Tore Skrøppa

Norwegian Forest Research Institute, 1432 Ås, Norway

Introduction

Norway spruce (Picea abies) is a young species in Norway. After the ice age, birch, poplar and Scots pine were the first tree species to establish. During the warm and dry period that followed, high-temperature demanding species such as lime, beech, oak, ash and hazel spread, and the timber line was 200-300 m higher than at present. It was not until approximately 2500 years ago, during a cooler and more humid period, that spruce started its introduction into the Norwegian landscape. The Nordic spruce populations have their origin in the taiga in northern Russia and Siberia. During a period of 3000 years the species spread through Finland and northern Sweden. The earliest identified establishments are from the years 500-400 BC in the border areas close to Sweden in Central Norway (Hafsten 1991, 1992). The invasion of the southeastern lowland area took place during the following 1000 years, but the migration up the valleys to the species' present altitudinal boundary was not completed until the period 1000-1500 AD. The coastal spruce forest in Central Norway was established rather late (approximately 1300 AD). The species never established naturally in western Norway, except for a few scattered populations, which have a late establishment and most likely are spread from the nearest source stands east of the mountain range (Hafsten 1991).

The present natural occurrence of Norway spruce is in southeastern Norway from sea level and up to 1000 m, and in Central and North Norway, north to lat. 67EN, at decreasing altitudes in the north. Outside this area the species has in this century been planted both in western Norway and north of its natural boundary in northern Norway. In both regions it has become an important timber species.

The Norway spruce forests have been strongly influenced by human activities. An excessive harvest started more than 300-400 years ago and strongly depleted the forest resources in some regions. At the beginning of this century the annual harvest in Norwegian forests exceeded annual growth, while the harvest is at present only around 50% of the gross annual production.

Norway spruce is the most important species in Norwegian forestry. The total forest area is 12 million hectares or 37% of the total land area. Productive forests cover 23% of the land area (7 million hectares), half of which is spruce forest. More than one-third of the forest is older than 80 years. The total annual harvest is 10 million m³, of which spruce amounts to 70%.

Norway has no laws or regulations specifically dealing with the conservation of the forest genetic resources. The Norwegian Forestry Act, however, provides general measures for the long-term preservation and sustainable utilization of the forests, which also relate to management of the genetic resources. Special recommendations are given for forestry activities in areas which have such location, conditions or characteristics that they should be managed with particular care. Where restrictions are deemed necessary, such areas may be classified as protection forest and be subject to regulations. Protection forests comprise approximately 20% of Norway's total forest area and are in particular located at high elevations, along coasts or in the far north. The Forestry Act is administered by the Ministry of Agriculture.

The maintenance of genetic diversity is one of the main motives in the regulations for the classification, trade and use of reproductive materials in forestry. Specific recommendations are given for the transfer of provenances and use of vegatatively propagated materials. Seed from native Norway spruce stands should not be transferred more than 200 km in the northern or southern direction. Vertically, transfers should be within the range of 300 m. Close to the altitudinal and boreal timber line only local provenances should be used. Seeds from Norway spruce seed orchards should be tested for growth rhythm and frost hardiness, which should determine their regional use.

Two other components of Norwegian legislation, administered by the Ministry of Environment, have importance in the management of the forest genetic resources. These are the Building and Planning Act and the Nature Conservation Act. The first one provides fundamental principles for land management limiting nonforestry development and urban expansion on forest land. The Nature Conservation Act provides for the classification of specific areas which are to be protected as national parks, nature reserves, landscape protection areas and natural monuments. Opportunity is given, moreover, for combining species protection and the conservation of areas in the form of what is called habitat preservation.

The Norway spruce genetic resources are not considered to be threatened in any part of its native range in Norway. Large areas of old-growth natural stands still exist, even if their abundance has been reduced, in particular in the lowlands in southeastern Norway. New forests are being established by natural regeneration over large areas and this method has gained importance during the last few years. Under certain ecological conditions, however, natural regeneration will not be sufficient for the establishment of a well-stocked Norway spruce stand, and planting is necessary.

Owing to a lack of Norway spruce seeds of local origin, seedlings of Central European provenances were planted in southeastern Norway during a 20-year period starting in the mid-1950s. In one county, Østfold, 35% of the total number of seedlings planted in the period 1960-1980 originated from provenances in Austria and in Schwarzwald, Germany. It was thought that the high altitude of the seed stands, between 800 and 1400 m, would compensate for the southern latitude. However, both practical observations and a recent survey in planted stands (Skrøppa et al. 1993) have shown that these stands are not well adapted to the northern climatic conditions. While 30% of the trees in 30-year-old planted stands of native origins were classified as having saw timber qualities, only 7% of the trees in the Central European stands obtained the same classification. These provenance transfers had a negative effect on timber quality, particuarly on sites where frosts commonly occur in late spring or early autumn. The stands established with seedlings from introduced provenances are in many cases mixed with stands of local seed origin and are often not recognizable. The seeds harvested in such areas, even in healthy stands, may be partly from local and partly from provenance hybrid crosses. Critical factors are the abundance of flowering in the stands of introduced provenances, the range of pollen migration and how fast the natural selection process proceeds.

Transfers of Norway spruce provenances from southern to northern latitudes and from low to high altitudes also have been made within Norway. Such transfers have in some cases resulted in plantations that show lack of adapation to the climatic conditions. However, as these plantations in many cases have failed and are rather scattered, they will in a few cases produce pollen or seeds in large enough quantities to have a practical consequences, either for natural regeneration or for seed collections.

The concept of genetic diversity of forest trees has not been an important topic in public discussions in Norway. The introduction of Central European Norway spruce provenances has been criticized, but on grounds of the reduced timber quality in the planted stands and not so much because of a possible threat to the local spruce genetic resources. The introduction of spruce and its replacement of Scots pine and deciduous tree stands in western and northern Norway outside its natural range are debated locally. The negative voices are based partly on ecological considerations from naturalist groups as well as a general reluctance to accept changes in the landscape.

Public awareness of forest genetic resources and the considerations of their importance for the future forests are generally missing.

The forest tree genetic resources have generally been managed through the reforestation strategies employed after harvesting. Natural regeneration is encouraged where it is a feasible and optimal regeneration method. Thirty-five years ago the annual volume of forest tree seedlings planted exceeded 100 million. This number has been drastically reduced, and in the last 10-year period 50-55 million spruce seedlings have been planted annually. During the last 5-year period there has been a reduction in the number of seedlings planted.

The gene conservation activities of forest trees in Norway are accomplished in three different ways: by nature conservation areas in national parks, protected landscape areas or nature reserves; by recently established conservation areas in productive coniferous forests, and by materials preserved in clonal archives or seed orchards as part of the tree breeding program.

The conservation of forest genetic resources has not been a motive for the establishment of nature conservation areas. Most national parks and nature reserves are located far north and at high altitudes and do not sample representative areas of the Norwegian coniferous forest. In total 20 000 ha of coniferous forest are conserved in these areas. They cannot be considered to play a major role in the conservation of the Norway spruce genetic resources.

Based on a national plan to conserve coniferous forest, altogether 25 000 ha of productive forest have been protected. Norway spruce is the main species in the larger part of these areas. The main intention was conservation of biological diversity in general, but conservation of the genetic resources also was a motive. These areas are distributed in different parts of the country and are stratified to be representative for all major ecological zones. The different areas vary in size, from 10 to several thousand hectares.

The more active gene conservation work is performed by the establishment of clonal archives or seed orchards of grafted Norway spruce clones. Selections of plus trees have been made in natural stands covering the entire distribution throughout the country to be included in breeding populations. More than 3000 selected trees have been grafted, most of these at several localities. They were grouped in breeding populations according to the latitude and altitude of the origin of the natural stand. However, it was soon realized that progeny tests are necessary to assess the genetic value of a selected plus tree, and more than 2000 of the selected trees have been tested by family tests planted in trials at several sites. Traits that have been measured include height and diameter growth, annual growth rhythm characteristics, climatic damage and stem and branch quality. In addition, a large number of families have been tested in artificial freezing experiments.

The grafted clones and their offspring in progeny tests are an important part of the gene conservation activities, as they are the only materials from which specific genetic information is available.

So far, no studies of isozyme or DNA genetic markers have been performed to characterize the genetic variability of the Norwegian spruce population. The genetic information available comes from quantitative genetic studies in provenance trials and family and clonal tests. The largest efforts have been made to characterize adaptation to the climatic conditions. Therefore measurements have in particular been made of annual growth rhythm traits: the timing and duration of the annual growth period, frost hardiness development in the autumn and dehardening in the spring, and the occurrence of climatic damage under field conditions. All studies demonstrate a clinal variation in growth rhythm characteristics of natural populations from the south to the north and from low to high altitudes. The southern and low altitude populations have the longest duration of the growth season, and, as a consequence, the highest growth potential. They also have the latest development of autumn frost hardiness. The only well-known characterizations of the adaptative process of spruce populations are the responses to temperature and photoperiod.

The genetic variation is large within all natural populations studied, also for traits that shown clinal variation at the provenance level. Genetic correlations between traits may change dramatically, depending on the genetic level, whether it be based on population, family or clonal means.

The general intentions with the genetic research in Norway spruce are: to describe and understand the genetic variability of the species, to develop strategies for breeding for better quality in well-adapted, high-yielding plantations, and to assure that sufficient genetic variability is conserved for the future evolution of the species.

At present the main research interest is focused on the genetic mechanisms behind the variability observed in phenotypic traits having importance for adaptation to the climatic conditions. Based on experimental evidence, our hypothesis is that genetic variation in such traits is not only regulated by classical (Mendelian) gene frequency differences, but also by other mechanisms (e.g. gene regulations), and that these factors are triggered by environmental influences during the generative reproductive process. If this is the case, then it will have large implications both for understanding the evolutionary process and for the conservation of the genetic resources of the species.

These effects were brought into focus by the location of seed orchards in warmer climates. The seedlings produced in Norway spruce seed orchards in Norway where the parental clones are transferred to seed orchard sites 6-8 degrees of latitude southwards or to 500-600 m lower in altitude, do not retain the annual growth rhythm of their parents, see Johnsen (1989a,b) and Skrøppa and Johnsen (1994). Progenies after controlled crosses in such orchards, as well as the open-pollinated orchard offspring, have in particular a later growth start in the spring, a delayed growth cessation and a later development of autumn frost hardiness than their sibs born in their native environment. The effects have been shown in freezing tests of 1- or 2-year-old seedlings, but are verified by growth rhythm studies in experiments with 10-year-old trees (Skrøppa 1994) and after clonal propagation (Johnsen 1989a). The population mean of seed orchard offspring is changed, but the genetic variation between different families for the traits seems to be retained. The environmental influences during the reproductive process have been verified by making identical crosses in a greenhouse and in a nearby seed orchard (Johnsen et al. 1995), and early and late in the spring in a heated greenhouse and outside the greenhouse (Johnsen and Skrøppa, unpublished).

Results from field trials and in practical plantings indicate that the observed effects may have practical consequences under extreme climatic situations in the field (Skrøppa, unpublished). The effects may either be positive or negative for the survival and quality of the plantation, depending on how the climatic extremes are related to the annual growth rhythm of the material. The situation seems to be similar to that of a provenance transfer. It will be advantageous under certain environmental conditions, but the opposite under other conditions.

Norway spruce is a young species in Norway and shows large flexibility to a wide range of environmental conditions. Its genetic resources are not considered to be threatened, both because of the existence of old-growth natural stands and the extensive use of natural regeneration. When new stands are established by planting, seeds are transferred over rather short distances or are of local origin. An extended use of seed-orchard seed in the future may change the genetic composition of the planted stands. As long as the seed orchards contain a relatively large number of parents, this should not be considered a threat to the genetic resources. However, a combined strategy for the long-term breeding and gene resource conservation should be developed. An understanding of the genetic mechanisms behind the environmental influence during reproduction on the adaptive properties of the offspring will be of fundamental importance for both the breeding and conservation activities.

Hafsten, U. 1991. Granskogens historie in Norge under opprulling [The history of spruce forest in Norway under exposure]. Blyttia 49:171-181.

Hafsten, U. 1992. Granskogens innvandring og spredning i Norge [Immigration and spread of spruce forest in Norway]. Norsk skogbruksmuseum, Årbok Nr. 13 1990-92:9-27.

Johnsen, Ø. 1989a. Phenotypic changes in progenies of northern clones of Picea abies (L.) Karst. grown in a southern seed orchard. I. Frost hardiness in a phytotron experiment. Scand. J. Forest Research 4:317-330.

Johnsen, Ø. 1989b. Phenotypic changes in progenies of northern clones of Picea abies (L.) Karst. grown in a southern seed orchard. II. Seasonal growth rhythm and height in field trials. Scand. J. Forest Research 4:331-341.

Johnsen, Ø., T. Skrøppa, G. Haug, I. Apeland and G. Østreng. 1995. Sexual reproduction in a greenhouse reduced autumn frost hardiness of Picea abies progenies. Tree Physiol. (in press).

Skrøppa, T. 1994. Growth rhythm and hardiness of Picea abies progenies of high altitude parents from seed produced at low elevations. Silvae Genetica 43:95-100.

Skrøppa, T., D.R. Martinsen and A. Følstad. 1993. Vekst og kvalitet av mellomeuropeiske og norske granprovenienser plantet i Østfold. [Summary: Growth and quality of Central European and native Norway spruce provenances planted in Østfold]. Research Paper of SKOGFORSK 7/93.

Skrøppa, T. and Ø. Johnsen. 1994. The genetic response of plant populations to a changing environment. Pp. 183-199 in NATO ANSI Series, Vol. I20. Biodiversity, Temperate Ecosystems, and Global Change (T.J.B. Boyle and C.E.B. Boyle, eds.). Springer Verlag, Berlin Heidelberg.

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