By Brad Withrow-Robinson, OSU Forestry and Natural Resources Extension – Benton, Linn and Polk Counties
Winter storms seem to inflict damage to trees and forests somewhere in the area most years. Winds, snow and ice can damage individual trees or entire forest stands- breaking out branches, snapping the main trunk or tipping over whole trees, leaving landowners with a mess and many unexpected decisions.
This winter has been an exception in the severity of the November 2014 ice storm that battered a swath of the interior Coast Range from the Kings Valley area south to Mary’s Peak (see previous article). This unusual event caused irregular and spotty damage reflecting fairly small differences in aspect and elevation. Many landowners are still surveying the damage and considering their need to salvage and wondering if they can thin the damage out while leaving a healthy stand. Damage is severe enough in some cases to be forcing the decision to clear cut and replant young stands rather than the early thinning they were due for.
Many factors will influence the decision of how to react to the damage including the extent of the damage to individual trees (how much of the trees crown was lost), the percent of trees damaged in a stand, the species, the terrain and availability of loggers and equipment.
Storm damage creates a clear immediate loss, but also many potential future losses. Windthrow and breakage immediately reduce the value and market options of salvaged logs, while damage to surviving trees cause future losses to defect and increased rot. Storm debris and may lead to beetle outbreaks that threaten undamaged trees in years ahead. Yikes.
Beetles are a concern for two reasons 1) they may accelerate sapwood decay and associated degrading of the log, and 2) they may build up in dead and damaged trees to the point where they can attack otherwise healthy trees. In this case we are talking about the Douglas-fir bark beetle.
It is important to keep the beetle’s life cycle and behavior in mind. Douglas-fir bark beetles fly each year from April into the early summer. They are looking for freshly down or stressed trees to colonize by boring through the bark and laying eggs in the inner bark. There the beetle grubs will be protected and nourished as they develop into subadults by late fall. They overwinter in the colonized log before emerging the following spring and repeating the cycle. A couple other important things to know are that the Douglas-fir bark beetle has just one generation per year (as opposed to more rapidly growing fivespined ips in pine (see previous article), and that it needs fairly large material – logs that are 9 or 10 inches in diameter and greater – to develop into adults. Also, abundance matters. The numbers I’ve heard in the past and confirmed by Dave Shaw, OSU Extension Forest Health Specialist, is that there needs to be about 10 logs, 10 or more inches in diameter to lead to serious beetle damage to standing trees, although it is likely that damage is progressive with growing amounts of larger logs. But the take home message is that you need some large material for this to become a problem, and that branches tops are not suitable nursery material for the bark beetle. A silver lining, but a very thin and wispy one indeed.
So how does this factor into the salvage decision? For situation 1, where you hope to avoid decay and degrade of salvaged logs, it is important to remove vulnerable logs as soon as possible, and ideally before the spring 2015 beetle flight. For situation 2, where you have significant amounts of downed or broken standing trees and hope to at least avoid a beetle population building up to damage the stand further, then it would be important to get out all suitable beetle rearing material (logs 10 inches and larger) before emergence of the storm-spawned generation in the spring of 2016.
You can anticipate one or more tours to consider options presented in a number of storm scenarios to be presented by Extension, the Small Woodlands Association and others. Please watch the Woodland Compass and Needle for details, or watch the Upcoming Events page on our website for details.