Betula Sect Research Articles

Vegetation and climate variability during the Last Interglacial evidenced in the pollen record from Lake Baikal

A pollen record from the core sediments collected in the northern part of Lake Baikal represents the latest stage of the Taz (Saale) Glaciation, Kazantsevo (Eemian) Interglacial (namely the Last Interglacial), and the earliest stage of the Zyryanka (Weichselian) Glaciation. According to the palaeomagnetic-based age model applied to the core, the Last Interglacial in the Lake Baikal record lasted about 10.6 ky from 128 to 117.4 ky BP, being more or less synchronous with the Marine Isotope Stage 5e. The reconstructed changes in the south Siberian vegetation and climate are summarised as follows: a major spread of shrub alder ( Alnus fruticosa) and shrub birches ( Betula sect. Nanae/ Fruticosae) in the study area was a characteristic feature during the late glacial phase of the Taz Glaciation. Boreal trees e.g. spruce ( Picea obovata) and birch ( Betula sect. Albae) started to play an important role in the regional vegetation with the onset of the interglacial conditions. Optimal conditions for Abies sibirica– P. obovata taiga development occurred ca. 126.3 ky BP. The maximum spread of birch forest-steppe communities took place at the low altitudes ca. 126.5–125.5 ky BP and Pinus sylvestris started to form forests in the northern Baikal area after ca. 124.4 ky BP. Re-expansion of the steppe communities, as well as shrubby alder and willow communities and the disappearance of forest vegetation occurred at about 117.4 ky BP, suggesting the end of the interglacial succession. The changes in the pollen assemblages recorded in the sediments from northern Baikal point to a certain instability of the interglacial climate. Three phases of climate deterioration have been distinguished: 126–125.5, 121.5–120, and 119.5–119 ky BP. The penultimate cooling signal may be correlated with the cool oscillation recorded in European pollen records. However, such far distant correlation requires more careful investigation.

Late Pleistocene and Holocene vegetation and climate on the northern Taymyr Peninsula, Arctic Russia

Pollen data from a Levinson‐Lessing Lake sediment core (74°28'N, 98°38'E) and Cape Sabler, Taymyr Lake permafrost sequences (74°33'N, 100°32'E) reveal substantial environmental changes on the northern Taymyr Peninsula during the last c. 32000 14C years. The continuous records confirm that a scarce steppe‐like vegetation with Poaceae, Artemisia and Cyperaceae dominated c. 32 000–10300 14C yr BP, while tundra‐like vegetation with Oxyria, Ranunculaceae and Caryophyllaceae grew in wetter areas. The coldest interval occurred c. 18000 yr BP. Lateglacial pollen data show several warming events followed by a climate deterioration c. 10500 14C yr BP, which may correspond with the Younger Dryas. The Late Pleistocene/Holocene transition, c. 10300–10000 14C yr BP, is characterized by a change from the herb‐dominated vegetation to shrubby tundra with Betula sect. Nanae and Salix. Alnus fruticosa arrived locally c. 9000–8500 14Cyr BP and disappeared c. 4000–3500 14Cyr BP. Communities of Betula sect. Nanae, broadly distributed at c. 10000–3500 14Cyr BP, almost disappeared when vegetation became similar to the modern herb tundra after 3500–3000 14Cyr BP. Quantitative climate reconstructions show Last Glacial Maximum summer temperature about 4°C below the present and Preboreal (c. 10 000 14C yr BP) temperature 2–4°C above the present. Maximum summer temperature occurred between 10 000 and 5500 14C yr BP; later summers were similar to present or slightly warmer.

Progression en im Synfloreszenzbau und in der Verbreitung bei den Betulaceae

Summary The synflorescence structure of almost all genera and sections of Betulaceae s.l. has been analysed. The different arrangement of the male and female catkins is traced back to a common hypothetical ancestral type with terminal male and basal female synflorescence branches and subfloral sympodial shoot innovation (similar to Alnus sect. Alnus ). From there, the following progressions are realized in separate lines: the translocation of the shoot innovation into the synflorescence; the tendency to monopodial ( Alnus subgen. Alnaster ) or sympodial ( Corylus avellana -group, Betula sect. Nanae ) proliferation of the synflorescence; the reduction of the number and size of the catkins; the protection of the female and male catkins during wintertime by bud scales. These progressions correspond to the formation of the shrubby growth form, to the reduction of the leaf size and of the number of lateral veins, and to an increasing extension of the distribution of Betula , Alnus and Corylus into cold and continental regions. In the light of fossil evidence, these progressive areas are explained by a successive southern shift and reduction of formerly large distribution ranges due to the cooling of the climate during the tertiary, and by a development of new taxa into the free cold regions. This explanation is contrary to the usual interpretation of similar distribution patterns by a successive development from a common southern evolution centre. The synflorescence proliferation is shown to be a principle of morphological progression also in other anemogamous trees, comparing them with their entomogamous relatives ( Fraxinus sect. Ornus — sect. Fraxinus , Acer sect. Platanoidea — sect. Negundo ). Hence, the synflorescence of Fraxinus excelsior and of Acer negundo are interpreted as to be not lateral, but proliferating terminal panicles.