METSÄNTUTKIMUSLAITOS SKOGSFORSKNINGSINSTITUTET FINNISH FOREST RESEARCH INSTITUTE www,metla,fi - PDF

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Management of birch - methods to produce high quality birch (Pentti Niemistö) Contents of the presentation Regeneration - problems and site aspects Growing of seedling stands and timing of first commercial

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Management of birch - methods to produce high quality birch (Pentti Niemistö) Contents of the presentation Regeneration - problems and site aspects Growing of seedling stands and timing of first commercial thinning Thinning intensity and rotation period Production of special price birch butt logs Betula pendula (silver birch) = Valuable broadleaved tree species Betlua pubescens (downy birch) NOT - Growth rate - Biological age - Stem quality (no differences in wood quality) - Sites and location Mean birch volume/ha (Korhonen 2007) Silver birch-% of total birch volume Birch regeneration and afforestation in Finland ha/year Betula pubescens, planted ha Betula pendula, direct seeded ha Betula pendula, planted ha Natural regeneration of Betula pendula: ha/year, total ha - About 20 % of total birch regeneration failed + 20 % in poor condition Afforestation of abandoned fields in Finland Birch, ha Total, ha Planting, a reliable method for birch regeneration: results from practical forestry in Finland (Saksa ) Mean height of valid birches: 162 cm 92 cm 111 cm Failure Poor Tolerable Good 0 Planted, 3 yr Direct seeded, 4 yr Natural reg. 5 yr Weed control - profitable and necessary (Hytönen& Jylhä 2005) Stem volume on the full ploughed field 11 years after silver birch planting, m³/ha Control Cover plant, Trifolium repens Cover plate, 50*50 cm Diklobenil Terbuthylatsin Kloritamid Unsuitable site and deficient weed control = fiasco photo: E. Oksanen More problems have existed in birch plantations on abandoned fields (Ferm ) Survival, % Years after palnting Vole, Microtus agrestis photo: H. Henttonen Birch saw fly (Cicadella viridis) and Gordonia multispora photo: A. Pouttu photo: A. Lilja Moose, Alces alces photo: R. Heikkilä photo: A Viherä-Aarnio Mean size and quality characters of stems (600 thickest/ha) in planted Betula pedula stands at the age of 30 years Mean diameter of trees, cm Thickest live branch, mm Thickest dead branch, mm Tapering of stem (d1.3-d6.0), mm Mean height of trees, m Agricultural land Forest land Height of live crow n base, m Height of dead crow n base, m Stems free of exterior defects, % Approximated rejection in the volume of logs, % Radius of pith discoloration 4 cm, % of stems Mean height of pith discoloration, m Frequency of knot discoloration in butt log, % of disces (Niemistö ) Stems free from infection of Phytobia betulae, % Number of Phytobia tunnels at breast height Hard stem discoloration, common in young planted birches (photo: P. Savilampi) Phytobia betulae (photo: J. Lehto, M. Rousi) The aim in pure Silver birch seedling stand : faultless stems/ha after the risk of moose damages at the height of 6-7 m, homogenous size and spacing. How to achieve: - Fertile sites with adequate moisture and air content: gentle slopes, fine sand and silt moraine soils and fine sandy soils - Effective site preparation and weed control before and after planting - Planting with tall seedlings of high quality and good health - Regeneration just after peak periods of vole - Protection against vole and hare, chase away moose and deer Thinning of pure silver birch stand photo: E. Oksanen Growing of silver birch seedling stand to first commercial thinning stage At density of 1600 stems/ha it is profitable to have first commercial thinning at m dominant height: - Live crown 50 % of tree height - Branches are dead along the length of butt log and self pruning will continue - Adequate stem size and volume/ha of removed trees for profitable thinning operation Live crown development and timing of first commercial thinning according to spacing trials Living crown, % of tree height 0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 % Initial density, plants/ha (living stems/ha at 24 m height) 5000 (2700) 2500 (1900) 1600 (1400) 1100 (930) 800 (760) 600 (500) 400 (370) Top height, m Spacing and stem wood production in Silver birch plantations m³/ha Influence of initial spacing on the total yield and commercial wood production ( 7 cm) of Betula pendula at the age of 27 years Total yield Commercial wood Initial spacing, trees/ha Spacing and quality of Silver birch stems mm Influence of initial spacing on the thickest branches and the taper of stems of Betula pendula at age of 20 y Taper (d1.3 - d6.0) Diameter of thickest branch Initial spacing, trees/ha Pruning is necessary when growing special quality birch timber Birch trees should be pruned in two phases: First time at the height of 6-7 m by secateurs up to the pruning height of m (about 600 stems/ha). Second time at the height of meters by clippers with long handle to the height of 5-6 meters ( stems/ha) Birch trees should be pruned during the growing season in July, or well before the growing season during the late winter or early spring Live branches are able to cut up to the branch diameter of 20 mm, but pruning of larger branches or use of a pruning saw will increase the risk of discoloration and rot in the stems Birch pruning photo: E. Oksanen Heavy thinning of silver birch stand photo: E. Oksanen Heavy thinning (35 % of ba.) decreased the volume growth of silver birch stand only 5 % in 15 year-period, and very heavy thinning (50 % of ba.) 14 %. 12 Annual volume growth after first commercial thinning, m³/ha/year years 1-10 years 1-5 years Unthinned Thinning, % of basal area Heavy thinning: Increase in growth of thickest and valuable birch stems Diameter growth during 10 years after first thinnin, mm/year Top diameter (100 thickest/ha) Mean diameter Unthinned Removed, % of basal area From the viewpoints of growth and practical management, the program of two heavy thinnings seems to be best for high quality silver birch stand, first to the density of stems/ha and the second to stems/ha photo: E. Oksanen Why??? Small or tolerable volume growth losses are compensated by increased growth of valuable stems After a heavy and profitable first thinning, a careful thinning from above and removal of saw logs are able in the second thinning stage Compared to larger number of thinnings, two heavy thinnings increase the volume of saw logs, decrease logging damages and shorten the rotation period The program of one thinning is not possible, because of - too small live crowns or - in other case - growth losses, - limited quality selection of stems along the rotation - risk of storm and snow damages Thinning experimet 859 in central Finland + last 20-yearprediction (by Motti stand simulator) Diameter growth of final crop trees, mm/year Uncommercial thinning, 1600 stems/ha 1. commercial thinning, 800 stems/ha commercial thinning, 400 stems/ha 4 2 Unthinned 2500 stems/ha Age Thinning experimet 859 in central Finland + last 20-yearprediction (by Motti stand simulator) Dbh, cm Thickest tree/ heavy thinning Medium tree/ Heavy thinning Smallest tree/ Heavy thinning Thickest tree/ Unthinned Medium tree/ Unthinned Smallest tree/ Unthinned Prediction Age Production of special price birch butt logs Pruning of young birches in two phases, but Phytobia betulae is still an esthetic fault in stems from pure stands = - Mixed stands - Hillsides to north - Heavy late thinnings - Long rotation? photo: E. Oksanen Long rotation = valuable stems... NO photo: E. Oksanen
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