Current issue: 58(5)

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Silva Fennica vol. 43 no. 5 | 2009

Category : Research article

article id 460, category Research article

Hong Ling, Sandhya Samarasinghe, G. Don Kulasiri. (2009). Modelling variability in full-field displacement profiles and Poisson ratio of wood in compression using stochastic neural networks. Silva Fennica vol. 43 no. 5 article id 460. https://doi.org/10.14214/sf.460

Keywords: wood; digital image correlation; displacement profiles; variability; micro structure; stochastic neural networks; Poisson ratio

Abstract | View details | Full text in PDF | Author Info

Vertical and horizontal displacement profiles in compression parallel-to-grain in a 20 x 20 mm area (30 x 21 or 630 points) in the Tangential–Longitudinal (T–L) and Radial Longitudinal (R–L) sections of small wood columns were obtained from digital image correlation applied to simultaneously captured images of the two surfaces. These consisted of 21 displacement realisations of 30 points along the length of the specimen. They revealed considerable local variations. Stochastic neural networks were successfully developed to simulate trends and noise across and along a specimen in both displacements as well as Poisson ratios in T–L and R–L sections for two selected load levels of 20kN and 40kN. These networks specifically embed noise characteristics extracted from data to generate realistic displacement and Poisson ratio realisations with inherent variability. Models were successfully validated using independent data extracted based on bootstrapping method with high accuracy with R² ranging from 0.79 to 0.91. The models were further validated successfully using a second approach involving Confidence Intervals generated from the data extracted from the models. Models and experimental results revealed that for 20kN load, both vertical and horizontal displacements in T–L section were less heterogeneous across the specimen (smaller vertical shearing and horizontal strain, respectively) than those in the R–L section. For the 40kN load, both displacement profiles in the T–L section were less noisy and more compact than those for the 20kN load indicating less heterogeneity due to compaction of structure. In the R–L section, larger vertical shearing and horizontal strains persisted at 40 kN load. Poisson ratio decreased with load and it was nonlinear in both sections but T–L section showed much less noise across the specimen than the R–L section.

Ling, Centre for Advanced Computational Solutions (C-fACS), Lincoln University, Canterbury, New Zealand E-mail: hl@nn.nz
Samarasinghe, Centre for Advanced Computational Solutions (C-fACS), Lincoln University, Canterbury, New Zealand E-mail: sandhya.samarasinghe@lincoln.ac.nz
Kulasiri, Centre for Advanced Computational Solutions (C-fACS), Lincoln University, Canterbury, New Zealand E-mail: gdk@nn.nz

article id 178, category Research article

Raili Hokajärvi, Teppo Hujala, Leena A. Leskinen, Jukka Tikkanen. (2009). Effectiveness of sermon policy instruments: forest management planning practices applying the activity theory approach. Silva Fennica vol. 43 no. 5 article id 178. https://doi.org/10.14214/sf.178

Keywords: forest policy; forest planning; activity theory; advisory; extension; non-industrial private forests; qualitative study

Abstract | View details | Full text in PDF | Author Info

Recent and ongoing societal changes have brought about a need to foster multiple-use forestry and to strengthen customer orientation in family forestry outreach. The study assesses how forest management planning in family forest holdings could be developed to tackle these challenges. The approach introduces a new way of evaluating the effectiveness of information- and communication-based policy instruments. Here, the cultural-historical activity theory is applied in studying the interwoven practices of present-day planning and the associated advisory services targeted at landowners. The data, comprising semi-structured in-depth interviews with 19 professional planners, were qualitatively examined, and a forest management planning activity model was constructed with the emphasis placed on the inherent contradictions of planning work. As the main contradiction, the forest and the forest owner compete as objects. The aims of making the forest productive and advising the landowners towards an increased activeness motivate forest management planning but the planners feel that they lack the opportunity to respond to the needs of the landowner. A wood-production-emphasizing interpretation of the benefits to the national economy frustrates the policy goal of genuinely promoting the goals of multiple-use forestry. The conclusion drawn is that the actors engaged in forest management planning can reveal the needs for change by discussing their opinions and practical innovations. This can be done with the aid of facilitation by e.g. researchers oriented to developmental work study.

Hokajärvi, Oulu University of Applied Sciences, School of Renewable Natural Resources, Metsäkouluntie 4–6, FI-90650 Oulu, Finland E-mail: raili.hokajarvi@oamk.fi
Hujala, Finnish Forest Research Institute, Joensuu Research Unit, P.O. Box 68, FI-80101 Joensuu, Finland E-mail: th@nn.fi
Leskinen, University of Eastern Finland, Department of Geographical and Historical Studies, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: lal@nn.fi
Tikkanen, Oulu University of Applied Sciences, School of Renewable Natural Resources, Metsäkouluntie 4–6, FI-90650 Oulu, Finland E-mail: jt@nn.fi

article id 177, category Research article

Tuomo Nurminen, Heikki Korpunen, Jori Uusitalo. (2009). Applying the activity-based costing to cut-to-length timber harvesting and trucking. Silva Fennica vol. 43 no. 5 article id 177. https://doi.org/10.14214/sf.177

Keywords: logistics; bucking; cutting; forest transport; long-distance transportation; trucking; time consumption; timber assortment; cost driver

Abstract | View details | Full text in PDF | Author Info

The supply chain of the forest industry has increasingly been adjusted to the customer’s needs for precision and quality. This has changed the operative environment both in the forest and on the roads. As the total removal of timber is increasingly divided into more log assortments, the lot size of each assortment decreases and the time consumed in sorting the logs increases. In this respect, the extra assortments have made harvesting work more difficult and affected the productivity of both cutting and forest transport; this has thus increased the harvesting costs. An activity-based cost (ABC) management system is introduced for timber harvesting and long-distance transport, based on the cut-to-length (CTL) method, in which the logistic costs are assigned to timber assortments and lots. Supplying timber is divided into three main processes: cutting, forest transport, and long-distance transportation. An ABC system was formulated separately for each of these main operations. Costs were traced to individual stands and to timber assortment lots from a stand. The cost object of the system is thus a lot of timber that makes up one assortment that has been cut, forwarded, and transported from the forest to the mill. Application of the ABC principle to timber harvesting and trucking was found to be relatively easy. The method developed gives estimates that are realistic to actual figures paid to contractors. The foremost use for this type of costing method should be as a tool to calculate the efficiency of an individual activity or of the whole logistic system.

Nurminen, Metsätoimisto Tuomo Nurminen, Joensuuntie 5 B 8, FI-41800 Korpilahti, Finland E-mail: tn@nn.fi
Korpunen, Finnish Forest Research Institute, Parkano Research Unit, Kaironiementie 54, FI-39700 Parkano, Finland E-mail: hk@nn.fi
Uusitalo, Finnish Forest Research Institute, Parkano Research Unit, Kaironiementie 54, FI-39700 Parkano, Finland E-mail: ju@nn.fi

article id 176, category Research article

María Pasalodos-Tato, Timo Pukkala, Antonio Rigueiro-Rodríguez, Esther Fernández-Nunez, María Rosa Mosquera-Losada. (2009). Optimal management of Pinus radiata silvopastoral systems established on abandoned agricultural land in Galicia (north-western Spain). Silva Fennica vol. 43 no. 5 article id 176. https://doi.org/10.14214/sf.176

Keywords: simulation; economic profitability; optimization; risk reduction; salvage

Abstract | View details | Full text in PDF | Author Info

Timber production has been the main objective in forest production in Galicia for a long time. Nevertheless, factors such as fire risk and the need to obtain non-timber benefits make other production alternatives like silvopastoral systems worth of consideration. Integration of grazing in the production system not only diversifies products and benefits, but also decreases fire risk by enhancing fuel control. Nonetheless, few studies have examined the economic profitability of these systems. This article analyses the economics of silvopastoral systems established on abandoned agricultural soils afforested with Pinus radiata D. Don. Different tree planting densities, discounting rates, grass values and fire risk scenarios were analysed. The technique employed is based on the combination of an optimization algorithm and a simulator of stand growth and grass yield. The most profitable schedules were obtained with initial stand densities of 1500 trees per hectare. However, with high unit values of pasture production (high value of grass), schedules with an initial stand density of 500 trees per hectare were the most profitable. When the risk of fire was included in the analyses, silvopastoral systems were always more profitable than timber production systems. With an assumption that grazing reduces fire risk thinnings should be done earlier and heavier to reduce the expected losses due to fire and to promote grass production. This lengthens the pasture period. In general, rotation lengt

Pasalodos-Tato, INIA, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria. Madrid, Spain E-mail: pasalodos.maria@inia.es
Pukkala, University of East Finland, Joensuu, Finland E-mail: tp@nn.fi
Rigueiro-Rodríguez, University of Santiago de Compostela, Lugo, Spain E-mail: arr@nn.es
Fernández-Nunez, University of Santiago de Compostela, Lugo, Spain E-mail: efn@nn.es
Mosquera-Losada, University of Santiago de Compostela, Lugo, Spain E-mail: mrml@nn.es

article id 175, category Research article

Heikki Hänninen, Jaana Luoranen, Risto Rikala, Heikki Smolander. (2009). Late termination of freezer storage increases the risk of autumn frost damage to Norway spruce seedlings. Silva Fennica vol. 43 no. 5 article id 175. https://doi.org/10.14214/sf.175

Keywords: Norway spruce; simulation; autumn frost damage; day degrees; freezer storage; growing season

Abstract | View details | Full text in PDF | Author Info

Over the last few years it has become increasingly common in artificial forest regeneration to extend the planting period by using freezer-stored seedlings for early summer plantings. Developmentally, however, planted freezer-stored seedlings lag behind seedlings planted earlier in the spring. As freezer-stored seedlings also start hardening later, they are more susceptible to early autumn frosts, especially in years when the thermal growing season ends and the first autumn frosts come earlier than usual. By means of computer simulations with a simple temperature sum model and long-term air-temperature data from three locations in Finland, we examined the effect of the freezer-storage termination date on the risk of autumn frost damage to the seedlings. The long-term simulations revealed a drastic effect of year-to-year variation in the thermal conditions during the growing season on the occurrence of autumn frost damage. Such results provide crucial information complementary to those obtained in field experiments, which are always restricted to a relatively short time period. Together with earlier field data, the present results suggest that at an average regeneration site in central Finland, the planting of seedlings whose storage has terminated on 15 June and 22 June involve autumn frost damage every tenth and every fifth year, respectively. The sensitivity analysis revealed that the temperature sum requirement of maturation has a great effect on the risk of autumn frost damage, thus pinpointing the need for experimental studies addressing this ecophysiological trait of the seedlings.

Hänninen, Plant Ecophysiology and Climate Change Group (PECC), Department of Biological and Environmental Sciences, Box 65, FI-00014 University of Helsinki, Finland E-mail: heikki.hanninen@helsinki.fi
Luoranen, Finnish Forest Research Institute, Suonenjoki Research Unit, Juntintie 154, FI-77600 Suonenjoki, Finland E-mail: jl@nn.fi
Rikala, Finnish Forest Research Institute, Suonenjoki Research Unit, Juntintie 154, FI-77600 Suonenjoki, Finland E-mail: rr@nn.fi
Smolander, Finnish Forest Research Institute, Suonenjoki Research Unit, Juntintie 154, FI-77600 Suonenjoki, Finland E-mail: hs@nn.fi

article id 174, category Research article

Akihiro Sumida, Taro Nakai, Masahito Yamada, Kiyomi Ono, Shigeru Uemura, Toshihiko Hara. (2009). Ground-based estimation of leaf area index and vertical distribution of leaf area density in a Betula ermanii forest. Silva Fennica vol. 43 no. 5 article id 174. https://doi.org/10.14214/sf.174

Keywords: allometry; leaf area density; LAI; leaf inclination angle; MacArthur–Horn method; pipe model; Betula ermanii

Abstract | View details | Full text in PDF | Author Info

We developed a ground-based method for estimating leaf area index (LAI) and vertical distribution of leaf area density (LAD) for two Betula ermanii plots, combining an allometric method for tree leaf area with the MacArthur–Horn (MH) method using a portable laser rangefinder, including a correction for changes in leaf inclination angle along the vertical gradient measured with a portable digital protractor from a canopy access tower in each plot. Vertical distribution of projected leaf area density obtained by the MH method (LADMH) was transformed to relative distribution for allotting fixed LAI to different heights. Hence, we first developed an allometric method for estimating tree leaf area for LAI determination. Trunk cross-sectional area at branching height (AB) was accurately estimated (r² = 0.97) from ground-based measurements of tree dimensions. We used this method to apply pipe model allometry between tree leaf area and AB, and estimated LAI (4.56 and 4.57 m² m^–2). We then examined how leaf inclination angle affected estimation of the vertical distribution of actual LAD. Leaf inclination angle measurements revealed that actual LAD in the upper canopy was 1.5–1.8-times higher than LADMH, because of steep leaf inclination, while the correction factor was 1.15–1.25 in the lower canopy. Due to the difference among heights, vertical distribution of LAD estimated with correction for vertical change in leaf inclination was more skewed to the upper canopy than that without correction. We also showed that error in LAD distribution can result if horizontal canopy heterogeneity is neglected when applying the MH method.

Sumida, Institute of Low Temperature Science, Hokkaido University, N19W8, Sapporo 060-0819, Japan E-mail: asumida@lowtem.hokudai.ac.jp
Nakai, International Arctic Research Center, University of Alaska Fairbanks, 930 Koyukuk Drive, P.O. Box 757340, Fairbanks, Alaska 99775-7340, USA E-mail: tn@nn.jp
Yamada, International Meteorological & Oceanographic Consultants Co., Ltd. Kawaguchi-cho 2-6528-87, Choshi, Chiba 288-0001, Japan E-mail: my@nn.jp
Ono, Institute of Low Temperature Science, Hokkaido University, N19W8, Sapporo 060-0819, Japan E-mail: ko@nn.jp
Uemura, Field Science Center for Northern Biosphere, Hokkaido University, Tokuda 250, Nayoro, Hokkaido 096-0071, Japan E-mail: su@nn.jp
Hara, Institute of Low Temperature Science, Hokkaido University, N19W8, Sapporo 060-0819, Japan E-mail: th@nn.jp

article id 173, category Research article

Erik Hellberg, Torbjörn Josefsson, Lars Östlund. (2009). The transformation of a Norway spruce dominated landscape since pre-industrial times in northern Sweden: the influence of modern forest management on forest structure. Silva Fennica vol. 43 no. 5 article id 173. https://doi.org/10.14214/sf.173

Keywords: birch; disturbance dynamics; forest history; deciduous forest; fire

Abstract | View details | Full text in PDF | Author Info

Logging history and the study of reference conditions in Scandinavian boreal forests has tended to focus on Scots pine dominated ecosystems. This paper presents a regional study of pre-industrial forest conditions and examines the effects of the industrial exploitation of ecosystems dominated by Norway spruce in northern Sweden. Historical records covering a period which preceded industrial logging in the study area (1917–1927) were used to obtain quantitative data on forest structure and influence of forest fires. These data were compared with a modern data set (2003) to analyse changes due to the industrial transformation of the forest. The early 20th century landscape was dominated by old, multi-cohorted spruce forests and mixed coniferous forests. It was found that fire affected both the structure and composition of the landscape. In post-burnt areas, even-aged forests dominated by deciduous species were the principal forest type. Between the early and modern data sets, profound changes in tree-species composition and age structure were documented. While the total volume of deciduous species increased substantially, the coverage of forests dominated by deciduous species decreased. There was also a significant increase in pine-dominated forests and in the total volume of pine. The industrial transformation of the studied landscapes has had profound effects on the structure of spruce forests, but much less so on deciduous forests. The study concludes that the present forest structure is a function of past management regimes, and that future transformations of the landscape will continue, thus affecting the natural variability and biodiversity of the forests.

Hellberg, Tunstigen 10, SE-831 43 Östersund, Sweden E-mail: eh@nn.se
Josefsson, Swedish University of Agricultural Sciences, Department of Forest Ecology and Management, SE-901 83 Umeå, Sweden E-mail: torbjorn.josefsson@svek.slu.se
Östlund, Swedish University of Agricultural Sciences, Department of Forest Ecology and Management, SE-901 83 Umeå, Sweden E-mail: lo@nn.se

article id 172, category Research article

Guntis Brumelis, Maris Strazds, Zanna Eglava. (2009). Stand structure and spatial pattern of regeneration of Pinus sylvestris in a natural treed mire in Latvia. Silva Fennica vol. 43 no. 5 article id 172. https://doi.org/10.14214/sf.172

Keywords: Pinus sylvestris; regeneration; natural forest; mire

Abstract | View details | Full text in PDF | Author Info

We examined the regeneration patterns of Pinus sylvestris L. in a natural treed mire in the hemiboreal zone in Latvia. Data on tree stem age and size was collected in 207 fine-scale plots (10 m²) and 4 medium-scale plots (400 m²). Size structure of living and dead trees was also estimated on transects 180-m and 250-m length and 10-m width. In addition, the vegetation was described in 1-m² plots to determine preferred microsites for P. sylvestris establishment. Pinus sylvestris showed continuous regeneration by an inverse J-shaped age and size structure. Pulses of mortality induced by fire were also evident. Regeneration of P. sylvestris was mostly on Sphagnum magellanicam Brid. hummocks free of competition from Ledum palustre L. and graminoids, which were found in small interspersed patches throughout the mire. The spatial pattern of tree cohorts differed, probably due to changing moisture conditions altering seedbed conditions and by fire-induced mortality in specific areas. Recent rapid invasion by Betula pubescens Ehrh. and Picea abies (L.) Karst. in a post-fire period since 1971 is probably associated with drier conditions.

Brumelis, Faculty of Biology, University of Latvia, Kronvalda bulv. 4, Riga LV1586, Latvia E-mail: guntis.brumelis@lu.lv
Strazds, Faculty of Biology, University of Latvia, Kronvalda bulv. 4, Riga LV1586, Latvia E-mail: ms@nn.lv
Eglava, Faculty of Biology, University of Latvia, Kronvalda bulv. 4, Riga LV1586, Latvia E-mail: ze@nn.lv

article id 171, category Research article

Takuo Nagaike. (2009). Snag abundance and species composition in a managed forest landscape in central Japan composed of Larix kaempferi plantations and secondary broadleaf forests. Silva Fennica vol. 43 no. 5 article id 171. https://doi.org/10.14214/sf.171

Keywords: snags; long-rotation plantation; plantation age; species composition

Abstract | View details | Full text in PDF | Author Info

Larix kaempferi is the main plantation species in the low-snow, cool-temperate zone of Japan. I studied L. kaempferi plantations of various stand ages in central Japan to examine and compare the effect of stand age on the abundance, size, and species composition of snags (standing dead trees) compared to those in secondary broadleaf forests. Plantations that were older than the standard rotation age had more and larger snags than young plantations, and the species diversity of snags was positively correlated with stand age. Because the density of living planted L. kaempferi showed little correlation with snag variables, whereas that of naturally regenerated tree species was positively correlated with snag variables, the density dependence of snag occurrence was stronger in naturally regenerated trees than in planted L. kaempferi. Snag species that were positively correlated with stand age were the main species in secondary broadleaf forests in this area. Basal area, density, and number of species of snags in standard-rotation plantations were significantly lower than in long-rotation plantations and secondary broadleaf forests. Long-rotation plantations are useful for retaining snags compared to standard-rotation plantations.

Nagaike, Yamanashi Forest Research Institute, Masuho, Yamanashi 400-0502, Japan E-mail: nagaike-zty@pref.yamanashi.lg.jp

article id 170, category Research article

Ryoichi Doi, Senaratne L. Ranamukhaarachchi. (2009). Community-level physiological profiling in monitoring rehabilitative effects of Acacia auriculiformis plantation on degraded land in Sakaerat, Thailand. Silva Fennica vol. 43 no. 5 article id 170. https://doi.org/10.14214/sf.170

Keywords: multivariate analysis; Acacia auriculiformis; community-level physiological profile; land degradation and rehabilitation; soil bacterial community

Abstract | View details | Full text in PDF | Author Info

This study was conducted to investigate the rehabilitative effects of planting Acacia auriculiformis trees on degraded land by observing variations in soil bacterial community profiles provided by community-level physiological profiling. Soil bacterial and physicochemical comparisons between an original evergreen forest and the Acacia plantation plot, established on an area severely degraded as a result of deforestation, showed that most soil characteristics were rehabilitated 18 to 19 years after the plantation of Acacia according to single variables, Shannon and Simpson diversity indices based on the community-level physiological profiles, principal component analysis and redundancy analysis. However, a more strict statistical comparison, discriminant analysis, completely discriminated between the Acacia plantation and the evergreen forest soils when the community-level physiological profiles were compared. Thus, the Acacia plantation soil was shown to still be in the process to full recovery. Here, we discuss the relevance of planting A. auriculiformis in land rehabilitation schemes in savanna regions.

Doi, AFE Building, School of Environment, Resources and Development, Asian Institute of Technology, Pathumthani 12120, Thailand E-mail: roird@aeiou.pt
Ranamukhaarachchi, AFE Building, School of Environment, Resources and Development, Asian Institute of Technology, Pathumthani 12120, Thailand E-mail: slr@nn.th

article id 169, category Research article

Susanne von Bargen, Elise Grubits, Risto Jalkanen, Carmen Büttner. (2009). Cherry leaf roll virus – an emerging virus in Finland? Silva Fennica vol. 43 no. 5 article id 169. https://doi.org/10.14214/sf.169

Keywords: Betula pendula; Betula pubescens; Betula nana; IC-RT-PCR; 3' non-coding region; CLRV; phylogenetic relationship

Abstract | View details | Full text in PDF | Author Info

Cherry leaf roll virus, CLRV, is a plant pathogen that infects a variety of deciduous trees and shrubs in temperate regions. Little is known about its occurrence at high latitudes and especially in Finnish birch species. Still, symptoms that seemed to be associated with CLRV such as vein banding, leaf roll and decline have been observed in birch trees throughout the country since the summer of 2002. Six different birch species, subspecies or varieties, i.e. Betula pubescens subsp. pubescens (downy birch), B. pendula (silver birch), B. nana (dwarf birch), B. pubescens var. appressa (Kiilopää birch), B. pubescens subsp. czerepanovii (mountain birch) and B. pendula var. carelica (curly birch) originating from all over Finland were assessed by immunocapture-reverse transcription-polymerase chain reaction (IC-RT-PCR) for CLRV infection. It was shown that CLRV is widely distributed in B. pendula and B. pubescens throughout the country. Furthermore, dwarf birch, mountain birch, Kiilopää birch and curly birch were confirmed to be previously unkown hosts of CLRV. Genetic analysis of virus sequence variants originating from Finnish birch trees revealed atypical phylogenetic relationships. In contrast to CLRV isolates from birches growing in the United Kingdom and Germany which clustered exclusively within group A, Finnish CLRV isolates belonged either to group B, D or E. Thus, virus population structure in Finnish birches seems to be more variable and host plant dependency seems not to apply for Finnish CLRV isolates.

Bargen, Humboldt-Universität zu Berlin, Department für Nutzpflanzen- und Tierwissenschaften, Fachgebiet Phytomedizin, Lentzeallee 55/57, 14195 Berlin, Germany E-mail: susanne.von.bargen@agrar.hu-berlin.de
Grubits, Humboldt-Universität zu Berlin, Department für Nutzpflanzen- und Tierwissenschaften, Fachgebiet Phytomedizin, Lentzeallee 55/57, 14195 Berlin, Germany E-mail: eg@nn.de
Jalkanen, Finnish Forest Research Institute, Rovaniemi Research Unit, P.O. Box 16, FI-96301 Rovaniemi, Finland E-mail: risto.jalkanen@metla.fi
Büttner, Humboldt-Universität zu Berlin, Department für Nutzpflanzen- und Tierwissenschaften, Fachgebiet Phytomedizin, Lentzeallee 55/57, 14195 Berlin, Germany E-mail: cb@nn.de

article id 168, category Research article

Saila Varis, Anne Pakkanen, Aina Galofré, Pertti Pulkkinen. (2009). The extent of south-north pollen transfer in Finnish Scots pine. Silva Fennica vol. 43 no. 5 article id 168. https://doi.org/10.14214/sf.168

Keywords: Pinus sylvestris; gene flow; adaptation; coniferous phenology; plant population biology; boreal forest dynamics

Abstract | View details | Full text in PDF | Author Info

In order to evaluate the possibility of long distance gene flow in Scots pine (Pinus sylvestris L.), we measured the amount and germinability of airborne pollen and flowering phenology in central, northern, and northernmost Finland during 1997–2000. Totally 2.3% of the detected germinable pollen grains were in the air prior to local pollen shedding. The mean number of germinable pollen grains m^–3 air per day was lower prior to local pollen shedding, but in the year 2000 there were more germinable pollen grains in the air of central study site prior to local pollen shedding. Prior to the onset of pollen shedding, 7.5% of female strobili which we observed were receptive. On average female strobili became receptive three days earlier than local pollen shedding started. During the period of pollen shedding in the central study site, we detected germinable airborne pollen in the northern site in years 1997, 1999 and 2000. At the northermost site, we detected germinable airborne pollen during the pollen-shedding period of the northern site in 2000. Our detection of germinable airborne pollen and synchrony of strobili maturation from south to north suggest that populations of Scots pine in central and northern Finland may provide genetic material to populations in northern and northernmost Finland, respectively.

Varis, Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: saila.varis@metla.fi
Pakkanen, Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: ap@nn.fi
Galofré, Passeig de l’estació 21, 5-1, 43800 Valls, Tarragona, Spain E-mail: ag@nn.fi
Pulkkinen, Finnish Forest Research Institute, Haapastensyrjä Breeding Station, Karkkilantie 247, FI-12600 Läyliäinen, Finland E-mail: pp@nn.fi

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