dying maple and alder trees

Asked August 6, 2019, 3:40 PM EDT

Hi I have five acres in rural Clackamas county near Boring on the west slope of Tower Hill. Over the last ten years or so, especially this last five, we are seeing our big leaf maples slowly dying. These are big trees probably over 40+ years old. The most recent one is really going quickly. Our alders are also seeing leaf loss. I have heard that several years of drought may be the cause. Is that true? Is there any way to curtail or reverse the seeming inevitability? I need suggestions. Please advise. Thank you.

Clackamas County Oregon forestry

1 Response

The decline of bigleaf maple and red alder that you are seeing is widespread in our area in the more marginal habitats. Climate stress is often a big factor for both species.

Red alder in the warm dry margins of the Willamette Valley and Puget Sound regions (which probably includes your west slope in Clackams Co.) have been suffering top dieback, whole tree mortality, triggered by heat/drought plus bark beetles and stem canker fungi as a common way they are finished off. See the article "Another stressful year for trees" on page 7 of https://extension.oregonstate.edu/sites/default/files/documents/8486/2018-wn-fall-920181.pdf

Bigleaf maple seem to be suffering from a more mysterious dieback, also likely involving drought and other secondary agents, resulting in trees dying in part or entirely. We normally think of maple as more drought tolerant than alder, but the dieback is similar.

There is not much you can do - try occasional deep watering in the driest months on high value trees. Deal with dead trees as best you can and plant a new tree that is more hardy. Consult with me directly for more information on likely species for the future.

See references on maple dieback: