Modelling light penetration edge effects for stream buffer design in mountain ash forest in southeastern Australia

Abstract

In this paper, we develop models to describe light environment edge effects in retained mountain ash/riparian forest in southeastern Australia following edge creation by clearfell logging. The models are then used in the design of functional buffers whose objective is light environment protection. The study uses hemispherical photographs taken before and after logging at distances from the cut edge ranging from 0–108 m and at heights above ground of 1, 3.4 and 6.8 m. Non-linear regression was used to develop relationships between the change in light penetration due to edge creation and distance from the edge. Vegetation and topographic variables were evaluated as additional explanatory variables. The study indicates that in this vegetation type the factors with the greatest influence on light alteration following edge creation are edge orientation, distance from the edge and height in the canopy. Light penetration edge effects were greatest at north-facing (toward the equator) edges and minimal at south-facing edges, where diffuse light increases due to increased sky view were the only additional light. On north-, east- and west-facing edges light penetration attenuated rapidly over the first 10–30 m of retained forest and reduced gradually thereafter. Light penetration was generally greater higher in the canopy. The regression models for relative change in light penetration, which weights the change in light by the pre-logging light environment, were used to develop a set of depth of edge influence indices for each edge orientation and height above ground. These indices can be used to prescribe buffer widths to achieve specific light environment protection objectives.