Holocene fossil record

This chapter examines the Holocene fossil record of the Great Lakes region for information on the process of tree migration. Seed dispersal and interactions with resident vegetation are considered because both factors could have constrained the rate of... 

Additional information about seed dispersal is contained in the fossil record. Dispersal events can be inferred wherever there is evidence that populations were founded at large distances from the source population. It is, of course, technically difficult to detect a small population using fossil pollen or macrofossils, and even more difficult to demonstrate that the small population was isolated from the main population (Davis et al., 1991). Pollen studies in Sweden, however, record the establishment of individual colonies of beech (Fagus sylvatica) in the late Holocene (Bjorkman, 1996) and macrofossils demonstrate that populations of spruce (Picea abies) grew far in advance of the expanding species front for thousands of years (Kullman, 1996). East of James Bay, Canada, small colonies of larch (Larix laricina) have become established in patches during the past 1500 years as the population has expanded. Some of these colonies have fused into a continuous distribution. 

In the case of freshwaters, the past effects of climate change on UV exposure have impacted sedimentary records in a remarkable way. Analysis of fossil diatom assemblages in Canadian subarctic lake sediments has provided evidence of the interactive impacts of climate change and solar UVR on CDOM concentrations during the Holocene [86]. 

Present-day researches have shown that the climate of Central Asia varied rather widely. The proxy paleoclimatic data (sporo-pollen analysis, reconstraction of the levels of ancient lakes, fossil soils, archeological materials) prove that in different time periods essential changes in the water and heat balance were recorded on the territory of the modem Aral basin. The major global climate events, the response to which is detected also in the climate of Central Asia, were Eemian (about 125,000 years ago), the Last Glacial Maximum (about 21,000 yeas ago), and the mid-Holocene optimum (about 6,000 years ago). 

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