Modelling late Quaternary changes in plant distribution, vegetation and climate using pollen data from Georgia, Caucasus

Abstract

Pollen analysis has made a substantial contribution to our understanding of how the world's plant populations have changed through time. The distribution and abundance of pollen taxa reflect, on a regional scale, spatial variations in the composition of plant communities and biomes (Wright, ABSTRACT Aim To use pollen data, numerical analysis and modelling to reconstruct late Quaternary vegetation and climate in a complex, mountainous environment.Location Georgia (Caucasus region).Methods Pollen data were assembled from various sources and used to map: (1) changing frequencies of individual taxa; (2) vegetation changes; and (3) reconstructed climatic parameters for the past 14,000 years. Numerical analyses were performed using two-way indicator species analysis (twinspan), detrended correspondence analysis (DCA), the modern analogue technique (MAT) and weighted averaging (WA). ResultsMapping of pollen taxa showed that Chenopodiaceae, Artemisia and Ephedra were most abundant in the study area during the late-glacial. Betula and Corylus expanded during the early Holocene, yielding to Abies, Carpinus, Fagus, Quercus and Castanea. Picea, Pinus, Juglans and Ostrya-type expanded during the late Holocene. Mixed forests grew in the moist, Black Sea refugium throughout the late Quaternary. Elsewhere in Georgia, the Pleistocene-Holocene transition is recorded as a shift from desert-steppes to oak-xerophyte communities and mixed forests. This kind of vegetation remained relatively stable until the mid-late Holocene, when coniferous forests and mountain grasslands advanced. DCA showed that rainfall was most strongly correlated with pollen composition in the study area (r 2 = 0.55). No temperature signal was detected. A weighted-averaging transfer function linking pollen percentages to annual precipitation was selected over a MAT model as it performed better when applied to a validation data set. Rainfall reconstructions indicate widespread aridity at the terminal Pleistocene, followed by a gradual increase in precipitation, peaking during the mid Holocene (7000-4000 cal. yr bp) and generally decreasing thereafter.Main conclusions On a regional scale, the results confirm those from previous studies of palaeovegetation and palaeoclimate in Western Asia. On a local scale, reconstructions from individual sites often diverge from the regional trend because of edaphic changes, ecological succession, human impacts and other disturbances. Some of these factors are probably responsible for the increasing heterogeneity of Georgia's vegetation in the latter half of the Holocene.

Mid Holocene vegetation reconstruction from Vanevan peat (south-eastern shore of Lake Sevan, Armenia)

“…Whether a forested phase is documented during the Mid Holocene in recent studies across Georgia (e.g. Connor and Kvavadze, 2008;Messager et al, 2013), only low resolution pollen analyses (Takhtajyan, 1941;Tumanyan, 1971;Tumajanov and Tumanyan, 1973;Sayadyan et al, 1977;Sayadyan, 1978) suggest that forests once existed in Armenia. Moreover, these studies (in Russian) are not up to today's standards (no dates or few datings on molluscs, up to 40% unidentified palynomorphs).…”

Leaf wax <i>n</i>-alkanes in modern plants and topsoils from eastern Georgia (Caucasus) – implications for reconstructing regional paleovegetation

“…Due to a rain-shadow that is caused by the high elevation of the Western and Central ranges of the Greater Caucasus and by the N-S-directed Likhi Range linking the Greater and Lesser Caucasus, there exists a significant climatic gradient with decreasing precipitation and more continental conditions going eastwards (Connor and Kvavadze, 2008). Our study of modern plant and topsoil material took place in eastern Georgia (see Fig.…”

Some like it hot: environmental determinism and the pastoral economies of the later prehistoric Eurasian steppe

“…The stark difference in proportions of livestock between the neighbouring countries of Georgia and Azerbaijan may be explained by their (largely) contrasting climates. The western parts of Georgia benefit from westerly airstreams originating over the Black Sea and the orographic effect of the Caucasus Mountains, and can receive more than 2500 mm of rainfall each year (Connor and Kvavadze 2008;Ye 2001). The mountain ranges form a rain-shadow over much of eastern Georgia, which can receive as little as 400 mm annually, and further eastward into the semidesert lowlands of Azerbaijan annual precipitation varies from~1100 mm in the northwest to~250 mm in the east (Connor and Kvavadze 2008;Mamedov et al 2009).…”