The impact of hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) onbalsam fir and spruce in New Brunswick, Canada

In 1989, the first recorded outbreak of hemlock looper (Lambdina fiscellari a fiscellaria (Guen.)) occurred in New Brunswick, Canada. Data were collect ed from ten plots established in an area infested from 1992-1994, to assess impacts of hemlock looper. Ocular and branch sample assessments of current defoliation and ocular assessments of total defoliation (all age classes o f foliage) were conducted for balsam fir (Abies balsamea [L.] Mill.), white spruce (Picea glauca [Moench] Voss), and black spruce (Picea mariana (Mill .) B.S.P.). Stand response was assessed and related to cumulative defoliati on. Ocular assessments were found to accurately estimate defoliation, which was significantly related to tree mortality. Ninety-two percent of balsam fu trees that had cumulative defoliation >90% died. Mortality of balsam fir was significantly (p < 0.05) related to tree size, in both lightly and sev erely defoliated plots; trees with DBH <11 cm sustained 22-48% higher morta lity than larger trees. Mortality of balsam fir, in terms of both percent s tems/ha and m(3)/ha merchantable volume, increased exponentially in relatio n to three estimates of cumulative (summed) plot mean defoliation. The stro ngest relationships (r(2) = 0.75-0.79) were between mortality and the ocula r defoliation assessment for 1990-1993 foliage. Tree mortality caused by th e looper outbreak ranged from 4-14% stems/ha in lightly defoliated and from 32-100% in severely defoliated plots; merchantable volume killed was 3-14 m(3)/ha and 51-119 m(3)/ha, respectively. Relationships between mortality a nd defoliation were similar when defoliation was assessed for 1987-1993 and 1990-1993 foliage age classes. (C) 1999 Elsevier Science B.V. All rights r eserved.