Brad Withrow-Robinson, Forestry & Natural Resources Extension Agent, Benton, Linn and Polk Counties.
I was recently on a tour where we looked at how growing conditions, productivity and plant communities all change across the landscape according to elevation, soils, rainfall, aspect and other factors. These are often included in the term “site productivity”. These factors give important insights to the ability of a site to support different types of plants, and also how well they will grow there. This capacity to produce biomass, or support tree growth is often expressed in the important forestry concept of site class as described in this article.
We traveled from near the crest of the Coast Range back to the Valley floor to watch changes in site class and vegetation. Our final stop was a rock sitting on a small hill beside a vineyard in Yamhill County, looking out across the Willamette Valley.
It is a large rock (about 90 tons), unrelated to any of the bedrock of the hill. This rock helps tell a story of events during the last ice age that shaped the Willamette valley and its historic vegetation. It influences the present, largely agricultural, vegetation as well. Continue reading