Great differentiation in examined traits con- Giertych firms the permanent diffusion of northeast- 1973, 1976b ern populations through mountain populations and vice-versa. The eastern and western Carpathian populations are also similar.
Populations from northeastern and central Barzdajn European mountains differ. The provenances 1996 from intermediate locations have cones similar to those from the northeast or from the mountains.
The provenances from central Poland are intermediate between northeastern and montane provenances or are similar to Carpathian sources.
Small differences between northeastern and central European montane populations indicate gene flow.
Extensive gene flow and historical events have erased strong differences between central European and northeastern populations; actual differentiation depends more on the geographic distance than on provenance.
Lewandow-ski et al. 1997
intermediate characteristics of Norway spruce populations from central Poland (CHYLARECKI and GIERTYCH 1969; GIERTYCH 1973, 1976; BARZDAJN 1996, 1997). Following the last glaciation, Picea abies from the Carpathians likely migrated first to the north (Fig. 5.2), followed by a migration from eastern Europe to the southwest. The traces of that first migration from the Carpathians northward are manifested in the Polessian populations, located north of the spruceless belt and exhibiting a high frequency of the cone trait var. acuminata, characteristic of populations of the eastern Carpathians, whereas the var. europaea, characteristic for the boreal part of the species range, occurs frequently in northern Byelorussia (JURKIEWICZ and PARFIE-NOW 1966; JURKEVICH and PARFENOV 1967). The similarity of cone traits among the Bialovezhan populations and the eastern Carpathian populations can also be explained on this basis (BARZDAJN 1996, 1997).
126.96.36.199. Human impacts on the contemporary distribution of Norway spruce in the "spruceless belt"
Human activities in the early historical period could have contributed to moderate range expansion of some tree species, including Norway spruce
(SRODON 1967b, 1977). However, extensive colonization and intensification of agriculture, resulting in deforestation, began in central Europe about 2000 years ago. Land use change likely fragmented and eliminated Norway spruce stands, especially in areas where it occurred naturally at low frequencies (JEDLINSKI1922, 1926, 1927, 1928; SRODON 1967b; BRODA1998).
Deforestation connected with human settlement has had the greatest impact on the contemporary range of Norway spruce. The permanent colonization of the Masovian and Podlassian regions began as early as 2000 years ago (HENSEL 1980). During this time agriculture expanded gradually at the expense of forests as human populations increased. Although the above-mentioned regions of central Europe have been densely populated since the Middle Ages, large contiguous forests still cover the region. Further colonization in the 14th and 15th centuries resulted in deforestation and fragmentation of the largest forest complexes (HENSEL 1980). The most fertile forestlands were converted to agriculture during that period (BRODA 1998). Consequently, the gradual reduction of Picea abies stands in the "spruceless belt" was largely the result of land use conversion from forest to agriculture, owing to the fact that the species occurred on the most productive and mesic sites (see Chapter 11).
Another cycle of intensive deforestation took place in the 18th and 19th centuries (ROMANOWSKA 1934; CZERWINSKI 1974). These regions were deforested much more in the 19th and the first decades of 20th centuries than at present. Today forests in the region are largely restricted to the most dry and sandy soils, which are less desirable for agriculture. The contemporary forest composition in the region is 40-50% planted Scots pine stands established about 70-80 years ago on abandoned agricultural lands (JAKUBOWSKA-GABA-RA 1985; BRODA 1998). In this region the occurrence of large forest stands is rare. However, it is worth noting that Norway spruce occurs in most large forest stands (JEDLINSKI 1922; TYMRAKIEWICZ 1935; SLOBODYAN 1962; SOKO-LOWSKI 1968c, 1972, 1974a; CZERWINSKI 1974; MEL'NYK 1993).
The presence of Norway spruce in this region was commonly associated with timber stands during the first decades of 20th century. Spruce stands were reported to occur only in administrative districts where forest cover exceeded 20% of the land area, whereas outside of the spruceless belt, the occurrence of the species was independent of the forest cover percentage (JEDLINSKI 1922). This relationship likely arises from an increase in suitable sites for Norway spruce outside the Masovian and Podlassian Lowlands.
Habitat loss and contemporary forestry practices are other key factors that limit the occurrence of Picea abies in the Masovian and Podlassian Lowlands. For example, wetland drainage and the lowering of the water table have altered the hydrology in many areas (JEDLINSKI 1927). Silvicultural practices, including clear-cutting that results in the removal and loss of Norway spruce seed trees, likely reduces natural regeneration of the species (see Chapter 13). Forestry practices in the region prefer the establishment of Scots pine plantations at the expense of Norway spruce and other forest trees. It should be noted that outside this region, the contemporary geographic area and coverage of Picea abies has increased largely as a result of it being a common species in plantation forestry for timber production in central Europe for the last 200 years (BORATYNSKA et al. 1980; ZYBURA 1990; SCHMIDT-VOGT 1991; MEL'NYK 1993).
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