The uniform height curve method for height-diameter modelling: an application to Sitka spruce in Britain

Height–diameter models are commonly used in forestry for the imputation of missing tree heights and as such underpin the calculation of many fundamental mensurational quantities needed to characterize forest growth and yield. Despite their importance, there are still no published height–diameter models for Britain. This paper reviews the uniform height curve methodology for modelling the height–diameter relationship in even-aged stands and proposes a way to adapt it for use in Britain. According to this methodology, a height–diameter model for individual trees in a stand can be fully characterized in terms of one global parameter uniquely defined for a given species and geographical region and one local parameter specific for each stand and measurement occasion, which can be easily estimated from knowledge of the characteristics of an average tree. The methodology was evaluated using permanent sample plot data for Sitka spruce (Picea sitchensis (Bong.) Carr.) and proved able to describe the height–diameter relationship reliably and with good accuracy. The flexibility and ease of application of this approach are ideal in all those applications (e.g. within a growth simulator) where more precise statistical calibrations cannot be used.