Conservation
Internet Links:
LIFE project website
RSPB website
Environmental Change Network website
Development of the Habitat
Neolithic farmers began to clear early woodland from about 4000BC.
From the Bronze Age cereals were increasingly grown on the chalk. Livestock were grazed when the soil became too impoverished to grow crops.
From the Middle Ages until the First World War sheep farming was the major activity. Only in times of national emergency was the land ploughed temporarily.
Evidence from the pollen record shows the sudden appearance of grasses, grassland herbs and cereals.
Intensive cultivation of these early periods is visible today as strip lynchets and Celtic fields.
With the repeal of the Corn Laws in the 19th century wheat growing became unprofitable and much of Porton Down reverted to the downland present today.
The Value of Chalk Grassland
Porton Down was purchased by the MOD in 1916. Sheep grazing was abandoned and rabbits became the major grazers on the shallow, nutrient-poor soils.
During the 1950s and 60s myxomatosis in rabbits resulted in a severe decline in grazing.
During and after both World Wars much of the chalk grassland in Britain was ploughed. Porton Down is the largest continuous unimproved tract remaining.
Soil conditions and grazing result in an abundant mixture of herbs and grasses which supports an equally diverse range of insects.
The lack of grazing allowed incursion by more vigorous plants such as coarser types of grass and eventually scrub came to predominate in some areas.
Porton Down's continued existence is of national importance and 1519 hectares of its 2750 hectares have been designated a Site of Special Scientific Interest (SSSI).
The Chalk Flora
Most of Porton Down is covered by a shallow, well-drained, chalk-based soil containing low levels of nutrients. These conditions favour the development of a rich variety of plants, up to 40 different species occuring in one square metre of turf. The plants are small and slow growing, having developed in response to a long history of grazing, by sheep or rabbits. The variety is maintained so long as the grazing pressure continues.
In some areas the mineral content of the chalk has been leached away, these support acid loving plants such as heather. Yet other areas have a thin layer of clay overlying the chalk where oak trees, gorse and bracken will grow. Some very low nutrient areas support a lichen-rich flora.
The grasslands are of various ages, from about 50 years to at least 200 years old. Some areas have never been ploughed. It is possible to correlate the age of a grassland with the presence of particular flowering species in it.
Juniper at Porton Down
Juniper is now almost confined to chalk and limestone soils in southern England and Porton Down is the most important site within this area, containing about 20% of the population. 20 species of juniper occur in southern England. Fifteen of these species have been found at Porton Down, more than on any other single site.
Juniper occurs in two distinct age groups at Porton Down. The oldest, now dead or dying, arose when sheep grazing pressure was reduced at the turn of the 20th century. This allowed juniper to establish on the grasslands.
The younger age group arose during the myxomatosis outbreaks of the 1950s and 60s when grazing pressure by rabbits was severely reduced.
Prior to 1969 most juniper seedlings had been grazed off but for ten or twenty years afterwards juniper were able to establish. By the mid-1970s rabbit grazing pressure was again very high and establishment has not occurred since.
There are 19 species of invertebrate which live only on juniper, 14 of these have been found at Porton Down. The very large population of juniper at Porton Down is crucial to the survival of these species.
Woodlands at Porton Down
Just over 10% of Porton Down's 2750 hectares are woodlands, containing both hardwoods and softwoods, which greatly increase the biodiversity found on the site.
The origin of most of the woodland is amenity planting towards the end of the 19th century. However, an ancient oak woodland in the south-west corner of the site includes one of Britain's best beech hanger habitats. The main woodlands are divided into five broad categories: old plantations, mixed woodlands, ancient woodlands, new plantations and regenerated woodlands.
The severe gales of 1987 and 1990 devastated mature beech woodlands at Porton Down. Subsequent planting with a mixture of species was undertaken.
During the period 1964 to 1999 approximately 34,000 trees were planted by the MOD which will maintain this habitat and safeguard the important county skyline features which are a visual reminder of our heritage.
The Stone Curlew
Found only in central southern England and East Anglia, the stone curlew (Burhinus oedicnemus) is one of the UK's rarest birds, suffering a huge decline in range and numbers in Britain in the last 50 years.
Intensive conservation efforts since the mid 1980s (population about 160 pairs) initiated the recovery to today's national population of 243 breeding pairs. The Royal Society for the Protection of Birds (RSPB) works closely with Dstl throughout the breeding season, all chicks being ringed to obtain information on breeding productivity and mortality from year to year.
Designated as a Specially Protected Area (SPA) in 1993 for its stone curlew, Porton Down currently supports 10% of the UK population.
The Antscape
The uniquely high density of anthills in an area of Porton Down has led to it being known as the antscape. Anthills are formed by the Yellow Meadow Ant (lasius flavus). It has been estimated that there are 3 million anthills containing 35 billion ants on these grasslands.
Anthills can only form in the absence of disturbance by farming operations and livestock trampling. Rabbit grazing keeps the turf short, favours the development of low growing herbs and allows the sun to warm the mounds. In its absence the anthills became shaded, resulting in temperatures too low for ant brood production and the mounds are abandoned.
A study of ants at Porton Down published in 2002 states that 20 species were present including a number of scarce species.
The Butterflies of Porton Down
Variation in habitats and a rich chalk downland flora combine to enable a very large and diverse population of butterflies to exist at Porton Down. Forty Four species (78% of the British list) have been recorded here, making Porton Down the best butterfly site in the UK.
Many butterfly species have suffered major population declines across Britain as their habitats are destroyed. Porton Down is now a valuable reservoir for a number of these species. Such sites are now a rarity and must be considered a national asset with every effort being made to ensure their continued survival.
Conservation Management
Chalk downland requires management in order to stem the continuing losses of this habitat. 62% of lowland calcareous grasslands were assessed as being in an unfavourable condition in 2001. The conversion from unfavourable to favourable condition will benefit many species of flora and fauna associated with chalk downland.
Scrub and Scots Pine encroachment are major problems and much work is being undertaken to remove significant amounts of these, thereby allowing the development of high quality chalk downland.
Inappropriate historic management including lack of adequate grazing has led to the development of rank grassland, as well as scrub encroachment.
In such areas grazing by livestock will be reintroduced.
Conservation Studies
Scientific studies take place at Porton Down to determine the wildlife present on the site, the effects of management on the wildlife and any changes, detrimental or otherwise, occurring
within populations.
A CCTV camera is being used to study the activities of nesting stone curlew at Dstl Porton Down.
The images gained will help us to better understand this rare bird. As the stone curlew is active at night the camera has infra-red capability that will enable nocturnal study.
Beetles and spiders are studied for a number of reasons including monitoring the validity of vegetation quality assessments.
Droppings present on transects situated on open grassland and in woodland are counted.
These counts enable comparison between years and give a measure of change in the rabbit population and the effect this is likely to have on vegetation.