Epsilon Archive for Student Projects

Abstract

Swedish forests primarily consist of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies
(L.) Karst.). Scots pine grows in stands with lower site index and Norway spruce in stands with
higher site index. Despite the differences both tree species can co-exist naturally in Sweden. Pine
and spruce mixed stands have a higher biodiversity than monocultures. Pests and pathogens usually
spread from one tree to another of the same species. A mixed forest is more resistant to pests and
pathogens due to the mix of tree species, making it more difficult for pests and pathogens to spread
through the stand. The disadvantages with mixed stands could be the decrease in volume production
and increase of cutting costs. Important to remember is that mixed stands can spread financial risks
and help forest managers move decision making into the future depending on the development of
the stand.
The main purpose of the thesis was to examine if Scots pine and Norway spruce planted every
second row could be a way to create mixed stands in central Sweden. Ten stands owned by Sveaskog
planted every second row with 2 000-2 300 pine and spruce seedlings haˉ¹ were examined. The
stands were planted 2009-2012 in Hälsingland and Dalarna, the site index varied from T19 to T24
and G18 to G27. A goal was set to reach 2 000 stems haˉ¹ after pre-commercial thinning. A
regression analysis showed that the number of pine stems was gradually decreasing as site index
increased. Spruce stems were gradually increasing as site index was increasing. The correlation was
only 5-10% however the decrease in pine stems and increase in spruce stems was significant for
both tree species. Breaking point seemed to be at approximately T22 and G22 where the number of
pine stems increased below T22, and the number of spruce stems increased above G22.
When site index varied within the stands, it showed in number of stems per tree species selected to
create future stands. Spruce was higher in number of stems in plots with higher site index and pine
was higher in number of stems in plots with lower site index. Height difference between pine and
spruce needed to be less than one meter for one tree species not to take over in the future stand. The
mean height for all stands were within the one-meter span. In summary, planting Scots pine and
Norway spruce every second row in central Sweden to create mixed species stands was successful
within the site index variation in this study