Age dependence of forest reflectance: Analysis of main driving factors

Abstract

As an analogy to forest yield tables, successional trajectories of forest reflectance can be established. Examples of such deterministic reflectance age trajectories for common northern temperate forest types in Estonia have been derived from airborne reflectance measurements and simulated by a forest reflectance model. In the simulations, the yield tables were used as input data. The primary controls on the reflectance age course are: changes in canopy closure, tree-storey leaf-area index, species composition, and background reflectance. In long-term monitoring of forest stands, the effects of sun and view angle and phenology must be considered. Successional reflectance trajectories may further form a basis for a forest inventory and monitoring system. Provided that the problems of normalization of multidate satellite imageries and seasonal signature variation are solved, the reflectance change of a particular forest stand may be compared to the change predicted by established reflectance successional trajectories. In case of normal forest development, the measured reflectance changes must be close to those predicted. Some kinds of the disturbance-type forest changes (e.g., extensive thinning due to damage) are detectable by optical methods.