Early development of pure and mixed tree species plantations in Snogeholm, southern Sweden

<div><p>There is a lack of experimental studies comparing the forest production of mixed tree species stands and monocultures. As a case study, in 1994 an experiment was established in an afforestation landscape in southern Sweden with 66 plots: 18 planted with single tree species (including most native Swedish trees, plus <i>Populus</i> and <i>Larix</i> hybrids) and 48 with various non-replicated mixtures. Fifteen years after planting, stand growth did not differ significantly between the mixtures and the monocultures. However, the monocultures did exhibit a higher variation in growth levels relative to the moderate but comparatively consistent growth levels exhibited by the mixtures; particularly those comprised of more than two species. A specific analysis of mixtures containing either the tree species <i>Picea abies</i> or <i>Quercus robur</i> and their corresponding monocultures demonstrated the importance of the tree species admixed as a determinant of production outcomes early in the rotation. In the case of <i>P. abies</i>, tree species mixtures tended to reduce production, whereas in the case of <i>Q. robur</i>, mixtures tended to increase production. In addition no consistent differences in the mean height and mean diameter growth of <i>P. abies</i> and <i>Q. robur</i> between mixtures and monocultures were detected. A major conclusion is that adding more than two species did not increase stand volume growth.</p></div>