Date of Award


Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)


Forest Resources


William H. Livingston

Second Committee Member

David B. Struble

Third Committee Member

Alan S. White


Balsam woolly adelgid (BWA) (Adelges piceae) is an insect pest of fir (Abies spp.) that was introduced to Maine in the early 1900’s. Within 50 years, it was found across the southern half of the state. BWA continued to kill balsam fir (Abies balsamea) in coastal sections of Maine but damage inland has been sporadic and scattered. Within the last decade increases in BWA damage severity and related fir mortality were reported in interior eastern Maine. This study investigated if the onset of BWA-related growth decline was a recent event; if climate trends coincided with growth reduction in BWA infested trees; and if damage severity varied with site and stand characteristics. Data were collected from 29- 0.08 ha (1/5th acre) plots in 3 eastern Maine climate zones. Increment cores of BWA- infested balsam fir and a nonhost species, and several tree and plot measurements, were gathered on each plot. Trees were divided into three groups for analysis, less affected fir (no dieback), more affected fir (have dieback) and nonhost. Three-year growth trends of the more affected fir were compared with the less affected fir and the nonhost. For the period of record there was no time when the more affected fir had significantly (P<0.10) reduced growth in comparison to the less affected fir on a region-wide basis. However, beginning in 1998 and continuing through 2001 growth trends of the more affected fir were significantly (P<0.10) less than nonhost trends region-wide. A chronology of rotholz occurrence suggests a buildup of adelgid populations from the late 1980’s continuing through 2003. Lethal temperatures for BWA in the study area have been less frequent since the 1940’s. It appears there has not been sufficient cold to appreciably slow the increase of adelgid populations since this time. An additional stress, the drought of 2001, coincided with a spike in fir mortality. Damage severity was positively correlated with age, negatively correlated with density and uncorrelated with latitude rank (which was used as a surrogate for climate zone). Damage severities between site classes based on soil-drainage were not significantly different (P<0.10). Mean diameter, height, age and uncompacted live crown ratio between less affected and more affected fir groups by plot were not consistently different. The study’s results indicate that given time, lack of competition for fir from other agents (e.g. spruce budworm) and a continuation of current climate conditions, adelgid populations will build up in the region of the study regardless of site and stand characteristics. Monitoring the condition of stands known to be infested with BWA is an important activity for managers. Management decisions need not be immediate as trees survive adelgid infestation for some time. However, productivity of affected stands will decrease and shorter rotations may be justified. Affected stands nearing merchantable size should be examined soon after a drought event because of the possible need to salvage dead trees. Unless lethal winter temperatures occur, BWA will continue to infest balsam fir stands and increase its damage as trees mature in eastern Maine.