What is the 5-year probability and expected severity of Douglas-fir mortality in a given location?
The following risk rating system (Table A2) is intended help assess Douglas-fir mortality risk over the next five years at a given point on the landscape, where higher values represent greater risk. This system is most applicable to sites with less than 45” of annual precipitation and/or more than 300mm of mean annual climatic water deficit (see sidebar), where Douglas-fir is present. Risk at this spatial scale is expected to vary based on beetle pressure as well as topographic factors, proximity to stand edges and soil factors, all of which are believed to influence tree moisture status.
Here risk refers to:
- The likelihood of observing Douglas-fir mortality in a one-acre plot at a given point on the landscape
- The probability that mortality will increase and intensify at this location
- The expected severity of mortality, measured as the percentage of the Douglas-fir basal area within a 1-acre area surrounding the sample point that is dead/dying.
Because topography and soils often vary considerably over short distances in SW Oregon, relative risk also tends to vary over short distances in this region.
When there is a desire to characterize the risk within a stand, multiple plots should be taken.
Table A2. Douglas-fir mortality risk rating for sites (≤ 1 acre)
