A MULTISPECIES NETWORK OF TREE-RING CHRONOLOGIES FROM GLACIER BAY NATIONAL PARK AND PRESERVE, ALASKA: A TOOL FOR EVALUATING FOREST HEALTH

Networks of tree-ring chronologies from the boreal regions of North America can provide useful information for the management of national parks. A collection of 14 tree-ring chronologies from Glacier Bay National Park and Preserve, southeastern Alaska, has been assembled from hemlock, cedar, spruce and pine species. The region has warmed 2 degrees Celsius over the past 50 years, forcing changes in ocean-atmosphere circulation and precipitation. The collection of tree sites ranges from just above sea level for yellow-cedar to over 800 meters for mountain hemlock with half of the high elevation sites from refugia, located just above ice expansions that were spared the multiple glaciations over the past several millennia.

Dendroclimatic analyses of this network shows changing climate sensitivity with ring-width and latewood density chronologies exhibiting increased growth at higher elevations and in some cases decline at lower limits. Identifying the mechanism of forest response is a challenge and may be linked to the earlier snowmelt and loss of insulation leading to frost damage in the root zone to increasing thermal stress for those species that became established during the cooler conditions of the Little Ice Age. The tree-ring records can also be utilized for climate reconstructions that can be coupled with analyses of past, present and future forest health. The exactly-dated century to millennia-long tree-ring series records provide a paleoperspective for ongoing changes that include increased growth at some high altitude sites and possible decline at lower elevations for some species. A crucial question for park management is how the composition of forests will change as species adjust to warming and whether the pace of ongoing environmental change will lead to widespread decline or a steady expansion of the ranges of individual species.