We have seen an unusual number of Western Hemlocks shed needles and die in the last few years. Tree mortality, in the form of tall standing snags, is common in the northwest quadrant the Seward peninsula. Hemlocks are losing their needles from the bottom-up, while drought effects usually lead to top-down loss. Dying hemlocks with dead lower branches (“brooms”) are common in the northern and central ares of the forest.
The PNW mortality is probably not related to the devastating decline of the Eastern Hemlock caused by an introduced insect, the Wooly Adelgid. We sometimes see adelgid symptoms on our native hemlocks, but the trees are mostly immune to its effects. Research programs in the Appalachians have arrived at, and locally apply, a temporary and a possible long term remedy.
Western Hemlock decline has been reported elsewhere in the Pacific northwest, well beyond Seward Park. Some combination of factors are probably involved: root and needle diseases, fungi and insects, all perhaps compounded by recent dry summers and higher than normal temperatures.
We hope that data collected at Seward Park may contribute to understanding the phenomenon.