Establishment and growth of Scots pine and Norway spruce: a comparison between species

The two by far most common and economically important tree species in Sweden are Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) H. Karst). Despite a long history and tradition of silvicultural research on these species, few studies comparing their growth at the same sites have been performed, preventing accurate species comparisons. Hence, the goal of this thesis was to examine growth differences between Scots pine and Norway spruce at different rotation stages and disentangle potential underlying reasons for the observed differences. To do so, field experiments with both species growing together were utilized, and the importance of species choice was highlighted. In Papers I-II it was shown that Scots pine seedlings had a higher early growth, and nitrogen (N) uptake was found to be a reason for the initial growth response. Site preparation was favorable for the growth of both species, however, Norway spruce seedlings were severely hampered in the low nutrient environment created by removing all the organic material. Such practices should be avoided when planting Norway spruce. It was also concluded that N2-fixation in fine roots did not explain the superior initial N uptake of Scots pine. In Paper III it was found that Scots pine produced 126% more stem wood than Norway spruce after 57 years. No overyielding could be found when both species grew in a mixture. However, a mixture provides several other benefits compared to monocultures. Species choice determines long-term possibilities and limitations and is important for more reasons than only growth parameters, as it has a significant influence on biodiversity and ecosystem services on different scales (Paper IV). In this regard, Scots pine has a potential to provide several win-wins. This thesis puts species choice in a wider context by increasing the scientific knowledge regarding growth patterns, growth responses, ecosystem services and biodiversity.