Fig 2 - uploaded by Alvaro Fuentealba
Content may be subject to copyright.
Mean (±2 SEM) masses of female and male spruce budworm ( Choristoneura fumiferana ) pupae according to drainage class in balsam fir ( Abies balsamea ). Nitrogen (C1) corresponds to balsam fir foliar N concentrations in the first collection. Bars with the same letter do not differ significantly at P < 0.05 according to Duncan ’ s multiple range test.
Source publication
Thinning has frequently been recommended for reducing damage caused by spruce budworm (Choristoneura fumiferana (Clemens)). It is believed that this technique enhances the mechanisms of resistance of trees (antibiosis and tolerance) to this insect. However, various research projects that have focused upon effects of this silvicultural tool on host...
Contexts in source publication
Context 1
... individu- ally, these included egg mass, average number of eggs laid by females, female mass, and overwintering larval survival (Table 8). In contrast, thinning intensity did not affect winter biology of insects reared on white spruce (Table 4B) and black spruce (Wilks ’ lambda: F (thinning) = 2.81, df = 10,4, P = 0.165). Furthermore, drainage class did not have a significant effect on winter biology of budworm progeny that had been reared on balsam fir and white spruce (Table 4), and there were no significant differences in winter biology of budworm progeny between black spruce and balsam fir on hydric sites (Wilks ’ lambda: F (species) = 1.07, df = 5,2, P = 0.548). Heavy thinning (40% of stand basal area removed) increased the amount of current-year foliage produced and the amount of current-year foliage remaining in balsam fir and white spruce after defoliation (Fig. 3). This pattern shows that heavy thinning (40%) increased host tree tolerance compared with light thinning (25% of stand basal area removed) and the unthinned controls 3 years after treatment. These results confirm, in part, findings reported by Bauce (1996) and Bauce et al. (2001), who found that thinning (25%) increased balsam fir resistance on well-drained sites by increasing foliar production and foliar concentrations of certain chemical compounds toxic to the budworm. In the current study, however, tree tolerance was increased in all drainage classes by using heavy thinning (40%), suggesting that heavy intensities (40%) are more appropriate for reducing budworm damage than are light intensities (25%). In fact, balsam fir and white spruce trees coming from heavily thinned stands had 73.6% and 70.7% more residual foliage (Fig. 3), respectively, available for photosynthesis (photosynthetic capacity) than those trees coming from control stands, even when insect population levels at the end of the development were relatively high (9 – 11 larvae per branch). Furthermore, lightly thinned (25%) and control stands exhibited severe defoliation (>75% of current-year foliage destroyed) (Fig. 4). This level of damage can result in reduction of volume growth by up to 20% after 1 year (Piene 1980) and greater tree mortality after 4 – 5 consecutive years of severe defoliation (Batzer 1973, Blais 1979). Heavily thinned stands (40%), in contrast, showed moderate levels of defoliation (<53%). Because volume growth is positively correlated with tree photosynthetic capacity, heavy thinning (40%) may attenuate wood losses at- tributed to tree mortality and volume growth reductions by diminishing defoliation (Fig. 4) and increasing the amount of foliage produced (Fig. 3). The lack of effectiveness of light thinning in increasing host tree tolerance may be explained by the high overall survival rate of spruce budworm (51.11%) found in this study compared with that reported (26.25%) by Bauce (1996) 2 years after treatment. Although the amount of current-year foliage destroyed can be affected by several factors, insect population levels are the most important (Blais 1979). Given that neither thinning nor drainage quality affected insect survival, it is difficult to explain the increase of this parameter. Climatic conditions may provide some clue to understanding the high survival rate of spruce budworm. It has been suggested that feeding rate and larval activity decrease with low temperatures and wet conditions (Greenbank 1956; Blais 1958), but the opposite conditions, such as those found in 2006 (Table 9), may stimulate insect feeding (Rouault et al. 2006) and reduce natural enemy performance (Gray 2008). According to Mattson et al. (1991), high temperatures can increase spruce budworm developmental rates and survival of large larvae. Consequently, climatic conditions may have increased spruce budworm survival and, therefore, the amount of foliage destroyed. Light thinning (25%) was capable of increasing balsam fir tolerance on hydric sites and white spruce tolerance on subhygric sites (Fig. 3), which demonstrates the importance of this variable in determining host tree resistance. Balsam fir (Hix et al. 1987) and white spruce (Wang and Klinka 1995) are best adapted to grow in well-drained sites, which provide adequate nutrients and moisture to support vigorous tree growth. This enhances the ability of these species to with- stand and recover from defoliation (Bélanger et al. 1995). This adaptation of balsam fir and white spruce may explain the respective increases in foliage produced in hydric and subhygric sites that are caused by thinning, since this technique reduced the number of trees competing for limited nutrients in poorly drained sites, increasing foliage produced and, therefore, balsam fir and white spruce tolerance (Fig. 3). The results also show that thinning increased budworm performance. Pupal mass was favoured by the treatments in balsam fir. In fact, pupae reared on trees coming from heavily thinned stands (40%) exhibited the greatest mass (Fig. 2). These results could be explained by the high content in foliar N and P found in balsam fir growing in thinned stands (Fig. 2; Table 6). Nitrogen is very important for budworm performance, since larvae fed on a food source with sufficient N have higher growth rates and shorter developmental times (Mattson et al. 1991; Bidon 1993; Carisey and Bauce 1997), while P has been positively correlated with increased pupal mass (Schmitt et al. 1983; Fuentealba and Bauce 2012 a ). Furthermore, mean egg mass, winter survival, and female mass were also favoured by thinning (40%) (Table 8). Spruce budworm overwintering survival relies on the nutritional reserves provided by the female parent (Carisey and Bauce 2002); therefore, the increase of foliar nutrients produced by thinning may have increased the quantity or quality of these reserves, which are very important because they represent the sole energy available to the progeny for embryogenesis and maintenance prior to hatching (Rossiter 1991) and can affect larval survival, development, and behaviour (Rossiter 1991; Carisey and Bauce 2002; Fuentealba and Bauce 2012 b ). Nevertheless, the positive effect of thinning on insect performance did not result in increased defoliation because the treatment also increased foliar production, offsetting the augmentation in foliage destroyed. This contrasting effect of thinning has also been reported by Bauce et al. (2001) in a balsam fir – spruce budworm system and by Moreau and Quiring (2011) in a balsam fir – Neodiprion abietis system. The former authors found that the positive effect of thinning on budworm performance disappeared with the passage of time, resulting in increased tree resistance to the insect for up to 8 years (Bauce et al. 2001). We may expect, therefore, host chemistry to stabilize in subsequent years, thereby ceas- ing favourable conditions to insect performance and increasing tree resistance. Finally, the lack of significant differences between balsam fir and black spruce growth and vigour on drainage class 5 confirms that thinning can be used to increase balsam fir resistance on hydric sites. One year after treatment, black spruce exhibited greater current-year foliar production and residual foliage than balsam fir on drainage class 5 (Fuentealba and Bauce 2012 a ), but this pattern is reversed 3 years after treatment. As for insect performance, there were no significant differences between insects reared on these species, but insects reared on balsam fir destroyed 35.1% more current- year foliage than those reared on black spruce. This result suggests that foliage of balsam fir growing on hydric sites is not an optimal source of food for spruce budworm, compel- ling the insect to increase its consumption rate. The high concentration of Ca in balsam fir foliage (Table 6) might have interfered with the uptake of micronutrients (Mattson et al. 1991), such as Fe and Zn, which are known to be important catalysts of several enzyme reactions (Mattson and Scriber 1987), forcing the insect to consume more food to meet its nutritional requirements. Furthermore, high concentrations of monoterpenes such as a -pinene and b -pinene in balsam fir foliage (Fig. 5) did not affect insect performance, implying that increases in total monoterpene concentrations do not necessarily render trees more resistant to budworm attack; rather, the augmentation of specific monoterpene concentrations increases tree resistance. Monoterpenes such as a -pinene and b -pinene are well-known oviposition stimulants for spruce budworm and do not cause toxic effects on the larvae (Städler 1974; Chen et al. 2002; Grant et al. 2007). Thinning (40%) increased balsam fir and white spruce tolerance to spruce budworm 3 years after the treatment was conducted by increasing foliar production and, therefore, tree resistance. This response occurred despite the fact that the treatment favoured the performance of spruce budworm that were reared on balsam fir by allowing insects access to a richer source of food. The effect of thinning intensity on tree tolerance and insect performance varied according to drainage quality, with the effect being more positive on well- drained sites because trees growing in these sites produced more foliage, thereby allowing them to cope more effectively with attacks by this defoliator. These results suggest that thinning (40%) may be used as preventive control measure during the low-density phase of the budworm population. However, the number of years that the effectiveness of this measure lasts remains to be documented. Black spruce was not significantly affected by thinning, but individuals of this species that were growing in thinned stands started to exhibit, 3 years after treatment, a trend to- wards producing more foliage than those growing in un- thinned stands. This response suggested that the species has started to positively react to thinning. Consequently, we may expect a significant increase in black ...
Context 2
... (Table 8). In contrast, thinning intensity did not affect winter biology of insects reared on white spruce (Table 4B) and black spruce (Wilks ’ lambda: F (thinning) = 2.81, df = 10,4, P = 0.165). Furthermore, drainage class did not have a significant effect on winter biology of budworm progeny that had been reared on balsam fir and white spruce (Table 4), and there were no significant differences in winter biology of budworm progeny between black spruce and balsam fir on hydric sites (Wilks ’ lambda: F (species) = 1.07, df = 5,2, P = 0.548). Heavy thinning (40% of stand basal area removed) increased the amount of current-year foliage produced and the amount of current-year foliage remaining in balsam fir and white spruce after defoliation (Fig. 3). This pattern shows that heavy thinning (40%) increased host tree tolerance compared with light thinning (25% of stand basal area removed) and the unthinned controls 3 years after treatment. These results confirm, in part, findings reported by Bauce (1996) and Bauce et al. (2001), who found that thinning (25%) increased balsam fir resistance on well-drained sites by increasing foliar production and foliar concentrations of certain chemical compounds toxic to the budworm. In the current study, however, tree tolerance was increased in all drainage classes by using heavy thinning (40%), suggesting that heavy intensities (40%) are more appropriate for reducing budworm damage than are light intensities (25%). In fact, balsam fir and white spruce trees coming from heavily thinned stands had 73.6% and 70.7% more residual foliage (Fig. 3), respectively, available for photosynthesis (photosynthetic capacity) than those trees coming from control stands, even when insect population levels at the end of the development were relatively high (9 – 11 larvae per branch). Furthermore, lightly thinned (25%) and control stands exhibited severe defoliation (>75% of current-year foliage destroyed) (Fig. 4). This level of damage can result in reduction of volume growth by up to 20% after 1 year (Piene 1980) and greater tree mortality after 4 – 5 consecutive years of severe defoliation (Batzer 1973, Blais 1979). Heavily thinned stands (40%), in contrast, showed moderate levels of defoliation (<53%). Because volume growth is positively correlated with tree photosynthetic capacity, heavy thinning (40%) may attenuate wood losses at- tributed to tree mortality and volume growth reductions by diminishing defoliation (Fig. 4) and increasing the amount of foliage produced (Fig. 3). The lack of effectiveness of light thinning in increasing host tree tolerance may be explained by the high overall survival rate of spruce budworm (51.11%) found in this study compared with that reported (26.25%) by Bauce (1996) 2 years after treatment. Although the amount of current-year foliage destroyed can be affected by several factors, insect population levels are the most important (Blais 1979). Given that neither thinning nor drainage quality affected insect survival, it is difficult to explain the increase of this parameter. Climatic conditions may provide some clue to understanding the high survival rate of spruce budworm. It has been suggested that feeding rate and larval activity decrease with low temperatures and wet conditions (Greenbank 1956; Blais 1958), but the opposite conditions, such as those found in 2006 (Table 9), may stimulate insect feeding (Rouault et al. 2006) and reduce natural enemy performance (Gray 2008). According to Mattson et al. (1991), high temperatures can increase spruce budworm developmental rates and survival of large larvae. Consequently, climatic conditions may have increased spruce budworm survival and, therefore, the amount of foliage destroyed. Light thinning (25%) was capable of increasing balsam fir tolerance on hydric sites and white spruce tolerance on subhygric sites (Fig. 3), which demonstrates the importance of this variable in determining host tree resistance. Balsam fir (Hix et al. 1987) and white spruce (Wang and Klinka 1995) are best adapted to grow in well-drained sites, which provide adequate nutrients and moisture to support vigorous tree growth. This enhances the ability of these species to with- stand and recover from defoliation (Bélanger et al. 1995). This adaptation of balsam fir and white spruce may explain the respective increases in foliage produced in hydric and subhygric sites that are caused by thinning, since this technique reduced the number of trees competing for limited nutrients in poorly drained sites, increasing foliage produced and, therefore, balsam fir and white spruce tolerance (Fig. 3). The results also show that thinning increased budworm performance. Pupal mass was favoured by the treatments in balsam fir. In fact, pupae reared on trees coming from heavily thinned stands (40%) exhibited the greatest mass (Fig. 2). These results could be explained by the high content in foliar N and P found in balsam fir growing in thinned stands (Fig. 2; Table 6). Nitrogen is very important for budworm performance, since larvae fed on a food source with sufficient N have higher growth rates and shorter developmental times (Mattson et al. 1991; Bidon 1993; Carisey and Bauce 1997), while P has been positively correlated with increased pupal mass (Schmitt et al. 1983; Fuentealba and Bauce 2012 a ). Furthermore, mean egg mass, winter survival, and female mass were also favoured by thinning (40%) (Table 8). Spruce budworm overwintering survival relies on the nutritional reserves provided by the female parent (Carisey and Bauce 2002); therefore, the increase of foliar nutrients produced by thinning may have increased the quantity or quality of these reserves, which are very important because they represent the sole energy available to the progeny for embryogenesis and maintenance prior to hatching (Rossiter 1991) and can affect larval survival, development, and behaviour (Rossiter 1991; Carisey and Bauce 2002; Fuentealba and Bauce 2012 b ). Nevertheless, the positive effect of thinning on insect performance did not result in increased defoliation because the treatment also increased foliar production, offsetting the augmentation in foliage destroyed. This contrasting effect of thinning has also been reported by Bauce et al. (2001) in a balsam fir – spruce budworm system and by Moreau and Quiring (2011) in a balsam fir – Neodiprion abietis system. The former authors found that the positive effect of thinning on budworm performance disappeared with the passage of time, resulting in increased tree resistance to the insect for up to 8 years (Bauce et al. 2001). We may expect, therefore, host chemistry to stabilize in subsequent years, thereby ceas- ing favourable conditions to insect performance and increasing tree resistance. Finally, the lack of significant differences between balsam fir and black spruce growth and vigour on drainage class 5 confirms that thinning can be used to increase balsam fir resistance on hydric sites. One year after treatment, black spruce exhibited greater current-year foliar production and residual foliage than balsam fir on drainage class 5 (Fuentealba and Bauce 2012 a ), but this pattern is reversed 3 years after treatment. As for insect performance, there were no significant differences between insects reared on these species, but insects reared on balsam fir destroyed 35.1% more current- year foliage than those reared on black spruce. This result suggests that foliage of balsam fir growing on hydric sites is not an optimal source of food for spruce budworm, compel- ling the insect to increase its consumption rate. The high concentration of Ca in balsam fir foliage (Table 6) might have interfered with the uptake of micronutrients (Mattson et al. 1991), such as Fe and Zn, which are known to be important catalysts of several enzyme reactions (Mattson and Scriber 1987), forcing the insect to consume more food to meet its nutritional requirements. Furthermore, high concentrations of monoterpenes such as a -pinene and b -pinene in balsam fir foliage (Fig. 5) did not affect insect performance, implying that increases in total monoterpene concentrations do not necessarily render trees more resistant to budworm attack; rather, the augmentation of specific monoterpene concentrations increases tree resistance. Monoterpenes such as a -pinene and b -pinene are well-known oviposition stimulants for spruce budworm and do not cause toxic effects on the larvae (Städler 1974; Chen et al. 2002; Grant et al. 2007). Thinning (40%) increased balsam fir and white spruce tolerance to spruce budworm 3 years after the treatment was conducted by increasing foliar production and, therefore, tree resistance. This response occurred despite the fact that the treatment favoured the performance of spruce budworm that were reared on balsam fir by allowing insects access to a richer source of food. The effect of thinning intensity on tree tolerance and insect performance varied according to drainage quality, with the effect being more positive on well- drained sites because trees growing in these sites produced more foliage, thereby allowing them to cope more effectively with attacks by this defoliator. These results suggest that thinning (40%) may be used as preventive control measure during the low-density phase of the budworm population. However, the number of years that the effectiveness of this measure lasts remains to be documented. Black spruce was not significantly affected by thinning, but individuals of this species that were growing in thinned stands started to exhibit, 3 years after treatment, a trend to- wards producing more foliage than those growing in un- thinned stands. This response suggested that the species has started to positively react to thinning. Consequently, we may expect a significant increase in black spruce resistance in the future. Finally, forest managers can use these results as guide- lines for planning thinning and B. ...
Context 3
... variables were affected by the factors studied ( Table 1). Duncan ’ s test was used for comparison of means (PROC GLM; SAS Institute Inc. 2003). Thinning intensity affected the overall suite of performance indicators for insects reared on balsam fir (Table 4A); indi- vidually, male mass ( F = 26.87, df = 2,18, P < 0.0001) and female mass ( F = 44.33, df = 2,18, P < 0.0001) were significantly affected by thinning intensity. Mean masses for both males and females were higher when 40% of stand basal area was removed compared with the other treatments (Fig. 2). Insect survival ( F = 2.49, df = 2,18, P = 0.111) and frass production ( F = 1.05, df = 2,18, P = 0.372) were not affected by the treatment. Insect survival was relatively high (9 – 11 larvae per branch). In contrast, thinning intensity did not influence the overall performance of insects reared on white spruce (Table 4B) and black spruce (Wilks ’ lambda: F thinning = 3.10, df = 12,2, P = 0.270). In contrast with thinning intensity, drainage class did not directly affect spruce budworm performance on balsam fir and white spruce (Table 4). Finally, there were no differences in budworm performance between insects reared on balsam fir and black spruce on hydric sites (Wilks ’ lambda: F thinning = 1.23, df = 12,2, P = 0.532). MANOVA of data for balsam fir and white spruce showed that drainage class and thinning intensity had a significant effect on host tree growth and vigour (Table 4). In contrast, growth and vigour were not affected by thinning intensity in black spruce (Wilks ’ lambda: F thinning = 7.60, df = 12,2, P = 0.122). Furthermore, there were no significant differences in growth and vigour between balsam fir and black spruce on hydric sites (Wilks ’ lambda: F species = 17.55, df = 6,1, P = 0.181). Balsam fir growing on thinned stands exhibited higher quantities of total current-year foliage produced (AFP) ( F = 4.77, df = 2,16, P = 0.024) and current-year foliage remaining (ARF) ( F = 15.40, df = 2,16, P = 0.0002) than those growing on unthinned stands after budworm defoliation. The same response was observed on white spruce for AFP ( F = 7.09, df = 2,9, P = 0.014) and ARF ( F = 12.82, df = 2,9, P = 0.002) (Fig. 3). Likewise, balsam fir ( F = 11.98, df = 2,16, P = 0.0007) and white spruce ( F = 7.06, df = 2,9, P = 0.014) individuals growing in heavily thinned stands (40% of stand basal area removed) exhibited the lowest defoliation percentage (Fig. 4). Drainage class had a significant overall effect on balsam fir performance based on the amount of current-year foliage that had been destroyed (AFD) (Fig. 3) and on defoliation effects caused by budworm (Fig. 4). Trees growing on drainage class 3 had the greatest DBH ( F = 34.63, df = 3,11, P < 0.0001) and AFD ( F = 5.11, df = 3,11, P = 0.017) com- pared with those growing on the other drainage classes. As for white spruce, drainage class had a significant effect on DBH ( F = 6.98, df = 2,9, P = 0.015) and AFD ( F = 15.11, df = 2,9, P = 0.001). White spruce individuals coming from drainage class 3 showed greater DBH and AFD than individuals coming from the other drainage classes. Chemical analysis indicated that balsam fir monoterpene concentrations in the first foliar collection were affected by drainage class 3 years after the treatment had been conducted (Table 4A), more specifically bornyl acetate, camphene, and a -pinene (Table 5). Concentrations of bornyl acetate and camphene were higher on drainage class 5, whereas the concentration of a -pinene was higher on drainage class 3 (Table 5). In contrast with the first collection, concentrations of monoterpenes in the second collection were not affected by thinning or drainage (Table 4A). Although thinning did not significantly affect total monoterpene concentrations in balsam fir, we observed that trees from thinned stands had 15% less bornyl acetate and 16% less camphene than trees from unthinned stands in the first foliage collection. Concentrations of monoterpenes in white spruce foliage were affected by neither treatment nor drainage class in both collections (Table 4B). As for black spruce, thinning did not significantly affect monoterpene concentrations in the first collection on hydric sites (Wilks ’ lambda: F (thinning effect on monoterpenes stimulants (G1)) = 2.99, df = 10,4, P = 0.151; F (thinning effect on toxic monoterpenes (G2)) = 0.98, df = 10,4, P = 0.560). The same result was observed in the second collection (Wilks ’ lambda: F (thinning effect on stimulant monoterpenes (G1)) = 2.99, df = 10,4, P = 0.151; F (thinning effect on toxic monoterpenes (G2)) = 0.98, df = 10,4, P = 0.560), but there were significant differences between black spruce and balsam fir in terms of monoterpene concentrations that had been classed in the oviposition stimulant group for both collections on drainage class 5 (Wilks ’ lambda: F (species effect on stimulant monoterpenes collection 1 (C1)) = 41.11, df = 5,2, P = 0.024; F (species effect on stimulant monoterpenes collection 2 (C2)) = 106.98, df = 5,2, P = 0.009) (Fig. 5). Drainage class influenced foliar nutrient concentrations of balsam fir during the first and second collections (Table 4A). Concentrations of foliar N and P in the first collection (Table 5), and concentrations of P in the second collection increased as drainage quality improved (Table 6), whereas the opposite pattern was observed for Ca in the first collection (Table 5). Thinning also increased foliar N and P and de- creased Ca in the first collection (Table 6), whereas no ...
Citations
... However, the antagonistic effect of tannins on Btk efficacy also seems to be affected by the concentrations of both tannin and Btk toxin (Bauce et al. 2006). Seasonal (Fuentealba and Bauce 2012a, 2012b, 2012c and yearly (Mattson et al. 1991;Bauce and Fuentealba 2013) variations in tannin concentrations are observed in white spruce, which may affect the interaction between these secondary compounds and Btk toxins. Furthermore, in the present study, we used a moderate dosage Btk formulation (30 BIU/ha) because it has been shown that high dosage Btk formulations (50 BIU/ha) do not enhance Btk lethal effects ). ...
Efficacy of commercial formulations of Bacillus thuringiensis ssp. kurstaki (Btk) against spruce budworm Choristoneura fumiferana in black spruce (Picea mariana (Mill.) BSP), white spruce (P. glauca (Moench) Voss) and balsam fir (Abies balsamea (L.) Mill.) was investigated in Québec’s Côte-Nord region. As expected, larval mortality was higher in Btk-treated plots (80.26 ± 2.34 %) than in control plots (66.32 ± 2.80 %). There were no differences in larval mortality among the three host tree species tested. Btk was most efficient in reducing spruce budworm defoliation when applied to black spruce and white spruce trees. Black spruce and white spruce exhibited lower final defoliation in Btk-treated plots than balsam fir. Btk applications produced a reduction in defoliation of 36 % in balsam fir, 44 % in white spruce and 41 % in black spruce. Control plots exhibited about 35 % higher amount of current-year foliage destroyed (AFD) and 56 % lower amount of current-year foliage remaining (ARF) than Btk-treated plots, whereas no differences in the amount of current-year foliage produced (AFP) were observed among host tree species. Black spruce trees showed the lowest AFD. Although not statistically significant, black spruce also showed the highest ARF. Our results suggest that Btk application is more efficient in protecting against spruce budworm damage when it is applied to spruce species than it is to balsam fir. It appears that the observed inter-specific differences in host tree foliage protection might be related to interactions between Btk, host tree foliage, and larval feeding behaviour.
... Manipulation of forest habitats using silviculture is repeatedly proposed as an intuitively appealing approach for managing defoliating insects because it may be effective, long-lasting, inexpensive and has a low environmental impact (Muzika & Liebhold, 2000). For example, thinning is suggested to reduce damage caused by spruce budworm Choristoneura fumiferana (Clemens), (Crook et al., 1979;Bauce, 1996;Bauce et al., 2001;Fuentealba & Bauce, 2012a) and western spruce budworm C. occidentalis Freeman (Mason et al., 1992). Fuentealba and Bauce (2012b) suggest that thinning might reduce some negative impacts of the spruce budworm up to 3 years after treatment through an increase of foliar production. ...
Silvicultural treatments are suggested as an option for controlling insect defoliators, although the effects of treatment on parasitism remain widely unknown. Therefore, in the present study, the influence of partial cutting on hemlock looper Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) parasitism is studied by comparing two cutting intensities (25% and 40% reduction of stand basal area) against controls.
Laboratory reared hemlock looper pupae are periodically exposed in each plot to determine parasitism rates for a period of 3 years after partial cutting treatments. Two and three years after partial cutting, wild hemlock looper larvae are also collected in the same plots. Malaise traps and meteorological data loggers are installed to measure the influence of partial cutting on parasitoid abundance and microclimate.
Parasitism of hemlock looper pupae is significantly lower in plots with the higher partial cutting intensity compared with control plots. Also temperature and humidity, as well as the number of Apechthis ontario (Cresson) (Hymenoptera: Ichneumonidae) females in plots, are significantly influenced by partial cutting. However, only mean and minimum temperature can significantly explain parasitism of hemlock looper pupae.
To sustain parasitism rates in forest stands vulnerable to hemlock looper defoliation at naturally high levels, it is recommended to refrain from partial cutting or to conduct this treatment at intensities lower than 40%.
... It has been suggested that thinning could reduce damage caused by spruce budworm (Crook et al. 1979, Bauce 1996, Bauce et al. 2001). Fuentealba and Bauce (2012b) found increased resistance to spruce budworm in balsam Þr trees 3 yr after stand thinning, mostly as a result of an increase in foliar production in residual trees. However, in the shorter term (Þrst year), tree resistance to defoliation was reduced through reduction in foliar monoterpenes (Bauce 1996, Fuentealba and Bauce 2012a). ...
Silvicultural treatments such as thinning have been suggested as management tools against the spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae). Among other things, parasitoids are also proposed to be influenced by silvicultural procedures, but the effect of thinning on spruce budworm's natural enemies has not been tested yet. In this study, the influence of partial cutting on parasitism of endemic spruce budworm populations has been investigated in mature balsam fir-white birch forests. Two intensities of partial cutting (25 and 40% stand basal area reduced) were conducted in 2009 and parasitism of introduced spruce budworm larvae and pupae was determined during the 3 yr after these treatments. Pupal parasitism was too low for comparison between treatments. However, 2 yr after treatments, parasitism of the fourth- and fifth-instar larvae was significantly reduced in plots with both intensities of partial cutting, which was attributed to the parasitoid Tranosema rostrale (Brischke). Three years after treatments, no significant influence of partial cutting on parasitism of spruce budworm larvae was found. This study suggests that the influence of partial cutting on parasitism of endemic spruce budworm populations is not consistent, but that under certain circumstances parasitism is reduced by partial cutting.
... This change in foliar chemical content have been manifested in positive effects on insect performance, such as shorter developmental times, greater pupal mass, and greater foliage consumption (Bauce, 1996;Fuentealba and Bauce, 2012a). However, positive effects of thinning on host tree foliar production in subsequent years resulted in increased tolerance and resistance against budworm (Bauce, 1996;Bauce et al., 2001;Fuentealba and Bauce, 2012b). ...
... Three years after treatment, conditions were still conducive to spruce budworm performance because of high foliar concentrations of foliar N and P, especially within balsam fir that were growing in heavily thinned stands (Fuentealba and Bauce, 2012b). The importance of both nutrients, which are vital for spruce budworm growth, development and survival (Mattson et al., 1983(Mattson et al., , 1991Schmitt et al., 1983;Bidon, 1993;Carisey and Bauce, 1997;Fuentealba and Bauce, 2012a), was confirmed by CCorA (Table 3). ...
... Consequently, the reduction of the number of trees that were competing for the limited resources in these latter kinds of site may have allowed remaining individuals to increase foliage production and, therefore, tree tolerance. Black spruce was not significantly affected by thinning, but this species produced more foliage in thinned stands than in unthinned stands, thereby increasing residual foliage and, therefore, black spruce tolerance (Fig. 5) (Fuentealba and Bauce, 2012b). ...
Forest management activities such as thinning have been proposed to reduce defoliation damage incurred by spruce budworm (Choristoneura fumiferana (Clem.)). Yet, information regarding thinning effects on tree and stand vulnerability to spruce budworm is equivocal. A better understanding of thinning with respect to host tree resistance and budworm performance could be useful to reduce its impacts while respecting forest ecological integrity. Our objectives were (1) to evaluate the effects of thinning and site drainage quality on balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss) and black spruce (P. mariana (Mill.) BSP) resistance to spruce budworm through time (6 years) and (2) to produce a resistance classification model that could be used by forest managers to determine when and where to apply this treatment. Field-rearing experiments of spruce budworm were conducted, together with foliar chemical analyses, along a gradient of stand thinning intensity (0%, control; 25%, light; 40%, heavy) and drainage class (rapidly drained, class 2; mesic with seepage, class 3; subhygric, class 4; hydric, class 5). Budworm performance was followed throughout the insect’s life cycle, including its winter biology. Balsam fir resistance, unlike that of white and black spruce, was significantly reduced 1 year after thinning. Fir response was related to increased defoliation linked to reduction of certain monoterpenes on mesic sites and to decreased foliage production on subhygric sites. On hydric sites, thinning increased fir resistance by increasing foliage production. We observed an opposite response 3 years after treatment. Heavy thinning (40%) positively affected balsam fir and white spruce tolerance and, therefore, tree resistance, by increasing foliage production and the amount remaining after budworm feeding throughout the study, except 6 years after thinning in white spruce growing on mesic sites. From the fourth year onward, black spruce resistance was positively affected by thinning. This response was observed despite thinning also having favoured insect performance (high female pupal mass), which resulted in greater foliage destruction in thinned stands. These findings suggest that thinning may be used to increase tree and stand resistance to spruce budworm. Our resistance classification system could be useful to forest managers in planning thinning that would reduce budworm impacts at the stand level.
Forest succession is a dynamic process of progressive compositional development of ecological communities of species following natural or anthropogenic disturbance. Despite a rich history of conceptual frameworks, models, and empirical advances, the complex interactions among climatic conditions, disturbances, edaphic factors, and silvicultural treatments still challenge our ability to accurately predict forest succession, hindering application to forest management. Our goal was to improve understanding of forest succession in the managed boreal forests of North America by clarifying advances in knowledge and limitations in our understanding. We reviewed 152 peer-reviewed papers to: (i) document conceptual developments in forest succession; (ii) summarize drivers of North American boreal forest succession, including changes to forest composition and successional trajectories given climate change; and (iii) discuss the implications of the synthesized information for boreal forest management. While the element of stochasticity is expected to increase under climate change, successional dynamics are anticipated to remain predominantly deterministic. Southern boreal forests are at increased risk of mortality due to warming-driven drought and increased fires. Following disturbance, regeneration is likely to favor deciduous hardwoods. In boreal mixedwoods, increased fires would promote jack pine, and also black spruce on hydric and xeric sites. Dynamics of the northern boreal will depend on the balance between precipitation and evapotranspiration. Forest management must carefully select prescriptions to promote forest regeneration and composition that consider the long-term effects of changing climate and disturbance regimes. For instance, combining retention cut with mechanical site preparation would maintain site productivity and reverse open black spruce stand development in northern boreal stands. Our work shows that multiple disturbances have compounding effects on forest development, but further work is needed to better define thresholds for synergistic and buffering interactions. Modeling of boreal forest succession can be improved by incorporating more of the influential factors, but this is often limited by the lack of data. This information will guide the development of forest management strategies by exploring combinations of prescribed fire and variable intensity selection cutting systems to reproduce the effects of multiple interacting natural disturbances under climate change on successional dynamics.
One promising approach to mitigate the negative impacts of insect pests in forests is to adapt forestry practices to create ecosystems that are more resistant and resilient to biotic disturbances. At the stand scale, local stand management practices often cause idiosyncratic effects on forest pests depending on the environmental context and the focal pest species. However, increasing tree diversity appears to be a general strategy for reducing pest damage across several forest types. At the landscape scale, increasing forest heterogeneity (e.g., intermixing different forest types and/or age classes) represents a promising frontier for improving forest resistance and resilience and for avoiding large-scale outbreaks. In addition to their greater resilience, heterogeneous forest landscapes frequently support a wide range of ecosystem functions and services. A challenge will be to develop cooperation and coordination among multiple actors at spatial scales that transcend historical practices in forest management.
Expected final online publication date for the Annual Review of Entomology, Volume 67 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
From the early descriptive work, focussed on documenting the forest insect fauna and the impacts of destructive species, Canadian forest entomology has passed through several distinct phases, each triggered by new societal demands of forests and of forest entomologists. We review the various stages that Canadian forest entomology gone through in the last 100 years. Following the initial descriptive and cataloguing phase, forest entomology entered a pest control or forest protection phase, which eventually evolved into the integrated pest management (IPM) era. Although IPM dominated the forest entomology discourse for at least two decades, this approach is now considered to be narrow and pest-centric and is being superseded by a more holistic approach where the emphasis is on ensuring the health and sustainability of forests at landscape levels. The new trends point away from the "command and control" approach of attempting to eradicate pests or reducing pest damage, and towards working with natural processes in the context of ecosystem management. We indicate several areas where 21st century forest entomology could make a contribution towards the sustainable management of Canadian forests.
Recent studies have commonly demonstrated the sensitivity of beetles (order Coleoptera) to forest management practices, managed forests generally supporting fewer beetles, fewer species, and a different community than unmanaged forests. In this study, we examine whether commercial thinning strategies that produce different dead wood volumes in plantations could be used to promote beetle diversity, abundance, and abundance across feeding guilds. To this end, we sampled beetles in the first two summers following thinning using flight intercept traps distributed in intensively-managed white spruce plantations and unmanaged, old coniferous forests. 60,385 beetles representing 48 families and 219 species were collected in the study. During both summers that followed thinning treatments, beetle abundance, richness, and abundance per feeding guild were similar to those observed in old forests. However, these effects began to fade during the second summer in plantations where woody debris had been removed. These results suggest that strategies of commercial thinning could be used to create resource pulses for beetles and favor their conservation in plantation landscapes, as long as woody debris are not harvested.
