Janis Birgelis

State Forest Service, Dept. of Forest, LV-1932 R§ga, Latvia

Introduction

The forest is one of Latvia's major assets, its most important and valuable natural resource, covering 2.82 million hectares (i.e. 44% of the total land area). This illustrates the great importance of the forest for the economy, landscape, environment, flora and fauna of Latvia. For many, the forest also has significance for leisure activities, recreation and hunting.

During the last 70 years, the forest cover area has had a stable growth trend: from 25% in 1923 to 44% in 1994. Despite that, there are significant regional variations; for example a higher forest coverage is in the central part, in the northeast as well as in the western part, where forests cover 50-60% of land area.

The various forest-growing conditions in Latvia are subdivided into five edaphic types: dry mineral (58.0%), wet mineral (10.4%), wet peat (12.0%), drained mineral (9.6%) and drained peat soils (10.0%). The distribution of tree species over the edaphic rows is not homogeneous.

Occurrence and origin of Norway spruce

The ecological position of Norway spruce in Latvia's flora has been stable since the postglacial era. As evidenced by pollen analyses and the data for forest resources today, the species covers about 530 000 ha or 20.6% of the total forested area. In accordance with the forestry development programme for 1992-2000 and 2030, the optimal share of Norway spruce is estimated to be about 24%. It means that the present occurrence of spruce in Latvia is close to an ecological optimum, particularly on dry mineral soils with fair productivity potential (oxalidosa site type), on wet mineral soils (myrtiloso-politrichosa site type), on drained mineral soil (myrtilosa mel) and on drained peat soil (myrtilosa turf.mel site type).

The share of Norway spruce in the structure of natural forests appears to reflect the selection pressure of the environment on the species. Latvia's forest resources data show the Norway spruce to predominate (33-37% of the total forest area) in the upland areas of Kurzeme (west) and Vidzeme (east-central part of Latvia). When comparing these figures with the data of K. Bambergs' paleobotanical studies, it can be shown that the pollen curves for spruce over the whole postglacial era, except for occasional fall-offs, show similar patterns. So, it appears that these areas are favourable for Norway spruce owing to the amount of precipitation and the temperature.

Geographical differences within a species may be attributed to both its migration route during the postglacial era and the natural selection controlled by the environment in the course of evolution. The immigration of spruce into the Baltic area during the postglacial era is believed to have followed two alternatives: either from the central Russian plains in the east or from the north, from the Baltics. In the latter case the related pattern is likely to become complicated owing to factors such as climatic conditions and distinct origin.

Conservation aims and current state of conservation activities

The conservation of forest genetic resources was initially started in 1986 by tree breeders at the Latvian Forestry Research Institute in Silava. The main aim was to conserve sufficient genetic variation for present purposes and future challenges. Among other species, two rather large (considering Latvia's forest conditions) overmature Norway spruce populations in the east and west part on 493 ha and 197 ha, respectively, were established as genetic reserves (see Table 1).

Table 1. The main characteristics of Norway spruce gene reserves

The data were analyzed in 1990. Among others, the species age structure was evaluated, results from previous studies summarized and, taking into account the geographical distribution and differences, the first attempt at forest gene conservation as a separate research project was initiated.

The main objective of gene conservation in Latvia is to maintain genetic variability among breeding material as well as to preserve the genetic potential of species for adaptation to future environmental conditions.

As it was stated in the gene conservation project, the most important and pressing task is a purposeful conservation of the spruce stands of natural origin. Silvicultural treatment of stands began at the end of the last century. In the 1970s, large areas were reforested with Norway spruce reproductive material of unknown origin. However, natural origin populations for the related research and conservation of the forest tree genepool are still common among older stands (more than 50 years). The following steps are to be taken:

C establishment of genetic reserves for in situ conservation of Norway spruce as a priority in Kurzeme and Vidzeme upland regions, known as the areas of optimum growing conditions for spruce; a large extent of spruce forests was destroyed by storm of 1990 and subsequent insect damage,

C special attention is to be paid to the spruce from the Latgale upland area (in the southeastern part of Latvia); the stock from these high-yield stands is noted for its high adaptability and productivity (the most significant features in future forests),

C in situ conservation of populations on wet mineral and drained peat soils,

C in situ regeneration, by using methods stimulating natural regeneration or by artificial methods in the overmature or endangered stands of the existing gene reserves,

C in cases of ex situ conservation, the material of nonidentifiable or foreign origin must be avoided in the surroundings of plantations,

C collection of material for seed bank with different aims (until now the existing Norway spruce seed bank contains 15 seed sources each representing 50 logged or still growing trees).

 

At present, the gene conservation project is underway. In accordance with the mentioned guidelines, significant work has been carried out during the last two years in establishing new conservation areas (see Table 2) of Norway spruce genetic resources.

* Without surroundings. Small conservation areas were accepted in most important regions.

The previous tree-breeding activities with Norway spruce were:

C 292 phenotypically selected individuals (plus trees) represented in 170 ha of seed orchards,

C ex situ conservation of 73 provenances in provenance field trials,

C ex situ conservation of about 100 plus tree progenies in seedling progeny tests.

 

The phenotypic composition of stands of natural origin was investigated at the Laboratory of Forest Tree Breeding during the 1960s and 1970s. The forms acuminata-europaea and europaea were identified. Types of branching largely depend on the site conditions, with pectinata branching being typical for higher productivity stands. The analysis of the related field data showed that this type of branching increased relatively in a west-east direction, but reached a higher proportion in the upland areas of Kurzeme and Vidzeme. They appear to be the most favoured regions for Norway spruce growth. Genetic differences were evaluated in progeny tests or by isozyme analyses.

Suitable markers for the assessment of geographical and genetic differentiation of Norway spruce were: time of spring flushing and growth termination, ability to develop lamma shoots, juvenile growth as well as shape of branching. The geographical differences were studied following the changes in climatic factors for different regions, with the total sum of active temperatures and the amount of precipitation as principal indicators.

In provenance trials in the country and abroad, Latvia's spruce is usually ranked among the provenances that are late flushing and fairly fast-growing, when tested against geographically diverse backgrounds.

The local provenances are distinguished by a higher degree of survival and better stem quality. When comparing progenies set into favourable site conditions, the provenances coming from the south of Latvia fall, with a few exceptions, under the group of fast-growing ones, while those coming from the north of Latvia are distinguished by lower survival and smaller stem dimensions. If the spruce coming from the southwest of Latvia is cultivated on frost areas and unfavourable soil conditions, the provenances of this region lose their advantages. So, the Remte seed orchard progeny (southwest of Latvia), which in provenance trials under favourable site conditions outperformed Dorna Cindreni (152 and 128 m³/ha at the age of 17 years, respectively), nearly died away on peat soils with late frost after repeated frosts. The Ranki provenance (Ogre region) survived and showed normal performance, while progenies coming from the southeast (Daugavpils, Rezekne, Jekabpils) showed a similar reaction to adverse environments. Fast-growing spruce showing a good adaptability to varying conditions has thus been found in the southeast of Latvia. The clonal breeding, underway since the late 1970s, is based on the material of this region. The related seed reforestation is recommended for all Latvia.

A pilot study on genetic structure, level of diversity and degree of differentiation at isoenzyme gene loci in five stands of Norway spruce was carried out. Eighteen enzyme systems were electrophoretically analyzed and 78 allele variants at 26 loci observed. Three rare alleles (at the gene loci controlling Aat, Lap and Dia), which had not been observed in earlier studies, were found in one of the studied populations (Ranki, central part of Latvia). It was shown that:

C the genepool in analyzed stands is practically identical, genetic distance does not exceed 0.008, the differentiation is less than 1%,

C the studied stands from different regions of Latvia have a high level of variability and fairly uniform genepool observed at isoenzyme loci.

 

On the contrary, differences of Latvia's Norway spruce populations in traits such as flushing time, juvenile growth rate or adaptability are significant and linked with geographical origin or ecological conditions.

To ensure a responsible approach and to raise the public awareness of plant genetic resources conservation in Latvia, discussion of the necessity of a National Plant Gene Conservation programme was started, which would include state authorities, research and NGO representatives. It should also be noted that there is an urgent need for an internationally accepted forest gene resources database, e.g. as a contribution to EUFORGEN.

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