OR/17/014 Recommendations and possible future work

Archer, N A L, Everest, J. 2017. Final Report: Emergent Forest dynamics and Natural Flood Management. British Geological Survey Internal Report, OR/17/014.

• If trees are planted with the objective of reducing flooding, soil type and geology must be taken into account. In this study, the moraine soils are very permeable and implementing drainage
• before tree planting, could increase rainfall infiltration rates, which may induce local river flooding.
• Long-term rainfall measurements under plantation canopies are necessary to understand rainfall interception at low and high rainfall intensity events, for understanding the planting of trees for reducing flooding.
• Widely spaced trees, that are left to mature beyond 100 years and encourage a diverse understory, may be a better way to promote springs, ecosystem diversity, and greater water storage in the upland hill slopes as exemplified in the Old Forest site. This type of system may be a better way to mitigate flooding in the permeable moraine substrates in upland Scotland.
• In terms of understanding the development of springs in the Cairngorms, this study provides a preliminary understanding of the possible connections of geology and the glacial fluvial processes that created the moraine system and perched water tables in the moraine depressions and lenses of more impermeable layers within moraine hillslopes. More work is needed to understand the possible interconnectivity of perched water tables and the relationship of vegetation and springs.
• The significantly higher number of old Scots pine trees dominating the drier moraine slopes and crests rather than the boggy moraine depressions, could be a result of the Scots pine preference for drier soils or other reasons such as historical overgrazing. Understanding the reason for such spatial distributions may be important for improving forestry management. For example, to avoid the high number of wind-blown trees in moraine depressions, it may be more economical not to plant trees in waterlogged soils.
• The significantly shallower soil observed in the plantation questions whether the ploughing of drainage lines may cause a reduction in soil depth and a decrease of response time of rainfall throughflow to rivers. This needs further investigation for flood mitigation.
• Further work is needed to understand responses of rainfall to spring water and rivers in the Cairngorms. To avoid perturbation of the SSSI conservation sites in Rothiemurchus estate, water sampling for heavy isotopes and possibly tracer dyes from soil, springs and streams would be appropriate to avoid damage to Old Forest sites.
• To understand hydrological characteristics where water can be stored and released in different peat types, such as forest and bog peats, further investigation is needed to characterise these soils for flood management.