The ability to create mixed stands by planting Norway spruce and Scots pine every second row

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