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Identifying High Hazard Sites
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High Hazard Site Before
Thinning |
After thinning |
Lodgepole Pine
Considerable research has been done on the susceptibility of lodgepole pine stands to mountain pine beetle attack. Several factors have been identified that affect the attractiveness of stands to mountain pine beetle. These are:
• the amount of susceptible lodgepole pine as part of the overall stand
• the age of the dominant pines
• the density of trees in the stand
• the geographic location of the stand
These factors are part of a model used to estimate how appealing a lodgepole pine stand is to beetles and how many trees might be lost if mountain pine beetle were to infest it. This information is only available for lodgepole pine and requires the collection of data to properly utilize. Details for determining this index can be found in the Management Guide.
This model is more applicable to larger stands of trees, but may be useful to small landowners as well. We can use principles from the system to help identify lodgepole pine stands that have a higher risk of beetle attack when beetles are in the area.
Lodgepole pine stands that are more susceptible to attack are:
- Older: Stands where the average age of a tree is greater than 80 years
- Larger: Stands where the average diameter of a tree is greater than 8 inches
- Denser: Stands where the density is greater than 120 square feet basal area/acre
Ponderosa Pine
Susceptibility of ponderosa pine stands is similar in principle to lodgepole pine, but specific criteria differ slightly.
Ponderosa pine stands that are more susceptible to attack are:
- Denser: Stands where the density is greater than 150 square feet basal area/acre
- Larger: Stands where the average diameter of a tree is greater than 10 inches
- Single-storied: Stands where trees are of uniform height
Characteristics that identify mountain pine beetle hazard in other host species, including ornamentals, have not been developed, but similar principles relative to age, diameter, and density likely apply.
Description of stands with a high susceptibility to mountain pine beetle attack
|
Average DBH of Hosts * |
Basal Area ** |
Other Characteristics |
Lodgepole Pine |
> 8 inches |
> 120 sq.ft./ac |
Average age 80-120 years Lodgepole pine majority of stand |
Ponderosa Pine |
> 10 inches |
> 150 sq.ft./ac |
Trees of uniform height |
*The diameter of a tree is measured at breast height or 4.5 feet above the ground. This is usually abbreviated as DBH.
** Basal area is the cross sectional area of a tree trunk commonly measured at breast height (4.5' above ground) including bark. Picture removing a disk from the tree at breast height and measuring how much area that disk has; that is the tree’s basal area. The basal area of a stand is the sum of each tree’s basal area over a specific land area, usually an acre. It can be measured with special tools. Basal area/acre is a measure of stocking or density of trees. For example, a stand where most trees (that are over 5 inches DBH) average 8 inches DBH, are evenly spaced, and the basal area is 120 square feet per acre, would have a tree to tree spacing about 11 feet. If the average diameter is 12 inches DBH, the spacing would be 17 feet.
The following table gives the number of trees per acre and the minimum distance between trees of the same diameter at basal areas of 120 and 150 square feet/acre.
Diameter |
Lodgepole Pine |
Ponderosa Pine |
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|
Trees per Acre |
Distance between Trees |
Trees per Acre |
Distance between Trees |
6 inches |
612 |
8 feet |
765 |
7.5 |
8 inches |
344 |
11 feet |
430 |
10 feet |
10 inches |
220 |
14 feet |
275 |
13 feet |
12 inches |
153 |
17 feet |
191 |
15 feet |
14 inches |
112 |
20 feet |
140 |
17.5 feet |
16 inches |
86 |
23 feet |
107 |
20 feet |
