Relationships between canopy transmittance and stand parameters in Sitka spruce and Scots pine stands in Britain

Abstract

Summary The changing emphasis within British forestry from a clearfell/replant system focussed on timber production, to multipurpose forestry encompassing biodiversity and recreation, has resulted in a need for changes to forest management. Manipulation of the forest canopy through thinnings is a powerful tool for forest managers to modify the canopy transmittance, and therefore the belowcanopy light levels. This helps to achieve specifi c objectives such as habitat management or seedling growth as part of transformation of an even-aged stand to a continuous cover forestry regime. In this study, hemispherical photography was used to assess canopy transmittance in a range of Sitka spruce ( Picea sitchensis (Bong.) Carr) and Scots pine ( Pinus sylvestris L.) stands in Britain. Speciesspecifi c relationships were developed between canopy transmittance and easily-measured stand parameters. The models that provided the best fi t to the data were based on basal area and stocking for Sitka spruce and basal area alone for Scots pine. The models indicate that a Sitka spruce stand with a basal area of 30 m 2 ha 1 should have a stocking density <450 stems ha 1 to favour growth of Sitka spruce seedlings. Similarly, a Scots pine stand should have a basal area <27 m 2 ha 1 to achieve transmittance suitable for growth of Scots pine seedlings. In conjunction with a knowledge of the light requirements of different vegetation types, these models can provide a valuable contribution to guidance on current and changing forest management practice.