Forest health in Western Washington Q&A
Additional Resources from Rachel Brooks
- Annual Forest Health Highlights Report (yearly updates)
- Aerial Surveys
- Field Guide to the Common Diseases and Insect Pests of Oregon and Washington Conifers (good for ID)
- PNW Plant Disease Management Handbook (good for more disease info)
- Managing Insects and Diseases of Oregon Conifers (good for management)
Answers from Rachel Brooks
Q). Many of our alders seem to be dying prematurely over the last few years. Has there been some disease or disorder attacking alders in Western Washington?
A). Alders are comparatively short lived trees, and thrive best in direct sunlight, often establishing after a disturbance event. Due to WA disturbance history, we’re seeing red alder stands now aging out in a lot of areas. Since alders don’t germinate and establish well in shade, such as the conditions found in an established alder stand, species composition will likely start to change as alder levels decrease. An aging out alder stand can look very messy.
Q). Is there a problem with Madronas in Washington state? Most in our area grow blackened leaves and these trees look unhealthy. What’s the best way to keep madrones healthy?
A). Madrones suffer from a variety of different diseases, with the blackening of leaves likely referring to a foliar blight caused by a fungal pathogen. Often the severity of foliar diseases is dictated by late winter/spring weather conditions and therefore it may seem worse some years compared to others. One way to help minimize fungal infections is by pruning branches of the tree and cutting back neighboring foliage to increase airflow and sunlight penetration to the tree. These dryer conditions are usually less conducive to foliar fungal infections.
Q). Given climate change and drought, would introduction of more drought-resistent species like Willamette Valley ponderosa pine be prudent?
A). I know of at least one tree farm that has done this near Toledo. Long-term success is hard to predict, but so far so good. That being said, they are attempting this on a subset of their land to see how it works, not as the only option. Remember diversity is what I always suggest when dealing with unpredictable future conditions!
Q). If the leaves at the top of a deciduous tree drop prematurely and before the ones from the bottom of the tree, is this drought damage and can the tree recover?
A). Leaf drop at the top of a deciduous tree may be caused by drought damage, or some other stressor. Deciduous trees can recover from premature leaf drop either by producing a second flush of leaves when conditions improve or by surviving until the following season. Waiting to see if the tree recovers is probably your best bet. If the crown is accessible, you can scrape off the bark with a fingernail to see if any of the branches or buds are currently alive.
Q). Aren’t there beneficial fungi on the forest floor that improve tree health and allow the trees to communicate?
A). Not all fungi are pathogenic – a lot play an important role in decomposition of materials and recycling of nutrients. In addition, some have direct mutualistic relationships with trees. Mycorrhizal fungi interact with a tree’s root system and helps expand the trees reach to water and nutrients, in return, the tree supplies the fungi with sugars. In addition, some research has shown how these fungal webs connect different trees together, moving around both chemical alarm signals and resources – a very cool subject that we have much more to learn and understand about.
Q). Is it true that a conk means the tree is dead from 16 feet below to 16 feet above the conk?
A). Many different species of fungi produce woody, shelf-like fruiting bodies referred to as conks. Some of these species are pathogenic to trees causing root or heart rots. Others are saprophytes, only decaying dead woody material and showing up after a tree or a portion of a tree has died. Without knowing the species of fungi producing the conk, it is hard to provide a good answer. It is likely safe to assume that if you see a conk on a living tree stem, the fungus has been infecting the tree for a significant amount of time prior to producing the conk and rot is present both above and below the conk. For example, if you see a conk produced by Porodaedalea pini (previously called Phellinus pini), the rough estimate I’ve heard is that decay extends internally 4-5 feet above or below the conk, which itself isn’t produced until 10 or 20 years after the tree was infected.
Q). Is light green moss covering Douglas-fir needles a problem?
A). Moss and lichen on trees are not pathogenic, meaning they don’t take nutrients or water from the tree. They may block sunlight required by needles for photosynthesis, but since trees tend to produce more foliage than is needed, this is not really a concern. In addition, Douglas-fir needles don’t function well in the shade anyways, that is why these trees in a dark forest self-prune off all of their lower branches (the needles turn into energy sinks, not energy producers). So it’s really just the top most and outer most needles, which tend not to have any moss or lichen growth on them, that are a priority for Douglas-firs. So, no, not a problem!
Q). Does resinosis always indicate a problem?
A). As far as my experience goes, resinosis (pitch being produced in the lower portion of a tree’s stem) doesn’t happen for no reason. Besides root rots, which I discussed in this lecture, I’ve seen resinosis due to mechanical injury as well, though damage has always been visible. This damage may be caused by animals, humans, or insects. Either way, if you see resinosis, look closer and try to determine the source – it means the tree is responding to something!