The effect of retention trees on the growth of norway spruce

The increased demand for wood and at the same time declining biodiversity, especially in species related to natural forests has brought to attention the need to find ways to maintain natural forest components also in managed stands, not only in specially protected areas. One possible method for increasing the number of species in a production forest is using retention trees. A forest stand in Southern Sweden was investigated to determine the effect of retained trees on the growth of Norway spruce (Picea abies). A total of thirty-three plots were established in 5.5 ha stand with retained oaks as plot centers, three oak release treatments (high release, medium release and no release) were carried out on the plots. The results showed a reduction in individual tree Norway spruce growth within the proximity of the retained oak. A larger diameter increment was recorded around the gaps in comparison with no release plots, so some of the loss in Norway spruce growth was compensated. At the whole stand level, there was no significant effect of the retained trees on the growth of the spruce; however, this could be caused by the imposed treatments and thinning in the stand, which might have evened out the total retained tree effect. Further investigation is needed in determining the compensation of growth around gaps and also a wider age range of Norway spruce stands should be evaluated