Neil Pederson
Lamont-Doherty Earth Observatory
Columbia University

Evidence of Accelerated Growth of Old Trees in Temperate Forests

Climatic warming over the last two centuries has altered growth of high latitude trees. Little is known as to how warming could impact trees in temperate forests, however. Analyses of radial growth will be presented from a multi-species network in the Hudson River Valley and four networks in the eastern US. The multi-species network supports prior studies to show that winter temperatures may be the primary temperature factor of growth in temperate forests. This network also shows white oak species to be more sensitive to winter temperatures at the southern end of the study transect where winters are milder. This surprising result could be caused by patterns of regional snow cover. Studies of snow cover over the 20th century can help explore this new snow cover-temperature sensitivity hypothesis. Chamaecyparis thyoides is the most sensitive species tested and holds promise for reconstructing temperature along the northeastern US coast. A network of 838 trees comprised of Quercus alba and Q. prinus covering Alabama to Michigan and New York indicates that growth has accelerated since the mid-1800s, even for the oldest known trees of both species. Networks of 153 Liriodendron tulipifera and 230 C. thyoides support these findings. Temperature is the primary factor for C. thyoides' accelerated growth. Mechanisms for increased growth rates for the other species are not clear. Although beyond the scope of this research, these results suggest that old-growth forests could be active carbon sinks because it does not seem necessarily true that trees decrease in growth as they age.