Years Of Severe Defoliation Research Articles

Relationships between Pikonema alaskensis larval density and shoot growth and production in young black spruce

Six years of field experiments were carried out to establish relationships between the density of larval yellowheaded spruce sawfly, Pikonema alaskensis (Roh.) (Hymenoptera: Tenthredinidae), and current-year shoot growth and production in juvenile, open-grown black spruce, Picea mariana [Mill.] B.S.P. In manipulative sleeve-cage experiments, larval density explained 36–65% of defoliation on branches and 27–37% of variation in shoot length in the year following defoliation. The negative impact of larval feeding on shoot elongation increased with each year of herbivory, resulting in a nearly 31% reduction in tree height after 5years of severe (i.e., c. 70% or more) defoliation. Production of current-year shoots was not influenced until 2o years following the initial bout of larval feeding and generally declined each year thereafter. Although a small but variable number of dormant (i.e., epicormic) shoots were produced each year, there was no apparent association with defoliation intensity. In field surveys, egg, mid-instar, and late-instar larval density explained, respectively 8%, 18%, and 33% of variation in shoot length growth in the following year. Despite some branches and trees sustaining multiple years of severe defoliation, there were no instances of either terminal shoot mortality or top kill (i.e., upper stem and branch mortality). Our study provides essential insect density–defoliation and defoliation–damage relationships for P. alaskensis in black spruce that may aid in establishing the first economic injury level for this destructive insect pest in Atlantic Canada.

Gap dynamics in aspen stands of the Clay Belt of northwestern Quebec following a forest tent caterpillar outbreak

Forest tent caterpillar (FTC; Malacosoma disstria Hübner) outbreaks represent an important natural disturbance in broadleaf-dominated stands; however, their effects on forest gap dynamics are not well understood. To describe such effects on canopy gaps and tree recruitment patterns, we investigated 20 trembling aspen (Populus tremuloides Michx.) dominated stands defoliated severely over 0 to 3 years during the last outbreak (1998–2003) in the northwestern Clay Belt of Quebec. Results show that canopy opening more than tripled (12.3%–43.7%) from 0 to 3 years of severe defoliation, and mean gap size was more than 12 times greater (7.2–87.5 m2) over the same gradient. Regeneration patterns suggest that aspen recruitment is not sufficient to completely restore closed canopies in stands defoliated 0, 1, and 2 years, whereas it should be sufficient in stands defoliated 3 years, where large gaps allow trembling aspen establishment. Our results clearly indicate that FTC outbreaks represent an important factor of gap formation in trembling aspen stands. At the stand level, gaps create uneven stand structures, and at the landscape level, FTC defoliation duration creates a large range of even to uneven stand structures.

Impacts of hemlock looper defoliation on growth and survival of balsam fir, black spruce and white birch in Newfoundland, Canada

Hemlock looper ( Lambdina fiscellaria fiscellaria (Guen.)) is an economically damaging defoliator that undergoes periodic outbreaks in Newfoundland, Canada. It defoliates and causes extensive tree mortality to its primary host, balsam fir ( Abies balsamea [L.] Mill.). We quantified tree survival using data from permanent sample plots (PSPs) and growth reduction or release using dendrochronology, and related these impacts to defoliation severity determined from annual aerial defoliation survey data. Such impact relationships are necessary as a fundamental input to a Decision Support System. Growth and survival of balsam fir, black spruce ( Picea mariana (Mill.) B.S.P.) and white birch ( Betula papyrifera Marsh.) were assessed from 1996 to 2008 in 48 Newfoundland Forest Service PSPs, selected based on four classes of defoliation severity. Two years of severe (71–100%) defoliation resulted in almost complete mortality for balsam fir, 10 years after defoliation, whereas survival was 70–80% for black spruce and white birch. Lower defoliation severity (1–2 years of moderate (31–70%) or 1 year of severe) resulted in approximately 60% survival for balsam fir and no reduction in survival for black spruce and white birch. Maximum growth reduction of balsam fir was 10–15% with 1 year of moderate-severe defoliation, 35–40% with 2 years of moderate defoliation, and about 50% with 2 years of severe defoliation. Growth recovered to pre-defoliation rates 5 years after defoliation ceased in all severity classes. Growth reduction and recovery of black spruce were more variable and lower than for balsam fir, and white birch exhibited only minor (<10%) growth reduction during the defoliation year or 1 year after defoliation. Control measures should focus on avoiding severe defoliation for two consecutive years.

Effects of Gypsy Moth Defoliation on Softwood and Hardwood Growth and Mortality in New Brunswick, Canada

Abstract The first major European gypsy moth (Lymantria dispar L.) outbreak occurred in central New Brunswick, Canada, on over 3,000 ha of forestland, from 2001ߝ2003. The outbreak was severe enough to result in considerable landowner concern and a privately funded aerial insecticide spray program to protect trees. Defoliation was unexpectedly severe on several tree species thought to be resistant or immune, as indicated from studies in the northeastern United States. Fifty plots (564 trees) were established and measured for standard mensurational characteristics, defoliation, and annual tree mortality, and after the cessation of defoliation, 44 trees were destructively stem analyzed to determine growth patterns. Balsam fir (Abies balsamea [L.] Mill.) with defoliation of more than 75% sustained specific volume increment reduction averaging 55% and 25% mortality after 2 years of severe defoliation. Red oak (Quercus rubra L.) sustained about 40% growth reduction, similar to results of previous studies. However, white birch (Betula papyrifera Marsh.) and trembling aspen (Populus tremuloides Michx.), with more than 75% defoliation for 2 years, sustained 43ߝ48% growth reduction, higher than in previous studies, and 4ߝ12% mortality. The gypsy moth range in Canada appears to be gradually expanding beyond previous climatic (cold winter temperature) limitations, and these results will help to predict future impacts.

Tree Mortality, Needle Biomass Recovery and Growth Losses in Scots Pine Following Defoliation by Diprion pini (L.) and Subsequent Attack by Tomicus piniperda (L.)

Tree mortality and growth losses following insect defoliation are poorly documented in Scandinavia. In 1990-1991, Diprion pini (L.) caused extensive defoliation to Scots pine in Lauhanvuori national park and surrounding areas in south-western Finland. Most trees lost all their foliage in 1990. In 1991, the outbreak area was sprayed with diflubenzuron (Dimilin®), except in the national park, where trees were severely defoliated again. No further defoliation occurred in 1992. In spring 1993, sprayed trees had ca 30% foliage, whereas unsprayed trees on average carried less than 10% of full foliage. The latter trees were susceptible to attack by Tomicus piniperda (L.), whereas the former largely escaped beetle attack. Beetle attacks peaked in 1993, and depletion of suitable host trees probably terminated the beetle outbreak in the area. Two years of severe defoliation resulted in substantial tree mortality and growth losses. In spring 1997, these unsprayed stands had suffered a ca. 50% loss in basal area which was mainly because of mortality, and about half of the dead trees had been attacked by T. piniperda. Surviving trees had ca 50% of full foliage, and radial growth had still not recovered. Basal area growth was reduced by 40-70%, depending on the amount of foliage left after the second year of defoliation. In contrast, tree mortality and beetle attack in the sprayed stands were negligible, and these trees had recovered full foliage and radial growth by spring 1997. Thus, one year of total defoliation resulted in an estimated loss in basal area growth of approximately 30% during ca. 5 yrs. In conclusion, the spraying operation was economically justified, as it prevented substantial tree mortality and reduced growth losses.

Patterns of balsam fir foliar production and growth in relation to defoliation by spruce budworm

Changes in foliar production caused by spruce budworm (Choristoneurafumiferana (Clem.)) defoliation and patterns of volume increment of surviving trees during and after the outbreak were determined in 20 mature balsam fir (Abiesbalsamea (L.) Mill.) stands on Cape Breton Island, Nova Scotia. Following the cessation of defoliation, the number of shoots increased 4-fold and mean shoot length doubled, resulting in a 12-fold increase in needle biomass. Average specific volume increment declined from 0.17–0.25 to 0.02–0.04 cm3•cm−2•year−1 after 4 years of severe defoliation; maximum increment reduction was 74–92%. Periodic radial increment and volume increment reduction (percent of mean increment in the previous decade) were both significantly related to cumulative (summed current annual) defoliation; a logistic regression equation explained 77% of the variation in volume loss. Differences in growth recovery among trees were determined by the temporal patterns of defoliation, with a 1-year lag before the beginning of volume increment recovery. Following 5 to 8 years of recovery, surviving trees had regained 48–82% of their predefoliation increment; however, absolute volume losses during the outbreak averaged 12–33 dm3/tree, or 32–48%.

Spruce budworm defoliation and growth loss in young balsam fir: recovery of growth in spaced stands

Trees defoliated by the spruce budworm (Choristoneurafumiferana (Clem.)) for 1 to 4 years and subsequently protected rapidly regained foliar biomass. Three plots of 25- to 30-year-old balsam fir (Abiesbalsamga (L.) Mill.) trees, on the Cape Breton Highlands of Nova Scotia, were studied. Two major factors contributed to the rapid growth recovery rates: the ability to produce epicormic shoots, combined with increased retention of older age-classes of needles, and the development of new foliage at the expense of volume growth. A complete recovery of volume increment occurred after 2 years of extreme defoliation, but not after 4 years of severe defoliation. Epicormic shoot production was only associated with shoot and bud destruction and therefore, growth recovery was slow after partial defoliation of only current foliage. In all plots studied, there was a lag of 2 to 3 years between increased foliar biomass and significant increases in volume increment.

An evaluation of growth response of young, spaced balsam fir to 3 years of spruce budworm spraying with Bacillusthuringiensis

Growth response of young, spaced balsam fir (Abiesbalsamea (L.) Mill.) to 3 successive years (1979–1981) of treatment with Bacillusthuringiensis Berliner for spruce budworm (Choristoneurafumiferana (Clem.)) control was examined in 20 plots on the Cape Breton Highlands, Nova Scotia. Defoliation commenced in 1976, 3 years before control operations began. Five plots were established both inside and outside the spray block, in areas that had been severely defoliated by budworm and in areas moderately defoliated. All plots in the severely defoliated area suffered heavy tree mortality, but mortality was significantly lower in the protected plots. In contrast, the moderately defoliated plots suffered virtually no tree mortality. The average volume increment of stem-analyzed trees from 1979 to 1981 was 0.63 dm3/tree for protected and 0.43 dm3/tree for unprotected trees in the severely defoliated area versus 4.15 dm3/tree for protected and 3.08 dm3/tree for unprotected trees in the moderately defoliated area. These volume increment values are equivalent to 8.8 m3/ha of growth between 1979 and 1981 for protected plots in the moderately defoliated area, compared with 6.1 m3/ha for unprotected plots. Therefore, a total gain of 2.7 m3/ha can be attributed to the 3 years of B. thuringiensis spraying. Long-term growth responses toB. thuringiensis spraying were not evaluated. Better results would be expected had protection started at the beginning of the budworm outbreak, instead of after 3 years of severe defoliation.

Vulnerability of Fir-Spruce Stands During Uncontrolled Spruce Budworm Outbreaks: A Review and Discussion

The concept of vulnerability to spruce budworm refers to the probability of tree mortality resulting from a given level of budworm attack. This paper reviews and analyses available information from the literature on stand vulnerability and timing of mortality during several budworm outbreaks. Timing of mortality during outbreaks appears to be fairly straightforward when considered in a general sense, with trees usually starting to die after four or five years of severe defoliation. Prediction of the total expected mortality in a given stand is more difficult, however, and attempts to relate mortality to stand characteristics have not shown strong relationships. Nevertheless, the data analysed suggest that for approximation purposes in a management sense, we can probably treat mortality during uncontrolled budworm outbreaks as a host-density dependent process. This is particularly so for fir in mature stands, where mortality approaches 100%, while fir in immature stands and spruce show lower, more variable mortality rates.

Effects of Different Population Levels of the European Pine Sawfly on Young Scotch Pine Trees

The larvae of the European pine sawfly, Neodiprion surtifer (Geoffroy), injure their hosts by old-growth defoliation, debarking, and current-shoot girdling. Defoliation is undoubtedly responsible for nearly all the growth loss. Both height growth and radial growth are inversely related to sawfly population levels, but radial growth is affected most, especially at higher population levels. The extent of growth loss is a function of the amount and the rate of foliage removed. Damage after 2 seasons depends upon the quantity of foliage available and removed in both seasons. Trees are seldom without foliage because some new-growth needles appear before all the old-growth needles can be consumed. Even at very heavy population levels defoliation seldom exceeds 90% when old and new foliage are considered together. Since new foliage continues to grow after the sawflies leave the host, the trees “recover” later in the season. Host mortality was not observed even after 3 years of severe defoliation.

The Black-headed Budworm in Eastern Canada

AbstractThe black-headed budworm, Acleris variana (Fern.), is a forest pest native to North America. Periodic outbreaks have been recorded since the late 1920's in eastern Canada, where the preferred host is balsam fir. An outbreak generally causes 2 years of severe defoliation but no tree mortality and only a slight loss in radial increment.Color patterns and measurements of the immature stages are given and limited data on age-interval survival rates are discussed. A key-factor analysis of 17 years’ data shows that population release is associated with years of low parasitism and favorable weather, while population decline is largely determined by late larval parasitism.