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Fig. 7.2 Recent sea level rise as recorded from 23 annual tide gauge records and satellite altimetry. (Reproduced with permission from www.globalwarmingart.)

Fig. 7.3 Shingle beach showing the diversity of plant forms that can be found growing close to the sea. Scots pine (Pinus sylvestris) and bearberry (Arctostaphylos uva-ursi) at Gothemshammar on the island of Gotland. The Baltic Sea is noted for its low salinity, which may account for the survival of bearberry so close to the shore.

Fig. 7.3 Shingle beach showing the diversity of plant forms that can be found growing close to the sea. Scots pine (Pinus sylvestris) and bearberry (Arctostaphylos uva-ursi) at Gothemshammar on the island of Gotland. The Baltic Sea is noted for its low salinity, which may account for the survival of bearberry so close to the shore.

discrete patches, the constant physical onslaught of the oceans has preserved the open shore as a long-distance migration pathway. The ocean itself aids this dispersal not just for species with floating, salt-tolerant seeds, but for many others that can be transported by rafting with driftwood and other maritime flotsam, or by birds using coastal migration routes (Fig. 7.5). Even the Arctic Ocean may have been a significant dispersal route during the ice ages. The movement of drift ice and driftwood dendrochronologically dated from the Late Weichse-lian or early Holocene suggests that the Arctic Ocean has long been a possible dispersal route for diaspores from eastern Siberia and north-west Russia to parts of the North Atlantic region. The extremely disjunct distribution of some vascular plants in northern Scandinavia and East Greenland which are also found in eastern Siberia (e.g. Draba sibirica, Oxytropis deflexa ssp. norvegica, Potentilla stipularis and Trisetum subalpestre) may be the result of this type of long-distance dispersal (Johansen & Hytteborn, 2001).

7.1.1 The concept of oceanicity

Ecologically, the term oceanicity is used to describe the climatic factors which modify the environment and ecology of a region within reach of maritime weather systems. In common with other terms used to denote environmental syndromes, 'oceanicity' describes a multi

Fig. 7.4 Distribution of coastal forests shown in black and identified by dominant tree species. A, Alnus japonica; B, Chamaecyparis formosensis; C, C. taiwanensis; D, C. lawsoniana; E, C. nootkatensis; F, C. obtusa; G, C. pisifera; H, C. thyoides; I, Picea glehnii; J, Pinus muricata; K, P. pumila; L, P. radiata; M, P. serotina; N, Sequoia sempervirens; O, Thuja orientalis; P, Taxodium distichum/Nyssa aquatica; Q, Yucatan species. (Map adapted with permission from Laderman, 1998b.)

Fig. 7.4 Distribution of coastal forests shown in black and identified by dominant tree species. A, Alnus japonica; B, Chamaecyparis formosensis; C, C. taiwanensis; D, C. lawsoniana; E, C. nootkatensis; F, C. obtusa; G, C. pisifera; H, C. thyoides; I, Picea glehnii; J, Pinus muricata; K, P. pumila; L, P. radiata; M, P. serotina; N, Sequoia sempervirens; O, Thuja orientalis; P, Taxodium distichum/Nyssa aquatica; Q, Yucatan species. (Map adapted with permission from Laderman, 1998b.)

faceted situation. Species found in proximity to the ocean may live there for a variety of ecological, physiological, and even historical reasons. Equally, species absent from areas near the sea, and therefore responding negatively to oceanicity, are also likely to have a diverse range of primary and secondary causes for this restriction in their distribution (Figs. 7.6-7.8). A lack of summer warmth may be important in some cases, but secondary causes, such as the unavailability of their preferred habitat and exposure to salt, may be sufficient to ensure their exclusion rather than any direct climatic factor. Quantification of 'oceanicity' in all its various manifestations has therefore to be pursued with caution, as it is merely a human perception of what may be involved in determining why proximity to the sea creates a particular environment which is suitable for certain species of plants but excludes others.

The commonest meteorological assessment of oceanicity is mean annual temperature range. In some cases this can be used directly; in other cases it can be adjusted for latitude and related to defined extremes of 'oceanicity', or its converse 'continentality', as with Conrad's Index of Continentality (Conrad, 1946).

A direct consequence of oceanicity is a decrease in potential water deficit due in part to the reduced evaporative power of oceanic climates and partly to increased precipitation in areas with high relief on their windward shores, as in western Scotland and Norway. Consequently, increasing oceanicity is likely to be associated with greater water saturation of the soil profile for lengthy periods of the year. The ecological consequences of prolonged soil saturation for bog growth need little elaboration. Bogs are important sources of information for the reconstruction of climatic history and as their surface topography is highly sensitive to changes in moisture they also serve as indicators of how oceanicity has varied with time. Many British bogs have profiles that show changes in bog surface vegetation from wet lawn to pool and hummock topography as the hydrological element of the oceanic environment fluctuates through the centuries (Barber, 1981; Chambers et al., 1997; Mauquoy & Barber, 1999; Fig. 7.9).

The differences between maritime and continental climates are most commonly described by modification of temperature extremes and as such can be meteorologically quantified and mapped (Fig. 6.7). This simplification of the concept of oceanicity to an expression of annual temperature amplitude, although it is unambiguous and meets many human environmental needs, nevertheless neglects many of the ways in which the ocean alters the terrestrial environment.

Fig. 7.5 Hoary cress (Lepidium draba) growing on a boulder beach site at its most northern UK distribution limit on the west mainland of Orkney (see inset). This species has a mainly southern distribution in the British Isles but is now becoming more common in coastal habitats possibly as a result of climatic warming.

Fig. 7.5 Hoary cress (Lepidium draba) growing on a boulder beach site at its most northern UK distribution limit on the west mainland of Orkney (see inset). This species has a mainly southern distribution in the British Isles but is now becoming more common in coastal habitats possibly as a result of climatic warming.

Fig. 7.6 Distribution of six species of flowering plants limited in distribution to areas adjacent to the sea. (Maps reproduced from Meusel & Jager, 1992.)

Plants are highly sensitive to many aspects of the maritime environment and respond to the influence of the ocean, even in regions that are a considerable distance from the sea, as a result of changes in temperature, rainfall, and variability and length of the growing season. Paludification can also be a consequence of oceanicity. The growth of Atlantic bogs in Scotland is one example, and another is the replacement of tundra by bog due to the proximity of the Arctic Ocean to the West Siberian Plain (see Section 5.4.3).

7.1.2 Physical versus biological fragility

In examining survival in any habitat it is essential to distinguish between physical and biological fragility. A shoreline, or dune system or even a mangrove forest may be physically fragile and suffer loss of terrain through storm erosion or excessive grazing and

Fig. 7.7 Distribution of six species of flowering plants which are less able to survive in areas adjacent to the sea. Note that there is a tendency for a north-south orientation in the western distribution limit which matches the orientation of zones of similar oceanicity in Fig. 7.6. (Maps reproduced from Meusel & Jager, 1992.)

Fig. 7.7 Distribution of six species of flowering plants which are less able to survive in areas adjacent to the sea. Note that there is a tendency for a north-south orientation in the western distribution limit which matches the orientation of zones of similar oceanicity in Fig. 7.6. (Maps reproduced from Meusel & Jager, 1992.)

trampling, yet despite this material damage, there may be no loss in biological diversity. The plants that grow in these physically disturbed sites are usually adequately adapted to their surroundings and even require a certain degree of disturbance to provide opportunities for regeneration, which also aids habitat renewal and the preservation of species diversity.

Regeneration in many such communities is dependent on disturbance. For conservation activities this can present a dilemma. Large areas of valuable terrain can be physically destroyed by erosion or biologically impoverished by herbivores. Sheep, deer, cattle and goats have all been known to damage coastal vegetation. Hurricanes have always caused periodic widespread destruction to mangrove forests from which they recover. Removal of herbivores can restore an initial lushness to vegetation with improved flowering. However, this can then lead to an increasing dominance of scrub and graminoid species with loss of diversity in the herbaceous flora. Similarly, coastal

Fig. 7.8 Reduction in continentality as measured by Conrad's Index (see text) in central Europe between the beginning and the end of the twentieth century penetrating into central Europe. Note the gradients in oceanicity (the inverse of continentality run parallel to the eastern distribution limits of the oceanic species shown above. (Map prepared by Dr C. E. Jeffree using temperature data from the Climatic Research Unit, 0.5° gridded 1901-1995 Global Climate Dataset; New et al., 1999, 2000.)

Fig. 7.8 Reduction in continentality as measured by Conrad's Index (see text) in central Europe between the beginning and the end of the twentieth century penetrating into central Europe. Note the gradients in oceanicity (the inverse of continentality run parallel to the eastern distribution limits of the oceanic species shown above. (Map prepared by Dr C. E. Jeffree using temperature data from the Climatic Research Unit, 0.5° gridded 1901-1995 Global Climate Dataset; New et al., 1999, 2000.)

Fig. 7.9 Detrended correspondence analysis of eigenvalue scores for plant fossil data in two northern England bogs. The position of each sample relative to the y-axis reflects the degree of soil surface wetness. (Reproduced with permission from Mauquoy & Barber, 1999.)

Fig. 7.10 An eroding salt marsh and falling shore level threatens to remove part of the historic St Andrews Old Course. Over the last 50 years many remedial measures in the forms of walls and groynes have been tried to arrest the erosion but the shore level continues to fall and erosion remains a serious threat to the integrity of the golf course.

Fig. 7.10 An eroding salt marsh and falling shore level threatens to remove part of the historic St Andrews Old Course. Over the last 50 years many remedial measures in the forms of walls and groynes have been tried to arrest the erosion but the shore level continues to fall and erosion remains a serious threat to the integrity of the golf course.

heaths can be invaded by trees, which if left undisturbed can dominate the landscape and reduce the diversity of the natural coastal plant communities. Coastal nature reserve management plans therefore usually attempt some form of robust protection policy. Similarly, when erosion encroaches on golf courses and other areas where territorial protection is paramount, concrete walls and groynes are frequently employed

(Fig. 7.10). Unfortunately, this form of protection frequently results in the loss of much of the upper shore vegetation causing the shore level to fall, eventually undermining the coastal defences which then require continual repair.

Finding a balance between protection and still allowing the periodic disturbance that is necessary for species regeneration is becoming an ever more serious problem in coastal habitats. Rising sea levels increase the demands on land for housing, industry, and recreation, and these multiple onslaughts tend to reduce coastal plant communities to vestigial ribbons along the edges of golf courses. Where once series of dunes, slacks and heathlands provided a broad band of varied communities that have been resilient over centuries to fire, floods, grazing and erosion, all that remains is a single dune front with some marram (Ammophila arenaria) and a few other grasses (Figs. 7.11-7.12). In the past the foreshore communities, although sometimes physically damaged during periods of stormy weather, could nevertheless recover as they were backed up by a natural coastal hinterland with a reserve of biodiversity. Today this ecological space is absent and the disturbance so frequent that recovery is greatly hindered.

Not all shores are equally susceptible to disturbance. The classical hard shores where the terrain consists of hard rock or cliffs may be subject to attack from the sea; nevertheless, they retain their status as hard shores and cliffs. Chalk cliffs may erode but the biological habitat is renewed rather than destroyed.

Fig. 7.11 The eroding West Sands of St Andrews (east Scotland) where removal of strand-line litter by regular raking in order to be awarded the prestigious European Blue Flag for beach cleanliness is resulting in the destruction of the last remains of a once vigorous and regenerating dune system.

Fig. 7.12 Actively growing line ofyellow dunes at Tentsmuir National Nature Reserve at a time ofrapid expansion in the 1970s due to the dominance of a lyme-grass (Leymus arenarius) creating low level dunes. Later colonization by marram (Ammophila arenaria, far distance) raises the height of the dunes and replaces the lyme-grass. This naturally accreting dune system is on the same region of the east coast of Scotland only 8 km to the north of the eroding dunes shown in Fig. 7.11.

Fig. 7.12 Actively growing line ofyellow dunes at Tentsmuir National Nature Reserve at a time ofrapid expansion in the 1970s due to the dominance of a lyme-grass (Leymus arenarius) creating low level dunes. Later colonization by marram (Ammophila arenaria, far distance) raises the height of the dunes and replaces the lyme-grass. This naturally accreting dune system is on the same region of the east coast of Scotland only 8 km to the north of the eroding dunes shown in Fig. 7.11.

It is the soft shores that are most likely to suffer from disturbance and erosion.

Soft shores vary in their plant communities and can therefore be expected to differ in their responses to erosion and disturbance. Some examples from different parts of the world are therefore discussed below not only in an attempt to highlight the ecological richness of maritime margins but also to draw attention to the range of adaptations that permit coastal plants to survive in such physically hazardous environments. If we wish to minimize the damage that they are likely to suffer in the years ahead it will be particularly important to give attention to the preservation of marginal coastal plant communities.

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