Arctic Tree-line and the Polar Front: Guest Weblog by Professor Harvey Nichols

Professor Harvey Nichols is on the faculty of the Department of Ecology and Evolutionary Biology.

His research interests are summarized on the University of Colorado-Boulder website as

“Research Interests: Paleo-ecology, arctic and alpine environments, and global change, with emphasis on pollen analysis (palynology) as a method of reconstructing past vegetation and climate to understand the present environment and to act as background for current environmental concerns. The program has involved over twenty expeditions into the arctic to study past movements of the arctic tree-line driven by climatic change, which now provides an important perspective and test for the Greenhouse Hypothesis. An agreement has been reached with the Central Siberian Botanical Institute to exchange American and Russian students to explore the Siberian and North American arctic tree-line for signs of atmospheric warming in a long-term research project.”

With his extensive expertise in tree line studies, I invited Professor Nichols to publish one of his very insightful poster presentations on the Climate Science weblog. His knowledge on this subject will inform all of us on the climate metric of high latitude tree line, and its dynamics over time.

The December 2000 American Geophysical Union poster is entitled “Arctic tree-line and the Polar Front: climatic changes past and present, possible sunspot linkage” , and the abstract reads,

“The arctic tree-line is sensitive to climatic changes as indicated by paleoecological studies and it is predicted by global circulation models to respond strongly to greenhouse warming. My Northern Canadian studies of tree-line reproduction in black and white spruce spanning two decades demonstrate a widespread switch from infertility due to cold summers (1960’s-1970’s) to pollen and cone production (1990’s), in line with climatic warming predictions. Ecotonal cone formation is usually sporadic and localized, but this large scale reproductive shift, along a 1500 km transect, suggests widespread biospheric response to climatic warming since the 1970’s across much of the Northwest Territories. Labrador, not included in the original study, has experienced a delayed response in a region of prolonged cooling. In 1995 I tested the hypothesis by examining arctic tree-line at a transect of sites in western Siberia where ecotonal larch trees were reproducing sexually, and greenhouse studies confirm that enough seeds were viable to allow seedling colonization of the tundra. Siberian colleagues noted that the age structure of these “tree-islands” based on tree-ring studies suggested that a recent warming response was identifiable. In 1996 I examined a series of “tree-islands” in the tundra of northern Yakutia in northeast Siberia. All the larch trees bore cones, but greenhouse studies show that seed viability was very low, possibly due to a persistent cold trough in the upper Westerlies. These Siberian studies (at 27 sites) represented only a modest fraction of the Eurasian treeline, but the widespread fertility at so many locations, plus the extensive Canadian evidence, and Fenno-Scandinavian findings, suggest that the predicted polar warming may be responsible, with Labrador and Yakutia showing lagging responses corresponding to troughs in the atmospheric Rossby waves.”

The paper and supplemental material is available at Arctic Tree-line and the Polar Front: Changes Past and Present, Possible Sunspot Linkage.