| Popis: |
Tree species choice is a central issue for forest management, and survey studies show that urgent improvements in regeneration practices are needed in Sweden. Most Swedish forest is regenerated with Scots pine (Pinus sylvestris L.) or Norway spruce (Picea abies (L.) H. Karst). However, direct yield comparisons of the two species are rare. The first objective of this thesis was to compare productivity of Scots pine and Norway spruce stands across latitude and fertility gradients in Sweden. To do so, long-term field experiments were combined with modelling in Heureka. In contrast to general perceptions and a majority of previous findings, Scots pine was more productive not only on poor sites but also on medium-fertile to fertile sites (Paper I). The second objective of this thesis (Papers II-IV) was to investigate the potential for cultivating Scots pine on medium-fertile to fertile sites. Effects of planting, natural regeneration and direct seeding were compared in terms of short-term regeneration outcomes, long-term volume production and financial revenue. This was done using empirical field experiments and simulations in Heureka. Results indicated that Scots pine may be successfully regenerated even on medium- to fertile sites. However, regeneration via planting was more reliable than natural regeneration or direct seeding. Natural regeneration and direct seeding generally had less certain outcomes, mainly because key processes such as seed production and germination depend on weather conditions. Experimental results confirm earlier findings that mechanical site preparation (MSP) increases both survival and growth of planted seedlings. For natural regeneration and direct seeding, MSP improves seeds' germination and seedlings' survival and growth. For planted seedlings, reduced pine weevil damage probably helped increased survival whereas reduced competition from ground vegetation helped natural regeneration and direct seeding. Dense shelterwoods had slower seedling growth. However, inexpensive regeneration and income from shelter trees made profit from natural regeneration in shelterwoods only slightly lower than planting on clearcuts. |
