Rolf Övergaard

Early development of pure and mixed tree species plantations in Snogeholm, southern Sweden

There is a lack of experimental studies comparing the forest production of mixed tree species stands and monocultures. As a case study, in 1994 an experiment was established in an afforestation landscape in southern Sweden with 66 plots: 18 planted with single tree species (including most native Swedish trees, plus Populus and Larix hybrids) and 48 with various non-replicated mixtures. Fifteen years after planting, stand growth did not differ significantly between the mixtures and the monocultures. However, the monocultures did exhibit a higher variation in growth levels relative to the moderate but comparatively consistent growth levels exhibited by the mixtures; particularly those comprised of more than two species. A specific analysis of mixtures containing either the tree species Picea abies or Quercus robur and their corresponding monocultures demonstrated the importance of the tree species admixed as a determinant of production outcomes early in the rotation. In the case of P. abies, tree species mixtures tended to reduce production, whereas in the case of Q. robur, mixtures tended to increase production. In addition no consistent differences in the mean height and mean diameter growth of P. abies and Q. robur between mixtures and monocultures were detected. A major conclusion is that adding more than two species did not increase stand volume growth.

Growth response of hybrid poplars to different types and levels of vegetation control

Poplar plantations established on agricultural or forest land can be adversely affected by abundant competing vegetation already present or that grows after planting. In this paper, we investigate how different intensities of manual vegetation control and mulching with polypropylene plastic effect poplar growth during the first two years after planting. Field data revealed that, during the first year, mulching with polypropylene plastic increased seedling growth more than manual vegetation control when performed over the same area. However, during the second year, these differences diminished and poplar seedlings continued to grow at the same rate irrespective of vegetation control. The difference in growth between treatments seems to be related to the fact that mulching positively influences water and nutrient availability to a greater extent that manual vegetation control during the early phase of establishment. Vegetation control also affected biomass allocation, with a relative increase in leaf biomass and decrease in stem biomass. The increase in leaf biomass associated with vegetation control was a result of both an increase in leaf number and increased leaf size.

Impact of seedling type on early growth of poplar plantations on forest and agricultural land

ABSTRACT Today, most poplar plantations in the temperate region are established on abandoned marginal agricultural land, but there is great potential for planting poplars on forest land as the available area is large and does not compete with food production. The objective of this study was to examine how different planting types (un-rooted cuttings, bare-rooted and containerized plants) affect the establishment and early growth of poplar plants on forest and agricultural sites. Our results suggest that on the agricultural site, survival and growth during the first two years are not influenced by plant type. However, at the forest sites, survival of rooted plants was superior compared to un-rooted cuttings. The height and biomass (stem and root) increment of bare-rooted plants was low; greater height and biomass growth was found for containerized plants. Container sizes had no effect on height growth, but leaf and stem biomasses were higher if the largest containers were used. When using the largest containers, concentrations of macronutrients (N, P) were increased compared to bare-rooted plants. Thus, these results suggest that practices for establishing poplar plantations of agricultural land include planting of un-rooted cutting, but on forest land, a plant grown in a container of 470 ml should be used. Together, this can reduce the cost of establishment, increase the available area for poplar plantations and have an impact on poplar plantation economics in Sweden.