Pelle Gemmel

Natural regeneration of Norway spruce, Scots pine and birch under Norway spruce shelterwoods of varying densities on a mesic-dry site in southern Sweden

The effects of shelterwood density and site preparation on the emergence, survival and growth of naturally regenerated Norway spruce (Picea abies L. Karst.), Scots pine (Pinus sylvestris L.) and birch (Betula pendula Roth and B. pubescens Ehrh.) seedlings were investigated in Norway spruce shelterwoods in southern Sweden over a 6 year period. The shelterwood densities ranged from 277 to 96 stems/ha and an adjacent clear-cut. Scarification increased the emergence of all species. Increased shelterwood density promoted the emergence of Norway spruce seedlings, while the emergence of Scots pine and birch seedlings were not significantly affected by the shelterwood density. The survival of birch was negatively correlated to increased shelterwood density, while the survival of Norway spruce and Scots pine were less affected. Soil scarification had no significant effect on the survival of Scots pine and birch. In Norway spruce, the survival was higher in mineral soil than in undisturbed soil. Seedling growth decreased with increased shelterwood density for all species. Removal cutting of shelterwoods produced a high mortality in Norway spruce and Scots pine, but not in birch. The Norway spruce seedlings were evenly distributed throughout the shelterwood, whereas Scots pine and birch seedlings appeared in patches. Findings from this study indicate that a mixed-species forest may be established by using the following natural regeneration method: a sparse shelterwood, combined with scarification. Then, the future tree species mixture can be controlled through pre-commercial thinning and, if necessary, by complementary planting.

Development of oak and beech seedlings planted under varying shelterwood densities and with different site preparation methods in southern Sweden

Effects of site preparation, shelterwood density and planting depth on the survival and growth of planted beech and oak seedlings were studied. Experiments were performed in one oak and one beech stand in southern Sweden. Two areas with different densities of shelterwood and one clearcut were established in each stand. Growth, damage and survival of the planted seedlings were observed for three years. Soil water potential was recorded weekly and radiation and soil temperatures were recorded continuously during the growing seasons.Neither site preparation methods nor planting depth affected oak seedling growth, when planting was carried out on fresh clearcuts or in shelterwoods, while growth of beech seedlings was positively affected by mounding. Growth of oak seedlings was inhibited by the shelterwood treatments. In beech seedlings, growth was lowest in dense shelterwood, while there was no difference in growth between seedlings on the clearcut area and in the shelterwood of low density. Differences in growth may be explained by differences in radiation and soil water potential.When planting was carried out on a one-year-old clearcut, site preparation improved the subsequent growth of oak and beech seedlings.

Scarification and seedfall affects natural regeneration of Scots pine under two shelterwood densities and a clear-cut in southern Sweden.

A study was undertaken to evaluate the effect of Scots pine (Pinus sylvestris) shelterwood density and timing of removal on the regeneration of forests with improved wood quality. This paper focuses on the effect of scarification and seedfall on the success of natural regeneration of Scots pine under two shelterwood densities and in a clear-cut. Wood quality aspects will be addressed later in the study. After 4 yrs, natural regeneration of Scots pine under a 200 stems ha-1 shelterwood reached 90000 seedlings ha-1, 53000 under a 160 stems ha-1 shelterwood and 3700 in a clear-cut. The high natural regeneration under the densest shelterwood resulted from a high seedfall, slower invasion by competing vegetation, consequent prolonged recruitment and low mortality. Since mortality largely decreased for both shelterwood densities and recruitment seems to continue, the success of regeneration should be maintained in the future if proper release operations are conducted. The latter could begin when seedlings reach a height of about 0.5 m and the cover should be maintained until they reach a height of about 6 m. Therefore, it may be possible to use 200 stems ha-1 Scots pine shelterwoods in southern Sweden to obtain dense stands and thus improve wood quality (stem taper, wood density, etc.).

Germination and early growth of sown Quercus robur L. in relation to soil preparation, sowing depths and prevention against predation.

A field experiment was established in the autumn of 1992 in order to study predation of acorns, germination and early growth of oak seedlings. The experiment was established on a clearcut and an adjacent oak shelterwood in southern Sweden. In the experiment, a total of 6 840 acorns were sown. The sowing was carried out with different vegetation control and soil preparation treatments and with different planting depths.The germination percentage was highest for acorns sown at five cm depth and lowest for acorns sown on top of the soil, and lower for acorns sown in areas where the humus layer had been removed than in areas where the humus layer was retained. There was no difference in the percentage germination after two growing seasons between acorns sown inside the shelterwood and acorns sown on the clearcut. The height of the seedlings was lowest when the humus was removed while the number of leaves per seedling was lowest for seedlings in untreated areas after two growing seasons. Furthermore, seedlings in untreated areas showed the lowest relative height growth rate during the second growing season. In spite of higher biomass of ground vegetation in undisturbed areas compared to treated areas, no effect of the soil and vegetation control treatments could be found on soil water potentials. The soil temperature and photosynthetic active radiation at seedling level were higher in areas where soil preparation and vegetation control had been performed. However, it was concluded that neither low soil water availability nor low light levels could be the only cause of lower relative height growth rate during the second growing season for seedlings in undisturbed areas.

The influence of site preparation on growth in Quercus robur L. seedlings in a southern Sweden clear-cut and shelterwood

Natural regeneration of Quercus spp. is regarded as a method with major problems for establishing new stands. A number of factors like quantity and quality of acorn production, heavy predation and browsing on acorns and seedlings and low growth rate of oak seedlings contribute in regeneration failures. To study the influence of light, nutrients and water on growth in Quercus robur L. seedlings in relation to site preparation, a field experiment was established. The experiment was carried out in a clear-cut and a shelterwood in southern Sweden from 1992 until 1995. Five different treatments were applied and acorns were then planted. The treatments were: herbicide, herbicide and mixing of the humus layer and the top 10 cm of the mineral soil, herbicide and removal of the humus layer, herbicide and deep cultivation down to 40 cm with the humus layer in the bottom and undisturbed control. Irrespective of the method, the different site preparation treatments after three years equally well prevented the growth of ground vegetation and increased the seedling growth. PPFD (photosynthetic photon flux density) at seedling level was about 20% of full light in the shelterwood and in the undisturbed control plots in the clear-cut. PPFD at the seedling level were about 60% of full light in the different site preparation treatments in the clear-cut. The mean cumulative soil water potential was about the same in undisturbed control plots in the clear-cut and shelterwood. In the different site preparation treatments, mean cumulative soil water potential indicated lower values in the clear-cut compared to the shelterwood. According to measurements of the leaf water potential, seedlings seemed to be more affected by water stress in the clear-cut. Nitrogen concentration in leaves was about the same in all treatments. Longer periods with shelterwoods in combination with the additional site preparation for ground vegetation control was recommended for practical forestry for improved growth of oak seedlings during natural regeneration. It does not seem to be important which method of additional ground vegetation control is chosen as long as the amount of ground vegetation is reduced. It was concluded that light level alone is not the key factor controlling growth of oak seedlings during natural regeneration. However, light and soil water content may interact and influence the growth of oak seedlings.

Changes in growth and allocation of growth in young Pinus sylvestris and Picea abies due to competition

Morphological characteristics of beeted Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) trees grown under differing influence from neighbouring trees were compared. The shape of Scots pine trees showed greater plasticity in response to competition than that of Norway spruce trees. When compared at the same height, Scots pine trees growing under strong influence from neighbours had smaller stem volumes and branch basal areas, shorter branches and decreased number of current shoots compared to Scots pine trees growing under weak influence from their neighbours. In Norway spruce, the only characteristic that was significantly affected by competition was the number of current shoots.

Carbon and nitrogen stocks in soil, trees and field vegetation in conifer plantations 10 years after deep soil cultivation and patch scarification

Abstract Biomass, total nitrogen (N) and total carbon (C) stocks were determined in trees, roots, field vegetation and soil in plots given two different site preparation treatments, deep soil cultivation (DSC) approximately 50 cm deep and patch scarification (PS), at three locations in Sweden 10 years after treatment. One location was planted with Pinus contorta, one with Picea abies and one with a mixture of P. abies and Pinus sylvestris. No differences were found in total ecosystem (trees, roots, field vegetation and soil) C and N stocks between the DSC and PS plots. In the DSC plots the tree biomass, tree N and C contents and total biomass were higher than in the PS plots, but the opposite was found for stocks in field vegetation. Biomass and C stocks in the total vegetation (trees, roots and field vegetation) were higher in the DSC plots. However, vegetation N stocks did not differ between the soil treatments, probably because the combined amount of leaf tissue in the trees and field vegetation did not differ between them. The proportions of biomass allocated to roots, stems and needles did not differ between the two treatments. However, the rooting was deeper in DSC plots, possibly because nutrient availability was higher, and subsoil density lower, following DSC than following PS.

The effect of precommercial thinning on the incidence of heterobasidion annosum in planted picea abies

Evaluation was made of the effect of precommercial thinning in 13–15 year old Norway spruce (Picea abies (L.) Karst.), on the incidence of Heterobasidion annosum in residual trees, more than 20 years after thinning. Five sites in southern Sweden were studied with the following treatments at each site: unthinned plot and plots thinned to 600, 1 000, 1 400, 1 800 and 2 500 stems ha−1. Only three trees out of 450 investigated, were found to be decayed. None of these trees were found to be infected by H. annosum as an effect of precommercial thinning. Control measures to prevent decay caused by H. annosum in residual trees do not appear warranted for precommercial thinning of young, planted, Norway spruce stands.

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 in supplementarily planted Picea abies regenerations

Abstract An experiment was established in 1978 in two Norway spruce [Picea abies (L.) Karst.] plantations in southern Sweden to study yield after mortality in patches with and without supplementarily planted (SP) seedlings. Gaps of different sizes were created by removing the originally planted seedlings. The gaps were either left unplanted or a supplementary planting was performed with one of four species [Norway spruce, Scots pine (Pinus sylvestris L.), lodgepole pine (Pinus contorta Dougl.) or hybrid larch (Larix deciduas Mill×L. Leptolepis Gord.)] 2 (at Knäred) or 6 years (at Ullasjö) after the original plantation. In 2002, most of the SP Scots pine, lodgepole pine and hybrid larch seedlings were dead or severely damaged by roe deer and moose. Survival was high among SP Norway spruces, but they had slower growth than the originally planted spruces. Growth was lower at Ullasjö than at Knäred. In Ullasjö, growth was lower in small gaps than in large gaps. Trees in original regeneration in areas surrounding unplanted gaps were larger than trees surrounding gaps with SP seedlings, which in turn were larger than originally planted trees in plots without gaps. In conclusion, because the original plantation surrounding unplanted gaps used a large part of the open space and growth of SP seedlings was slow, supplementary planting resulted in an insignificant growth increase. However, supplementary planting may increase the timber quality of trees surrounding the gaps, although this effect remains to be quantified.