Trädslagsinverkan på markvegetationens utveckling i odlingsförsök med tall och contorta

Abstract: In the 1970's it was predicted that in the beginning of the 21st century there would be a timber shortage in Sweden and a large scale introduction of the exotic tree species lodgepole pine started. An introduction of a foreign tree species means a risk of a negative influence on the forests ecosystem. Today, the stands that were established in the 70's are middle-aged and the effect on the forest floor vegetation can be studied. This study is focused on the composition of the field and ground layer vegetation in comparable plantations with Scots pine (Pinus sylvestris (L.)) and lodgepole pine (P. contorta Dougl. ex Loud, var. latifolia Engelm). Data was collected at nine of SCA:s experimental sites, established in the beginning of the 1970's. Scots pine and lodgepole pine were planted in pairs at similar ground conditions. The trial was included in HUGIN's young-stand-inventory in the year 1979 at which tree stands and forest floor vegetation were described at five permenant plots of 100 m2 per experimental plantation and tree species. The plots were inventoried in the years 1984, 1991 and 2007. The analysis concerns appearance and percentage cover of different species in forest floor vegetation and the development since previous measurements. For the appearance of species in the forest floor vegetation, there were almost no differences between the two tree species. The concluded differences in forest floor vegetation between stands of Scots pine and lodgepole pine were: • Lower percentage cover of field vegetation in lodgepole pine than in Scots pine (although not significant). • The cover of bilberry was lower in lodgepole pine than in Scots pine (almost significant). • Herbs, grasses and cowberry did not differ between tree species. • No differences could be seen for the cover or composition of bottom vegetation. Changes over time from the young-stand phase (10-15 years old) to thinning phase (about 40 years old): • The cover percentage without field vegetation has increased from about 10 to 20 %. • The cover of wavy hair grass decreased from 65 to 35 %, while the cover of herbs increased from about 3 to 10 %. • The cover of bilberry increased from 10 to 30 % and the cover of cowberry increased from 5 to 20 %. • The area percentage without bottom vegetation increased from 35 to 45 %, as for the cover of mesic soil mosses. • The cover of hairy-cap mosses decreased from 20 to 5 %. • Lichens and swamp mosses were almost lacking, during the studied period. The concluded differences between the two tree species were small in this study, while the changes over time were big and mainly follow the dynamics of previous studies. Thinning appeared to have a positive effect on the forest most species except for herbs that decreased. The total share of field vegetation was lower, while the bottom vegetation cover was higher, on thinned plots.