primarily to agriculture, forestry, mineral extraction and
development. Uncontrolled wild fires have also been a particular threat to bryophyte
and lichen-rich heathland. The main factors affecting the habitat at present are the
encroachment of trees and scrub and the simplification of vegetation structure due to
a lack of conservation management such as light grazing, controlled burning and
cutting. Nutrient enrichment, particularly deposition of nitrogen compounds,
fragmentation and disturbance from developments such as housing and road
constructions 4 .
2.2.2 Scrub and Woodland encroachment
Without regular management most heathlands will rapidly be lost to either bracken
dominated communities or to encroaching trees and scrub, mostly birch Betula ssp.
and Scots pine Pinus sylvestris (Gimingham, 1972;Power pers. comm.; Marrs, Hicks
& Fuller, 1986),. Most European heathlands including those in the UK were originally
derived from woodland (e.g.Dimbleby, 1962; Kaland, 1986; Odgaard, 1994) but
following the clearance of trees, human activities such as farming, grazing, cutting
and turf-stripping have kept the heaths open. Although the resulting heathland soils
have lost their bases and some of their nutrients from the leaching effects of
rainwater, these nutrient poor and acid soils are still capable of supporting trees
particularly when there are nearby seed sources and adequate phosphorus
availability in the soils (Manning, Putwain & Webb, 2005). Invasion by trees and
scrub has been seen as one of the main threats to heathland in recent years and was
one of the mainsprings for the successful European bid for funding for 38 projects
across the southern counties under `The Tomorrows Heathland Heritage’ initiative
led by English Nature.
2.2.3 Atmospheric nutrient inputs
Airborne nitrogen (as ammonia and nitrous oxides) from burning fossil fuels by
industry, traffic, aviation, shipping and agriculture pose one of the greatest threats to
heathland in Europe. Heathland systems are generally poor in nutrients and many of
the plant species can only survive and compete successfully on soils with low
nitrogen availability (Bobbink et al., 2002). Nitrogen compounds also increase
acidification in soils. The addition of nitrogen in rain or dust particles, results in an
increase in the nitrogen in the vegetation, litter and upper soil layers, and this builds
up over time. Heather growth can initially benefit from inputs of nitrogen, but where
4 (Habitat Action Plan – Lowland Heath, Biodiversity: UK Steering Group Report,
1995)
26