Permanent plots are essential for tracking long-term forest change and have become more important given the projected increase in widespread tree mortality and forest health issues associated with climate change, invasive pests, altered disturbance regimes, and other novel stressors. Inventory and monitoring plots can reveal otherwise undetected loss of tree biomass, initiating targeted biological investigations. Shore pine is an understudied subspecies of lodgepole pine that reaches its northern extent in southeast Alaska. U.S. Forest Service Forest Inventory Analysis data detected a significant loss of live shore pine biomass in Alaska, with greater losses among larger trees and no known cause. We installed 46 permanent plots to monitor shore pine health and survival. Mortality was higher in shore pine (13%) than most associated conifers, and 43% of pines > 40 cm diameter at breast height were dead. Western gall rust, bole wounds, and Dothistroma needle blight were the most common forms of damage to live shore pine. Western gall rust bole gall presence best predicted crown dieback. Shore pine had more bole wounds than associated trees, with wound incidence and severity of live trees increasing with tree diameter. Secondary bark beetles and stain fungi were detected on dying and dead shore pine. Prevalent biotic injury and stressful site conditions accumulate, making large, old shore pine vulnerable to secondary bark beetle attack and vectored stain fungi. This study outlines how inventory networks can detect changes in tree biomass, highlighting knowledge gaps and prompting intensive, long-term monitoring.