Contemporary richness of holarctic trees and the historical pattern of glacial retreat (original) (raw)
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Quaternary International, 2012
Postglacial climate changes and vegetation responses were studied using a combination of biological and physical indicators preserved in lake sediments. Low-frequency trends, high-frequency events and rapid shifts in temperature and moisture balance were probed using pollenbased quantitative temperature reconstructions and oxygen-isotopes from authigenic carbonate and aquatic cellulose, respectively. Pollen and plant macrofossils were employed to shed light on the presence and response rates of plant populations in response to climate changes, particularly focusing on common boreal and temperate tree species. Additional geochemical and isotopic tracers facilitated the interpretation of pollen-and oxygen-isotope data.
Leuschner, H.H., U. Sass-Klaassen, E. Jansma, M.G.L. Baillie & M. Spurk 2003. Population dynamics and long-term growth depressions in European bog oaks as indicators of climate changes in the Holocene. (In: Schleser et al. (eds.), 2003., 2003
The dendrochronological data set of absolutely dated sub-fossil oak trunks from Irish, Dutchand German bogs consists of some 2600 series. They cover the period from 6000 BC to AD1700. The distribution of the trees in time shows distinct changes in the frequency,germination and dying-off. One way to graphically represent germination and dying-off phases is to calculate the ‘mean age’ of all trees at every calendar year. Where trees areuniformly ageing the mean age chronology rises; recruitment of juvenile trees and dying-off of old trees causes the chronology to drop. The GDO-events (sudden drop) coincide withgrowth depressions in the regional ring-width chronologies. Regional mean-age chronologiesof the bog oaks contain similar elements, sometimes over long periods. This observationindicates common large-scale climate forcing.
Millennial-scale variability during the last glacial in vegetation records from Europe
Quaternary Science Reviews, 2010
This paper evaluates the evidence for millennial-scale variability in pollen records of the last glacial (Marine Isotope Stages 4, 3, and 2; 73.5–14.7 calendar ka BP) from the European continent, taking into account information derived from long, continuous terrestrial records, the fragmentary northern European terrestrial record, and marine pollen records of the European continental margins. Pollen records from these numerous European sites provide evidence for multiple intervals of relatively warm and humid conditions during the last glacial, which promoted the establishment of grassland and shrub tundra in northwestern Europe, shrub- and forest-tundra in northeastern Europe, open boreal forest in central western Europe and the Alpine region, and open temperate forest in southern Europe. The northern limit for temperate forest development during these intervals was at ∼45°N, with a subsequent northward transition to tundra across a latitudinal band of ∼15° in western and central Europe, and a greater northward extension of boreal forest in eastern Europe, with boreal forest elements detected close to their present-day limits at ∼70°N. A much smaller number of sites with sufficiently high temporal resolution provide evidence that warming intervals correspond to millennial-scale variability as recorded in Greenland ice cores. A synthesis of sites providing high-resolution terrestrial and marine records from Europe is undertaken in order to examine geographical and temporal patterns in the expression of Dansgaard–Oeschger (D–O) cycles in the European vegetation. Detailed comparison of temperate forest development at these sites during four specific D–O cycles (D–O 16–17, 14, 12 and 8) reveals contrasts between vegetation response at southernmost European latitudes (below 40°N) and at latitudes above 40°N. At southernmost latitudes, marked forest development occurred during all four D–O cycles including D–O 16–17 and 8, while at latitudes above 40°N, forest development was stronger during D–O 14 and 12 than either D–O 16–17 or 8.
Journal of Biogeography, 2013
Aim To assess statistically the relative importance of climate and human impact on forest composition in the late Holocene. Location Estonia, boreonemoral Europe. Methods Data on forest composition (10 most abundant tree and shrub taxa) for the late Holocene (5100–50 calibrated years before 1950) were derived from 18 pollen records and then transformed into land-cover estimates using the REVEALS vegetation reconstruction model. Human impact was quantified with palaeoecological estimates of openness, frequencies of hemerophilous pollen types (taxa growing in habitats influenced by human activities) and microscopic charcoal particles. Climate data generated with the ECBilt-CLIO- VECODE climate model provided summer and winter temperature data. The modelled data were supported by sedimentary stable oxygen isotope (d18O) records. Redundancy analysis (RDA), variation partitioning and linear mixed effects (LME) models were applied for statistical analyses. Results Both climate and human impact were statistically significant predic- tors of forest compositional change during the late Holocene. While climate exerted a dominant influence on forest composition in the beginning of the study period, human impact was the strongest driver of forest composition change in the middle of the study period, c. 4000–2000 years ago, when per- manent agriculture became established and expanded. The late Holocene cool- ing negatively affected populations of nemoral deciduous taxa (Tilia, Corylus, Ulmus, Quercus, Alnus and Fraxinus), allowing boreal taxa (Betula, Salix, Picea and Pinus) to succeed. Whereas human impact has favoured populations of early-successional taxa that colonize abandoned agricultural fields (Betula, Salix, Alnus) or that can grow on less fertile soils (Pinus), it has limited taxa such as Picea that tend to grow on more mesic and fertile soils. Main conclusions Combining palaeoecological and palaeoclimatological data from multiple sources facilitates quantitative characterization of factors driving forest composition dynamics on millennial time-scales. Our results suggest that in addition to the climatic influence on forest composition, the relative abun- dance of individual forest taxa has been significantly influenced by human impact over the last four millennia.
Realized climatic niches of deciduous trees: comparing western Eurasia and eastern North America
Journal of Biogeography, 2007
Floristic similarities between the temperate deciduous forest regions of the northern hemisphere have been recognized since the time of Linnaeus (Boufford & Spongberg, 1983), including intercontinental differences in tree species richness and underlying processes (e.g. Latham & Ricklefs, 1992; Huntley, 1993; Svenning, 2003). Modern palaeoclimatological research has suggested that unfavourable climatic conditions in the glacial refugia during both glacial and interglacial periods played an important role in the much higher extinction rate in Europe than in eastern North America (Bennett et al., 1991; Huntley, 1993). The climate in southern Europe during the last glacial maximum was characterized by strong summer aridity, and the predominant vegetation has been reconstructed as some form of grassland or shrubland, with trees probably restricted to particularly favourable locations (Allen & Huntley, 2000; Elenga et al., 2000). Under such arid conditions, temperate
Trees tell of past climates: but are they speaking less clearly today?
… of the Royal …, 1998
The annual growth of trees, as represented by a variety of ring-width, densitometric, or chemical parameters, represents a combined record of di¡erent environmental forcings, one of which is climate. Along with climate, relatively large-scale positive growth in£uences such as hypothesized`fertilization' due to increased levels of atmospheric carbon dioxide or various nitrogenous compounds, or possibly deleterious e¡ects of`acid rain' or increased ultra-violet radiation, might all be expected to exert some in£uence on recent tree growth rates. Inferring the details of past climate variability from tree-ring data remains a largely empirical exercise, but one that goes hand-in-hand with the development of techniques that seek to identify and isolate the confounding in£uence of local and larger-scale non-climatic factors.