Introduction
Trees and woodlands deliver wide-ranging benefits to people and the environment, including carbon sequestration, flood mitigation, local cooling, air quality improvements, habitat creation, and improved mental and physical health. Reclaiming and then regenerating previously used land to create accessible woodland and treescapes can help to deliver these benefits.
As the climate continues to change, UK winters are projected to become wetter and milder, and summers hotter and drier. The risks associated with these changing conditions will affect the resilience of trees and woodlands across the UK.
For woodlands on reclaimed land (where interventions were required prior to tree planting), inherent challenges (Box 1) related to previous land use may exacerbate some of these climate change risks.
It is important to identify and address these challenges during the reclamation process and through climate change adaptation-focused management strategies in order to fulfil the benefits that woodland creation can offer.
Four climate change risks impacting trees and woodlands on previously used land are outlined below, along with suggestions for addressing them.
Box 1: Previously used land typically requires intervention before trees can be established
Common challenges addressed during reclamation include:
- Shallow soils
- Soil compaction
- Drainage and waterlogging
- Low soil organic matter
- Unusual nutrient ratios
- No or limited infrastructure (e.g. roads, access points)
Residual conditions after regeneration that negatively impact tree establishment include:
- Poor soil structure
- Low soil biodiversity
Drought
The risk: Hotter, drier summers and prolonged periods of drought can cause water stress in trees. Trees rely on water held in the soil to persist through dry periods.
Challenge related to previously used land: If not adequately addressed through good reclamation practice, the typically poor soils on previously used land (Box 1) can contribute to low infiltration, sub-optimal percolation, and low water holding capacity. Low water availability in soil can result in higher levels of dieback or even premature death, when compared with trees on better quality soils.
Addressing the risk: Young trees are at higher mortality risk from drought than older trees that are well established. The early tree establishment phases are therefore critical to successful woodland creation. Improving soil water holding capacity during the reclamation processes through cultivation, increased soil thickness, and addition of organic matter may also be beneficial. Choosing drought-tolerant tree species may further mitigate this risk.
Wildfire
The risk: Projected hotter, drier summers will increase the risk of wildfire in forests and woodland.
Challenge related to previously used land: Many previously used sites are in urban or peri-urban areas. Areas closer to urbanisation often have higher fire ignition risk.
Ignition risk is exacerbated on recreational sites, as fires from barbecues and other human activities are more likely.
Some previous site activities, such as landfilling, can also increase fire risk if not adequately addressed in the land reclamation and regeneration processes.
Addressing the risk: Fire contingency planning with input from neighbouring landowners can help to reduce wildfire risk.
Design, planning, and investment in firebreaks, fire-fighting infrastructure, roads, paths, and emergency access provision can also lower wildfire risk and reduce spread should a fire occur.
Addressing climate risks, including drought or pest risks, can help reduce tree mortality and limit fuel loads.
Wind
The risk: Extreme wind events are projected to increase in frequency, with increased instances of heavy rain and associated wet soils likely to exacerbate windthrow risk to trees.
Challenge related to previously used land: Tree anchorage is a key factor in windthrow risk. Regenerated land often has shallow soil depth and poor soil structure, which can reduce rooting depth. Poor tree anchorage reduces stability and increases the likelihood of trees rocking in the wind or being uprooted. Site waterlogging may also influence tree stability.
Addressing the risk: Increasing soil thickness and/or reducing compaction during the reclamation process may reduce windthrow risk.
Comprehensive site investigation and good practice in reclamation and site design can improve effectiveness of on-site water management, reducing the risk of waterlogging (which in turn may make trees less susceptible to windthrow).
Adaptation measures that are recommended for managing windthrow risk on conventional woodland sites (e.g. thinning, use of a wider range of species, and continuous cover forestry) may be beneficial on previously used sites, although further research is required to inform best practice.
Flooding and waterlogging
The risk: Flood risk is expected to become more widespread in the projected climate, leading to increased waterlogging risk for woodland on previously used land.
Challenge related to previously used land: Trees on waterlogged sites may experience root damage, leaving them vulnerable to risks such as wind damage or disease.
Addressing the risk: Flooding and waterlogging risk must be addressed through the regeneration process, including undertaking appropriate topography and drainage assessments.
Where soil remediation has taken place, residual low-level contamination may persist. There is a risk of increased mobility of this residual contamination associated with flooding and waterlogging, which may have a negative effect on human, environmental, and aquifer health. Assessing potential future residual contaminant mobility during regeneration can help mitigate this risk.
Conclusion
Previously used land has huge potential for woodland creation across the UK, but the additional risks from the changing climate must be addressed. This will require action during the reclamation process, when the trees are being established during the regeneration phase, and through management into the future to ensure successful and beneficial woodland creation.
More information
Further information on climate change risks and woodland on regenerated land.
Optimal Thickness of Soil Model (OpTS) (to calculate required soil thickness for trees on regenerated land).
UKFS guidance:
- Building wildfire resilience into forest management planning
- Adapting forest and woodland management to the changing climate
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Contact: www.forestresearch.gov.uk/contact-us
To discuss any aspect of Forest Research’s work on woodland on regenerated land, contact: Kieron.Doick@ForestResearch.gov.uk