Declining Deodra Cedar
Thank you for your question. The drought conditions over the past few summers have been extra hard on the conifers in the Willamette Valley. At times, the symptoms of water stress may be delayed, such that a tree that is stressed during one summer may not show browning leaves until the following spring. In addition, the impacts of drought on tree health can last over several years as the tree's hydrological system recovers. Each spring since 2014, we have noticed unusual browning on many conifer species (Douglas-fir, Western redcedar, giant sequoias, cedars, etc.). This browning can range from a few needles or leaves here and there, to whole branches, to whole sections of the crown, to the entire crown. In the case of a few needles here and there, the tree will typically bounce back. In the case of a dead top or entire crown, the tree is more likely to die. From the pictures you have sent, I tend to think you are dealing with the former case. You can do a few things to protect your trees from continued drought stress this summer, if you have the time and resources. For one, do everything you can to make sure the tree is healthy, such as removing competing vegetation from the understory, avoiding injury and root compaction by not operating heavy equipment beneath the tree, and avoiding herbicide use around the tree. You can also give the tree a heavy, deep watering on the morning of days that you know will be very hot and dry. You can read more about drought stress management in Oregon by reading this publication from the Oregon Department of Forestry.