Current issue: 56(4)
Under compilation: 57(1)
Growth, crown structure, flowering and seed production of silver birch (Betula pendula Roth) seedlings, grafts and micropropagated plants was compared during four years in a polythene greenhouse experiment. The growth of the seedlings was clearly the most vigorous and that of the grafts the weakest, the micropropagated plants being intermediate. The seedlings had the highest and the grafts the lowest number of branches before cutting the tops of the plants, but the differences between the material types were no more significant after cutting the tops. The grafts had significantly shorter and thinner branches than the seedlings and the micropropagated plants, whereas the differences in branch length and branch thickness between the latter two groups were not significant. The grafts started flowering at the age of two years, one year earlier than the other two types of material. At the age of four years the micropropagated plants had abundant seed production, about 75% of that of the seedlings and about two times higher than that of the grafts. Thus, the micropropagated plants can be used instead of grafts when establishing polythene greenhouse seed orchards of birch.
Seed production of micropropagated plants, seedlings and grafts of Silver birch (Betula pendula Roth) in a polyethylene greenhouse experiment was followed for five years. The grafts started flowering and seed production at the age of two years, one year earlier than other two types of material. At the age of three the seed production of both micropropagated plants and seedlings was already more than two times higher than that of the grafts. Variation between the clones was high and plant type x clone interaction was significant. At the age of four, in 1993, seed production was high in all three types of material. Seed production of the micropropagated plants was two times higher than that of the grafts but about 75% of that of the seedlings. In 1994 seed production of all three plant types was very low, which shows large variation between different years. The early development of the plant material types suggests that micropropagated plants have higher seed production than grafts and could well be used instead of grafts in polythene greenhouse seed orchards.
Application of growth regulators, primarily gibberellins, has become an efficient method of flowering regulation in many coniferous forest trees. In this paper some results are discussed with respect to various genetic processes in seed orchards. It is concluded that there are still several unsolved problems in the regulation of flowering in forest seed orchards. These problems are related to different genetic processes occurring in the seed orchards and they should be taken into account in endeavouring to produce genetically improved seeds.
The aim of this present study was to elucidate the quality of seed of foreign tree species grown in Finland, and the factors which have affected the quality of the seed yields. Due to the smallness of the material, however, no far-fetching conclusions can be drawn. The bulk of the seeds were collected in the fall of 1964. The samples of seeds were X-rayed and their classification to empty seeds and full seeds of four quality classes was done on the basis of the anatomical structures. The species studied (a total of 34 species) belonged to the following genera: Abies, Chamaecyparis, Larix, Picea, Pinus, Pseudotsuga, Thuja and Tsuga.
The percentage of empty seeds was throughout quite high. The reasons for the generation of empty seeds probably originate from the special nature of the stands from which the seeds were collected. As a rule, the stands were young and small in area, which may have caused weak pollination and self-pollination leading to embryo mortality. Also, insect damages were observed.
Seeds with albumen still discernible, although the embryo had died, occurred to some extent. In some Larix species, even the bulk of the seeds recorded as full belonged in this group.
The ripening of seeds with embryos was quite successful in spite of the fact that the temperature sum of the year of ripening was slightly below the average in Finland. For instance, all Abies species ripened almost completely.
According to the results, it can be expected that the tree species examined in this study are able to produce rich yields of good-quality seed in Finland, provided that the ovules are well pollinated and self-pollination does not take place to a large extent.
The PDF includes a summary in English.
Silva Fennica Issue 80 includes presentations held in 1952 in the 7th professional development courses, arranged for foresters working in the Forest Service. The presentations focus on practical issues in forest management and administration, especially in regional level. The education was arranged by Forest Service.
This presentation describes principles of breeding of forest trees and the selection of fast growing, healthy and qualitatively good trees, named plus trees, for seed production in Finland.
Silva Fennica issue 52 includes presentations held in professional development courses, arranged for foresters working in public administration in 1938. The presentations focus on practical issues in forest management and administration, especially in regional level. The education was arranged by Forest Service.
This presentation describes a study of forest management practices suitable for in Hylocomnium-Myrtillus site type forests, typical for Northern Finland. A special problem for the forest site type is poor regeneration due weak seed production of Norway spruce (Picea abies L. Karst.) and thick moss layer.
Temperatures needed in extracting Scots pine (Pinus sylvestris L.) seeds is relatively high, however, there is little information on its effect on germination of the seeds. This survey aimed at studying how different temperatures affect both extraction result and germination of Scots pine seeds. Comparisons between different temperatures (20, 30, 40, 50, 60 and 70 ºC) were made from cones collected from same sample trees, three trees in total.
Temperatures 20 and 30 ºC resulted in incomplete opening of the cones, and gave thus smaller amount of seeds. Complete extraction requires at the least the temperature of 40 ºC. The result is slightly better in 50 ºC, but germination of the seeds is little lower. Temperatures 60 and 70 ºC improve the results, but in the cost of germination. The main reason for lower germination percentage was that the higher temperatures release more empty and defective seeds from the cones. Results of different sample trees were different due to, for instance, quality and size of cones. Higher temperatures accelerated the extraction. According to the study, perfect extraction in 40 ºC requires longer extraction time than when the temperature of 50 ºC is used. In practice, 50 ºC temperature or even little higher temperatures can be used when the extraction time is shorter. Decessive factors in choosing the temperature would be the humidity of cones and length of extraction time.
The PDF includes a summary in German.
The northern range of small leaved lime (Tilia cordata Mill.) in Finland has remained the same since the end of 1800s, but according to the studies of subfossiles of lime found in peatlands, the northern limit has once been higher than at the present. The northernmost natural specimens of the species in Reisjärvi do not produce seed, and are therefore probably a relict. The article includes a review on the distribution of the species in Finland and its capacity to regenerate. The natural regeneration of lime in Finland is at present very rare. The species has lost its ability to sexual reproduction, but reproduces readily vegetatively.
The PDF includes a summary in German.
The success of natural regeneration of Scots pine (Pinus sylvestris L.) is dependent on the amount and quality of seeds produced in each year. While seed production of Scots pine in Northern Finland is well known, there is little information about frequency of good seed years in Southern and Central Finland. The success of regeneration of Scots pine was studied by defining from the growth rings of felled sample trees in which year they started to grow. The aim was to choose sample trees so that they would form a continual series from seedlings to 100 years old trees. In the material there was too little sample trees from certain years. However, within the period of 1827-1910 it could be identified 13 good regeneration years of pine in Southern Finland. According to the study, pine has regenerated very well every 6th year and at least moderately well every 4th year. When compared to the previous studies made in Northern Finland, part of the good regeneration years seems to be same both in Northern and Southern Finland. Regeneration of Scots pine is affected also by the type and condition of the site.
The PDF includes a summary in German.
The study deals with the preconditions for natural regeneration of the pine at the polar tree line in northern Finland and Sweden. The data has been collected in three summers from 1909 to 1911 in areas of Inari and Utsjoki in Finland and Kaaresuvanto, Jukkasjärvi und Pajala in Sweden. The yearly variation of seed production of pine is studied and compared with the age of the stand, site factors and weather conditions.
Intensity of reproduction is dependent on different preconditions for pistils and stamens and hence the total reproduction (formation of cones) can vary very much depending on the weather.According the study, the formation of cones varies yearly and is particularly strong every three to four years. Supposedly the same model applies to whole polar tree line of the Fennoscandia. There seem to be no difference between northern and southern parts of Scandinavia when it comes to frequency of good cone years though they not always occur in the same years.
Flowering time and characteristics of cones and seed development of Scots pine (Pinus sylvestris L.) plus tree clones originating from various parts of Finland and planted (grafts) in Southern Finland (61° 48’ N, 29° 19’ E) were studied during 1976-1978.
The flowering time (in terms of period unit (p.u.) sums for flowering) of the Scots pine plus tree clones showed characteristics specific to each population and the characteristics appear mainly adapted to the local temperature factor within Finland. Generally, the development of floral organs, cones and seed in the spring and summer seasons also showed a temperature dependence in that the reproductive organs are developed rapidly and/or favourably under higher temperature conditions within its optimum range.
In this respect, establishment of northern Scots pine seed orchards in Central or Southern Finland or an optimum flowering, and a favourable seed development with an optimum physiological reproductive isolation from surrounding Scots pine populations can be justified. Problem arising from the north-south transfer of seed orchards and the significance of trees’ growth rhythm are discussed in connection with tree improvement.
The PDF includes a summary in Finnish.
After a decades-long increasing trend, the recent results of the National Forest Inventory (NFI) reported a decline of forest growth in North Finland. The aim of this study was to assess climatic and reproduction influences behind the growth decline. We used tree-ring data that had been collected by NFI using systematic sampling. The tree-ring width series were detrended using the regional curve standardisation (RCS) removing age-related trends. The resulting tree-ring indices of Scots pine (Pinus sylvestris L.) showed decadal variations with low increment in the 1990s, and high increment in the 1980s and the early years of the current century. Thereafter, a prolonged growth reduction for pine started both on the mineral soil sites and peatlands. The tree-ring indices of Norway spruce (Picea abies (L.) Karst.) had less pronounced decadal variations and no trend-like reduction over the last 15 years. High spring and summer temperatures were found to enhance radial growth, but high winter temperatures were related to low growth for pine and spruce in the following summer. Temperature variation, accompanied by variables indicating years of drought and intensive flowering, accounted for 34% annual growth variance of pine and 21–44% for spruce. Thus, the results imply that climatic factors may have to some extent contributed to the recent growth reduction of pine. Due to its ecological and economic consequences growth decline needs to be further monitored and investigated. Moreover, analyses of stand and age structure, potentially affecting the growth decline, were beyond the scope of this paper, but also warrant further investigation.
Light is an important environmental factor for all green plants. Its intensity, spectral composition and photoperiod can affect the regulatory pathways in plants that lead to floral initiation. In this report, results are presented from three experiments in which supplemental light with metal halide lamps (250 µmol m–2 s–1, 20 hours day–1, approx. 6 weeks) was tested as a complement to other flowering stimulation treatments (elevated temperature, treatment with gibberellin A4 and A 7 (GA4/7), restricted water supply) applied to potted Picea abies (L.) Karst. in the greenhouse. Flower stimulation in a greenhouse resulted in more floral initiation compared to flower stimulation outdoors. Supplemental light treatment increased floral initiation further, and to a larger extent in female than in male flowers. It also increased the proportion of trees and genotypes that induced reproductive buds. In a practical application of the supplemental light treatment to potted Picea abies breeding material, 90.6% of the clones produced either female or male flowers, or both. A subset of the same material kept outdoors, and thus subjected to natural light and temperatures, produced no flowers despite being treated with GA4/7 and receiving a restricted water supply. In conclusion, supplemental light treatment facilitates breeding programmes, and seed production of highly improved base material from new selections for vegetative production programmes, to be more efficient.
Seed orchards are the link between tree breeding and reforestation. This paper presents data on cone, seed and pollen production and seed quality gathered over 21 years in a Pinus sylvestris (L.) experimental seed orchard containing plots with 14 different combinations of stand density and targeted pruning height. The treatments’ stand densities ranged from 267 to 4000 stems ha-1, and the target graft heights ranged from 2 to 6 meters. Pollen production began at the same orchard age for all studied combinations of stand density and target height but the level of pollen production per hectare increased more rapidly in treatments with higher stand densities. In treatments with dense spacing, cone and seed production initially increased more rapidly than in treatments with wider spacing, thereby providing an earlier return on investment and a shorter seed production lag time. However, the levels of cone and seed production in such treatments over the entire study period were not appreciably different to those achieved in treatments with wider spacing and higher target height. The treatments did not differ substantially with respect to seed quality. These results show that comparable levels of seed production can be obtained with different combinations of stand density and target height, giving seed orchard owners and managers a wide range of viable management options.