Changes in species diversity over time

6.4.1 Plants, lichens and fungi indicative of old woodland

Biodiversity may be related to the age and previous history of the ecosystem concerned. For example, the richness of epiphytic lichen communities is frequently related to the length of time the dominant trees have been established in the forest. Fagus sylvatica has a south-western distribution in Sweden where aged beech trees in old forest stands often have an extremely rich lichen flora including the rare Lobaria pulmonaria, a leafy green lichen found throughout the northern hemisphere. As well as the age of the individual trees, the age and 'continuity' of the forest stand are very important. In the county of Halland, Sweden certain lichen species, such as Pyrenula nitida, Catinaria laureri and

Bacidia rosella occur only in areas which have been covered by beech for many hundreds of years. In contrast, planted Fagus sylvatica forests on ground that lacks 'beech continuity' are never inhabited by these species (Hultengren, 1999).

Such lichens are thought formerly to have been widespread and relatively common in virgin forests throughout Europe (Rose, 1988), forming part of the Lobarion assemblage of foliose and crustose lichens which develop as a late-succession grouping on the bark of large trees. They include species of the genera Lobaria, Sticta, Pseudocyphellaria, Parmeliella, Pannaria, Nephroma, Peltigera and Parmelia. Lobarion occurred through most of Europe well into the nineteenth century, but changes in forest practice and pollution have greatly reduced its area; it is now largely confined to montane forests and the lowland oceanic zone from south-west Norway to the Iberian Peninsula.

The diversity of lichens and fungi also varies with the antiquity of the forest; ancient woodlands such as Windsor Forest possess extremely rich fungal communities and are relict centres of diversity. Fungal indicator species have been used to indicate the conservation value of boreal conifer forests for some years, and in countries such as Sweden and Estonia are employed in countrywide surveys to locate woodland key habitats. Independent investigations in England and Denmark have shown their value with regard to beech forests. The computer database of the British Mycological Society is of great value in such investigations though its records have to be used with care, bearing in mind that levels of monitoring vary widely over the country. Moreover, the existence of records for many different fungal species for a woodland may not necessarily imply that the site is ofhigh conservation value; some taxa are of greater value than others as far as conservation is concerned. The diversity of saprotrophic fungi in beech forests has been shown to be related to the age and continuity of woodlands in the same way as that of lichens by Ainsworth (2004, 2005), who surveyed saprotrophs growing on large-diameter beech logs in Windsor Forest for a decade. Standing and fallen wood, including coarse woody debris (CWD) is an important element in the biodiversity of forests (see Section 7.7); Peterken (1996) provides detailed information concerning the amounts present in a number of managed and natural woodlands.

The above work was the basis for generating a list of 30 fungal species used to define British beech forests of high conservation value. The 30 indicators now used on bulky beech substrata such as logs and branches in Britain, belong to several fungal groups and are also found on other species of tree. Besides the species depicted in Fig. 6.6, they include thick tarcrust Camarops polysperma, spiral tarcrust Eutypa spinosa (an ascomycete whose fruit-bodies spiral down beech trunks), toothed powdercap Flammulaster muricatus,

Animals Change Over Time

Figure 6.6 Four saprophytic indicators for bulky beech substrata. (a) Woolly oyster Hohenbuehelia mastrucata, a gill fungus without a stem. Species of this genus capture and prey on nematode worms. (b) Fox cockleshell Lentinellus vulpinus. (c) Spongy mazegill Spongipellis delectans, with its strikingly patterned lower surfaces. (d) Coral tooth Hericium coralloides, whose fruit-bodies are irregular masses of white branches bearing combs of downward-pointing spines beneath. (Photographs by Martyn Ainsworth.)

Figure 6.6 Four saprophytic indicators for bulky beech substrata. (a) Woolly oyster Hohenbuehelia mastrucata, a gill fungus without a stem. Species of this genus capture and prey on nematode worms. (b) Fox cockleshell Lentinellus vulpinus. (c) Spongy mazegill Spongipellis delectans, with its strikingly patterned lower surfaces. (d) Coral tooth Hericium coralloides, whose fruit-bodies are irregular masses of white branches bearing combs of downward-pointing spines beneath. (Photographs by Martyn Ainsworth.)

fragrant toothcrust Mycoacia nothofagi, and a number of gilled and poroid bracket fungi.

In Denmark a list of 42 species of potential indicators was proposed by Heilmann-Clausen and Christensen (2000) and subsequently used, with variations, in much of continental Europe. The use of a single European list for such indicators is not straightforward because of the differing geographic (and dynamic) ranges of the fungi involved. Nevertheless, results obtained when a list of 21 European indicators was applied to 126 European beech forests were extremely interesting. Two Slovakian communities come top, both with a score of 16 out of the 21 possible, followed by others from the Czech Republic (15), France (15) and Denmark (14). The Wood Crates (13) and Denny Wood (12) areas of the New Forest in the UK were respectively 6th and 8th. All of the 11 British beech forests were in the top 30, so the use of this relatively new method of assessment has emphasized their conservation value; one hopes that even with global warming beech forests will continue to grow in the Cotswolds, Chilterns, Wye Valley and North and South Downs. Box 6.1 deals with an example of the conservation value of ancient communities of a particular tree species.

Certain vascular species are also indicative ofold forest and are consequently of value in the UK when attempting to get some idea of woodland age and particularly in determining which are ancient woodlands (see Section 9.1.4 for a definition). These Ancient Woodland Vascular Plant Indicators (AWVPs) are to some extent influenced by topography and geographical location, but many are useful over considerable areas. Peterken (1993, 1996) did much pioneer work on this subject in Britain, continental Europe and North America. The best indicators have a strong affinity for ancient woods, show little or no ability to colonize secondary woodland and are rarely found in recent woodland or other habitats. In central Lincolnshire smooth-stalked

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  • Gabriel
    How has the diversity of species changed over time.?
    1 month ago

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