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Wet Woodland

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"Wet woodland" describes a range of woodland and scrub that occurs on poorly drained or seasonally waterlogged soils.

It is an extremely good habitat for insects and other 'invertebrates' like snails and spiders, supporting a very large number of species, many of which are now rare in Northern Ireland.

Alder, birch and willow are normally the predominant tree species, with ash and oak on drier areas.

The boundaries with drier woodland may be sharp or gradual and may change with time, so wet woodland frequently occurs in a mosaic with other woodland habitat types and with open habitats such as fens.

In general, wet woodland is unmanaged in Northern Ireland and is often used for grazing and shelter by livestock. Wet woodland also provides cover and breeding sites for the otter and is of value for bats and a number of breeding birds.

Wet woodland is found on a range of soil types including nutrient-rich mineral and acid soils and nutrient-poor peaty soils. It can be found on floodplains, on fens, mires and bogs, along streams and hill-side flushes, and in peaty hollows.

Historical info about Wet Woodland

There is no precise data on the total extent of this type of woodland in the UK, but a crude estimate would be about 50,000 - 70,000 ha, with approxmately 2,600 ha found in Northern Ireland.

The historical large scale clearance of woodlands in Northern Ireland means that much of the current wet woodland resource is largely secondary and of relatively recent origin (less than 100 years old).

The expansion of wet woodland can sometimes be viewed as undesirable as it reduces the area of other priority habitat types, such as reedbed. However, the combination of wet woodland and fen often enhances the nature conservation value of a site.

Species living in and around Wet Woodland

The main tree species making up wet woodland are willow, alder and downy birch with oak and ash present on occasion.

Threats to Wet Woodland

There have been considerable losses of wet woodland habitats in Britain in the last century. The reasons are:

  • Clearance, conversion to other land-uses and the lowering of water-tables through drainage.
  • Inappropriate grazing levels and poaching of the soil by sheep, cattle and deer, leading to a change in the woodland structure, reduction of ground flora and difficulties for regeneration.
  • Water level changes - due to drainage, agricultural practices, peat extraction or water abstraction, flood prevention measures, river control and canalization.
  • Deforestation for agriculture, industry or residential development. This can also lead to greater ecological isolation of existing woods through the removal of trees in field boundaries and small patches of wet woodland and scrub in fields.
  • Formal landfill applications and illegal dumping of building rubble, agricultural and domestic waste leading to changes in the composition of the ground flora.
  • Nutrient enrichment - leading to changes in soils and ground flora, may occur from spray drift from nearby agricultural land. In addition, pesticide drift into woodland margins may cause localised damage to some flora and fauna.
  • Poor water quality arising from eutrophication (is an increase in chemical nutrients), industrial effluents or rubbish dumping leading to changes in the composition of the ground flora.
  • Invasion by non-native species (e.g. Himalayan balsam)
  • Air pollution - from cars and/or industry and agro-chemical application may influence bryophyte and lichen communities.
  • Diseases such as root disease of alder.
  • Climate change- potentially resulting in changes in the vegetation communities.
  • Lack of woodland management – can result in loss of structural diversity and reduction of the biodiversity value of the habitat.