Decidious and mixed forests - Protected areas and high conservation value forests in the Barent

Deciduous trees in this analysis include two birch species (silver birch Betula pendula and downy birch Betula pubescens), aspen (Populus tremula), alders (Black alder Alnus glutinosa and grey alder Alnus incana) and trunk forming tree-like willows (Salix spp.). All of these are typical pioneer trees in boreal forest succession.

These trees form the majority of deciduous tree biomass and coverage in the study area (map 5). In addition to trunk forming goat willow (Salix caprea), bay willow (Salix pentandra) and almond willow (Salix triandra), also bush forming willows are involved. Large bush forming willows are important especially in subarctic and arctic ecosystems as well as along larger rivers and shores of waters with natural flooding dynamics and in river estuaries. Mountain birch (Betula pubescens subsp.

czerepanovii, syn. Betula tortuosa) forms extensive low growing forests especially in the northwestern subarctic parts of the Barents Region.

In Russia there are several large bush forming willow species along large lowland rivers in alluvial riparian habitats (like Salix viminalis, S. dasyclados, S. burjatica and S. acutifolia). These habitats do not occur in the Fennoscandian part of the study area. Other deciduous tree species like rowan (Sorbus aucuparia) and bird cherry (Prunus padus) are typical and common through most of the area but does not normally form continuous stands or if rarely so, the stands are very small.

All natural deciduous stands with herb-rich undergrowth are rare and have high biodiversity value. Black alder grows in the southern and middle parts of the area and is an important key species of herb-rich swamp forests. Both black alder and bay willow are typical in wet habitats and both can remain for several generations at suitable sites. Grey alder has a wider distribution and it is also a typical pioneer tree at rich soils after disturbance. It has benefitted from former slash-and-burn agriculture as well as from forest grazing.

Many deciduous tree species display a genetic variation across the Barents Region, and especially in the north-south direction. Northern individuals often belong to another infraspecific taxon as compared to individuals of the southern boreal zone.

Even some broadleaved trees with southern distribution like lime (Tilia cordata) and elms (Ulmus glabra and Ulmus laevis) reach the Barents Region but they are very rare and mainly scattered along the southern boreal zone of the Russian part of the study area. These stands and mixed stands with these broadleaved species usually only cover small areas, but they have very high biodiversity values.

In the north and along mountains a wide belt of intact natural deciduous forests form a transition zone between arctic-alpine tundra vegetation and coniferous forests. The mountain birch belt is clearly visible in Sweden along the Scandes and more widely in northern parts of Swedish Lapland. It is also found in Finland in the northern part of the north boreal zone, above and close to the coniferous timberline. The same mountain birch zone continues to the Kola Peninsula. Also in Norway different kinds of mountain birch forests are abundant through most of Finnmark, and they are well connected to the Finnish mountain birch forests.

Mountain birch forests are typical in the somewhat maritime climate of the

Map 5. Distribution of deciduous forests in the study area and in southern Finland

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60°0'0"N 60°0'0"NDeciduous forests within known HCV forest areas

”Silver Taiga”

northwestern parts of the Barents Region. In the more continental parts of Arctic and Subarctic Russia this zone is less prevailing.

The natural dynamics of this subartic mountain birch area is characterized by occasional outbreaks of autumnal moth (Epirrita autumnata) and in maritime area also winter moth (Operophtera brumata). These outbreaks can result in secondary tundra, which may slowly recover if the grazing pressure of reindeer is not too high. In fact, the mountain birch belt also includes clones and small forests of aspen and thickets of willows. This vegetation zone is very prone to climate change.

Farther south in the boreal zone deciduous stands have mainly a human induced origin and they often represent secondary successional stages after forest management such as final felling. Most of the boreal deciduous dominated forests outside the mountain birch belt (map 5) represent young or mature successional secondary stands of boreal forests. These are usually dominated by quick growing deciduous trees. They are mainly a result of clearcuttings or selective harvestings or other human activities, but some are also a consequence of natural dynamics like forest fires and larger windfalls. Stands dominated by deciduous trees may prevail also in the boreal landscape, and especially in herb-rich luxurious forests, alluvial and swamp forests.

In the study area the distribution pattern of mixed deciduous forests is rather similar as compared to pure deciduous stands (map 5). In natural conditions deciduous forest with mixed spruce (Picea abies/Picea obovata), Siberian fir (Abies sibirica) and/or pine (Pinus sylvestris) are more common than pure deciduous stands. Dominance of deciduous and mixed deciduous forests in the landscape is often indicating secondary forests. These are typically later stages of forest succession towards more coniferous dominated stands.

Old deciduous trees are important for biodiversity both in natural and managed forests. Deciduous trees like giant aspens are also present in old growth coniferous forests at least in small quantities. Especially deciduous stands with old and large aspen trees or other old and partly decaying deciduous trees are among the most valuable stands from a nature conservation point of view. If mixed coniferous stands are connected to younger deciduous stands they can be sources of dispersal of species connected to larger and older deciduous trees. Almost all deciduous stands below the mountain birch belt, with the exception of alluvial forests, deciduous swamps and mires, and certain paludified forests, have the capacity to turn into mixed and later successional coniferous stand.

Deciduous trees (e.g. mainly birches Betula pendula and especially Betula pubescens) are rather evenly distributed below the mountain birch belt in the Swedish part of the study area, likewise in northern Finland. However, the volume of deciduous trees in Finland seems to be lower than in Sweden or some adjacent areas of Russia. This is probably a result of many different factors. Probably it is more a consequence of differences in the classification of forest cover types in the land cover datasets of each country than real differences in land use history and management (see Chapter 3). Silvicultural practices have been rather similar in Finland and Sweden including avoidance of birch cultivation during the second half of the last century.

In Russia the distribution pattern of deciduous trees is very variable. In some regions there are larger pure or mixed aspen stands. This is obvious in the southern part of the Republic of Karelia, where soils are rather rich in nutrients.

These forests are secondary in character and in some cases former agricultural lands, especially around Lake Onega and in the Olonets district. The abundance Map 6. Distribution of deciduous and mixed forests in the study area and in southern

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”Silver Taiga”

of deciduous trees in Russia also reflects a more or less natural succession after logging. In Finland and Sweden a new generation of trees (pine and spruce) is more often established after logging by planting and young deciduous trees are most often actively removed.

In the Arkhangelsk Region some areas are rather clearly dominated by deciduous tree stands. Most of Arkhangelsk Region is located in a sediment bedrock area where soils are often rich in calcium. Therefore, in these areas forests develop quickly into deciduous and mixed stands after disturbances. Due to the long forestry history in the region, many secondary birch and aspen stands are already rather old and provide important environments for many rare forest species. Deciduous trees are less common in areas dominated by old growth coniferous forests, and deciduous trees are not that common in mire areas either. However, sometimes downy birch also grows on mires.

In the Republic of Komi most of the deciduous forests are secondary. Especially the wide deciduous and mixed forests areas in the southern half of Komi have this origin. The bedrock is sedimentary. In north and in east close to the Ural mountains the dominance of deciduous forest is less clear. Green alder (Alnus viridis subsp. fruticosa) is a bush or small tree that grows on moist, nutrient poor soils in subarctic habitats of the Nenets Autonomous District. In northern Europe it occurs only in the northeastern part of the Barents Region.

In document Protected areas and high conservation value forests in the Barents Euro-Arctic Region – Sweden, Finland and Russia (sivua 32-36)