Tree-ring width and maximum latewood density at the North American tree line: parameters of climatic change

In remote subarctic North America, instrumental records are very short and sparsely distributed. Yet a long-term understanding of subarctic climate is critical to studies of global change. Annual tree-ring width and maximum latewood density are complementary, high-resolution parameters with different environmental and physiological controls that can be used to assess recent centuries of climatic change. In this paper we present a comparison of the different temperature information inferred from these parameters for white spruce (Piceaglauca (Moench) Voss), a dominant North American latitudinal tree line species. Ring-width and maximum latewood density chronologies (with a common period from 1720–1977) are shown for five sites along a widely spaced transect of the forest–tundra transition in northern Canada. The positive temperature response of maximum latewood density to year to year local temperatures is more consistent and covers a longer portion of the growing season than does that of ring width. Unlike density, the ring-width data show a preference for cold spring conditions. Some, but not all, of the ring-width and density series display increases during the recent century's large-scale climatic warming trend. It is concluded that both types of parameters are necessary for understanding changes in climate and forest dynamics at the northern tree line.