By Amy Grotta, OSU Forestry & Natural Resources Extension – Columbia, Washington, & Yamhill Counties
We’ve discussed ongoing drought stress a number of times on this blog. But when do we consider it dry enough to be called a drought? There’s actually a system for that. The United States Drought Monitor updates and releases a national map each week, showing which areas of the country are experiencing drought, and how extreme the conditions are. A variety of data sources go into their models, which I won’t begin to explain here, but their website has a lot of good information on how they determine drought conditions. In fact, all the data and visual tools on the Drought Monitor website feed the data geek in me; so if you like this sort of thing I encourage you to check it out.
If it seems like this blog has been a broken record stuck on the drought track the last few years, you’re not imagining things. But today, I want to highlight that in northwest Oregon we begin 2019 in a state of Moderate Drought, according to the Drought Monitor (see figure below; click to enlarge), even though we are in the midst of the rainy season.
It is unusual to experience drought in the middle of winter in northwest Oregon. In fact, there’s only been one other year in this century (2014) when our corner of the state was classified as in a Moderate Drought (or worse) in the first week of January. (2000 is the earliest year that data are available from this source.) We can attribute it to two things: first, we began the water year (October 1) already in a Severe Drought; and then second, we received abnormally low rainfall last November. November is typically among our rainiest months; however in 2018 we received less than half our normal November rainfall (3.2” recorded in St. Helens, for example, compared to an average of 7.1” for the month).
We gained some ground in December, but at this point it’s possible that our forests will enter the growing season with a slight soil water deficit. We need some more good rainy weather in January and February to avoid that.
You might be wondering why dwell on this when there’s nothing that we can do about the weather. Well, maybe this year you might do a few things a little differently, just in case we don’t get an appreciable uptick in rain. Are you planting trees this winter? Maybe you take a little extra time to try to find planting “microsites”; such spots on the north side of pieces of slash where the soil will stay a bit more shaded and moist. Do you have a healthy well-stocked 10- to 15-year old Douglas-fir plantation? Maybe this is the year that you consider young stand thinning (or precommercial thinning) to reduce demand for water in the stand. This could be a good activity to carry out with a chainsaw before spring. (Note: DO NOT do this in ponderosa pine or you are inviting the Ips beetle in to attack your trees. In fact, best to avoid creating ponderosa pine slash in droughty years).
Note that I preface all of these suggestions with “maybe”. We can’t predict what the rest of the winter will look like. We do know that there are ways to reduce water stress for young trees (see above). So it’s really up to you to decide whether it’s important enough to put in the extra time (or money, if you’re paying someone to do work for you).
I have more to say about long-term drought adaptations, but I will save that for another time. Yes, the broken record may continue to skip…