Wet woodland

Overall vulnerability

Feature(s) assessed:

• Wet woodland

Special qualities:

• Internationally important and locally distinctive wildlife and habitats
• Vital benefits for millions of people that flow beyond the landscape boundary

Feature description:

Wet woodland occurs on permanently wet or seasonally wet soils and is usually dominated by alder, birch and willow trees. Wet woodlands are found on floodplains, flushed slopes, valley sides, cloughs, and along stream edges. It also occurs as a mosaic within other habitats including dry woodlands, bogs and fens, for example as willow scrub on moorland.

In the PDNP wet woodland is most common in the Dark Peak and South West Peak, with approximately 90 hectares of priority habitat mapped. However, it is likely that more is unrecorded and within mosaics of other habitats. Nevertheless, the total is one of the smallest for any habitat in the PDNP and wet woodland is therefore a very rare habitat.

This habitat is important as it provides cover and breeding sites for a wide range of species that are not commonly found elsewhere, particularly dead wood invertebrates, ground flora such as kingcup and greater tussock sedge (also found in open rush pasture), birds such as willow tit (a rare and declining species on the UK Red List), and mammals including otter.

How vulnerable is wet woodland?

Wet woodland in the PDNP has been rated ‘high’ on our vulnerability scale. This score is due to high sensitivity and exposure to climate change variables, coupled with a poor, highly fragmented current condition, and a moderate adaptive capacity.

Wet woodlands in the PDNP are already highly fragmented, but many of the remaining patches are in good condition. Wet woodlands with low tree species diversity are likely to more vulnerable than those that are more diverse. The area of wet woodland in the PDNP may be reduced by climate change.

Current condition:

As with the rest of the UK, large tracts of the PDNP’s wet woodland have been lost through land use changes. Land clearance and drainage for agriculture and forestry has reduced wet woodland extent to a highly fragmented version of its former range. Overgrazing has also been detrimental as it prevents ground flora and sapling establishment. Surviving wet woodland occurs on the margins of other habitats, such as mosaics on Ramsley Moor and Warslow Moors, and on floodplains like the River Derwent where the land has not been reclaimed for agriculture. This is mostly in good condition. Abandoned sites such as disused railway lines and extraction sites have developed into new patches of wet woodland in recent years, for example at Rowsley Sidings. Ongoing land use changes are a risk factor, particularly within mosaic habitats.

Many wet woodlands in the PDNP occur on flushed slopes and near watercourses. This means they are easily affected by agricultural run-off, in the form of water pollution and nutrient enrichment. In some areas mismanagement of water levels is resulting in scrub invasion, while other wet woodlands are particularly at risk from invasive or nuisance species due to their close proximity to waterways. Himalayan balsam is a common problem as the seeds spread quickly allowing it to take over the woodland understory, which then prevents seedlings and woodland ground flora from establishing.

Sensitive management of riverside trees and wet woodlands has begun in parts of the PDNP, as its role in flood alleviation is increasingly being recognised. Although likely undervalued compared to bogs and marshes, wet woodlands help stabilise slopes and banks and are able to absorb large amounts of water as rivers and streams overflow. Land management practices continue to influence the state of the PDNP wet woodlands. Removal of old trees removes fungi, mosses and other flora and fauna from a site. Work is being carried out by local Wildlife Trusts, Trent Rivers Trust and others. The very small extent of wet woodland remaining in the PDNP will require careful management to prevent further degradation.

What are the potential impacts of climate change?

Overall potential impact rating

Direct impacts of climate change

Climate change has the potential to have a severe negative impact on the PDNP’s wet woodland, both directly and indirectly. The habitat is restricted to areas with wet soils, predominantly on slopes and near waterways. Rainfall is a limiting factor that has the potential to greatly alter the distribution of wet woodland as it becomes more variable.

Wet woodland tree species are very sensitive to the direct effects of changed precipitation levels – predicted to occur through wetter winters and drier summers. Waterlogging and drought are likely to lead to a change in community composition and habitat structure, along with a reduction in species productivity. Waterlogging in low lying areas could increase the dominance of some tree species such as alder and willow, while drier soils on slopes could see the loss of these species and will likely convert to dry woodland. Many remaining areas of wet woodland are dependent on water input from springs and seepages. Changes in precipitation may lead to these drying out and seasonal or permanent disappearance, with significant loss of associated wet woodland flora and invertebrate fauna. In some cases the habitat may again be lost to drier woodland. Data Certainty: High

The increased mean temperatures and fewer frost events that are expected with warmer winters are likely to cause changes in the growing season of plants. Already seen in some species, trees will likely have earlier bud burst, putting them at an increased risk of frost or cold damage. Other trees may have reduced winter chilling and incomplete winter hardening leading to reduced seed germination in some species. Warmer temperatures combined with reduced rainfall may leave boreal and sub-boreal bryophyte and moss species susceptible to drying which could lead to species losses in some areas. Data Certainty: High

Storm events may kill older trees which are an essential part of healthy wet woodland Gaps may be replaced by scrubby stands Data Certainty: High. Erosion of river banks may reduce bankside tree cover, changing otter habitat, impacting on water temperature regimes, reducing diversity of river habitat, and reducing overall woodland size. Data Certainty: Moderate Habitat structure and community composition may change as non-native invasive species such as Himalayan balsam continue to spread. Data Certainty: Moderate Nutrient levels could also be impacted by concentration or flushing. Data Certainty: Low

Human behaviour change

While many wet woodlands have already been degraded by land use changes, they remain sensitive to future changes in farming and forestry pressures. As some wet woodlands dry out they may become more suitable for grazing or forestry, putting the habitat at risk. Increases in water abstraction during dry periods will exacerbate the direct effects of climate change, creating drier areas and limiting potential for expansion. Data Certainty: Low

With hotter, drier summers predicted, it is likely the PDNP will see increased visitor numbers, with growing numbers near waterways and woodlands. This poses a risk for ground flora that can be easily trampled if people leave designated paths. Rank species such as nettles and thistles could increase and other ground flora may be impacted. Higher visitor numbers will also cause an increased disturbance to wildlife potentially resulting in the loss of breeding habitat for birds and otters. Data Certainty: Low Conversely, the increased interest in this habitat as a flood, erosion and water quality management tool could create opportunities for wet woodland restoration, expansion or further creation. Wet woodland found or created along river valleys will be especially useful in natural flood management and slowing the flow of water. Data Certainty: Moderate

Invasive or other species interactions

Warmer winters are also likely to lead to the increased survival and prevalence plant diseases such as Phytophthora. Alder is one of the wet woodland tree species that is commonly affected by Phytophthora. Damage and death of these trees along with others affected by disease will change the community composition and could affect the overall health of the woodland. Data Certainty: High

Other indirect climate change impacts

Drier woodlands with reduced humidity would likely cause a decline in species requiring damp habitats including crane flies and other invertebrates in the wet woodland assemblage. This in turn would reduce the availability of food for birds and their young, which may lead to a decline in some woodland birds. Wet woodland specialists such as the rare marsh tit will be at greater risk. Changes to soil moisture levels could also facilitate the invasion of drought tolerant species. Data Certainty: Moderate

What is the adaptive capacity of wet woodland?

Overall adaptive capacity rating

Despite wet woodland being a highly fragmented habitat type in the PDNP with strict hydrological requirements, the dominant tree species are widespread and a range of management and restoration options are available, giving this habitat a moderate adaptive capacity within the PDNP.

Wet woodlands are often small and highly fragmented across the landscape. Data Certainty: High The poor connectivity between sites is detrimental to both the flora and fauna found within them. Tree species and ground flora have limited dispersal ability, particularly as habitat location is limited by water availability and soil moisture. Data Certainty: High However, many of the dominant tree species present in wet woodlands are expected to be relatively resilient to climate change. Data Certainty: Moderate Some birds and mammals that utilise wet woodlands may be able to disperse, or find similar habitat traits in dry woodlands, providing resilience. However, species with a poor dispersal ability are likely to suffer. The willow tit for example, already scarce, may be vulnerable to extinction in the PDNP. Ground flora and invertebrate communities may be most at risk as their dispersal range is more limited and they are more likely to depend on high humidity and high soil moisture levels. Data Certainty: Moderate

Tree diversity is an important factor in climate change resilience. Wet woodlands with low tree diversity have a greatly reduced capacity to adapt. Should a species-specific tree disease outbreak occur (for example Phytophthora in alder trees), the whole woodland may be lost quite rapidly. With an increased diversity of tree species the woodland has a much greater resilience. As wet woodlands occur on a range of soil types (both nutrient-rich mineral soils and nutrient-poor organic soils), their greatest limiting factor is soil moisture and the availability of other tree species to regenerate. Data Certainty: Moderate

Some environmental stewardship options are available for maintenance and/or restoration of wet woodland within farmed landscapes. Data Certainty: High Good availability of financial resources and information means that management organisations may be able to facilitate works to increase the resilience of wet woodland in the PDNP. Data Certainty: High Policy or management actions may be undertaken to partially overcome or offset climate change stressors, by promoting structural and species diversity within existing wet woodlands and managing water availability across catchments. Data Certainty: Moderate

Key adaptation recommendations for wet woodland:

Improve current condition to increase resilience

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are aimed at improving the condition of the feature at present, therefore making it better able to withstand future changes to climate.

• Map existing wet woodland habitat to assess value and content.
• Continue with sensitive woodland management.
• Continue with work on managing invasive species such as Himalayan balsam.
• Continue management of woodland along watercourses to reduce flood risk.
• Evaluate whether the introduction of beavers would be a feasible and appropriate method of delivering ecosystem service benefits such as flood mitigation, water quality and wet woodland creation.

Improve current condition to increase resilience: Targeted conservation efforts for important sites and at risk areas

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are conservation measures aimed at those sites that will have the biggest impact for this feature – either because they are particularly important for the feature or because they are most at risk from climate change.

• Identify sites for wet woodland restoration, expansion and/or creation. Care should be taken to ensure this is not at the expense of other wetland habitats that are of value. Some sites could just be scattered trees, others more dense woodland and wet scrub – smaller willows of various locally native types.

Improve current condition to increase resilience: Increase structural diversity to improve resilience at a landscape scale

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations focus on increasing the structural diversity of the area or habitat in which the feature is found. This can help to offset the effects of climate change on the feature, as well as to allow it to be in a better position to recover from future climate changes.

• Establish trees and encourage natural regeneration to increase species diversity, structural diversity, and patch size.
• Evaluate whether there are benefits in establishing scrub to stabilise eroding edges of blanket peat, and implement if appropriate.

Adaptations that could aid other features

These recommendations are changes that could be made to this feature, which will have a positive impact on the ability of other vulnerable features to withstand future climate change.

• Increase woodland cover – to keep waterways cool and to provide shelter for other species as temperatures increase.
• Increase connectivity between woodlands to provide wildlife corridors.