Читать книгу The Isles of Scilly - Rosemary Parslow - Страница 54

Tresco and Bryher face each other across the narrow channel that forms the sheltered anchorage of New Grimsby Harbour. Tresco is the second largest and arguably the best known of the Isles of Scilly, on account of the famed Abbey Gardens. The island is just over 3km long and 1.7km wide, and covers approximately 298 hectares. At the north end is one of the most extensive areas of waved heath in the islands, on a plateau some 30 metres high. Across the middle of Tresco, almost dividing the island in two, is the long, water-filled gash that is the Great Pool, with the Abbey Pool slightly to the south. North of Great Pool is a broad band of farmland that stretches to Old Grimsby on the east coast (Fig. 40). South of Great Pool are the Abbey Gardens and woodland around Tresco Abbey. Beyond the Gardens and on the eastern side of the island are extensive sand dunes and stretches of dune heathland. Other than rocky Gimble Porth, and the northern fringes of the island, the coastline of Tresco is mainly composed of dunes and sandy beaches.

General impressions of Tresco tend to be coloured by the presence of the Abbey Gardens and the farm, and especially the very large area of planted woodland that dominates the landscape. The island has a much more managed atmosphere than the other off-islands. This may be partly due to its history, but is mainly because almost the whole island is under one tenancy and has been mostly managed as one estate for a very long time. The present incumbent of Tresco, Robert Dorrien-Smith, took on the estate in 1973.

Even before the visitor reaches the Gardens their influence and that of the tenure of Augustus Smith and the Dorrien-Smith family is evident everywhere on Tresco. Apart from the gardens themselves, this influence is most evident in the sand dunes around Appletree Banks and Pentle Bay, where a hotch-potch of exotic plants have become established among the native dune species. Throughout the dunes are clumps of rhodostachys, the very similar Tresco rhodostachys Ochagavia carnea, bugle lily Watsonia borbonica, Agapanthus praecox

FIG 40. Old Grimsby Harbour, on the east coast of Tresco, June 2002. (Rosemary Parslow)

and red-hot pokers Kniphofia sp. growing among the marram, with balm-leaved figwort, Babington’s leek and sand sedge Carex arenaria. Where the dune has become flattened and consolidated, dune grassland and heathland have formed. Rushy Bank, just beside the road from the landing at Carn Near quay, is particularly interesting, with many unusual plants: orange bird’s-foot (found some years growing all along the edge of the concrete road) and small adder’s-tongue fern can be found here, and on the heathers nearby are rich growths of lichens, including some of the lungworts. Also beside the road at Carn Near there are banks of the extraordinary wireplant moulding itself over the other vegetation in a parody of topiary. Below the dunes, at the back of the beach, is one of the very few places where a few plants of the rare shore dock Rumex rupestris grow among the masses of the coastal form of curled dock Rumex crispus var. littoreus (see Chapter 9). As this section of coast is actively eroding, the future of this shore dock site is probably limited.

Tresco has its own heliport, opened in 1983 (Fig. 41). The island has a hotel, the first to be established on an off-island, and an established time-share business. With the draw of the Gardens, Tresco attracts more visitors than any of the islands other than St Mary’s. The heliport is on a beautiful mown stretch of grassland just beside the Gardens and is well worth looking at (but not when

FIG 41. Tresco, looking north from Oliver’s Battery across coastal dunes, the heliport and plantations, April 2005. (Rosemary Parslow)

helicopters are landing!). Like the airfield on St Mary’s it frequently attracts feeding waders and other birds. In autumn it can be one of the places to look for rare pipits and larks.

Towards the edge of the Abbey Pool (Fig. 42) the grassland is seasonally waterlogged so a band of marsh pennywort, lesser spearwort and other wetland plants extends all round the edge, and similarly around the south side of the Great Pool. When Borlase visited Tresco in 1756 he commented on ‘a most beautiful piece of fresh water edged round with Camomel Turf, on which neither Brier, Thistle, nor Flag appears. I judged it to be half a mile long, and a furlong wide.’ The chamomile turf is still there but no longer so extensive. The fine silt drawdown zone (much enriched by droppings from gulls and waterfowl) around the edge of the Abbey Pool supports a variable array of tiny wetland plants, depending on how much mud is exposed. During periods of drought some of the submerged aquatic plants become visible as the water level drops, and those growing on the mud spread quickly; six-stamened waterwort Elatine hexandra, for example, on these occasions can turn the surface of the mud bright red. Abbey Pool has a resident population of wild and domestic waterfowl, but like anywhere in Scilly it has seen some notable rarities at times.

Great Pool is much more extensive. The lake stretches right across the middle of the island, virtually dividing it in two. Surrounding Great Pool are reedbeds, areas of willow carr and some stretches of muddy foreshore. A painting of the lake and the surroundings by Augustus Smith’s sister Mrs Frances Le Marchant, executed in September 1868, shows the lake to be much more open than now, with the reedbeds only marginal (in King, 1985). The lake attracts many waterbirds, both migrants and the resident species, including gadwall, mallard and moorhen, and is an important feeding area for migrating waders. Among the reeds and in open patches along the foreshore are many common wetland plants, lesser spearwort, royal fern, bulrush (reedmace) Typha latifolia and yellow iris. The rattling songs of reed Acrocephalus scirpaceus and sedge warbler A. schoenobaenus can be heard from the reedbeds around the lake during summer. Good views across the lake can be obtained from the bird hides that are approached by boardwalks from the track north of the pool. One hide was erected in memory of the late David Hunt, the ‘Scilly Birdman’, who was resident on Tresco before moving to St Mary’s (see Chapter 4).

Much of Tresco is under agriculture, with pasture and arable fields (Fig. 43). The Tresco Estate currently runs a large herd of beef cattle. There is more tree cover generally, so that in autumn the island attracts rare migrant birds from

FIG 42. Tresco Abbey and Abbey Pool, April 2005. (Rosemary Parslow)

FIG 43. Arable fields and pine shelterbelt on Tresco. (Rosemary Parslow)

North America and elsewhere to tease the ‘twitchers’ who also flock to the islands.

Across the north end of the island is Castle Down, one of the largest areas of wind-eroded waved heath in the islands. This is a fascinating place, a plateau covered in low heather only about ankle height where the plants form long ridges as they are rolled over by the wind, with large patches of exposed bare ground between the waves. This type of heathland is not particularly species-rich but very atmospheric when the heathers are in flower and the whole place is full of the hum of bees. Besides bell heather and ling, there are several common species of grass, patches of English stonecrop, lousewort and bird’s-foot-trefoil, and lichens and mosses. The tread of many feet on the pathways across the Down, exacerbated by the eroding effect of wind and rain, have caused the braiding of many pathways. On some places on the paths are many shallow temporary pools with a transient wetland flora of starworts and lesser spearwort. Ruins of all that remains of King Charles’s Castle are on one of the high points at the western edge of Castle Down. Besides having a good population of ferns and sea stork’s-bill Erodium maritimum among its stones, the top of the castle makes a good vantage point for looking down into the Tresco Channel between Tresco and Bryher, and over the tower of Cromwell’s Castle on the headland below.

Gimble Porth on the eastern side of the headland is backed with low cliffs where gulls nest, and where some years there is a kittiwake Rissa tridactyla colony. Piper’s Hole is a deep cavern in the north-facing cliffs that can be approached by scrambling down the cliff, but a boat is needed to explore properly. It was very popular with holiday visitors in the past, and there are still postcards on sale showing it lit up with lanterns in the early 1900s. The cave consists of a long boulder-filled passage over 20m long leading to a large underground pool that can be traversed by boat (a punt used to be kept there in the past) to reach the inner chamber, which is over 40m deep. The cave system was investigated in 1993 by Philip and Myrtle Ashmole and specimens of the cavernicolous fauna collected, including a springtail new to Britain, Onychiurus argus, a troglophile species otherwise known from caves in Spain, France and Belgium (Ashmole & Ashmole, 1995).

The plantations and windbreaks originally planted by Augustus Smith and his successors are now coming to the end of their life. Much planting and felling has taken place to remove and replace the fallen timber. The woodlands are a mixture of planted trees and shrubs, escapees from the Gardens, as well as wild plants and ferns – a botanical recorder’s headache. Protected by the plantations are the ‘subtropical’ Abbey Gardens (Fig. 44). These are densely planted with a

FIG 44. Tresco Abbey Gardens, April 2005. (Rosemary Parslow)

great range of plants from countries with a Mediterranean climate, Australasia, the Canary Islands, South Africa and parts of South America (see Chapter 13). Visitors to the Abbey Gardens will also remark on the extraordinarily tame birds. In 2004 the entrance to the Gardens was updated and the tea room moved. If you visit the tea garden, kamikaze robins Erithacus rubecula snatch crumbs from your lips and blackbirds, chaffinches Fringilla coelebs and other birds will help themselves to cake from your plate. At certain times of the year the odd appearance of the house sparrows Passer domesticus, starlings Sturnus vulgaris and blackbirds – with bright yellow caps of pollen from drinking the nectar of Puya chilensis plants – has occasionally led to them being identified as something far more exotic! Another curious phenomenon in the former tea garden was the pecking of holes in the mortar of a wall by dozens of house sparrows, presumably seeking minerals after the manner of some tropical parrots.

Some of the exotic plants that grow around Tresco and the other islands are spread intentionally when people take cuttings or seeds to cultivate for their own gardens or pass around to their friends. Other plants escape from the Gardens by natural means, blown by the wind or otherwise carried accidentally, to end up elsewhere in the islands. Many of these are now established as part of the Scillonian flora. Perhaps the most unusual inhabitants of the Gardens are the two species of New Zealand stick insects that have been part of the fauna for about a century and are now found elsewhere around Tresco. Recently they have also reached St Mary’s. Also from New Zealand but less obvious are the woodland hoppers Arcitalitrus dorrieni, the little back amphipods that now live under every rock and log on the island. These are the most obvious and well-known examples, but there are many other insects and other invertebrate species that originally arrived as stowaways with horticultural material from abroad.

It is not just insects and other animals that have arrived in Scilly with introduced plants. A series of discoveries of rare introduced bryophytes began in 1961 when Miss R. J. Murphy discovered two unexpected liverworts on Tresco, Lophocolea semiteres, new to the northern hemisphere, and a new species of Telaranea that was named T. murphyae after her by Mrs Paton in 1965. Telaranea murphyae may have been introduced to Tresco from the southern hemisphere, as has happened with many other species such as Lophocolea semiteres and L. bispinosa, which are found only on Scilly and in Scotland, pointing to introduction with exotic plants. Besides Lophocolea bispinosa, found by Mrs Paton in 1967, was a moss Calyptrochaeta apiculata, later also found in East Sussex.

Since then, the moss Sematophyllum substrumulosum was first recorded as new to Britain on several of the islands (it has since been discovered to have been found, but not identified, in West Sussex in 1964). It was growing on the bark of Monterey pine in 1995 and again may have arrived with horticultural material (Paton & Holyoak, 2005). Other species recorded have included two mosses rare in Britain (Chenia leptophylla, Didymodon australasiae) and another that has become very widespread and common (Campylopus introflexus). By 2003 some of the alien bryophytes had greatly extended their ranges since the 1960s, with both alien Lophocolea species now widespread throughout the islands, and Telaranea murphyae had spread from Tresco to St Mary’s.