Читать книгу The Isles of Scilly - Rosemary Parslow - Страница 55

St Martin’s is a long narrow island with a mainly west-to-east axis. It is just over 3km long by 1.5km wide and covers 238 hectares if you include White Island (15ha). First impressions of St Martin’s are of long, empty white beaches (Fig. 45), intense turquoise sea, little clusters of houses tucked into the hillside and the strangely modern-looking (it actually dates from 1683) conical red and white banded tower of the daymark on high ground on Chapel Down at the eastern end of the island.

FIG 45. The south coast of St Martin’s, looking towards Tresco at low tide with the sand flats exposed. June 2005. (Rosemary Parslow)

As on St Agnes, the individual hamlets are named, rather unoriginally, Lower, Middle and Higher Town. They are strung out along the two-kilometre concrete road from Lower Town quay in the west to Higher Town Bay and New Quay, just over halfway along the length of the island. Beyond the farmland to the east the land rises up to the heathland on Chapel Down. Heathland also extends all along the northern edge of the island; only the insert of the dune grassland of the Plains and in some places wetter areas and a small pool break the continuity. Around the higher and exposed land are rocky promontories and cliffs where seabirds nest. Looking northeast from the cliffs on a clear day you can often see the cliffs of Land’s End, 45km away.

The southern shores of St Martin’s are mainly sandy, with sand dunes and just a few stretches of low cliff. Along the back of the dunes at Higher Town Bay are small bulb fields, frequently inundated by blown sand (Fig. 46). Indeed, much of St Martin’s is composed of blown sand that has been deposited over the whole top of the island in the past. This has led to some of the most impressive arable weed populations in Scilly being found here, including unusual species not found elsewhere in the islands. The sandy soils are also found around Higher Town Bay, where the cricket field is mown maritime grassland dominated by

FIG 46. Bulb fields with rosy garlic Allium roseum, whistling jacks and great brome, St Martin’s, May 2003. (Rosemary Parslow)

chamomile and several species of clover, including both suffocated Trifolium suffocatum and subterranean clover. The cricket field is low-lying and sometimes floods completely – perhaps not ideal for the cricket, but maybe why there is a superb show of chamomile most summers. The sand-dune areas around the quay and along the track ways are also places where some rare clovers are found. Suffocated clover can be difficult to find, as blown sand often drifts over the plants and completely buries them. It also flowers early in the year so has usually dried up and disappeared by early summer. In the corner of the cricket field is a small brackish pool, sometimes covered by the pretty white and yellow buttercup flowers of brackish water-crowfoot.

The dune system along the Higher Town Bay is typical of the NVC (National Vegetation Community) SD7 semi-fixed dune, relatively species-poor but with some interesting herbs such as balm-leaved figwort and Babington’s leek. In places bracken and the evergreen shrub Pittosporum crassifolium are invading the dune. A sub-prostrate form of wild privet occurs along the edge of the track. There are species of unstable foredune habitats such as sea rocket Cakile maritima where there are breaks in the dune. In summer this is one of the best places to see ringlet butterfly Aphantopus hyperantus, a recent arrival in Scilly. At the back of Lawrence’s Bay is a low cliff with a hanging curtain of the succulent Sally-my-handsome Carpobrotus acinaciformis, with its distinctive curved leaves and carmine flowers.

There is a series of rocky headlands with exposed rocks and thin soils along the north side of St Martin’s. Wind-eroded heather and gorse heathland cover the area between Top Rock Hill and the separate group of the Rabbit Rocks. The slopes below the hill are covered with bracken and gorse communities on deeper soils and a fringe of maritime grassland towards the coast. At Round Bowl both small adder’s-tongue fern and orange bird’s-foot have been recorded, but the dune is being invaded by heath and scrub species in this area. Pernagie is a group of small bracken fields below the hill with maritime grassland and a small area of heathland at Pernagie Point. The westernmost headland on St Martin’s is Tinkler’s Hill. The top of the hill has a cover of gorse scrub surrounding a smaller area of heather. At the bottom of the hill is heathland and coastal grassland alongside Porth Seal, where small adder’s-tongue fern may be found. Porth Seal is a geological SSSI on account of the raised beach and important deposits; pollen analysis from the site demonstrated the arctic tundra nature of the Devensian environment. Chaffweed Anagallis minima grows along some wet cart ruts across the heathland, but is easily overlooked. Turfy Hill may have got its name from the practice of cutting turf there formerly. Now the area is dominated by bracken communities, with smaller patches of heather and gorse. Small adder’s-tongue fern also occurs in this area, and one of the large species of New Zealand flax, Phormium colensoi, is well established and spreading.

Burnt Hill is the small promontory of open land on the north of the island between Turfy Hill and Chapel Down. It consists of mainly heather-dominated maritime heath and grassland. Inland from the promontory the heathland becomes dominated by bracken communities and a large area of gorse. Many areas of gorse and bracken are being managed to encourage the re-establishment of heathland plants. Chapel Down, where the land rises up towards the daymark, is dominated by waved heathland with scattered granite boulders and exposed granite platform very prominent towards the east. Many of the rare heathland plants, including small adder’s-tongue fern, orange bird’s-foot and chaffweed, are also found here, and this is also the territory of the St Martin’s ant Formica rufibarbis (see Chapter 14). There are steep cliffs around the edge of the headland with colonies of nesting seabirds during the summer. Above the cliffs are areas of bracken communities and gorse scrub. At Coldwind Pit near the coast there are a number of unusual aquatic plants growing in and around the pool.

On the north side of St Martin’s is an unusual open area called the Plains (Fig. 47). Formerly open grassland and low heath that had developed from dune grassland, it is becoming overgrown by gorse and scrub. Formerly small adder’s-tongue

FIG 47. North coast of St Martin’s, with the Plains and Round Island lighthouse in the distance. (Rosemary Parslow)

FIG 48. Mouse-ear hawkweed is one of the unusual species found in dune grassland on the Plains, St Martin’s. (Alma Hathway)

fern was widely distributed throughout the Plains until it became submerged by taller vegetation. Rare plants such as orange bird’s-foot and a patch of mouse-ear hawkweed Hieracium pilosella at its only known station in Scilly can be found here still (Fig. 48). Above the Plains among the dense thickets of common gorse it is also possible to find the strange pink nets of the parasitic heath dodder Cuscuta epithymum, another plant apparently only found in this one place in Scilly. The headlands and slopes along the northern side of St Martin’s also have spreading, triffid-like, populations of New Zealand flax, although control measures to reduce their numbers started in 2005. It is likely similar measures will be taken against another invasive alien, Myrtus luma, a myrtle-like shrub. Nearer the coast the dune is still active and sea spurge and Portland spurge are among the plants growing on the edge. A sand bar joins St Martin’s to the small, uninhabited White Island (see Chapter 7).