Spruce branch girdling causing discoloration in tree.
Observation by Michael Opheim:
This is something I have never seen here before. I had noticed it a few times but never paid it attention because of the Spruce Aphid hitting the area and thinking that was the cause. After seeing a post about Spruce Rust I got to thinking that this might be that since it is on the outside of the limb and not how Spruce Aphids would be attacking the trees. As I have looked around more I see it on a lot of the trees in the Seldovia area. Being our trees are all ready weak from the Spruce Aphid and the few Spruce Bark Beetles that seem to be around this could maybe have a big impact on our trees. I know this is generally not fatal to the trees if it is spruce rust but in their weekend condition it makes me wonder.
Robin Mulvey, Southeast Alaska Forest Pathologist with the U.S. Forest Service, writes
Thanks for sharing this observation. It is hard to tell what is going on without close-up pictures of the damage, but this does not look like spruce needle rust or spruce broom rust. The tree crowns look a little thin like they were defoliated by spruce aphid in 2017 when damage hit the Kenai hard. The colder winter of 2017-2018 knocked the spruce aphid populations back and they have not caused notable new damage this year. Spruce aphids feed on the older needle age classes. To me, the damage looks like some form of branch-girdling. You can see newly-girdled branches (bright yellow-red) and older girdled branches (faded red-brown dead branches). Now the question is: what is girdling the branches? The three options that come to mind are: (1) mammal feeding (what types of rodents are present in this area? squirrels?), (2) boring insects, or (3) fungal canker pathogens. If you can easily get back to this area and collect some affected branches (including some healthy, unaffected branch tissue in the sample) I would gladly take a look at samples or close-up pictures of the damage! We have an FHP office in Anchorage, and I am located in Juneau. Here is a link to you USFS Forest Health Protection staff page
Comments from LEO Editors:
Branch girdling is the removal of strips of bark around the trunk or branches of a tree. Overtime, the area above the stripped bark, or girdle, will die. Mammals, birds, and insects that feed on tree bark may create girdles, but it also may also be done by foresters to thin out thick clusters of trees. EricaLujan
