Articles by Veli Pohjonen

Yield of Cupressus lusitanica Mill. was modelled by predicting the diameter distribution of trees at given stand ages. The beta distribution was used as a theoretical distribution. The models used for the calculation of diameter distribution were based on 66 temporal sample plots with varying age, site and stand density. The growing sites of Cupressus lusitanica were divided into four classes on the basis of age and dominant height. Using the stand models developed in the study, the yield and profitability of different thinning schedules was evaluated by a simulation technique. In the simulated treatment regimes, the mean annual increment varied from 6.6 m³/ha in the poorest site class to 16.6 m³/ha in the best class with rotation lengths ranging from 25 years (best sites) to 34 years (poorest sites). With typical planting densities (1,600 trees/ha), thinnings increase the total harvest by a few percentage points and improved the profitability of plantation forestry.
The PDF includes an abstract in Finnish.

• Pohjonen, E-mail: vp@mm.unknown
• Pukkala, E-mail: tp@mm.unknown

Linear programming was used to analyse the land use alternatives in the Debre Birhan Fuelwood Plantation area, in the central highlands of Ethiopia. The region represents a rural, high-altitude area, where the main land uses are grazing and cultivation of barley, wheat and pulses. To alleviate fuelwood shortage, large plantations of Eucalyptus globulus Labill. have been established. Livestock has traditionally used the major part of the production capacity of the sites. A decrease in the number of cattle would facilitate a considerable increase in the production of cereals, pulses, fuelwood and construction timber. The optimal share of the land for arable crops, grazing and tree plantations would be about 40, 45 and 15% respectively.

The PDF includes an abstract in Finnish.

• Pukkala, E-mail: tp@mm.unknown
• Pohjonen, E-mail: vp@mm.unknown

The economic analysis is based on computer simulations which covered a seedling rotation and three successive coppice rotations. Calculations were carried out for the four site productivity classes in Eucalyptus globulus plantations. The rotation length that maximized the land expectation value is 12–20 years for seedling rotation and 8–16 years for coppice rotations with discounting rates 2–8%. The mean wood production is over 40 m³/ha/a in the best site class and about 10 m³/ha/a in the poorest class with rotation lengths ranging from 10 to over 20 years. Thinnings increase the wood production and land expectation value by a few percentage points. In areas suitable to Eucalyptus globulus growth, the land expectation value is considerably higher in forestry than in agriculture, except in very poor areas or with very high rate of interest.

The PDF includes an abstract in Finnish.

• Pohjonen, E-mail: vp@mm.unknown
• Pukkala, E-mail: tp@mm.unknown

Salix 'Aquatica Gigantea', widely experimented and promising species for temperate zone short rotation forestry, has since 1950 recorded in Finland 23 times with different clone numbers. Salix x dasyclados Wimm., by morphological, cultivational and productivity characteristics similar willow has been recorded 16 times.

The nomenclature and origin of both willows have remained unclear in field research. Recent observations, based on morphological analyses and chromosome studies suggest that ’Aguatica gigantea’ and most S. x dasuclados clones can be collected under one Siberian species: Salix burjatica Nasarov. The true Salix x dasyclados Wimm. is a female hybrid S. x viminalis x cinerea, famous West-European basket willow that has been very little experimented in Finland.

The PDF includes an abstract in Finnish.

• Pohjonen, E-mail: vp@mm.unknown

Light intensity inside the canopy varies considerably both in space and time. A new apparatus was developed which is disturbed as little as possible by the above-mentioned variation. The construction is based on the linear relationships between light intensity (measured using silicon diodes) and photosynthesis. This procedure permits linear operations (summing and integration) to be carried out on the output of the diodes without any loss of accuracy. There are five diodes in each assimilation chamber. A model, in which the independent variables include ligth, measured with the present equipment, and temperature, fits the photosynthetic rates well even inside the canopy.

The PDF includes a summary in Finnish.

• Hari, E-mail: ph@mm.unknown
• Huhtamaa, E-mail: mh@mm.unknown
• Pelkonen, E-mail: pp@mm.unknown
• Pohjonen, E-mail: vp@mm.unknown
• Salminen, E-mail: rs@mm.unknown

The effect of spacing on the first-year yield and height increment of Alnus incana (L.) Moench, Populus tremula L. x Populus tremuloides Michx. (Populus x wettsteinii), Salix ’Aquatica Gigantea’, and Salix phylicifolia L. was studied at the Arctic Circle Agricultural Experimental Station in Northern Finland. S. ’Aquatica Gigantea’ gave yields which were twice as high as those of the other species in the study. The highest yields were of the order of 60 tons per hectare (fresh yield including foliage). The annual height growth in S. ’Aquatica Gigantea’ was about 100 cm, in the others about 30–50 cm. S. ’Aquatica Gigantea’ had a maximal height growth when the distance between the seedlings was 25 cm.

The PDF includes a summary in English.

• Pohjonen, E-mail: vp@mm.unknown

Willow (Salix sp.) species and clones have been selected in Finland, originally for basket willow husbandry, since 1910's. Screening for biomass willows started in 1973 by the Foundation for Forest Tree Breeding. Biomass willow research for energy started in 1978. The objective of the study was, based on theoretical background, on historical record of Finnish willow research between 1910–80 and on analysis of the Finnish biomass willow research of the 1980s, a further selection of exotic and indigenous willows for energy and chemicals.

Swedish selection of 63 exotics, mainly of Salix viminalis L. and S. burjatica Nazarov, was screened in Kompparnäs willow research site in the southern coast of Finland in 1983–89. S. viminalis showed both high yield potential and good crop certainty. The yield variation in S. burjatica were big due to rust (Melampsora sp.) infection followed by lowered winter hardiness. Three recommendable S. viminalis clones for Southern Finland were found.

Finnish indigenous species were screened based on collection (375 clones) in 1974–74 of the Foundation for Forest Tree Breeding, and the Finnish 4H-organization (566 clones) in 1978–79 in test sites in Suomusjärvi, Nurmijärvi, Kannus and Haapavesi. Salix myrsinifolia Salisb. was most productive of the indigenous willows. Five recommendable clones were selected. The second most productive indigenous was S. phylicifolia, with three recommendable clones. Based on willow hybridization studies in the Finnish Forest Research Institute, a considerable additional selection effect, boosted by heterosis, was found from the progenies. Further intraspecific crossings of geographically distant clones of S. myrsinifolia are recommended.

Based on the results, S. viminalis is recommended for practical biomass forestry application in the southernmost agroclimatic zone of Finland. S. myrsinifolia is recommended for further research and development in the other zones.

The PDF includes a summary in Finnish.

• Pohjonen, E-mail: vp@mm.unknown