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 below-canopy light levels. This helps to achieve specific 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. Species-specific relationships were developed between canopy transmittance and easily-measured stand parameters. The models that provided the best fit 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 m² 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 m² 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.

The canopy-scope was recently introduced as a cheap, robust, portable and easy to use instrument for assessing canopy openness in forests. In this study, the method was tested in predominantly coniferous plantation forests, which were different in species and structure to the forests where the instrument was originally tested. The relationship between canopy openness (calculated from hemispherical photography) and canopy-scope score at individual points, despite being statistically significant, showed considerable scatter, especially at low values. Consequently, the canopy-scope is not recommended for obtaining estimates of canopy openness at a single point within plantation conifer stands. However, good results were obtained when values were averaged across a plot. Eight to 10 canopy-scope measurements in 0.25 ha were found to be sufficient to estimate canopy openness.