The Spruceless Belt In Central Europe

The determination of the geographic range of Picea abies in central Europe and the origin of a spruceless belt between the mountains of central Europe and northeastern Europe has served as an intriguing puzzle for a number of investigators. Additionally, a natural disjunction in the species range in the western Carpathians has been discussed previously. The problems concerning both disjunctions have been summarized by SRODON (1967a, b) and the seminal study of SCHMIDT-VOGT (1977). The aim of the present work is to summarize the prior findings and include literature evidence from paleobotany, biogeography, as well as genetic and morphological evidence to understand the present geographic distribution of Norway spruce in central Europe.

5.1.1. The history of the spruceless belt

RIVOLI (1884) first described the geographic range of Norway spruce in central Europe. STRZELECKI (1894) produced a precise distribution of the spruce forests in the western and eastern Carpathians. By contrast, earlier published reports were largely superficial and incomplete. For example, a number of reports describe the presence or absence of spruce forests in particular parts of the Polish kingdom (Kluk 1808; SZUBERT 1930; WAGA 1848). The oldest range maps of Norway spruce in central Europe depict the Carpathian forests (HERBICH 1860; BRODOWICZ 1888).

The range of Norway spruce in the Russian empire, including Polish lands under occupation, was drawn by KOPPEN (1889), but was very schematic and incomplete. The first complete range map of Norway spruce in central Europe was prepared by RACIBORSKI (1912), and was probably based on the earlier published data of RIVOLI (1884) and STRZELECKI (1894). This map was later modified and supplemented by SZAFER (1916), RACIBORSKI and SZAFER (1919), and KULCZYNSKI and WIERDAK (1928). All these maps fail to delin eate a spruceless belt between the Carpathians and the northern, boreal part of the species contemporary range (Fig. 5.1).

Following World War I, a map of Picea abies distribution in the Polish Kingdom compiled by LASPEYRES was published (PAX 1918). Areas lacking spruce forests on the Masovian Lowland between the central European montane and northeastern European lowland portions of the species range were shown for the first time. Three years later RIVOLI (1921) depicted the distribution of Norway spruce stands in central and northern Europe and distinguished four range limits as follows: 1) the northern, polar limit; 2) the southern boundary of the northern, lowland portion of the species range; 3) the lower limit of the central European mountain ranges; and 4) the upper altitudinal limit in the central European mountain ranges.

The mapped locations of the range limits (after RIVOLI 1921) were dependent upon climate and largely correlated with the isotherms of the summer months and modified based on regional site conditions. In furthering RIVOLI'S work, SZAFER (1921) examined the biogeography of Norway spruce in central Europe (mainly contemporary Poland) using the concept of latitudinal limits to the spruce range known from Scandinavian literature sources. He also depicted the distribution of Norway spruce in central Europe in which the "spruceless belt" was fully shown for the first time (Fig. 5.1).

SZAFER'S map (1921) was subsequently edited numerous times with only minor corrections (e.g. SZAFER 1935, 1937, 1959, 1972; JEDLINSKI 1928; OBMINSKI 1947; STECKI and KOSCIELNY 1955; WLOCZEWSKI 1968), despite evidence that the spruceless belt, in fact, contained numerous dispersed and isolated spruce stands. Thus, the depiction of a Norway spruce range with a spruceless belt in central Europe on the Masovian and Podlasian Lowlands and in Polessia and Volhynia is largely based on duplication of SZAFER'S map, despite contrary evidence (SRODON 1967a, b). The contemporary distribution of stands of Picea abies of natural origin in Poland and Ukraine (BORATYNSKA et all. 1980; MEL'NYK 1993, see also Chapter 4) clearly reveals that the area considered to be free of spruce is, in fact, covered with dispersed spruce stands.

5.1.2. The disjunction

The factors that determine the range limits of tree species are autogenic and anthropogenic in origin. The autogenic factors underpinning tree species distribution, especially in central Europe, are linked to the ecological characteristics of the species, its migration history in the Holocene, and the geographic distribution of potential habitats. Human activities have played an important role in the vegetation history in central Europe. Evidence of human activities extends to the prehistoric era in the Masovian-Podlassian Lowland, Polessia, and Volhynia regions (HENSEL1980, BRODA1998).

Figure 5.1. Geographic range limits of the Norway spruce in central Europe after various authors (Boratynski1998)

Figure 5.1. Geographic range limits of the Norway spruce in central Europe after various authors (Boratynski1998)

1 - after RACIBORSKI (1912) and RACIBORSKI and SZAFER (1919); 2 - after SZAFER (1921); 3 - after SZAFER (1959, 1972); 4 - after SRODON (1967b); 5 - the island localities after JEDLINSKI (1926, 1927), WIERDAK (1927a, b), PACZOSKI (1930), Grob (1934), Tymrakiewicz (1935), Sokolowski (1968c, 1972, 1974a), SLOBODYAN (1962), GOLUBETS (1972), Kondratyuk (1968), KOZLOVSKAYA and PARFENOV (1972) and MELNYK (1993)

5.1.2.1. Characteristics of the spruceless belt

On the basis of the site requirements of Picea abies and the distribution of the potential habits in the spruceless belt, it appears that a lack of suitable sites does not limit the occurrence of the species there. The ecological properties and site requirements of Norway spruce (see Chapter 11) enables the species to grow and even prosper in the area, but only on the most mesic and productive sites (JEDLINSKI 1922,1926, 1927, 1928; PACZOSKI 1925, 1930). Rich and sufficiently mesic forest sites are present in the Masovian-Podlassian Lowland, Polessia, and Volhynia. However, these sites cover rather small areas, particularly in Masovia and Podlassia (SOKOLOWSKI 1968c; MATUSZKIEWICZ et al. 1995).

5.1.2.2. Holocene migration history

The migration routes of Picea abies during the Holocene in central Europe have been described previously (e.g. SZAFER 1931, 1935; SRODON 1967b, 1977; Huntley and Birks 1984; Huntley 1988, Giesecke and Bennett 2004, see Chapter 1). The southern limit of the species on the Scandinavian Peninsula and also on the central European lowlands is thought to represent an ongoing migration (SZAFER 1931, 1935; SCHMIDT-VOGT 1977). SZAFER'S view was that the northern, boreal range and southwestern, Carpathian range were joined during the Holocene climatic optimum about 4000-5000 years before present (BP) in Podlassia and Masovia (SZAFER 1931). However, the pollen diagrams later did not appear to support this hypothesis (SZAFER 1935), nor did the palynological investigations of the peat bogs of the spruceless belt (LUBLINEROWNA1934). Contemporary pollen maps also show a low proportion of Norway spruce pollen grains throughout the spruceless belt region (RALSKA-JASIEWICZOWA1983; Huntley and Birks 1983). However, this evidence does not preclude the occurrence of dispersed stands of the species. For example, pollen diagrams of the contemporary layers of the peat bogs ("0 BP", see Fig. 5.2) contain a rather small fraction of spruce pollen grains when compared with the distribution of the natural and planted stands of the species in Poland (Fig. 5.3). Thus, even a low frequency (below 2%) of spruce pollen grains does not rule out the occurrence of the species, as noted by SRODON (1967b, 1977). SRODON (1967b, 1977) suggests that the boreal and southern ranges of Norway spruce met in the spruceless belt during the Atlantic period of the Holocene. This idea is supported by the observation of spruce pollen grain frequencies of about 2% in the isopollen maps of 6000,5000, and particularly of 4000 BP (Fig. 5.2).

5.1.2.3. Intraspecific variability

The Norway spruce in central Europe originated from at least three Pleistocene refugia (SZAFER 1931,1935; SRODON 1967b, STASZKIEWICZ 1966, 1967, 1976; RALSKA-JASIEWICZOWA 1983; HUNTLEY and BIRKS 1983). Consequently, it may be supposed that populations from the boreal part of the species range differ from those originating in the southern portion in terms of growth, morphology, and phenology. The biometric traits of cones, seeds, and pollen grains of Norway spruce populations from various parts of the species range have been compared. PACZOSKI'S (1925) work was the first of such studies and described significant differences between cones of populations of Norway spruce from the Bialowieza Primeval Forest in northeastern Poland and the Tatra Mts in southern Poland (Table 1). Another interesting early study compared of 119 samples of seeds from foresters' seed collections in Poland (TYSZKIEWICZ 1934b) and demonstrated large differences between northeastern and southern seed sources.

Figure 5.2. Range expansion of Norway spruce throughout the Holocene in central Europe

A - isopollen maps compiled from RALSKA-JASIEWICZOWA (1983) and RybnÎôKOVÂ and RybnÎCek (1988), modified; B - distribution of the species in Poland (ZAJ^C and ZAJ^C 2001)

15° 16° 17° 18° 19° 20° 21° 22° 23°

above

Figure 5.3. The role of Norway spruce in the forests of Poland (after Boratynski 1998)

Participation of the area covered with the Norway spruce stands in the forest area of Polish State Forests (after ZYBURA'S data)

Most studies of geographic variation confirm differences between northeastern and southwestern, mountain population groups, yet the differences are not always significant (Table 1). Evidence from isoenzyme studies suggests that more or less sustained gene flow has occurred between the northeastern and southwestern, mountain populations of the species in Poland (LEWAN-DOWSKI et al. 1997; LEWANDOWSKI and BURCZYK 2002). The mountain populations of the eastern and western Carpathians differ from each other. However, the pattern of variation indicates that gene flow has occurred among most of the studied populations. The genetic evidence supports the observed

Table 1. Studies of population and range-wide trait variation ofPicea abies in central Europe

Trait

Number of samples

Remarks and results

Source of data

Seed

Pollen

119 from Poland

15 from Europe

Cones

0 0

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