Growth of residual forest stands after severe density reduction due to natural disturbances and silvicultural interventions

More and more forest stands are being fragmented by natural disturbances, especially at an advanced age. While many studies focus on the structure and growth behavior of the failing trees, the present study focuses on the post-disturbance residual stands. This study was based on 34 long-term experiments in Norway spruce ( Picea abies (L.) KARST.), Scots pine ( Pinus sylvestris L.), European beech ( Fagus sylvatica L.), and sessile oak (Quercus petraea (MATT.) LIEBL.) in southern Germany, which cover stands abruptly disturbed by e.g. bark beetle infestation, windthrow or snow breakage as well as on fully stocked stands as reference. Firstly, it is shown how the disturbances are reflected in the deviation from the self-thinning slope on a slope steeper than α dq , N = − 2 . The analysis showed that the growth of the stands remaining after the disturbanceswas declining less than would be expected given the decline in density and stock. Declines in stock of 1 % are associated with growth losses of only 0.5 %. Secondly, the analyses of the density growth relationship showed, that the post-disturbance residual stands deviate upward from the expected density-growth behavior; i.e., the growth rates are above the level expected for proportional growth-density behavior. On average the IV/IVref-values amounted to 1.59 ± 0.07 (mean ± se ), i.e., the remaining stands grew 59 % more than expected under growth reduction proportional to stand density. Thirdly, analysis of the relationship between post-disturbance residual stand density and growth resulted in models and in a tabulation of the expected stand growth depending on the state of disruption. Across all tree species a reduction in density to half of the reference stand is expected to result in growth declines to 0.74, i.e., growth reduction of 26 %. With a reduction in density to one-fifth, growth declines to 28 % of the fully stocked reference stands. The causes of the partial compensation of tree losses by accelerated growth of the post-disturbance residual stands was discussed. The results expand the understanding and the knowledge for silviculturally planning and managing the remaining stands after forest disturbances. • 34 long-term experiments of four most common tree species in Europe were analyzed. • Growth of stands after disturbances was compared with undisturbed reference plots. • Disturbances shifted the diameter-tree number slope below α dq , N = -2.0. • Disturbed stands grew more than expected. • A density reduction to 50 % resulted in growth reductions of only 26 %. • Tree losses were partially compensated by accelerated growth of the remaining stand.