Wet Woodland (Uk Bap Priority Habitat)

WET WOODLAND (UK BAP PRIORITY HABITAT)

Summary

This is woodland on wet acidic to neutral soils in a variety of situations such as flushed slopes, wet hollows, valley floors and the edges of wetlands, rivers, streams and lochs. The most common trees in this habitat are willows, downy birch and alder. The ground vegetation is very varied and can include large grasses, sedges, rushes, herbs and mosses. Epiphytic bryophytes and lichens can be abundant and diverse.

This habitat is widespread in Scotland, in both upland and lowland areas. Associated habitats are equally varied and include drier woodland of all priority types found in Scotland, heaths, bogs, other mires, fens, reedbeds, open water, grasslands and enclosed farmland.

Good management for conservation in this habitat generally aim towards maintaining a diversity of species, sizes and age classes of trees and shrubs, encouraging diversity in the structure and species composition of the ground vegetation, maintaining rich bryophyte and lichen assemblages on rocks and trees especially in the west, maintaining good quantities of standing and fallen dead wood, and controlling the extent and spread of non-native trees and shrubs, especially rhododendron, Rhododendron ponticum.

What is it?

This is woodland on wet soils in a variety of situations such as flushed slopes, wet hollows, valley floors and the edges of wetlands, rivers, streams and lochs. The commonest trees are grey willow Salix cinerea, eared willow S. aurita, goat willow S. caprea, alder Alnus glutinosa and downy birch Betula pubescens, but there can be others such as bay willow S. pentandra, purple willow S. purpurea, crack willow S. fragilis, osier S. viminalis and ash Fraxinus excelsior.

The soils vary from more or less neutral (in NVC types W1-3 and W5-7) to acidic (W4), though in terms of canopy species there can be much similarity right through the range of variation in soil acidity and hence NVC communities. In particular alder and the willows Salix cinerea and S. aurita can be common on both neutral and acid soils, but birch is generally the commonest species on the more acid soils, where ash and the other willows are scarcer.

The ground vegetation consists mainly of large grasses such as reed canary-grass, Phalaris arundinacea, common reed, Phragmites australis and purple moor-grass Molinia caerulea, sedges such as bottle sedge, Carex rostrata, common sedge, C. nigra, glaucous sedge C. flacca, remote sedge, C. remota and greater tussock-sedge C. paniculata, rushes such as soft rush, Juncus effusus and sharp-flowered rush, J. acutiflorus, herbs such as meadowsweet, Filipendula ulmaria, wild angelica, Angelica sylvestris, common valerian, Valeriana officinalis, common marsh-bedstraw, Galium palustre, marsh marigold, Caltha palustris, water mint, Mentha aquatica, marsh thistle, Cirsium palustre and yellow pimpernel, Lysimachia nemorum, and mosses such as pointed spear-moss Calliergonella cuspidata, Sphagnum spp. and common hair-cap moss Polytrichum commune. The main variation in ground vegetation is between the examples of W4 on acid soils which are often dominated by Molinia, Sphagnum and P. commune and those on more neutral soils with various mixtures of the other species listed above.

The constantly wet ground combined with the shelter of trees and shrubs helps to keep air humidity generally high, and this encourages the growth of epiphytic bryophytes and lichens including some scarce species, especially in western areas with a wet and equable oceanic climate.

How do I recognise it?

Differentiation from other Priority Habitats

To a large degree the Wet woodland priority habitat is separable from others on the basis of its component NVC types. The communities W1, W2, W3, W5 and W6, and the sub- communities W4c, W7a and W7b are all unique to this priority habitat. This leaves only two sub-communities which overlap with other priority habitats: W4b and W7c.

In previously published definitions of this priority habitat, the less wet examples of W4b, and those which are in mosaics with drier W10e, W11, W16 and W17 woodland, are considered to be best placed in the Upland oakwood or Upland birchwoods priority habitat depending on location and dominance of oak or birch. However, W4b is generally as wet as other Wet woodland NVC communities and is generally very distinct from other Upland oakwood and Upland birchwood NVC types: there is therefore a good case for treating it as Wet woodland. Using patch size as a guide can be a useful approach such that a small area of W4b within a larger area of W11 would classify as Upland birchwood; whereas if the W4b is largely associated with W4c then it would classify as Wet woodland.

W7c varies in habitat, wetness and tree and shrub species. Examples on flushed slopes with some ash, elm, rowan or hazel belong in the Upland mixed ashwoods priority habitat. Wetter examples on hollows and valley floors, with little or no ash, elm, rowan or hazel do not fit comfortably into the Upland mixed ashwoods habitat and are better classed as Wet woodland.

Definition in relation to other habitat classifications

Classification Habitat types belonging to this UK BAP priority habitat W1-3 (all examples) W4b (wetter examples) W4c (all examples) W5-6 (all examples) NVC W7a and b (all examples) W7c (wetter examples, i.e. with alder/willow but little or no ash, elm, hazel etc, situated in wet hollows and valley floors) (drier W7c belongs in the Upland mixed ashwoods priority habitat). (All of the above NVC communities are included in the Scottish Biodiversity List.) A1: examples of NVC types W1-3, W4b/c, W5-6, W7a/b and wetter examples of W7c (see notes in NVC section above) with canopy cover >30% A2: scrub forms of W1-3, W4b/c, W5-6, W7a/b and wetter examples of W7c (see notes in NVC section above) Phase 1 A3: examples of W1-3, W4b/c, W5-6, W7a/b and wetter examples of W7c (see notes in NVC section above) with canopy cover <30% A4: felled W1-3, W4b/c, W5-6, W7a/b and wetter examples of W7c (see notes in NVC section above)

UK BAP broad All examples of this priority habitat belong to the broad habitat - habitat Broadleaved, mixed and yew woodland

Definition in relation to legislative classifications

Classification Habitat types belonging to this UK BAP priority habitat H91D0 (all examples except those with a canopy of native pine, Habitats Directive which are in the Native pine woodlands priority habitat). Annex I H91E0 (all examples).

SNH SSSI habitat All examples of the Wet woodland priority habitat belong within features the Wet woodland SSSI feature type.

Where is it?

This priority habitat occupies poorly drained acidic to neutral or slightly basic soils in a range of topographical situations including flat valley floors, wet hollows, hillside benches or flushes, and periodically flooded areas close to rivers, streams and lakes. Associated habitats are equally varied. In upland areas they typically include drier forms of woodland in the Upland oakwood, Upland birchwoods, Upland mixed ashwoods and Native pine woodlands priority habitats as well as open grassland including Upland calcareous grassland priority habitat, heath including the Upland heathland priority habitat, bog of the Blanket bog priority habitat and other types of wetland including the Upland flushes, fens and swamps priority habitat. Lowland examples can be associated with other woodland types including the Lowland mixed deciduous woodland priority habitat, open semi-natural habitats including the Lowland fens, Reedbeds and Purple moor grass and rush pastures priority habitats, and more intensively managed enclosed arable or pasture land or urban habitats.

This priority habitat is widespread and common in Scotland, especially in upland areas. In the lowlands it occurs mainly as thinly scattered small patches. The Native Woodland Survey of Scotland (2014) gives the area of this priority habitat in Scotland as 44,742ha. For reference see the National Report at p22 Table 3 http://www.forestry.gov.uk/PDF/FCMS126.pdf/$FILE/FCMS126.pdf .

What is special about it?

Some species of special conservation status recorded in this priority habitat in Scotland are listed below.

EC Scottish Wildlife & UK BAP Habitats Bio- Red Country- Common priority Directive diversity Data side Act Group name Latin name list Annex II List List (1981) amphibian common toad Bufo bufo y y y great crested amphibian Triturus cristatus y y y y newt ten-spotted Cryptocephalus beetle y y pot beetle decemmaculatus six-spotted pot Cryptocephalus beetle y y beetle sexpunctatus bird lesser redpoll Carduelis cabaret y y y bird cuckoo Cuculus canorus y y y bird reed bunting Emberiza schoeniclus y y spotted bird Muscicapa striata y y y flycatcher bird willow tit Poecile montanus y y y bird marsh tit Poecile palustris y y y bird starling Sturnus vulgaris y y y bird song thrush Turdus philomelos y y y chequered Carterocephalus butterfly y y y skipper palaemon flowering Scottish small- Calamagrostis scotica y y y plant reed flowering Scandinavian Calamagrostis y y plant small-reed purpurea Scottish fly Lipsothrix ecucullata y y yellow splinter northern fly Lipsothrix errans y y yellow splinter southern fly Lipsothrix nervosa y y yellow splinter orange fungus Cantharellus friesii y y chanterelle blackening Cantharellus fungus y y chanterelle melanoxeros lichen a lichen Collema fasciculare y y y lichen a lichen Leptogium brebissonii y y y Pseudocyphellaria lichen a lichen y y y norvegica lichen a lichen Sclerophora pallida y y y lichen a lichen Usnea florida y y mammal noctule Nyctalus noctula y y y y soprano mammal Pipistrellus pygmaeus y y y pipistrelle brown long- mammal Plecotus auritus y y y y eared bat argent and moth Rheumaptera hastata y y sable spider a money- Monocephalus y y EC Scottish Wildlife & UK BAP Habitats Bio- Red Country- Common priority Directive diversity Data side Act Group name Latin name list Annex II List List (1981) spider castaneipes a money- Notioscopus spider y y spider sarcinatus

How do we manage it?

Good management for conservation should aim towards the following:

 Maintaining a good diversity of species, sizes and age classes of trees and shrubs

If felling or thinning takes place this should ideally not reduce the variation in species, sizes and age classes of trees and shrubs. In many woods natural regeneration can be encouraged, generally by at least a temporary reduction or removal of grazing, as a means of increasing the numbers of young trees, thereby helping to maintain the woodland in the long term. Birch, willow and alder will all regenerate quite readily depending on the conditions. Willow will dominate in the wettest conditions, where aquatic habitats are turning marshy. Alder regenerates well on bare mineral soils, including sand and river gravels. Birch will regenerate in most other conditions. The benefits of management for natural regeneration should of course be balanced against any possible detrimental effects. An increased height and density of ground vegetation can lead to reductions in populations of insects and small plants. A very dense tree/shrub canopy can outshade light-demanding species such as many lichens. In some situations where marshes and bogs are particularly rich, woodland colonisation can become problematic. In these circumstances management might be concentrated on trying to maintain open, wet conditions. Having some open glades will provide general habitat diversity, and can be important for groups such as insects, birds and, on trees at edges of glades, lichens.

 Encouraging diversity in the structure and species composition of the ground vegetation

If grazing is only light to moderate this can allow some tree and shrub regeneration and good flowering and seed-setting of ground flora plants, and also prevent damaging trampling which can disrupt soft, wet soils and low carpets of small herbs and mosses.

 Maintaining rich assemblages of bryophytes and lichens on trees, especially in the west

To a large extent this means maintaining shaded conditions so that shade- and humidity-demanding bryophytes and lichens including many uncommon species do not suffer from too much exposure to sunlight and wind. The canopy is quite shrubby and dense in many wet woodlands, for example where it includes grey willow and eared willow, and this helps to maintain shade and humidity. However, it is good to avoid overshading because many bryophytes and lichens of interest are intolerant of very heavy shade. Where felling or thinning is planned in western woods it is best to assess the richness of the trees and shrubs concerned, and that of nearby rocks, and to carry out the planned management only where these epiphytic and saxicolous floras are not especially rich or do not include species of special interest.

 Maintaining good quantities of standing and fallen dead wood

Dead wood is best left in the woodland because it is an important habitat for birds, insects and, on fallen rotting logs, bryophytes, especially liverworts. Fallen dead wood also helps to provide variety in habitat structure on the ground, and the additional shade and shelter close to fallen timber helps to maintain the humid conditions needed by some woodland species.

 Controlling the extent and spread of non-native trees and shrubs, especially rhododendron, Rhododendron ponticum

Non-native trees and shrubs can occur in this habitat as a result of deliberate under- or inter-planting, or by seeding in from nearby sources. However, they tend to be less common here than in drier woods. The commonest of such species here are conifers such as spruces and pines and, mainly in the west, rhododendron. All of these have the potential to grow thickly and cast such heavy shade and leaf litter as to impoverish the native woodland ecosystem. Control of these species is desirable in order to prevent ecological impoverishment of the habitat. Rhododendron ponticum is the most serious of these alien woody species because it can invade an area in a relatively short time forming such dense thickets that almost all plant life is overshaded and smothered by leaf litter. Although not very common in wet woodlands rhododendron is common and invasive in the types of humid western woodland, which are of international importance for the oceanic bryophyte, lichen and fern floras. Removal of rhododendron is therefore desirable from such woods and their surroundings. Alder woodlands on floodplains are also vulnerable to invasion by non-native plants such as Japanese knotweed Fallopia japonica, giant hogweed Heracleum mantegazzianum, and Himalayan balsam Impatiens glandulifera which are spread by water.

References, links and further reading

Averis, A., Averis, B., Birks, J., Horsfield, D., Thompson, D., and Yeo, M., (2004), An Illustrated Guide to British Upland Vegetation, c.470, figs, B5 softback, ISBN 1 86107 553 7 http://jncc.defra.gov.uk/page-2463

Ellis, N.E. and Munro, K. (2004). A preliminary review of the distribution and extent of BAP priority habitats across Scotland. Scottish Natural Heritage Commissioned Report No.044 (ROAME No. F00NA02). https://www.nature.scot/information-library-data-and-research/information-library

Rodwell, JS, ed 1991a British plant communities Volume 1: Woodlands and scrub. Cambridge, Cambridge University Press

Usher, M.B. (Ed.). 2000. Action for Scotland's Biodiversity. Edinburgh, The Scottish Executive and The Stationery Office.

UK BAP 2008 http://jncc.defra.gov.uk/pdf/UKBAP_BAPHabitats-64-WetWoodland.pdf

Common Standards Monitoring guidance http://www.jncc.gov.uk/page-2199

Native Woodland Survey of Scotland http://scotland.forestry.gov.uk/supporting/strategy- policy-guidance/native-woodland-survey-of-scotland-nwss

Managing native woodlands http://scotland.forestry.gov.uk/supporting/strategy-policy- guidance/biodiversity/native-woodlands

Managing invasive rhododendron http://www.forestry.gov.uk/fr/rhododendroncontrol

National Biodiversity Network (NBN) Gateway https://data.nbn.org.uk/

Scottish Natural Heritage website: http://www.nature.scot

UK BAP information on JNCC website: http://jncc.defra.gov.uk/default.aspx?page=5155