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Estimating cumulative defoliation of balsam fir from hemlock looper and balsam fir sawfly using aerial defoliation survey in western Newfoundland, Canada
Forest Ecology and Management 259 (2010) 591–597
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Estimating cumulative defoliation of balsam fir from hemlock looper and balsam fir sawfly using aerial defoliation survey in western Newfoundland, Canada Javed Iqbal *, David A. MacLean Faculty of Forestry and Environmental Management, University of New Brunswick, P.O. Box 4400, Fredericton, N.B., E3B 5A3 Canada
A R T I C L E I N F O
A B S T R A C T
Article history: Received 21 September 2009 Received in revised form 9 November 2009 Accepted 12 November 2009
Both hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) and balsam fir sawfly (Neodiprion abietis (Harris)) undergo periodic outbreaks in eastern Canada and cause significant growth and mortality losses to forests. Tree growth and mortality are closely related to cumulative defoliation estimates, which integrate annual defoliation over multiple years. Our objective was to determine a method to estimate cumulative defoliation of balsam fir (Abies balsamea [L.] Mill) due to these insects in western Newfoundland, using aerial defoliation survey data, as an essential input to modeling impacts for Decision Support Systems. Interpretation of aerial defoliation survey data for hemlock looper and balsam fir sawfly is problematic because both insects feed upon multiple age classes of foliage. Current-year (2008) aerial defoliation survey data were compared with ground estimates of defoliation by age class from 45 plots (450 trees and 395 mid-crown branch samples), representing a range of defoliation severity classes for each insect. Cumulative defoliation was calculated using defoliation per foliage age class, weighted by relative foliage mass for a given age of foliage. Three significantly different severity classes were defined based on cumulative defoliation values derived from aerial defoliation survey: (i) 1year moderate (30–70%) defoliation, (ii) 1-year severe (71–100%) defoliation with calculated cumulative defoliation values of 19 and 39%, respectively, for balsam fir sawfly, 21 and 34% respectively for hemlock looper; and (iii) 2–3 years of moderate–severe defoliation, with cumulative defoliation ranging between 59 and 64% for balsam fir sawfly and 49% for hemlock looper. Defoliation severity from aerial defoliation survey alone hence can be misleading if defoliation measurements are not converted to cumulative defoliation values. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Cumulative defoliation Decision Support System Balsam fir sawfly Hemlock looper Aerial defoliation survey
1. Introduction Balsam fir (Abies balsamea [L.] Mill) is a tree species vulnerable to defoliation by many different insects. Spruce budworm (Choristoneura fumiferana (Clem.)), balsam fir sawfly (Neodiprion abietis (Harris)), and hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) have been the most damaging defoliators of balsam fir in eastern Canada, with moderate–severe defoliation areas of 31 million, 522 000, and 858 000 ha, respectively, from 1975 to 2007 in Atlantic Canada (Canadian Council of Forest Ministers, 2008). Spruce budworm is the most widespread insect defoliator of balsam fir, but balsam fir sawfly and hemlock looper have both undergone periodic outbreaks in eastern Canada. Balsam fir sawfly has become a serious pest of young managed balsam fir stands in western Newfoundland, Canada, and the current outbreak, which began in
* Corresponding author. Present address: University of New Brunswick, Faculty of Forestry and Environmental Management, P.O. Box 4400, Fredericton, New Brunswick, E3B 5A3 Canada. Tel.: +1 506 453 4501; fax: +1 506 453 3538. E-mail address: [email protected] (J. Iqbal). 0378-1127/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2009.11.017
1991, is the longest ever recorded (Piene et al., 2001; Moreau, 2006). The long balsam fir sawfly outbreak duration has been attributed to extensive precommercial thinnings (Ostaff et al., 2006). Hemlock looper outbreaks have occurred in Newfoundland from 1910 to 1915, 1920 to 1926, 1929 to 1935, 1946 to 1955, 1959 to 1964, 1966 to 1972, 1984 to 1989 and 1995 to 2004 (Otvos et al., 1979; Canadian Council of Forest Ministers, 2008). Hemlock looper is of particular concern as severe defoliation of all age classes of foliage is very destructive, causing tree mortality after just 1 or 2 years of severe defoliation (Hudak et al., 1978; MacLean and Ebert, 1999). To assist insect and forest management decision-making, a spruce budworm Decision Support System (SBW-DSS) was developed by the Canadian Forest Service (MacLean and Porter, 1995). In the SBW-DSS, annual defoliation data obtained from aerial surveys and various projected defoliation scenarios are converted into cumulative 5-year defoliation. These estimates are used to model tree growth loss and mortality of stands in the inventory database of a Geographic Information System (GIS) (MacLean et al., 2001). The SBW-DSS helps forest managers predict budworm outbreak effects on forest structure and productivity, forecast forest growing stock and sustainable
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Fig. 1. Schematic representation of a balsam fir branch with (a) no defoliation; and after severe defoliation due to (b) spruce budworm, consuming current-year foliage, (c) balsam fir sawfly, feeding on 1 year and older foliage, and (d) hemlock looper, feeding on all age classes of foliage.
harvest levels, optimize insecticide protection programs, and use silviculture and harvest scheduling to restructure forest management to reduce future damage (Hennigar et al., 2007). In order to develop a comparable DSS for balsam fir sawfly and hemlock looper, an initial requirement is a method to determine cumulative defoliation, which integrates a sequence of annual foliage losses, for these insects. The measure of cumulative defoliation differs for spruce budworm, balsam fir sawfly and hemlock looper because of their different modes of feeding (Fig. 1): spruce budworm feed on current-year foliage (although ‘back-feeding’ on older age classes of foliage can occur, it is restricted to extremely high population levels when all currentyear foliages have already been consumed, and is rare), balsam fir sawfly feed on all age classes except current-year foliage (Martineau, 1984), while hemlock looper is a wasteful feeder of all age classes of foliage (Dobesberger, 1989). Aerial defoliation surveys are commonly used to assess annual defoliation over large areas, and are currently the only operational method to provide such data (MacLean and MacKinnon, 1996). Aerial defoliation survey data describe the intensity and spatial extent of defoliation based upon the characteristic reddish-brown coloration of host foliage resulting after feeding. The method depends upon the observer’s ability to recognize defoliation class and to identify locations (Dorais and Kettela, 1982). Given the mode of feeding of spruce budworm, annual aerial defoliation surveys provide a direct measure of damage to the current-year foliage only. Because balsam fir foliage is retained for about 5 years (>95% foliage naturally falls after 5 years, Piene et al., 2001), current defoliation does not gauge the cumulative impact of successive years of defoliation. Yearly cumulative defoliation (CD), which serves as an input to the SBW-DSS, is calculated (MacLean et al., 2001) from aerial defoliation survey sequences for a given area by weighting estimates of current defoliation (C) in year t by relative foliage
mass for that age of foliage, based on data for undefoliated balsam fir trees (Kleinschmidt et al., 1980): CDt ¼ 0:28C t þ 0:26C t1 þ 0:22C t2 þ 0:13t3 þ 0:08C t4 þ 0:03C t5
(1)
This model assumes that natural needle fall diminishes the proportion of foliage with age from 28% for current-year foliage to 3% for 5-year old foliage. A similar approach to estimate cumulative defoliation cannot be used for balsam fir sawfly and hemlock looper, because annual aerial defoliation survey data contain defoliation of all foliage age classes except current year (for balsam fir sawfly) or all foliage (for hemlock looper). Thus overlaying successive years of defoliation also becomes problematic for these insects. Our objectives in this study were to (i) quantify balsam fir defoliation per age class of foliage due to balsam fir sawfly and hemlock looper from plots, while relating it to aerial defoliation survey data, and (ii) determine cumulative defoliation values for a range of aerial defoliation survey severity classes, for use in modeling of balsam fir sawfly and hemlock looper impacts and development of DSS. 2. Methods 2.1. Aerial defoliation survey data Newfoundland and Labrador Department of Natural Resources conducts annual aerial defoliation surveys and records hemlock looper and balsam fir sawfly defoliation by species and severity level (nil, moderate 31–70%, or severe 71–100%) on sketch maps. Aerial defoliation surveys are conducted during a 1–3 week period after the completion of feeding (usually from mid-late August) using helicopters (Hubert Crummey, personal communication, September 2008). A distinct reddish-brown coloration of foliage
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ple years and defoliation levels, a total of six defoliation severity classes were distinguished for balsam fir sawfly and four classes for hemlock looper (Table 1), ranging from only 1 year of moderate to 3 successive years of severe defoliation. 2.2. Plot selection
Fig. 2. Map of hemlock looper and balsam fir sawfly defoliation in western Newfoundland during 2008. There are four (hemlock looper) and six (balsam fir sawfly) severity classes based on 2008 and previous years of defoliation. ‘M’ denotes moderate (31–70%) while ‘S’ represents severe (71–100%) defoliation. In case of multiple years of defoliation, previous years are represented first, e.g. ‘MS’ = moderate defoliation in 2007, and severe defoliation in 2008.
In September 2008, soon after the aerial defoliation survey and availability of digital sketch maps, a ground survey was conducted in each of the above 10 defined defoliation severity classes. Balsam fir stands that had been precommercially thinned (2500– 5000 trees/ha) and of intermediate age (25–40 years) were selected from the inventory data after an overlay using ArcGIS (ESRI) in each severity class for balsam fir sawfly. Similarly, mature and over-mature (>50 years) balsam fir stands were selected for hemlock looper. Five plots were established in each severity class starting from a predetermined, readily identifiable location. The first plot was located 50 m from the stand edge while four additional plots were located along a linear transect with each plot 50 m apart, if the defoliated area and stand size permitted. In total, 29 plots were established for balsam fir sawfly near the town of Deer Lake in western Newfoundland [498100 N, 578250 W], and 16 plots were established for hemlock looper in the northern peninsula, near the town of Plum Point [518100 N, 568550 W] (Fig. 2). 2.3. Field measurements
due to the desiccation of damaged needles (MacLean and Ebert, 1999) helps the observer judge the area and severity of defoliation. In other areas like New Brunswick, fixed-wing aircraft along flight lines 2–5 km apart are used (Miller and Kettela, 1975) for spruce budworm aerial defoliation surveys, and these have been found to be 82–85% correct in differentiating three defoliation classes 0–30, 31–70, and 71–100% defoliation (MacLean and MacKinnon, 1996; Taylor and MacLean, 2008). No measure of measurement accuracy is available for aerial surveys conducted with helicopters, but they can be assumed to be of higher accuracy based on low altitude, slow speed flights, and means of closer observation in case of doubt. Records from the sketch maps are digitized and stored in Arc/ Info GIS format. Data on spatial accuracy and transfer error rates are not available, but would be included in the overall aerial defoliation survey accuracy assessments reported above. All areas that sustained hemlock looper or balsam fir sawfly defoliation in 2008 on the island of Newfoundland were overlaid with defoliation maps for 2007 and 2006 using ArcView GIS 9.2 (Environmental Systems Research Institute (ESRI)) (Fig. 2), to assign multi-year (2006–2008) defoliation severity classes. Hence, while looking at annual defoliation for 2008, areas with multiple years of defoliation were also recorded. A total of 3 years of defoliation occurrence per site were noted for balsam fir sawfly and 2 years for hemlock looper, among 2008 defoliated areas. Considering multi-
In each plot, 10 dominant or co-dominant balsam fir trees that were closest to the centre of each prism plot (basal area factor 2 m2 ha1) were selected. Each tree was examined using binoculars and defoliation was visually estimated and recorded in six defoliation severity classes (0–10%, 11–20%, 21–40%, 41–60%, 61– 80% and 81–100%) for each age class of foliage (current, 1–5-year old foliage). Three trees were selected randomly from each plot and three branches were cut from different cardinal directions of the mid-crown of each tree using pole pruners. Defoliation of each age class of foliage was again visually estimated using the shoot-count method (developed by Fettes, 1950 and discussed in more detail by Sanders, 1980) and recorded in similar classes as described above. Mean defoliation per age class of foliage was calculated using the midpoints of defoliation classes (MacLean and Lidstone, 1982). Natural needle fall of balsam fir is taken into account in calculation of cumulative defoliation (Eq. (1)). To calculate cumulative defoliation of each aerial defoliation survey severity class for balsam fir sawfly and hemlock looper, the same form of Eq. (1) was used, but substituting defoliation in different years by defoliation per age class of foliage (f): CDt ¼ 0:2C f þ 0:26C f 1 þ 0:22 f 2 þ 0:13 f 3 þ 0:08 f 4 þ 0:03 f 5
(2)
Table 1 Defoliation severity classes based on sequences of 2006–2008 defoliation caused by balsam fir sawfly and hemlock looper in Newfoundland, determined from aerial survey data. Area and number of plots established are given for each defoliation severity class. Defoliation severity class
Balsam fir sawfly
Hemlock looper
Defoliation
1 2 3 4 5 6
2006
2007
2008
– – – – M S
– – M S S S
M S S S M S
Number of plots
Area (ha)
5 5 4 5 5 5
4363 5489 931 11,166 623 1558
Defoliation 2006
2007
2008
– – – –
– – M M
M S M S
M = moderate defoliation (30–70% of total tree foliage); S = severe defoliation (71–100% of total tree foliage).
Number of plots
Area (ha)
5 4 4 3
943 88 14 2
594
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2.4. Data analyses Both an independent-samples t-test as well as two-factor analysis of variance (ANOVA) were used to test whether mean defoliation differed significantly, with ANOVA factors (i) method of data collection (binocular-aided visual estimation for whole-trees, versus shoot-count defoliation estimation from cut branches), and (ii) foliage age class. One-way ANOVA was used to test for differences in mean defoliation per age class of foliage within a severity class. Where a significant effect was found, a post hoc analysis using the Games–Howell test was done, due to an obvious difference in population variance and unequal sample sizes. A similar analysis for differences between defoliation severity classes within a given insect (Table 1) was done using two-factor ANOVA. Significant differences in means for all tests was determined at the p = 0.05 level. Analyses were conducted using SPSS ver. 16.0.0 (SPSS, 2007). Mean values of defoliation per age class of foliage were used as input in Eq. (2) to calculate cumulative defoliation for each defoliation severity class. 3. Results For balsam fir sawfly, a t-test [t (2110) = 1.403, p = 0.16] as well as a two-factor ANOVA [F (11, 2111) = 104.3, p = 0.08] showed no significant differences between the whole-tree, binocular versus branch-level, shoot-count methods of defoliation estimation. On the other hand, for hemlock looper there were significant differences between whole-tree, binocular and branch-level, shoot-count methods [t (1150) = 2.064, p = 0.04; F (11,
1151) = 8.624, p = 0.03]. Hemlock looper defoliation measured using binoculars on trees was underestimated from that of the shoot-count method on branches for older foliage, i.e., 3, 4 and 5 years old, by 8.2, 13.7, and 19.2%, respectively. Due to this difference, only defoliation measured from branch-level samples (which are considered more accurate) was used in further analyses for hemlock looper. There was very little balsam fir sawfly defoliation (<14%) for current-year foliage in all severity classes (Fig. 3). 1–3-year old foliage were defoliated more (18–28% and 51–55% mean defoliation in severity classes 1 and 2, 1 year of moderate and severe defoliation, respectively) than 4–5-year old foliage (mean defoliation of 11–15% and 33–40% in severity classes 1 and 2, respectively). In case of multiple-year defoliation (severity classes 3–6), current-year foliage was defoliated least (8–14%). 1-Year old foliage showed mean defoliation of 69–79%, while 2-year and older foliage had the highest mean defoliation (79–89%). A higher variability (SE > 2) occurred for defoliation of 2–5-year old foliage in single year defoliation classes, i.e., 1 and 2 (Table 2). Total mean defoliation combining all defoliation severity classes was 17.5% and 40% for severity class 1 and 2, respectively, but ranged from 67 to 74% for severity classes 3 to 6. There were significant differences in defoliation among the six balsam fir sawfly defoliation severity classes, as determined from one-way ANOVA, and Games–Howell post hoc tests showed that current-year foliage differed significantly (p < 0.05) from all other foliage age classes (Table 2). For hemlock looper, severity classes 1 and 3 with moderate defoliation over 1 or 2 years showed similar 20–34% defoliation in all age classes of foliage, and relatively high variability (SE > 2) (Fig. 4). Analysis showed no significant differences in defoliation
Fig. 3. Mean SE defoliation per age class of foliage due to balsam fir sawfly for six defoliation severity classes (as described in Fig. 2).
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Table 2 Defoliation of balsam fir caused by balsam fir sawfly and hemlock looper, estimated per age class of foliage on sampled branches. Defoliation severity class
Balsam fir sawfly 1M 2S 3 MS 4 SS 5 MSM 6 SSS Mean Hemlock looper 1M 2S 3 MM 4 MS Mean
N
Mean defoliation (%) by foliage age (year) (S.E.) Current
1
2
588 570 456 570 570 570
6.1* 8.4* 8.5* 13.6* 12.2* 11.7*
27.1 (1.8) 52.5 (2.6) 79.2* (1.2) 78.0* (1.4) 69.1* (1.8) 77.4* (1.1)
26.8 54.2 86.1 83.5 79.9 87.5
10.1
63.9
69.6
69.7
270 216 216 162
22.4 26.8 20.6 36.7
26.6
32.9
(0.4) (0.6) (0.5) (1.1) (0.8) (0.7)
(3.2) (2.5) (2.5) (3.3)
24.1 34.4 24.2 48.9
(2.6) (3.0) (2.7) (3.5)
31.6
20.4 37.2 22.2 46.7
Mean 3
(2.2) (2.8) (0.9) (1.1) (1.6) (0.7)
(2.7) (2.8) (1.9) (3.4)
36.7
18.5 51.2 88.4 87.5 84.1 88.5
4 (2.3) (2.6) (0.6) (0.8) (1.1) (0.6)
14.8 40.3 87.9 87.1 81.8 88.9
66.8
64.4
24 (3.2) 45.4 (3.1) 21.0 (2.2) 56.3 (3.2)
30.3 55.9 20.4 65.6
43.1
47.9
5 (1.9) (2.7) (0.7) (0.9) (1.1) (0.5)
11.4 (1.5) 33.16 (2.2) 87.1 (0.9) 87.1 (1.1) 78.6 (1.5) 88.9 (0.5)
17.5z 40.0z 72.9 72.8 67.6 73.8
(3.5) (3.7) (2.4) (3.1)
33.8 60.1 24.2 73.7
25.8 43.4z 22.1 54.6z
(4.0) (4.5) (2.0) (3.4)
M = moderate defoliation (30–70% of total tree foliage); S = severe defoliation (71–100% of total tree foliage). A sequence of M and S indicates annual defoliation levels over multiple years, with the last value showing severity in the latest year; e.g. MS = 1 year of moderate defoliation followed by 1 year severe defoliation. N = number of trees and/or branches measured. * Statistically different mean defoliation (Games–Howell test) within a severity class (row) from other age classes at p 0.05 following a significant 1-way ANOVA. z Statistically different mean defoliation of a severity class from the other severity classes for the same insect at p 0.05 following a significant 2-factor ANOVA.
per age class of foliage among the four defoliation severity classes (Table 2). For hemlock looper severity classes 2 and 4, where plots were defoliated severely over 1 or 2 years, a gradient of increasing defoliation occurred from current-year (26.8% and 36.7% mean defoliation in severity classes 2 and 4, respectively) to 5-year old foliage (60.1% and 73.7%, respectively). Older age classes (4 and 5 years) were defoliated to a much lower extent (20–34%) in moderately compared to severely defoliated areas (55–74%). Total mean defoliation combining all age classes was 22–26% for severity classes 1 and 3, versus 43% and 55% for classes 2 and 4, respectively. A two-factor ANOVA for differences in defoliation per age class of foliage between the defoliation severity classes showed two significant groupings for each of hemlock looper (severity classes 2 and 4, with total mean defoliation over all age classes of 43% and 55%) and balsam fir sawfly (severity classes 1 and 2 with 17% and 40%). Three homogeneous subsets based on Tukey’s HSD were
revealed for each of balsam fir sawfly and hemlock looper. After calculation of cumulative defoliation using Eq. (2) (Table 3), three similar homogeneous subsets were distinguished for defoliation of each insect: Group A with cumulative defoliation <30%, Group B 31–40%, and the most severe Group C with cumulative defoliation >40%. 4. Discussion Cumulative defoliation classes were quantitatively defined for use with annual aerial survey data for hemlock looper and balsam fir sawfly in western Newfoundland. These classes integrate annual defoliation estimates, which are necessary components of DSS for managing forests impacted by these insects. Defoliation severity from aerial defoliation survey alone can be misleading as seen in the results, if defoliation measurements are not converted
Fig. 4. Mean SE defoliation per age class of foliage due to hemlock looper for four defoliation severity classes (as described in Fig. 2).
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Table 3 Calculated cumulative defoliation for each defoliation severity class determined from aerial defoliation survey data using Eq. (2). Defoliation severity class
1 2 3 4 5 6
M S MSb SSc MSM SSS
Balsam fir sawfly
Hemlock looper
Cumulative defoliation (%)
Impact severity class
19 39 63 63 59 64
A B C C C C
a
Cumulative defoliation (%)
Impact severity classa
21 34 25 49
A B A C
M = moderate defoliation (30–70% of total tree foliage); S = severe defoliation (71–100% of total tree foliage). A sequence of M and S indicates annual defoliation levels over multiple years with the last value showing severity in the latest year; e.g. MS = 1 year of moderate defoliation followed by 1 year severe defoliation. a Assigned based on homogeneous subsets after post hoc analysis as described in Table 2. Generalized class ranges of <30% (A), 31–40% (B) and >40% (C) cumulative defoliation apply. b MM in the case of hemlock looper. c MS in the case of hemlock looper.
to cumulative defoliation values for insects like balsam fir sawfly and hemlock looper that feed on multiple ages of foliage. Significant differences between defoliation measured by different methods for hemlock looper (i.e., binocular-aided visual estimation vs. shoot-count visual estimation on individual sampled shoots per age class on cut mid-crown branches) were presumably due to the fact that older foliage was obscured from the observer due to younger foliage and height of trees (mature and over-mature stands were targeted for hemlock looper). MacLean and Ebert (1999) previously noted that it is difficult to estimate defoliation of more than three age classes of foliage using binoculars, because newer foliage obscures older age classes. Balsam fir sawfly defoliation measured using binocular-aided visual estimates was not significantly different from that estimated on sampled shoots on mid-crown branches on intermediate–aged, thinned balsam 7–10 m in height. Measurement of defoliation on branches using the shoot-count method or larval sampling is more accurate (Parsons et al., 2005), but is not practically feasible on a large scale due to time and resources involved. Stands that sustained moderate or severe balsam fir sawfly defoliation for only a single year (Fig. 3, severity classes 1 and 2) showed that 1–3-year old foliage age classes were defoliated the most (18–28% and 52–55% for severity class 1 and 2, respectively), 4- or 5-year old foliage less (11–15% and 33–41%), and currentyear foliage was defoliated the least (6–9%). These results are similar to earlier studies that stated that balsam fir sawfly larvae consume more 1–3-year old foliage than current or older foliage (Parsons et al., 2003; Moreau et al., 2003). The oldest age classes of foliage (4 and 5 years old) were defoliated more (78–89%) in stands that sustained more than 1 year of defoliation—i.e., defoliation severity classes 3–6 (Fig. 3). Since defoliation occurred for 2 or 3 years, older age classes of foliage were fed upon after most 1–3year old foliage had been consumed. For balsam fir sawfly, there was no significant difference in cumulative defoliation values for multiple-year defoliation severity classes, with combinations of 2 or 3 years of moderate or severe defoliation all resulting in 59–64% cumulative defoliation (Table 3). This might be attributed to limitations of aerial defoliation surveys in detecting level of defoliation for insects that feed on multiple age classes of foliage. However, it also may reflect the inherent pattern of balsam fir sawfly feeding, with 1 year of feeding consuming 18–27% (moderately defoliated) or 51– 55 (severely defoliated) of 1–3-year old foliage, a second year increasing 4–5-year old foliage to 78–89%, and only 8–14% of current-year foliage consumed. The fact that in all cases 86–94% of current-year foliage remains on the trees definitely influences aerial survey values. Our results showing that hemlock looper defoliation was similar on all age classes of foliage (Fig. 4) were comparable to earlier studies (e.g., Dobesberger, 1989). Total mean defoliation
over all age class of foliage for severity class 3 (22.1%) logically should be higher than that of severity class 1 (25.8%). As discussed with balsam fir sawfly, the limitations in measuring defoliation by insects that feed on multiple ages of foliage also apply to hemlock looper. For spruce budworm, where defoliation repeatedly (year after year) occurs on current-year foliage, defoliated areas on trees are readily visible and hence it is relatively easy to estimate defoliation levels. For both balsam fir sawfly and hemlock looper, defoliation on older age classes is hidden from an observer in a helicopter or on the ground by current-year undefoliated foliage, possibly contributing to underestimation of defoliation. Also since tree crowns appear thinned and devoid of foliage, an overestimation of currentyear defoliation may occur in areas already defoliated in previous years. Aerial defoliation surveys have long been used by forest managers as an efficient and economical method to detect and appraise pest damage over large forest areas. Cumulative defoliation is an effective means to predict growth reduction and mortality caused by insects (Erdle and MacLean, 1999; MacLean et al., 2001). Therefore, our results are important in order to derive cumulative defoliation from aerial defoliation survey values for insects feeding on multiple age class of foliage. Cumulative defoliation values as estimated and presented in Table 3 can directly be used by pest managers and modelers for use in DSS for balsam fir sawfly and hemlock looper instead of calculating as in Eq. (1) (for spruce budworm). Since impacts caused by defoliation are directly related to amount of foliage removed by insects, the three impact severity classes of defoliation defined here reflect different defoliation-impact relationships that must be quantified in developing DSS for hemlock looper and balsam fir sawfly. Acknowledgements We thank Scott Payne and Hubert Crummey, Newfoundland Forest Service for providing annual defoliation survey data and helpful discussion. Funding for this project was provided by the Atlantic Canada Opportunities Agency Atlantic Innovation Fund project ‘‘Integrated research, development and commercialization of biological forest pest control products and application technologies’’. References Canadian Council of Forest Ministers, 2008. Forest insect national tables for areas of moderate to severe defoliation. [Online] URL: http://nfdp.ccfm.org/insects/ national_e.php (accessed 19.12.08). Dobesberger, E.J., 1989. A sequential decision plan for the management of the eastern hemlock looper. Lambdina fiscellaria fiscellaria (Lepidoptera: Geometridae), in Newfoundland. Can. J. For. Res. 19, 916–991.
J. Iqbal, D.A. MacLean / Forest Ecology and Management 259 (2010) 591–597 Dorais, L., Kettela, E.G., 1982. A review of entomological survey and assessment techniques used in regional spruce budworm, Choristoneura fumiferana (Clem.), surveys and in the assessment of operational spray programs. In: Report, Committee for Standardization of Survey and Assessment Techniques, Eastern Spruce Budworm Council, Quebec Department of Energy and Resources, QC, Canada. Erdle, T.A., MacLean, D.A., 1999. Stand growth model calibration for use in forest pest impact assessment. For. Chron. 75, 141–152. Fettes, J.J., 1950. Investigations of sampling techniques for population studies of the spruce budworm on balsam fir in Ontario. Can. For. Serv., For. Insect. Lab, Sault Ste. Marie, ON. Annu. Tech. Rep., vol. 4. pp. 163–401. Hennigar, C.R., MacLean, D.A., Porter, K.B., Quiring, D.T., 2007. Optimized harvest planning under alternative foliage-protection scenarios to reduce volume losses to spruce budworm. Can. J. For. Res. 37, 1755–1769. Hudak, J., LaFlamme, G., Meades, J.P., 1978. Deterioration of balsam fir damaged by the eastern hemlock looper in Newfoundland. Can. For. Serv., Nfld. For. Res. Cent., St. John’s, NL. Inf. Rep. N-X-157. Kleinschmidt, S., Baskerville, G.L., Solomon, D.S., 1980. Foliage weight distribution in upper crown of balsam fir. USDA For. Serv., Res. Pap. NE-455. MacLean, D.A., Ebert, P., 1999. The impact of hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) on balsam fir and spruce in New Brunswick. Canada. For. Ecol. Manage. 120, 77–87. MacLean, D.A., Lidstone, R.G., 1982. Defoliation by spruce budworm: estimation by ocular and shoot-count methods and variability among branches, trees and stands. Can. J. For. Res. 12, 582–594. MacLean, D.A., MacKinnon, W.E., 1996. Accuracy of aerial sketch-mapping estimates of spruce budworm defoliation in New Brunswick. Can. J. For. Res. 26, 2099–2108. MacLean, D.A., Porter, K.B., 1995. A DSS for budworm and forest management: maximizing protection benefits and forecasting inventories. In: Power, J.M., Strome, M., Daniel, T.C. (Eds.), Decision Support 2001, Toronto, ON, 12–16 September, 1994. American Society of Photogrammetry and Remote Sensing, Bethesda, MD, pp. 530–540. MacLean, D.A., Erdle, T.A., MacKinnon, W.E., Porter, K.B., Beaton, K.P., Cormier, G., Morehouse, S., Budd, M., 2001. The Spruce Budworm Decision Support System:
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forest protection planning to sustain long-term wood supply. Can. J. For. Res. 31, 1742–1757. Martineau, R., 1984. Insects Harmful to Forest Trees. Ministry of Supply and Services Canada, Ottawa, ON, Canada. Miller, C.A., Kettela, E.G., 1975. Aerial control operations against the spruce budworm in New Brunswick 1952–73. In: Prebble, M.L. (Ed.), Aerial Control of Forest Insects in Canada. Environ. Can., Ottawa, ON, Canada, pp. 94–112. Moreau, G., 2006. Past and present outbreaks of the balsam fir sawfly in western Newfoundland: an analytical review. For. Ecol. Manage. 221, 215–219. Moreau, G., Quiring, D.T., Eveleigh, E.S., Bauce, E., 2003. Advantages of a mixed diet: feeding on several foliar age classes increases the performance of a specialist insect herbivore. Oecologia 135, 391–399. Otvos, I.S., Clarke, L.J., Durling, D.S., 1979. A history of recorded eastern hemlock looper outbreaks in Newfoundland. Can. For. Serv., Nfld. For. Res. Cent., St. John’s, NL. Inf. Rep. N-X-179. Ostaff, D., Piene, H., Quiring, D., Moreau, G., Farrell, J., Scarr, T., 2006. Influence of pre-commercial thinning of balsam fir on defoliation by the balsam fir sawfly. For. Ecol. Manage. 223, 342–348. Parsons, K., Quiring, D., Piene, H., Farrell, J., 2003. Temporal patterns of balsam fir sawfly defoliation and growth loss in young balsam fir. For. Ecol. Manage. 184, 33–46. Parsons, K., Quiring, D., Piene, H., Moreau, G., 2005. Relationship between balsam fir sawfly density and defoliation in balsam fir. For. Ecol. Manage. 205, 325–331. Piene, H., Ostaff, D., Eveleigh, E., 2001. Growth loss and recovery following defoliation by the balsam fir sawfly in young, spaced balsam fir stands. Can. Entomol. 133, 675–686. Sanders, C.J., 1980. A summary of current techniques used for sampling spruce budworm populations and estimating defoliation in eastern Canada. Can. For. Serv., Great Lakes For. Res. Cent., Sault Ste. Marie, ON, Canada Inf. Rep. O-X-306. SPSS, 2007. Version 16.0.0. SPSS Inc., Chicago. Taylor, S.L., MacLean, D.A., 2008. Validation of spruce budworm outbreak history developed from aerial sketch-mapping of defoliation in New Brunswick. North. J. Appl. For. 25, 139–145.
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Estimating cumulative defoliation of balsam fir from hemlock looper and balsam fir sawfly using aerial defoliation survey in western Newfoundland, Canada Javed Iqbal *, David A. MacLean Faculty of Forestry and Environmental Management, University of New Brunswick, P.O. Box 4400, Fredericton, N.B., E3B 5A3 Canada
A R T I C L E I N F O
A B S T R A C T
Article history: Received 21 September 2009 Received in revised form 9 November 2009 Accepted 12 November 2009
Both hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) and balsam fir sawfly (Neodiprion abietis (Harris)) undergo periodic outbreaks in eastern Canada and cause significant growth and mortality losses to forests. Tree growth and mortality are closely related to cumulative defoliation estimates, which integrate annual defoliation over multiple years. Our objective was to determine a method to estimate cumulative defoliation of balsam fir (Abies balsamea [L.] Mill) due to these insects in western Newfoundland, using aerial defoliation survey data, as an essential input to modeling impacts for Decision Support Systems. Interpretation of aerial defoliation survey data for hemlock looper and balsam fir sawfly is problematic because both insects feed upon multiple age classes of foliage. Current-year (2008) aerial defoliation survey data were compared with ground estimates of defoliation by age class from 45 plots (450 trees and 395 mid-crown branch samples), representing a range of defoliation severity classes for each insect. Cumulative defoliation was calculated using defoliation per foliage age class, weighted by relative foliage mass for a given age of foliage. Three significantly different severity classes were defined based on cumulative defoliation values derived from aerial defoliation survey: (i) 1year moderate (30–70%) defoliation, (ii) 1-year severe (71–100%) defoliation with calculated cumulative defoliation values of 19 and 39%, respectively, for balsam fir sawfly, 21 and 34% respectively for hemlock looper; and (iii) 2–3 years of moderate–severe defoliation, with cumulative defoliation ranging between 59 and 64% for balsam fir sawfly and 49% for hemlock looper. Defoliation severity from aerial defoliation survey alone hence can be misleading if defoliation measurements are not converted to cumulative defoliation values. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Cumulative defoliation Decision Support System Balsam fir sawfly Hemlock looper Aerial defoliation survey
1. Introduction Balsam fir (Abies balsamea [L.] Mill) is a tree species vulnerable to defoliation by many different insects. Spruce budworm (Choristoneura fumiferana (Clem.)), balsam fir sawfly (Neodiprion abietis (Harris)), and hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) have been the most damaging defoliators of balsam fir in eastern Canada, with moderate–severe defoliation areas of 31 million, 522 000, and 858 000 ha, respectively, from 1975 to 2007 in Atlantic Canada (Canadian Council of Forest Ministers, 2008). Spruce budworm is the most widespread insect defoliator of balsam fir, but balsam fir sawfly and hemlock looper have both undergone periodic outbreaks in eastern Canada. Balsam fir sawfly has become a serious pest of young managed balsam fir stands in western Newfoundland, Canada, and the current outbreak, which began in
* Corresponding author. Present address: University of New Brunswick, Faculty of Forestry and Environmental Management, P.O. Box 4400, Fredericton, New Brunswick, E3B 5A3 Canada. Tel.: +1 506 453 4501; fax: +1 506 453 3538. E-mail address: [email protected] (J. Iqbal). 0378-1127/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2009.11.017
1991, is the longest ever recorded (Piene et al., 2001; Moreau, 2006). The long balsam fir sawfly outbreak duration has been attributed to extensive precommercial thinnings (Ostaff et al., 2006). Hemlock looper outbreaks have occurred in Newfoundland from 1910 to 1915, 1920 to 1926, 1929 to 1935, 1946 to 1955, 1959 to 1964, 1966 to 1972, 1984 to 1989 and 1995 to 2004 (Otvos et al., 1979; Canadian Council of Forest Ministers, 2008). Hemlock looper is of particular concern as severe defoliation of all age classes of foliage is very destructive, causing tree mortality after just 1 or 2 years of severe defoliation (Hudak et al., 1978; MacLean and Ebert, 1999). To assist insect and forest management decision-making, a spruce budworm Decision Support System (SBW-DSS) was developed by the Canadian Forest Service (MacLean and Porter, 1995). In the SBW-DSS, annual defoliation data obtained from aerial surveys and various projected defoliation scenarios are converted into cumulative 5-year defoliation. These estimates are used to model tree growth loss and mortality of stands in the inventory database of a Geographic Information System (GIS) (MacLean et al., 2001). The SBW-DSS helps forest managers predict budworm outbreak effects on forest structure and productivity, forecast forest growing stock and sustainable
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Fig. 1. Schematic representation of a balsam fir branch with (a) no defoliation; and after severe defoliation due to (b) spruce budworm, consuming current-year foliage, (c) balsam fir sawfly, feeding on 1 year and older foliage, and (d) hemlock looper, feeding on all age classes of foliage.
harvest levels, optimize insecticide protection programs, and use silviculture and harvest scheduling to restructure forest management to reduce future damage (Hennigar et al., 2007). In order to develop a comparable DSS for balsam fir sawfly and hemlock looper, an initial requirement is a method to determine cumulative defoliation, which integrates a sequence of annual foliage losses, for these insects. The measure of cumulative defoliation differs for spruce budworm, balsam fir sawfly and hemlock looper because of their different modes of feeding (Fig. 1): spruce budworm feed on current-year foliage (although ‘back-feeding’ on older age classes of foliage can occur, it is restricted to extremely high population levels when all currentyear foliages have already been consumed, and is rare), balsam fir sawfly feed on all age classes except current-year foliage (Martineau, 1984), while hemlock looper is a wasteful feeder of all age classes of foliage (Dobesberger, 1989). Aerial defoliation surveys are commonly used to assess annual defoliation over large areas, and are currently the only operational method to provide such data (MacLean and MacKinnon, 1996). Aerial defoliation survey data describe the intensity and spatial extent of defoliation based upon the characteristic reddish-brown coloration of host foliage resulting after feeding. The method depends upon the observer’s ability to recognize defoliation class and to identify locations (Dorais and Kettela, 1982). Given the mode of feeding of spruce budworm, annual aerial defoliation surveys provide a direct measure of damage to the current-year foliage only. Because balsam fir foliage is retained for about 5 years (>95% foliage naturally falls after 5 years, Piene et al., 2001), current defoliation does not gauge the cumulative impact of successive years of defoliation. Yearly cumulative defoliation (CD), which serves as an input to the SBW-DSS, is calculated (MacLean et al., 2001) from aerial defoliation survey sequences for a given area by weighting estimates of current defoliation (C) in year t by relative foliage
mass for that age of foliage, based on data for undefoliated balsam fir trees (Kleinschmidt et al., 1980): CDt ¼ 0:28C t þ 0:26C t1 þ 0:22C t2 þ 0:13t3 þ 0:08C t4 þ 0:03C t5
(1)
This model assumes that natural needle fall diminishes the proportion of foliage with age from 28% for current-year foliage to 3% for 5-year old foliage. A similar approach to estimate cumulative defoliation cannot be used for balsam fir sawfly and hemlock looper, because annual aerial defoliation survey data contain defoliation of all foliage age classes except current year (for balsam fir sawfly) or all foliage (for hemlock looper). Thus overlaying successive years of defoliation also becomes problematic for these insects. Our objectives in this study were to (i) quantify balsam fir defoliation per age class of foliage due to balsam fir sawfly and hemlock looper from plots, while relating it to aerial defoliation survey data, and (ii) determine cumulative defoliation values for a range of aerial defoliation survey severity classes, for use in modeling of balsam fir sawfly and hemlock looper impacts and development of DSS. 2. Methods 2.1. Aerial defoliation survey data Newfoundland and Labrador Department of Natural Resources conducts annual aerial defoliation surveys and records hemlock looper and balsam fir sawfly defoliation by species and severity level (nil, moderate 31–70%, or severe 71–100%) on sketch maps. Aerial defoliation surveys are conducted during a 1–3 week period after the completion of feeding (usually from mid-late August) using helicopters (Hubert Crummey, personal communication, September 2008). A distinct reddish-brown coloration of foliage
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ple years and defoliation levels, a total of six defoliation severity classes were distinguished for balsam fir sawfly and four classes for hemlock looper (Table 1), ranging from only 1 year of moderate to 3 successive years of severe defoliation. 2.2. Plot selection
Fig. 2. Map of hemlock looper and balsam fir sawfly defoliation in western Newfoundland during 2008. There are four (hemlock looper) and six (balsam fir sawfly) severity classes based on 2008 and previous years of defoliation. ‘M’ denotes moderate (31–70%) while ‘S’ represents severe (71–100%) defoliation. In case of multiple years of defoliation, previous years are represented first, e.g. ‘MS’ = moderate defoliation in 2007, and severe defoliation in 2008.
In September 2008, soon after the aerial defoliation survey and availability of digital sketch maps, a ground survey was conducted in each of the above 10 defined defoliation severity classes. Balsam fir stands that had been precommercially thinned (2500– 5000 trees/ha) and of intermediate age (25–40 years) were selected from the inventory data after an overlay using ArcGIS (ESRI) in each severity class for balsam fir sawfly. Similarly, mature and over-mature (>50 years) balsam fir stands were selected for hemlock looper. Five plots were established in each severity class starting from a predetermined, readily identifiable location. The first plot was located 50 m from the stand edge while four additional plots were located along a linear transect with each plot 50 m apart, if the defoliated area and stand size permitted. In total, 29 plots were established for balsam fir sawfly near the town of Deer Lake in western Newfoundland [498100 N, 578250 W], and 16 plots were established for hemlock looper in the northern peninsula, near the town of Plum Point [518100 N, 568550 W] (Fig. 2). 2.3. Field measurements
due to the desiccation of damaged needles (MacLean and Ebert, 1999) helps the observer judge the area and severity of defoliation. In other areas like New Brunswick, fixed-wing aircraft along flight lines 2–5 km apart are used (Miller and Kettela, 1975) for spruce budworm aerial defoliation surveys, and these have been found to be 82–85% correct in differentiating three defoliation classes 0–30, 31–70, and 71–100% defoliation (MacLean and MacKinnon, 1996; Taylor and MacLean, 2008). No measure of measurement accuracy is available for aerial surveys conducted with helicopters, but they can be assumed to be of higher accuracy based on low altitude, slow speed flights, and means of closer observation in case of doubt. Records from the sketch maps are digitized and stored in Arc/ Info GIS format. Data on spatial accuracy and transfer error rates are not available, but would be included in the overall aerial defoliation survey accuracy assessments reported above. All areas that sustained hemlock looper or balsam fir sawfly defoliation in 2008 on the island of Newfoundland were overlaid with defoliation maps for 2007 and 2006 using ArcView GIS 9.2 (Environmental Systems Research Institute (ESRI)) (Fig. 2), to assign multi-year (2006–2008) defoliation severity classes. Hence, while looking at annual defoliation for 2008, areas with multiple years of defoliation were also recorded. A total of 3 years of defoliation occurrence per site were noted for balsam fir sawfly and 2 years for hemlock looper, among 2008 defoliated areas. Considering multi-
In each plot, 10 dominant or co-dominant balsam fir trees that were closest to the centre of each prism plot (basal area factor 2 m2 ha1) were selected. Each tree was examined using binoculars and defoliation was visually estimated and recorded in six defoliation severity classes (0–10%, 11–20%, 21–40%, 41–60%, 61– 80% and 81–100%) for each age class of foliage (current, 1–5-year old foliage). Three trees were selected randomly from each plot and three branches were cut from different cardinal directions of the mid-crown of each tree using pole pruners. Defoliation of each age class of foliage was again visually estimated using the shoot-count method (developed by Fettes, 1950 and discussed in more detail by Sanders, 1980) and recorded in similar classes as described above. Mean defoliation per age class of foliage was calculated using the midpoints of defoliation classes (MacLean and Lidstone, 1982). Natural needle fall of balsam fir is taken into account in calculation of cumulative defoliation (Eq. (1)). To calculate cumulative defoliation of each aerial defoliation survey severity class for balsam fir sawfly and hemlock looper, the same form of Eq. (1) was used, but substituting defoliation in different years by defoliation per age class of foliage (f): CDt ¼ 0:2C f þ 0:26C f 1 þ 0:22 f 2 þ 0:13 f 3 þ 0:08 f 4 þ 0:03 f 5
(2)
Table 1 Defoliation severity classes based on sequences of 2006–2008 defoliation caused by balsam fir sawfly and hemlock looper in Newfoundland, determined from aerial survey data. Area and number of plots established are given for each defoliation severity class. Defoliation severity class
Balsam fir sawfly
Hemlock looper
Defoliation
1 2 3 4 5 6
2006
2007
2008
– – – – M S
– – M S S S
M S S S M S
Number of plots
Area (ha)
5 5 4 5 5 5
4363 5489 931 11,166 623 1558
Defoliation 2006
2007
2008
– – – –
– – M M
M S M S
M = moderate defoliation (30–70% of total tree foliage); S = severe defoliation (71–100% of total tree foliage).
Number of plots
Area (ha)
5 4 4 3
943 88 14 2
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2.4. Data analyses Both an independent-samples t-test as well as two-factor analysis of variance (ANOVA) were used to test whether mean defoliation differed significantly, with ANOVA factors (i) method of data collection (binocular-aided visual estimation for whole-trees, versus shoot-count defoliation estimation from cut branches), and (ii) foliage age class. One-way ANOVA was used to test for differences in mean defoliation per age class of foliage within a severity class. Where a significant effect was found, a post hoc analysis using the Games–Howell test was done, due to an obvious difference in population variance and unequal sample sizes. A similar analysis for differences between defoliation severity classes within a given insect (Table 1) was done using two-factor ANOVA. Significant differences in means for all tests was determined at the p = 0.05 level. Analyses were conducted using SPSS ver. 16.0.0 (SPSS, 2007). Mean values of defoliation per age class of foliage were used as input in Eq. (2) to calculate cumulative defoliation for each defoliation severity class. 3. Results For balsam fir sawfly, a t-test [t (2110) = 1.403, p = 0.16] as well as a two-factor ANOVA [F (11, 2111) = 104.3, p = 0.08] showed no significant differences between the whole-tree, binocular versus branch-level, shoot-count methods of defoliation estimation. On the other hand, for hemlock looper there were significant differences between whole-tree, binocular and branch-level, shoot-count methods [t (1150) = 2.064, p = 0.04; F (11,
1151) = 8.624, p = 0.03]. Hemlock looper defoliation measured using binoculars on trees was underestimated from that of the shoot-count method on branches for older foliage, i.e., 3, 4 and 5 years old, by 8.2, 13.7, and 19.2%, respectively. Due to this difference, only defoliation measured from branch-level samples (which are considered more accurate) was used in further analyses for hemlock looper. There was very little balsam fir sawfly defoliation (<14%) for current-year foliage in all severity classes (Fig. 3). 1–3-year old foliage were defoliated more (18–28% and 51–55% mean defoliation in severity classes 1 and 2, 1 year of moderate and severe defoliation, respectively) than 4–5-year old foliage (mean defoliation of 11–15% and 33–40% in severity classes 1 and 2, respectively). In case of multiple-year defoliation (severity classes 3–6), current-year foliage was defoliated least (8–14%). 1-Year old foliage showed mean defoliation of 69–79%, while 2-year and older foliage had the highest mean defoliation (79–89%). A higher variability (SE > 2) occurred for defoliation of 2–5-year old foliage in single year defoliation classes, i.e., 1 and 2 (Table 2). Total mean defoliation combining all defoliation severity classes was 17.5% and 40% for severity class 1 and 2, respectively, but ranged from 67 to 74% for severity classes 3 to 6. There were significant differences in defoliation among the six balsam fir sawfly defoliation severity classes, as determined from one-way ANOVA, and Games–Howell post hoc tests showed that current-year foliage differed significantly (p < 0.05) from all other foliage age classes (Table 2). For hemlock looper, severity classes 1 and 3 with moderate defoliation over 1 or 2 years showed similar 20–34% defoliation in all age classes of foliage, and relatively high variability (SE > 2) (Fig. 4). Analysis showed no significant differences in defoliation
Fig. 3. Mean SE defoliation per age class of foliage due to balsam fir sawfly for six defoliation severity classes (as described in Fig. 2).
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Table 2 Defoliation of balsam fir caused by balsam fir sawfly and hemlock looper, estimated per age class of foliage on sampled branches. Defoliation severity class
Balsam fir sawfly 1M 2S 3 MS 4 SS 5 MSM 6 SSS Mean Hemlock looper 1M 2S 3 MM 4 MS Mean
N
Mean defoliation (%) by foliage age (year) (S.E.) Current
1
2
588 570 456 570 570 570
6.1* 8.4* 8.5* 13.6* 12.2* 11.7*
27.1 (1.8) 52.5 (2.6) 79.2* (1.2) 78.0* (1.4) 69.1* (1.8) 77.4* (1.1)
26.8 54.2 86.1 83.5 79.9 87.5
10.1
63.9
69.6
69.7
270 216 216 162
22.4 26.8 20.6 36.7
26.6
32.9
(0.4) (0.6) (0.5) (1.1) (0.8) (0.7)
(3.2) (2.5) (2.5) (3.3)
24.1 34.4 24.2 48.9
(2.6) (3.0) (2.7) (3.5)
31.6
20.4 37.2 22.2 46.7
Mean 3
(2.2) (2.8) (0.9) (1.1) (1.6) (0.7)
(2.7) (2.8) (1.9) (3.4)
36.7
18.5 51.2 88.4 87.5 84.1 88.5
4 (2.3) (2.6) (0.6) (0.8) (1.1) (0.6)
14.8 40.3 87.9 87.1 81.8 88.9
66.8
64.4
24 (3.2) 45.4 (3.1) 21.0 (2.2) 56.3 (3.2)
30.3 55.9 20.4 65.6
43.1
47.9
5 (1.9) (2.7) (0.7) (0.9) (1.1) (0.5)
11.4 (1.5) 33.16 (2.2) 87.1 (0.9) 87.1 (1.1) 78.6 (1.5) 88.9 (0.5)
17.5z 40.0z 72.9 72.8 67.6 73.8
(3.5) (3.7) (2.4) (3.1)
33.8 60.1 24.2 73.7
25.8 43.4z 22.1 54.6z
(4.0) (4.5) (2.0) (3.4)
M = moderate defoliation (30–70% of total tree foliage); S = severe defoliation (71–100% of total tree foliage). A sequence of M and S indicates annual defoliation levels over multiple years, with the last value showing severity in the latest year; e.g. MS = 1 year of moderate defoliation followed by 1 year severe defoliation. N = number of trees and/or branches measured. * Statistically different mean defoliation (Games–Howell test) within a severity class (row) from other age classes at p 0.05 following a significant 1-way ANOVA. z Statistically different mean defoliation of a severity class from the other severity classes for the same insect at p 0.05 following a significant 2-factor ANOVA.
per age class of foliage among the four defoliation severity classes (Table 2). For hemlock looper severity classes 2 and 4, where plots were defoliated severely over 1 or 2 years, a gradient of increasing defoliation occurred from current-year (26.8% and 36.7% mean defoliation in severity classes 2 and 4, respectively) to 5-year old foliage (60.1% and 73.7%, respectively). Older age classes (4 and 5 years) were defoliated to a much lower extent (20–34%) in moderately compared to severely defoliated areas (55–74%). Total mean defoliation combining all age classes was 22–26% for severity classes 1 and 3, versus 43% and 55% for classes 2 and 4, respectively. A two-factor ANOVA for differences in defoliation per age class of foliage between the defoliation severity classes showed two significant groupings for each of hemlock looper (severity classes 2 and 4, with total mean defoliation over all age classes of 43% and 55%) and balsam fir sawfly (severity classes 1 and 2 with 17% and 40%). Three homogeneous subsets based on Tukey’s HSD were
revealed for each of balsam fir sawfly and hemlock looper. After calculation of cumulative defoliation using Eq. (2) (Table 3), three similar homogeneous subsets were distinguished for defoliation of each insect: Group A with cumulative defoliation <30%, Group B 31–40%, and the most severe Group C with cumulative defoliation >40%. 4. Discussion Cumulative defoliation classes were quantitatively defined for use with annual aerial survey data for hemlock looper and balsam fir sawfly in western Newfoundland. These classes integrate annual defoliation estimates, which are necessary components of DSS for managing forests impacted by these insects. Defoliation severity from aerial defoliation survey alone can be misleading as seen in the results, if defoliation measurements are not converted
Fig. 4. Mean SE defoliation per age class of foliage due to hemlock looper for four defoliation severity classes (as described in Fig. 2).
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Table 3 Calculated cumulative defoliation for each defoliation severity class determined from aerial defoliation survey data using Eq. (2). Defoliation severity class
1 2 3 4 5 6
M S MSb SSc MSM SSS
Balsam fir sawfly
Hemlock looper
Cumulative defoliation (%)
Impact severity class
19 39 63 63 59 64
A B C C C C
a
Cumulative defoliation (%)
Impact severity classa
21 34 25 49
A B A C
M = moderate defoliation (30–70% of total tree foliage); S = severe defoliation (71–100% of total tree foliage). A sequence of M and S indicates annual defoliation levels over multiple years with the last value showing severity in the latest year; e.g. MS = 1 year of moderate defoliation followed by 1 year severe defoliation. a Assigned based on homogeneous subsets after post hoc analysis as described in Table 2. Generalized class ranges of <30% (A), 31–40% (B) and >40% (C) cumulative defoliation apply. b MM in the case of hemlock looper. c MS in the case of hemlock looper.
to cumulative defoliation values for insects like balsam fir sawfly and hemlock looper that feed on multiple ages of foliage. Significant differences between defoliation measured by different methods for hemlock looper (i.e., binocular-aided visual estimation vs. shoot-count visual estimation on individual sampled shoots per age class on cut mid-crown branches) were presumably due to the fact that older foliage was obscured from the observer due to younger foliage and height of trees (mature and over-mature stands were targeted for hemlock looper). MacLean and Ebert (1999) previously noted that it is difficult to estimate defoliation of more than three age classes of foliage using binoculars, because newer foliage obscures older age classes. Balsam fir sawfly defoliation measured using binocular-aided visual estimates was not significantly different from that estimated on sampled shoots on mid-crown branches on intermediate–aged, thinned balsam 7–10 m in height. Measurement of defoliation on branches using the shoot-count method or larval sampling is more accurate (Parsons et al., 2005), but is not practically feasible on a large scale due to time and resources involved. Stands that sustained moderate or severe balsam fir sawfly defoliation for only a single year (Fig. 3, severity classes 1 and 2) showed that 1–3-year old foliage age classes were defoliated the most (18–28% and 52–55% for severity class 1 and 2, respectively), 4- or 5-year old foliage less (11–15% and 33–41%), and currentyear foliage was defoliated the least (6–9%). These results are similar to earlier studies that stated that balsam fir sawfly larvae consume more 1–3-year old foliage than current or older foliage (Parsons et al., 2003; Moreau et al., 2003). The oldest age classes of foliage (4 and 5 years old) were defoliated more (78–89%) in stands that sustained more than 1 year of defoliation—i.e., defoliation severity classes 3–6 (Fig. 3). Since defoliation occurred for 2 or 3 years, older age classes of foliage were fed upon after most 1–3year old foliage had been consumed. For balsam fir sawfly, there was no significant difference in cumulative defoliation values for multiple-year defoliation severity classes, with combinations of 2 or 3 years of moderate or severe defoliation all resulting in 59–64% cumulative defoliation (Table 3). This might be attributed to limitations of aerial defoliation surveys in detecting level of defoliation for insects that feed on multiple age classes of foliage. However, it also may reflect the inherent pattern of balsam fir sawfly feeding, with 1 year of feeding consuming 18–27% (moderately defoliated) or 51– 55 (severely defoliated) of 1–3-year old foliage, a second year increasing 4–5-year old foliage to 78–89%, and only 8–14% of current-year foliage consumed. The fact that in all cases 86–94% of current-year foliage remains on the trees definitely influences aerial survey values. Our results showing that hemlock looper defoliation was similar on all age classes of foliage (Fig. 4) were comparable to earlier studies (e.g., Dobesberger, 1989). Total mean defoliation
over all age class of foliage for severity class 3 (22.1%) logically should be higher than that of severity class 1 (25.8%). As discussed with balsam fir sawfly, the limitations in measuring defoliation by insects that feed on multiple ages of foliage also apply to hemlock looper. For spruce budworm, where defoliation repeatedly (year after year) occurs on current-year foliage, defoliated areas on trees are readily visible and hence it is relatively easy to estimate defoliation levels. For both balsam fir sawfly and hemlock looper, defoliation on older age classes is hidden from an observer in a helicopter or on the ground by current-year undefoliated foliage, possibly contributing to underestimation of defoliation. Also since tree crowns appear thinned and devoid of foliage, an overestimation of currentyear defoliation may occur in areas already defoliated in previous years. Aerial defoliation surveys have long been used by forest managers as an efficient and economical method to detect and appraise pest damage over large forest areas. Cumulative defoliation is an effective means to predict growth reduction and mortality caused by insects (Erdle and MacLean, 1999; MacLean et al., 2001). Therefore, our results are important in order to derive cumulative defoliation from aerial defoliation survey values for insects feeding on multiple age class of foliage. Cumulative defoliation values as estimated and presented in Table 3 can directly be used by pest managers and modelers for use in DSS for balsam fir sawfly and hemlock looper instead of calculating as in Eq. (1) (for spruce budworm). Since impacts caused by defoliation are directly related to amount of foliage removed by insects, the three impact severity classes of defoliation defined here reflect different defoliation-impact relationships that must be quantified in developing DSS for hemlock looper and balsam fir sawfly. Acknowledgements We thank Scott Payne and Hubert Crummey, Newfoundland Forest Service for providing annual defoliation survey data and helpful discussion. Funding for this project was provided by the Atlantic Canada Opportunities Agency Atlantic Innovation Fund project ‘‘Integrated research, development and commercialization of biological forest pest control products and application technologies’’. References Canadian Council of Forest Ministers, 2008. Forest insect national tables for areas of moderate to severe defoliation. [Online] URL: http://nfdp.ccfm.org/insects/ national_e.php (accessed 19.12.08). Dobesberger, E.J., 1989. A sequential decision plan for the management of the eastern hemlock looper. Lambdina fiscellaria fiscellaria (Lepidoptera: Geometridae), in Newfoundland. Can. J. For. Res. 19, 916–991.
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