Brad Withrow-Robinson, OSU Forestry & Natural Resources Extension agent, Benton, Linn and Polk Counties.
We have been dedicating a fair amount of screen space and class time lately to the idea that many family forest landowners would benefit from thinning their young stands. We explored the reasons to consider young stand thinning (YST) as well as some approaches in a series of posts on YST . YST is consistent with the situation and goals of many family forest landowners, which often include growing older and more diverse forests.
That said, like many other well-grounded activities, YST is not without some potential drawbacks.
Few of them are significant enough to justify not thinning at all, but each requires some thought and consideration to avoid unintended consequences. We present some of those potential drawbacks that you need to consider when planning a YST, along with some links to other information, below.
Weeds. Yes, blackberries and other weeds can make YST difficult, and may slow the growth of your trees, but do not change the need for YST if you find that you have more trees per acre (tpa) than your desired target. YST is probably a better justification for keeping ahead the weeds, than weeds are a justification for delaying or not doing YST.
Sunscald, yes your trees can be burned if young tender bark is abruptly exposed to the sun and gets too hot. We see it particularly on warm, dry, south facing sites, and it is more commonly seen because of pruning than thinning. If your site meets that description, it might be wise to thin and prune separately. Consider modifying the pruning operation (do smaller lifts, leave a SW facing branch or two in exposed places like south facing road sides, don’t prune those areas in late summer).
Insects and diseases are the most significant concerns related to YST. There is the potential to create a bug problem while trying to avoid a density related stress problems. The outcome depends on the amount, timing and handling of the slash produced. The cause for concern varies by tree species.
Valley ponderosa pine. We have written about problems with slash and the ips beetle before and also directed people or one or another excellent ODF bulletin about ips and also about slash management. These destructive bark beetles thrive on stress and also disturbances that produce debris they use to multiply. Creating lots of slash in a thinning operation can easily lead to an ips outbreak, and certainly represents the biggest single challenge to managing pine.
Douglas-fir. Black stain root rot is an increasing problem in some areas in western Oregon. It is caused by a fungus, but it is carried
by insects that are keyed-in on stress and disturbance (just like the ips). Local outbreaks in young plantations may be associated with nearby disturbances such as harvests, road construction or brushing. It can also be associated with YST. Where other local disturbances or presence of disease cause concern, the most significant management recommendation is to avoid attracting and feeding the insect vectors by thinning in summer, after the insects’ breeding season. Look for more about this disease in future blogs/articles.
Swiss Needle Cast is present throughout western Oregon, but it is most significant along the coast where it must be considered as part of every management decision. Potential implications of SNC to young stand thinning include retaining alternate species, and selecting among Douglas-fir based on needle retention.
Young stand thinning is an important woodland management practice that can help you keep your woodland vigorous and resilient to drought and other stress. A little caution can help it deliver on that promise.