The history of spruce in the pleistocene

Macrofossils of spruce, including P. abies, are known from several European sites originating in the Neogene and its boundary with the Pleistocene, as well as in sediments of the oldest Interglacial known as the Tegelenian. In southern Poland, in the Pliocene site of Kroscienko as well as the sites included in the Pliocene and early Pleistocene in Mizerna, spruce cones and needles have been found and identified as Picea excelsa (Lam) LlNK/oss. (SRODON 1967b).

Throughout central Europe, spruce regularly occurred in all interglacial periods as well as the warmer interstadials during the Quaternary (ZAGWIJN 1992). The geographic extent of spruce was then much wider than in the Holo-cene and included areas on the southern shores of the Baltic, North Sea, and the British Isles, including Ireland. The presence and abundance of spruce has been associated with specific positions in the interglacial stratigraphic successions (JaNczyk-Kopikowa 1991). The dominance of spruce in pollen diagrams during successive interglacials was associated mainly with their waning phases that presumably coincided with a colder and wetter climate.

During the Mazovian Glacial of the middle Pleistocene, Norway spruce was abundant and dispersed throughout Europe (SRODON 1967b). During the interglacial period, spruce has been noted in several woodland phases and in two of them was comparatively more abundant than other woodland pollen flora. Analyses of sediments of this interglacial from Podlasie (Krupinski 1995) show a widespread occurrence of spruce. The decline in relative abundance of spruce was associated with an increase in the proportion of fir (genus Abies). The second period of a marked abundance of spruce was associated with the waning of the Mazovian interglacial.

During the Eemian interglacial, a peak in Norway spruce pollen abundance has been noted (E-6 pollen level). In order to emphasize the contribution of this species to vegetation patterns noted in the interglacial succession, this level (r. paz) has been termed Picea-Abies-Alnus (Mamakowa 1989) and also Picea-Abies (TOBOLSKI1991). Relatively short periods of geographic expansion of spruce during the interglacials were interspersed between long periods of glaciation during which the species likely found protection in mountain refugia in southern Europe. There, under conditions of oscillating and harsh climates and thousands of years of isolation, new variants arose and remain within present-day populations of this species.

In the Brorup Interstadial of the last glaciation, approximately 60,000 years ago, spruce last occupied a geographic area larger than its contemporary range. The highest values of relative abundance in the pollen record occurred in this period, often exceeding 70%, in the Alps and approximately 50% in the Central Massif. Consequently, P. abies forests likely dominated the Alps and its northern slopes. A large proportion of Norway spruce pollen, up to 40%, is also found on the coast of the North sea throughout this period. Near the northwestern shore of the Baltic Sea in Skania (southern Sweden), the proportion of spruce pollen exceeds 20% (TOBOLSKI 1991). At the height of the Vistulian Glacial, Norway spruce was found in refugia scattered along the edges of the Periglacial zone. During this period the range limits were likely closer to the contemporary range limits than in the earlier glacial periods. It is from these refugia that Norway spruce began its migratory expansion as early as the Late Glacial period.

Both serbian and siberian spruce played a minor role in the vegetation of the Pleistocene of central Europe. Fossil finds of Serbian spruce were described on the basis of fossil cones, needles, as well as pollen and given the name Picea omoricoides (WEBER 1898). WEBER (1898) postulated that these macrofossils belong to an extinct and previously widespread species, and that contemporary Serbian spruce is a relic form of this fossil taxon. Pollen grains identified as P. omoricoides are noted most often in the waning sectors of interglacial profiles. These are almost exclusively found along with the pollen of Norway spruce and not only in the sediments of the Tegelenian and Mazovian interglacial, but also in earlier sediments from the Eemian interglacial and the Brorup Interstadial of the last glaciation. The range of P.

omoricoides expanded extensively in the early phases of the Vistulian Glacial, reaching the Frisian coast and the Jutland Peninsula to the west, whereas in the south, it remained a small component of the vegetation in the foothills of the Alps. Its distribution likely mirrored the unique climate of the early Vistulian period in northwestern Europe, marked by a strong continental climate (TOBOLSKI 1991).

Siberian spruce (P. abies ssp. obovata) presently occupies vast areas of eastern Europe and Asia. During the Pleistocene its range extended further west, as shown in the occurrence of fossil spruce cones from sites of the Eemian interglacial in the vicinity of Moscow, Grodno, and northeastern Poland. SRODON (1967b) presents evidence phase of a migration of Siberian spruce into present-day Poland during at the waning of the central Polish Glaciation (l.c. p. 10). Macrofossil finds demonstrate that near the end of the central Polish Glaciation, a taiga type of forest encroached into central Europe in which Siberian spruce played an important role. it cannot be ruled out that a past westward expansion of Pleistocene Siberian spruce may have played a significant role in the origins of contemporary Norway spruce (SRODON 1977).

Was this article helpful?

0 0

Post a comment