CGRG Bibliography of Canadian Geomorphology
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Author : Haas, J.N.; Kuijper, W.J.; Williams, N.E.; and McAndrews, J.H.
Date : 2000.
Title : Multi-proxy paleolimnological evidence of catastrophic hemlock (Tsuga canadensis) decline in Northeastern North America due to severe summer drought 5700-5100 years ago.
Publication : 8th International Paleolimnology Symposium, August 20 to August 24, 2000. Queen's University, Kingston, Ontario
Issue :
Page(s) :
Abstract
High resolution paleoecological analyses from Shepherd Lake on Bruce Peninsula (Ontario, Canada) show that rapid, decenial to centenial lake level fluctuations were responsible for alterations in the aquatic biodiversity 5700-5100 years ago. Abundant thermophilic aquatics such as the Bushy najad Najas flexilis, and the charophyte algae Chara foliolosa, as well as major species composition changes of caddis-flies (Trichoptera), chironomids and molluscs indicate water table regressions of several meters, which are likely linked to warmer and drier summer climate. The impact of this summer drought on the upland flora is visible in the classical hemlock decline (Tsuga canadensis) starting 5700 years ago. This reduction of Tsuga values from 30% tree cover to less than 5% within a few centuries is found in large parts of northeastern America. Our results from Shepherd Lake imply that drought heavilly affected hemlock trees because of their inability to sustain reduced soil and atmospheric humidity. Therefore, the mid-Holocene near-extinction of hemlock and subsequent rapid forest composition changes were triggered by drought and not by insect calamities as proposed by several authors in the last decades.
Bibliography of Canadian Geomorphology