Wet woodland
Mike Dilger highlights the wildlife to be found in our mossier, boggier woods
Deterring all but the most determined of naturalists, wet woodlands have to be some of the wildest and yet most natural of all our British woodlands. Characterised by tussocky sedges and a tall herb layer, which combine to conceal swampy pools harbouring partly submerged fallen trunks, this secretive and sometimes forbidding habitat will certainly reward those venturing off the beaten track.
Scattered across the UK, wet woodland is dominated by trees able to thrive in either poorly drained or seasonally flooded soils, such as the various willows, birch and alder. This habitat can also be encountered anywhere from floodplains, fens and bogs, to hillside flushes and even peaty hollows. Rarely covering expansive areas, it more frequently forms a mosaic with other habitats, such as drier woodland. Here, the boundary between these different forest types can either be sharp or gradual – it depends on the site’s specific hydrological conditions and how the surrounding land is managed.
Wet woodland has a long, grand tradition in
Britain, having colonised open areas following the last glacial retreat about 12,000 years ago. However, it can also be a relatively ephemeral habitat, as the very presence of trees can eventually cause a gradual drying out of the soil, ultimately leading to the woodland’s colonisation by species less tolerant of waterlogged conditions, such as ash and oak.
But at those locations where bog mosses proliferate, these bryophytes will often cooperate to impede tree growth. The tussle for supremacy between moss and trees means that the natural succession of either is halted in its tracks. Also, a lack of nutrients, as seen in many Scottish bogs, can result in the Scot’s pines and birches becoming stunted. And with the trees in such a weakened state, this may again result in the status quo being maintained,
as neither dry woodland nor wetland are able to gain the upper hand.
Wet, wet, wet
Any forested areas on floodplains are perhaps the most dynamic of all wet woodlands, as they may be forced to respond quite dramatically after big flood events, or more gradually while following the meandering course of the river. Frequently found on flat, fertile land, most of these woodlands would have been earmarked for agricultural production during the early land clearances and so only pockets remain today in places such as the New Forest and northern Scotland.
While admittedly containing relatively few specialised species, wet woodlands’
humidity and abundance of dead and rotting wood can make it attractive to a range of birds. Willow tits, for example, are frequently encountered in this habitat, due to their predilection for excavating nestholes from rotten wood, while siskin and redpoll will also find the alder catkins and birch seed hard to resist. And while oaks undeniably support the highest number of associated invertebrates, the very fact that willow and birch are second and third on this ‘useful tree’ list means that wet woodlands can be home to a surprisingly diverse suite of moths and other insects.
Mammals also have representation here, with otters using wet woodland for cover and breeding sites, while water shrews can be spotted in those areas with least pollution and disturbance. It’s worth mentioning too that this habitat can be created by beavers, which will quickly transform most dry woodlands into a vibrant waterscape.
A final note: when accessing wet woodland, best stick to the established trails or boardwalks, which should be positioned for you to enjoy the very best this habitat has to offer.
Willow tits are frequently encountered due to their predilection for excavating nestholes from rotten wood.