Descriptions of Damage Agent Severity Ratings

Damage agent severity ratings have been expanded since the standards were last updated in 2000.

Mortality Severity Ratings

These ratings include all disturbances that typically result in tree mortality, including bark beetles, root diseases, stem diseases, yellow cedar decline, and some types of abiotic and animal damage.


Severity

Code

Percent of Trees in Polygon Recently Killed


Trace

T

<1%

Light

L

1 to 10%

Moderate

M

11 to 29%

Severe

S

30 to 49%

Very Severe

V

>50%


Defoliation Severity Ratings

These ratings include defoliating insect and foliar disease damage, and some types of abiotic and animal damage that do not typically result in tree mortality.


Severity

Code

Description


Light

L

Some branch tip and upper crown defoliation, barely visible from the air.

Moderate

M

Thin foliage, top third of many trees severely defoliated, some completely stripped, easily visible from the air.

Severe

S

Bare branch tips and completely defoliated tops, most trees sustaining  more than 50% total defoliation, many trees completely stripped.


Aspen and Birch Decline Ratings


Severity

Code

Description


Light

L

Decline with no mortality
The first detectable stage, characterized by thin crowns and no individuals without visible foliage.

Moderate

M

Decline with light to moderate mortality
Thin crowns are accompanied by individuals devoid of foliage. Greater than an estimated 50% of individuals have some foliage.

Severe

S

Decline with heavy mortality
Crowns are very thin and greater than 50% of standing stems are devoid of foliage.