Spatio-temporal Modelling of Forest Growth Spanning 50 Years – The Effects of Different Thinning Strategies

Models for tree growth in the literature include spatial models and dynamic models. Spatial models have been mostly restricted to Gaussian variograms and comparisons at single time points while dynamic models ignore tree competition due to spatial proximity. Here we model tree growth in forest plots with a spatio-temporal covariance structure and compare plots with different thinnings. Tree growth is measured by diameter at breast height. A model was fitted using a sum-metric spatio-temporal variogram. Fixed effects of age, number of neighbours and polygon area were also considered. Predicted values for models were computed using regression-kriging and mean squared error of prediction was used to compare models and thinning strategies. Over time the correlation of a single tree followed a wave variogram while the spatio-temporal anisotropy parameter captured the changing spatial wave intensity. Thinned plots clearly outperformed unthinned plots in terms of total tree growth.