Wet Heath

Overall vulnerability

Feature assessed:

• Wet heath

Special quality:

• Internationally important and locally distinctive wildlife and habitats

Feature description:

Wet heath is an uncommon habitat in the PDNP, occurring on acidic and waterlogged peat soils in patches throughout heathland. Like other heath habitats (such as heather moorland), it is characterised by a greater than 25% cover of dwarf shrubs. It is distinguished from other heath habitats by a higher water table or otherwise waterlogged soil and a greater abundance of wet ground plant species. Cross-leaved heath is usually found here, as well as a greater abundance of Sphagnum mosses and common cotton-grass.

Wet heath habitat in good condition is quite similar to active blanket bog. Wet heath generally has shallower peat and is less rich in some characteristic blanket bog species such as hare’s tail cotton grass. Blanket bog is assessed separately.

There are approximately 550 hectares of wet heath priority habitat mapped in the PDNP, but as this occurs in patches throughout heathland and heath type is not always specified, this may be an underestimation. This is a fairly fragmented habitat type, but is continuous with other heathland habitats and so likely has reasonable connectivity through the large area of heathland in the Dark Peak and South West Peak.

Wet heath is more species rich than other heathland habitats, and provides a refuge for blanket bog species that otherwise may be lost in some areas of the PDNP, and represents an intermediate stage between areas of dry heath and blanket bog. Rarer species within the PDNP such as round leaved sundew and bog cranberry can be found in wet heaths and have the potential to spread into more over time.

How vulnerable is wet heath?

Wet heath in the PDNP has been rated ‘high’ on our vulnerability scale. This score is due to high sensitivity and exposure to climate change variables, with poorly documented current condition, and moderate adaptive capacity.

As wet heath depends on waterlogged soils, drying out of some sites represents the greatest risk, with potential reduction of Sphagnum cover adding to the problem. Despite being fragmented, wet heath grades into similar habitat types and so has reasonable connectivity. Organisational and financial support for moorland rewetting will benefit wet heath and counter some of the effects of climate change.

Current condition:

The current condition of wet heath habitats in the PDNP is not well known as it is probably an under-recorded habitat. It is likely that it is in a similar condition to other heath habitats and subject to the same pressures. There are no Site of Special Scientific Interest (SSSI) units designated for wet heath, but most wet heath in the PDNP will be covered by the Dark Peak, Eastern Moors, Goyt Valley, and Leek Moors SSSIs, as well as the South Pennines Special Area of Conservation (SAC).

Due to historical contamination from industrial pollution in the PDNP, wet heath is likely to occur on heavily polluted peat. It is more at risk than other heath types due to its wetter nature, as heavy metals will be brought into solution by acidic water. Bare ground and increased nutrient levels have also allowed generalists such as rosebay willowherb to colonise in some areas. Nitrogen deposition is especially damaging, allowing vascular plants to outcompete and exclude Sphagnum mosses and increasing the susceptibility of heather to heather beetle. Heather beetle is a persistent presence and affects some areas, attacking mainly common heather and cross-leaved heath to a lesser extent.

Large areas of heathland are still managed for grouse or sheep production. Overgrazing and excessive burning is a threat to wet heath habitat due to removal of vegetation and exposure of bare peat facilitating erosion. The drainage associated with these land uses is also a threat to wet heath as waterlogged conditions are required to maintain the habitat. Historical drainage has likely converted much wet heath into other heathland such as heather moorland. However, without management of some kind, wet heath would naturally succeed into scrubland over time.

Damage associated with high visitor numbers is possible, but likely less than other heathland types. The scattered and wetter nature of wet heath means that high footfall and especially vehicle damage is unlikely due to the difficulty of the terrain, and so risk of erosion is lower. Wildfire damage will still affect some areas but will be lessened by wetter ground and less heather dominance.

What are the potential impacts of climate change?

Overall potential impact rating

As a waterlogged environment, in which evapotranspiration and precipitation must be balanced, the greatest risks to wet heath habitats are related to changes in hydrological conditions. Loss of key species and replacement by drier heath species is also a key concern, as well as changes in management and human behaviour.

Direct impacts of climate change

Drier summer conditions are likely to be damaging for wet heath communities. A greater frequency and severity of summer droughts will be devastating for some areas. Wet ground species will be disadvantaged during the dry summer months, and may be replaced by more drought tolerant species. Cross-leaved heath is especially sensitive as it requires permanently wet conditions. As a result, this key species could be lost and replaced with common heather or other dwarf shrubs. Wet heath found outside peat areas may be at greater risk, as waterlogged conditions may be maintained by podzol formed iron pans, which are much more susceptible to drying due to their shallow nature. Data Certainty: High

Increased winter rainfall may cause higher levels of nitrogen deposition on wet heaths. Sphagnum mosses’ nitrogen uptake advantage over vascular plants is lost with increased nitrogen availability, and so they may be outcompeted and lost from some areas. Data Certainty: High Increased nitrogen levels reduce Sphagnum production of polyphenol, a key chemical preventing decomposition in peat, meaning peat degradation may increase. Data Certainty: High Nitrogen deposition also affects dwarf shrub species: Both heather and cross-leaved heath are sensitive to nitrogen deposition, which causes greater sensitivity to drought, frost, and heather beetle outbreaks. Data Certainty: High

Compounding the reduced Sphagnum and dwarf shrub growth, more competitive grass species will have increased growth in higher nitrogen conditions, allowing species such as purple moor-grass to colonise and dominate. Data Certainty: High These grass species will also have the advantage of a longer growing season due to rising temperatures, allowing them to outcompete other plant species, causing the species composition to move towards a lowland heath or acid grassland assemblage. Data Certainty: High

Other indirect climate change impacts

More ‘sunny’ days during summer leading to higher light conditions can cause photoinhibition in sphagnum mosses, reducing their extent and limiting peat formation. As Sphagnum mosses are a key species for water retention, this could exacerbate the drying out of some sites. Data Certainty: High

Drier summer conditions will likely also increase the risk of wildfire on moorland. Drought can cause even wet heath vegetation to dry out and become susceptible to ignition accidentally, from arson, or through managed burns running out of control at other times of year. Fires cause loss of vegetation as well as opening up bare ground to erosion and peat loss. Data Certainty: High Aggressive colonisers such as purple moor-grass may also move in, changing the community composition and reducing species richness. Data Certainty: High

Human behaviour change

Greater visitor numbers due to hot dry summers could be a threat to wet heaths, causing trampling of vegetation and increased path erosion, which may cause damage to wet heath habitats. However this effect may be partially mitigated by the less accessible nature and scarcity of wet heath. Wildfire risk may also increase with greater visitor numbers during hot, dry summers, though due to the waterlogged nature of wet heath the risk will potentially be less for these areas than for drier heather dominated moorlands. Data Certainty: High

Wet heath is also susceptible to changes in management. Drying out of some sites due to climate change may make wet heath areas more desirable for grazing. Intensive management such as burning and high stocking levels would have a severe negative impact on wet heath habitats, pushing the community composition toward that of heather moorland or acid grassland Data Certainty: Low. Intensification of grazing can also lead to erosion and nutrient loading, having negative effects on dwarf shrubs and Sphagnum mosses. Data Certainty: Moderate

Invasive or other species interactions

Due to higher annual average temperatures, heather beetle and other pest species may increase in number and range. Both heather and cross-leaved heath are affected by heather beetle, and so may be stunted or removed from some areas, and be replaced by other species such as purple moor grass. Data Certainty: High Sedimentation or erosion

Increase in winter rainfall, especially as storm events, could be damaging for wet heath. Heavy rain and severe winds may damage plants, and increased runoff can cause soil erosion. As wet heath is generally found on thin peat soils, such erosion can lead to root damage, which in turn increases susceptibility of dwarf shrubs to winter desiccation, meaning community composition may be altered. Data Certainty: High

Nutrient changes or environmental contamination

Changes in rainfall patterns may also affect nutrient cycles. Increased winter rainfall may cause flushing of nutrients from waterlogged environments, intensifying the already nutrient poor conditions. Conversely, increased precipitation is likely to increase nitrogen deposition. Summer droughts may also cause an increase in concentration of nutrients due to lower water tables. Data Certainty: Low Nutrient availability changes could impact the community composition of wet heath.

What is the adaptive capacity of wet heath?

Overall adaptive capacity rating

Resources are available for the management and restoration of heathland (including wet heath) through multiple sources. Environmental Stewardship options are available to individual landowners that have an interest in conserving their land. Data Certainty: High There are also currently many organisations operating in the PDNP that can conduct or facilitate works to increase the resilience of heathland e.g. Moors for the Future Partnership, Eastern Moors Partnership, The National Trust and RSPB. Moorland rewetting is a stated aim of many of these organisations, which could increase the area and resilience of wet heath. Data Certainty: High However, although management can be taken to partially offset the effects of climate change, there is limited agreement about future land use due to conflicting interests of different stakeholders; the aims of conservation organisations potentially conflict with those managing their land for sheep farming or grouse shooting. Data Certainty: Moderate

The exact extent of wet heath is unknown, but it is a fragmented habitat with low connectivity across the landscape. It does, however, grade into other heathland types and blanket bog, so there is some potential connectivity for most species. Long distance seed dispersal is a barrier to the spread of wet heath, meaning some wet heath species will struggle to naturally colonise suitable ground if it is available. Data Certainty: Low

Wet heath species can be vulnerable to changing conditions due to their water requirements; diverse communities will be more resilient than those dominated by one or two species. Multiple plant species will take up more available water during times of water stress, and some plant species play a vital role in the response of below-ground biotic processes. Data Certainty: Low The loss of cross-leaved heath due to drier conditions would be difficult to recover from, but it may be replaced by other dwarf shrubs. Wet heath in good condition is afforded some protection from invasion by species such as bracken by nature of its being waterlogged. Data Certainty: High Wet heath in mosaic with other heathland and scrubland may be more adaptable. Data Certainty: Low

Key adaptation recommendations for wet heath:

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.

• Updated habitat mapping taking into account peat depth is needed to determine exact size and extent of current wet heath resource.
• Moorland rewetting work should be continued as a top priority.
• Identify sites that can act as climate change refugia due to their favourable topography, aspect, hydrology, or good species diversity, and manage these sensitively.
• Minimise erosion through management of access, appropriate grazing levels, and reduction of burning.
• Develop fire contingency plans, and ensure management of habitats reduces fire risk e.g. rewetting and increasing species or structural diversity. Influence visitor and behaviour management plans and practices to minimise ignition risk.

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

• Strengthen footpaths and manage increased visitor access to minimise disturbance in key areas.
• Careful livestock management at high risk sites.

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.

• Structural diversity within heathland vegetation should be increased - including wet heath patches, diverse age classes of dwarf shrubs, and scattered trees and scrub to provide refugia for sensitive plants and invertebrates.

Accept that habitats need to be dynamic and not fixed. Consider that designated site boundaries may need to change as habitats move/change to create larger functional sites, and features of interest may change. Liaise with other protected landscapes to share knowledge and management techniques, and contribute to the national picture.Adapt land use for future conditions

These recommendations are adaptations to the way in which people use the land. Flexibility in land management - reacting to or pre-empting changes caused by the future climate - should afford this feature a better chance of persisting.

• Create future conservation objectives in the knowledge that wet heath and other habitat types will move along a continuum, and so the ideal location to target actions for particular species will change with the climate.