CASE STUDIES OF DIVERGENCE ALONG THE NORTH PACIFIC RIM

High latitude climate has been significantly changing and is predicted to do so into the future. As a result temperature-sensitive forests have also been responding variously, releasing, declining or tracking the warming. In some cases this change is recognized as a divergence, where tree growth diverges from climate trends. Divergence has been primarily documented in temperature-sensitive tree species at interior sites in the Arctic. This study examines the diverse divergence from case studies in coastal areas along the Pacific Rim.

Dendroclimatic analysis of tree ring data from low elevation yellow cedar are consistent with decreased tree growth caused by warming, resulting in a loss of insulating snow cover and frost damage to the root zone. Low-elevation mountain hemlocks similarly show signs of decreasing ring width, whereas at high elevation sites growth is releasing. Two additional species located in coastal areas, shore pine from S.E. Alaska and larck from Sakhalin Island in the Russian Fareast, show decline in ring widths at some sites, and ongoing climate analysis of the ring width series from these species can help identify the influence that climate may have in their decline. In the case of shore pine, decline at one site began in the 1950’s and now opportunistic biotic factors have likely help to sustain the reduction in growth. On Sakhalin Island a drop in growth aligns with a decrease in sea ice, here we are testing the hypothesis that earlier springs may result in de-hardening and damage from late frosts and thus the warming is detrimental to growth.

Although decline in forests related to climate are widely reported in the Arctic, our case studies here show that coastal forests from the North Pacific too are being impacted, however the mechanisms at work often differ from site to site.