For what, when, and where is green-tree retention better than clear-cutting? A review of the biodiversity aspects

Summary In Europe, two commercially important treelike birch species occur naturally: silver birch ( Betula pendula Roth) and downy birch ( Betula pubescens Ehrh.). Both species have a wide natural distribution area on the Eurasian continent, ranging from the Atlantic to eastern Siberia. Although birches occur throughout almost the whole of Europe, the most abundant birch resources are in the temperate and boreal forests of Northern Europe. In the Baltic and Nordic countries, the proportion of birch out of the total volume of the growing stock varies between 11 and 28 per cent. In Northern Europe, birch is commercially the most important broadleaved tree species. Birches are light-demanding early successional pioneer species, which grow both in mixed stands and in pure stands. This article provides an overview of the most important ecological characteristics and typical growth and yield patterns of birch, based on European scientifi c literature. Growth and yield research on birch has been relatively active in Northern Europe, where numerous growth and yield models have been developed during the last decades. In this paper, a list of published scientifi c articles on growth modelling is provided and is grouped according to the different types of model. When growing in forest stands, birches have a relatively straight slender stem form. The current practices and silvicultural recommendations, based on research directed at high-quality timber production in silver birch stands, are reviewed. Although the emphasis is on even-aged pure silver birch stands, the management of mixed stands as well as the silviculture of downy birch and curly birch are also briefl y discussed.

Silviculture of birch (Betula pendula Roth and Betula pubescens Ehrh.) in northern Europe.

Tissue culture of ornamental pot plant: A critical review on present scenario and future prospects

Summary Plant interactions can be defi ned as the ways plants act upon the growth, fi tness, survival and reproduction of other plants, largely by modifying their environment. These interactions can be positive (facilitation) or negative (competition or exploitation). During plantation establishment or natural forest regeneration after a disturbance, high light levels and, sometimes, increased availability of water and nutrients favour the development of opportunistic, fast-growing herbaceous and woody species which capture resources at the expense of crop trees. As a consequence, the growth and survival of crop trees can be dramatically reduced. Although the effects of this competition are well documented, the physical and physiological mechanisms of competition are not. Moreover, the competition process is never constant in time or space. We present a conceptual competition model based on plant growth forms common in global forests, i.e. graminoids, forbs, small shrubs, large shrubs and mid-storey trees, and main-storey trees. Their competitive attributes and successional dynamics are examined. An overview is presented on the way forest vegetation management (FVM) treatments infl uence these components and outcomes regarding crop tree performance and diversity conservation. Finally, a synthesis of literature yields FVM guidelines for effi ciently optimizing crop tree performance and safeguarding diversity. Future research needs to further sustainable FVM are presented.

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Designing forest vegetation management strategies based on the mechanisms and dynamics of crop tree competition by neighbouring vegetation

Forest restoration projects have become increasingly common around the world and planting trees is almost always a key component. Low seedling survival and growth may result in restoration failures and various mechanical site preparation techniques for treatment of soils and vegetation are important tools used to help counteract this. In this article, we synthesize the current state-of-knowledge concerning mechanical site preparation for improved tree establishment when carried out in different forest restoration situations, point out critical research gaps and provide some recommendations for future directions. Mechanical site preparation often results in improved seedling survival and growth. However, if not intensive methods with much soil disturbance are used, it is a rather ineffective tool for controlling competing vegetation. Methods such as scarification, mounding and subsoiling also lead to multiple interactions among soil physical and chemical properties that affect plant survival and growth, and it may be difficult to determine the actual cause–effect relationship of any positive seedling responses. Most research to date on mechanical site preparation and plantation performance has been conducted using a few conifer tree species. Seedling responses differ among tree species and alternative species are often used during restoration compared to production forestry indicating a need for additional research for improved understanding. Several management objectives such as soil protection and increased biodiversity are many times relevant during forest restoration, and mechanical site preparation methods should be implemented carefully because they can have large impacts on the environment.

https://www.nrs.fs.fed.us/pubs/jrnl/2012/nrs_2012_lof_001.pdf

Mechanical site preparation for forest restoration

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

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

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.

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

Six broadleaved tree species and Picea abies (L.) Karst. were planted under spruce plantations of varying densities, in Sweden. Treatments included control (994 stems ha −1 ), dense (538 stems ha −1 ), sparse (294 stems ha −1 ) and gap (0 stems ha −1 ) overstory treatments. There was an increase in height and diameter growth from control to sparse overstory treatment of all underplanted tree species except for ash (Fraxinus excelsior L.) and Norway maple (Acer platanoides L.). Site conditions may have hampered the growth of these species, as well as wild cherry (Prunus avium L.). Both oak (Quercus robur L.) and spruce had greater growth in the gap treatment, relative to the other treatments. Insecticide application did not influence seedling growth or survival. The performance of beech (Fagus sylvatica L.), lime (Tilia cordata Mill.), spruce and oak was consistent with shade tolerance ranking. Beech and lime had a very high survival rate, even under the densest canopy. The growth and mortality of ash, maple and wild cherry differed significantly from what was expected. This experiment demonstrated significant variation in interspecific growth and mortality between seven planted tree species in relation to canopy density. Correct site and species selection is crucial when underplanting in shelterwood systems.

Growth and mortality in underplanted tree seedlings in response to variations in canopy closure of Norway spruce stands

Hypocotyl explants of Beta vulgaris L. were grown on defined agar media with different combinations of IAA and kinetin at varying concentrations of nitrogen or sucrose. The cultures were kept in light (18 h a day) at 27°C for 5 weeks. Root initiation and callus growth were recorded and the callus tissue was analysed for N and K.



Root formation was found to increase with increasing nitrogen concentration (from 5 mM to 23.3 mM) in the medium at 10.0 mg/1 of IAA, whereas no stimulation was found at 0.1 mg/1 of IAA. When raising the sucrose level from 20 g/1 to 100 mg/1 at 10.0 mg/1 of IAA and 1.0 mg/1 of kinetin, root initiation was also stimulated. At a lower kinetin and auxin level, however, no increase was recorded.



Callus growth was affected by changes in the nitrogen or sucrose concentration of the culture media. The nitrogen content of the callus tissue increased with rising nitrogen concentration of the media. When raising the sucrose level instead of the nitrogen level, the nitrogen content of the tissue decreased.

Torkel Welander

Papers

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

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

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

Growth and mortality in underplanted tree seedlings in response to variations in canopy closure of Norway spruce stands

Effects of Nitrogen, Sucrose, IAA and Kinetin on Explants of Beta vulgaris Grown in vitro