Modelling growth of Norway spruce on former agricultural lands in Latvia

Adequate growth forecasts are essential for forest management planning. In order to make such forecasts, accurate growth models are required. Due to the rapid growth of Norway spruce (L.) Karst. planted on former agricultural lands, existing growth models are unable to predict the development of Norway spruce with sufficient accuracy. Therefore, the aim of this study was to develop new height development and diameter models for Norway spruce up to 15 years of age. Data used in development of the models was obtained from twelve Norway spruce plantations established on fertile agricultural lands located in eastern Latvia. Height development was modelled using dynamic site equations derived using the generalized algebraic difference approach (GADA). In total fifteen different equations were estimated using non-linear least-square regression. Diameter models were developed using multiple linear regression. Subsequently, further development of the stands was simulated using stand-level management simulation tool StandWise of Heureka-DSS. \n \n Of the fifteen tested equations, the best fit and prediction statistics were achieved using Chapman-Richards and Sloboda models. However, the best overall performance was demonstrated by Chapman-Richards model. Diameter was estimating with a linear regression model. Stand level projections showed that MAImax for stands considered in this study varied between 14.7 – 17.6 m3 ha-1 year-1. According to LEV estimates, optimal rotation age of the stands varied between 41 – 48 years. \n \n With the development of height and diameter growth functions, it is now possible to model development of planted Norway spruce stands from 5 years of age. Furthermore, further development of trees with estimated heights and diameters can be modelled using simulation systems such as Heureka-DSS.