Risk Assessment-Trees

What is the probability that a given Douglas-fir tree will die in the next 2 years? This question is particularly relevant when marking trees for take or leave in a thinning.  Three factors are used to assess the likelihood of individual tree mortality (Table A1): beetle pressure, severity of crown decline, and abundance of pitch droplets within bark crevices.  Beetle pressure refers to the abundance of beetles in the local area, as evidenced by the amount of recent mortality in the vicinity of the tree that is being assessed.  This represents a contagion effect,  the dispersal of beetle from infested trees to nearby un-infested trees. Infestation can be verified by the presence of trees with woodpecker shaved or flaked bark and/or the presence of flatheaded fir borer larvae, adults, and galleries under the bark of symptomatic trees  (chop bark away and examine bark/wood surface area).  Judging the severity of crown decline is subjective but in general trees with more severe decline will have more of the symptoms described above and/or symptoms will be more advanced. 

As we gather additional monitoring data, this rating system will be refined.

Table A1.  Proposed drought/FFB mortality risk rating for individual Douglas-fir trees

PointsRisk FactorScore
Beetle pressure
4DF mortality from FFB is found within 1-acre plot (120’ radius)
0DF mortality from FFB not found within 1-acre plot
Beetle pressure points =________
Crown decline
3Severe crown decline
2Moderate crown decline
1Light crown decline
0No recent crown decline
Crown decline points =________
Abundance of pitch jewels
3Abundant pitch jewels
1Light pitch jewels
0Pitch jewels absent
Pitch jewels =________
Total PointsRelative Risk Category
≥62-year mortality probability high
3-52-year mortality probability moderate
0-22-year mortality probability low
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