The position of the Isle of Portland, projecting into the English Channel along the South Coast, gives it a sunny and mild climate which is reflected in its rich flora and fauna. It can be considered a ‘biodiversity hotspot’.
This richness has resulted in the designation of the Isle of Portland Site of Special Scientific Interest (SSSI), which covers 351 hectares of the island. The cliffs and undercliffs are included within the UNESCO Jurassic Coast World Heritage Site for its geology and geomorphology.
Much of the coastline is in a fairly natural state, with internationally important outcrops of Portland Sand and Portland Stone Formations.
Portland Bill and the adjacent cliff tops have a rich flora, with the pink flowering Thrift in April and May, followed by the white Sea Carrot in June and July, and the yellow Golden Samphire in July and August. It is also home to the rare Portland Bill Sea-lavender, which is not known elsewhere in the world.
The cliffs here are home to one of the few seabird colonies along the South Coast. The area is known for its three lighthouses. The Lower Lighthouse has been used as a bird observatory since 1961. The Isle is ideally placed for observing and studying migrating birds and moths. The Bird Observatory owns some of the old strip fields, that are being managed for birds and arable plants.
The wide undercliff on the east side appears wild, but was the first area where the famous building stone, the Portland Freestone, was quarried. The landslips and toppling that formed the undercliffs allowed easy access to the stone. Once quarrying ceased here the land was used for grazing the island’s own Portland Sheep.
Today the area, which is sheltered from the prevailing westerly winds, is a mosaic of grassland, scrub, boulders and scree and one of the richest areas for wildlife.
The ‘top’ of the island is now a mixture of large quarries, farmland and the villages. The older abandoned quarries, notably at King Barrow and Tout, have naturally re-vegetated and are nature reserves with fine examples of limestone grassland.
The Isle of Portland is known for its important populations of butterflies including six species of blues. It has some of the largest colonies of Chalkhill and Small Blue in Dorset, plus a unique variety of the Silver-Studded Blue. The rare Lulworth Skipper colonised Portland in the 1980s and has increased significantly. It is still confined to the Dorset coast in Britain.
Pressures and threats
There are many factors affecting the habitats found on the island. Since the effective cessation of commercial farming, particularly arable, there has been a decline in the arable birds and plants.
There is also a lack of grazing animals to manage the remaining semi-natural limestone grassland, leading to an increase in coarse grasses and scrub, and a reduction in the shorter turf that supports many of the Isle’s special rare plants and insects.
The mild climate means that many garden plants thrive, and some of these have naturalised and colonised the semi-natural habitats, to detriment of the grassland flora and fauna. A recent project removed much of the non-native Cotoneaster that had colonised the limestone grassland and covered large areas.
