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Breeding efficiency in Tomicus piniperda and shootdamage after late autumn thinning of young Pinussylvestris standsErkki Annila a & Risto Heikkilä aa Finnish Forest Research Institute, P.O. Box 18, Vantaa, SF‐01301, Finland
Version of record first published: 10 Dec 2008.
To cite this article: Erkki Annila & Risto Heikkilä (1991): Breeding efficiency in Tomicus piniperda and shoot damage after lateautumn thinning of young Pinus sylvestris stands, Scandinavian Journal of Forest Research, 6:1-4, 197-207
To link to this article: http://dx.doi.org/10.1080/02827589109382661
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Scand J. For Res. 6: 197-207, 1991
Breeding Efficiency in Tomicus piniperda and Shoot Damageafter Late Autumn Thinning of Young Pinus sylvestris Stands
ERKKI ANNILA and RISTO HEIKKILÄFinnish Forest Research Institute, P.O. Box 18, SF-01301 Vantaa, Finland
Annila, E. and Heikkilä, R. (Finnish Forest Research Institute, P.O. Box 18, SF-01301Vantaa, Finland). Breeding efficiency in Tomicus piniperda and shoot damage after lateautumn thinning of young Pinus sylvestris stands. Accepted Sept. 5, 1990. Scand. J. For.Res. 6: 197-207, 1991.
The breeding of the pine shoot beetle (Tomicus piniperda) after thinning of young Scotspine stands in late autumn, and subsequent shoot damage, were studied in southern,central and northern Finland during three successive years (1977-79). No distinct increasein the attack density or beetle population was observed on the felled trees during the studyperiod. Shoot damage on the standing trees remained low, and was not considered to haveany marked negative effect on tree growth or further development of the pine stand. Nonoticeable difference was found between the different parts of the country. The economicimportance of beetle damage resulting from late autumn thinnings was estimated to be low.Key words: Tomicus piniperda, shoot damage, thinnings, Scots pine.
INTRODUCTION
Scots pine stands growing close to sawmills, timberyards, unloading points along timberfloatways etc., are often seriously damaged by the pine shoot beetle, Tomicus piniperda(Coleóptera, Scolytidae). At such sites there is a lot of green timber with bark in spring andearly summer which provide good breeding possibilities for pine shoot beetles. Adultbeetles emerge from the timber after mid summer, and attack the young shoots of thesurrounding trees. The shoots wither, die and drop to the ground in autumn or winter, orremain attached to the tree. As a result of consecutive attacks, the annual increment maydecrease to half that of healthy trees (Nilsson, 1974).
When young pine stands are cleaned or thinned a number of trees are left lying on theground. According to the thinning instructions for forest owners, young pine stands shouldbe thinned when the height of the trees is from 3 to 4 metres. At that stage there is norough bark, necessary for the successful breeding of pine shoot beetles, at the base of thecut trees.
Sometimes thinning is delayed. If the trees have already developed rough bark, thinningduring winter may result in considerable shoot losses by beetles in the standing trees thefollowing summer (Butovitsch, 1954; Lekander & Langström, 1976; Langström, 1979;1986). Therefore, thinning is recommended to be done in June or July, after the main flightof the pine shoot beetle. The felled stems will then dry during the summer, and will nolonger be suitable as breeding material the following spring (Langström, 1986). .
However, there is a risk that the root rot fungus, Heterobasidion annosum (Fr.) Bref,can infest unseasoned stumps in summer (Rishbeth, 1951a; 1951 b; Petäistö, 1978; Jo-kinen, 1984) and spread to living trees through the roots (Rennerfelt, 1952; Molin, 1957).The fungus kills pines within a few years and spreads to the neighbouring trees, thusresulting in a gradually expanding opening in the stand.
The aim of the present study was to investigate how intensively pine shoot beetlesreproduce after thinning in late autumn in different parts of Finland, and whether the shoot
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damage is so serious that it would be necessary to thin in summer and run the risk of rootrot fungus infestation in the stand.
MATERIALS AND METHODS
Field studies were carried out during 1976-80 in five different young pine stands situated insouthern, central, and northern Finland (Ruokolahti N 61°25' E 28°57' two stands, LieksaN 63°22' E 30°15' two stands, Rovaniemi N 66°18' E 26°40'). In each stand an area of aboutone hectare was thinned in October or November during three consecutive years(1976-78). The aim of the consecutive thinnings was to achieve maximum beetle popula-tions. All the felled trees were left lying on the ground, apart from one site (Lieksa) wherethe largest trees (DBH >7 cm) were removed from the stand before the emergence of thenew beetle generation.
The height and diameter over bark (DBH) of the living and felled trees (Table 1), as wellas the height and diameter of the stumps, were measured the following summer on circularsample plots of 100 m2. Felled trees with a diameter of 11 cm (/i=ll) or 12 cm (n=3) weregrouped in the 10 cm diameter class. In addition, the length of rough bark on the felledtrees was measured. Between 15 and 25 sample plots were investigated at 20 m intervals ineach stand per year. /
Table 1. Sample plot data-
Stand no.,locality
Year ofcutting
Experimental stands1.RuokolahtiTorsantaka
2.Ruokolahti.Pohjalankila
3.LieksaMustapuro
4.LieksaMäkrävaara
5.RovaniemiKivalo
19761977197819761977 .1978197619771978197619771978197619771978
Additional stands6.Janakkala
7.Vilppula
8.Karvia
1978
1978
19781979
Felled trees
No. oftrees/ha
1273835910
1 185157510782 85029002 SU
760919
1324972723
1 140
679
1204
700700
DBH(cm)
6.96.87.05.74.35.34.34.24.34.74.44.55.75.16.5 .
-
_-
Remaining
No. oftrees/ha
198017831 7201 82019082 3281 1441022
9561 128
714982
169614081 196
1400
1700
2 4002400
trees
Height(m)
7.28.18.46.57.17.09.88.5
10.510.39.6
11.57.37.28.5
9.5
12.5
6.56.6
DBH(cm)
9.49.9
10.48.68.38.89.8
10.311.811.111.012.49.18.7
10.7
12.5
15.0
10.010.2
No ofsampletrees
8167948481
1002073487
1143645
13793
135
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Scand. J. For. Res. 6 (1991) Breeding efficiency in Tomicus piniperda 199
•oN"cO"5u
1 0 0
so -
60 -
40 -
20 -
4 6 8DBH cm
10 12
Fig. 1. Percentage of felled treescolonized by the pine shoot beetlein the different diameter classes(r=0.825,p<0.001, n=34). 95%confidence limits for the regressionline.
The number of exit holes and egg galleries on the felled trees and stumps was counted onevery third sample plot in late August or September. One-metre-long sections of the felledtrees were taken in. stands nos. 1 and 2 in early October in order to investigate theproportion of offspring still present in the trees at the beginning of the winter. A total of 50samples were studied in the laboratory, and the different developmental stages werecounted. The number of shoots killed by the beetles and subsequently fallen to the groundwas counted on circular sample plots at 20 m intervals during the following spring. Thesize of the sample plot was dependent on stand density, and ranged from 4.37 to 14 m2
such that it corresponded to the area occupied by a single tree. Since shoots killed bybeetles may remain attached to the crown, ten trees were felled in each stand and theattached, dead shoots counted.
Shoot damage after thinning was also studied at three additional locations: Janakkala (N60°53' E 24°45'), Vilppula (N 62°05' E 24°15'), and Karvia (N 62°10' E 22°50').
RESULTS
Attack density
The percentage of felled trees colonized by the pine shoot beetle was highly dependent onthe diameter at breast height (Fig. 1). None of the trees less than 3 cm in diameter wereattacked. All trees with a diameter of 9 cm or more were colonized. Although the totalnumber of egg galleries varied considerably between different trees, it was clearly relatedto the size of the tree (Fig. 2). The variation in attack density, expressed as the number ofegg galleries per square metre, was also high, even within the same diameter class. Thelargest value observed was 328 egg galleries per square metre.
The average number of egg galleries per stump ranged from 0.2 to 1.5. The total numberof egg galleries, as well as the attack density, were not dependent on the diameter nor onthe height of the stump. No marked difference was found in attack density between thetrees and stumps, apart from the stands in Ruokolahti where the number of egg galleries instumps was very low.
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aa
3oó
12
Fig. 2. Relationship between the to-tal number of egg galleries per treeand the diameter at breast height(r=0.565,p<0.001, n=1422). 95%confidence limits for the regressionline.
Breeding successAll trees with a DBH of 10 cm or more produced new beetles. Breeding was totallyunsuccessful in 5% of those trees with a DBH of less than 10 cm. The average number ofexit holes per tree ranged from 20 to 40 in the different stands, and was highly dependenton the tree diameter (Fig. 3). The production of new beetles in the stumps was about onetenth of that in the stems.
The number of exit holes per egg gallery was higher in large trees than in small ones, butthe correlation was not very strong. The average number varied between 3 and 6. In thestumps the number of exit holes was lower than that of the parent beetles. However, itmust be borne in mind that several beetles can emerge from the same hole.
The relative production, expressed as the number of exit holes per square metre of
\
d
Fig. 3. Relationship between thenumber of exit holes per tree andthe diameter at breast height. Stand-ard error is indicated.
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Scand. J. For. Res. 6 (1991) Breeding efficiency in Tomicus piniperda 201
rough bark area, was also positively related to tree size. The variation between trees, aswell as between stands, was considerable. It is worth mentioning that the production washighest in northern Finland (Rovaniemi), about three times that in southern Finland(Ruokolahti).
The proportion of offspring which had not emerged by the beginning of October, butwere still present in the bark, was 36% of the number of exit holes in 1977 and 13% in1978. The proportion of larvae and pupae was 78% and 50% in the respective years, therest being callow adults.
Variation between yearsContrary to expectations, there was no general increasing trend in the percentage ofcolonized trees, attack density or population growth rate in any stand as a result ofthinnings carried out in consecutive years (Fig. 4). The between-year variation appeared tobe due to normal fluctuations in the population density of the pine shoot beetle. Differ-ences in attack density or beetle production between the different localities were alsosmall.
Stand no. 5 (Rovaniemi) was the only site where the total number of beetles producedper hectare increased during the three-year period (Table 2). The beetle populationdecreased slightly at the other locations, especially in stands nos. 3 and 4 where the largesttrunks had been removed before the emergence of the new beetles. The proportion ofbeetles emerging from stumps was low, apart from stand no. 3 where the number ofstumps was much higher than that in the other stands (Table 1).
The number of beetles per remaining standing tree in stands nos. 1 and 4 varied onlyslightly between years. Beetle pressure was decreasing in stands nos. 2 and 3, and it wasincreasing during the study period only in stand no. 5 (Table 2). Of course, such pressure isnot only dependent on the number of beetles produced, but also on the density of the treesremaining in the stand (cf. Table 1).
Shoot damageThe number of shoots killed by beetles per tree remained fairly low in every localityincluding the additional study stands (nos. 6, 7, 8).
There was a clear relationship between the production of new beetles and the number ofshoots fallen to the ground. No clear increase in shoot damage was recorded during thestudy period (Table 2). The effect of removing the largest trees from stands nos. 3 and 4was reflected in the decreasing number of fallen shoots.
The number of shoots attacked by beetles but still attached to the crown variedconsiderably between trees. The average proportion of such shoots was 13% of the totalnumber of shoots killed by pine shoot beetles. The numbers presented in Table 2 includeall shoots destroyed by beetles. Some of the shoots attacked by beetles had rejected theintruder and recovered from the damage. The number of shoots killed per tree was 73 % ofthe number of exit holes on the felled trees (Table 2).
The relationship between the number of trees felled per hectare and the number ofshoots killed by pine shoot beetles was not very clear. On an average, shoot damage pertree was more stable in the southern localities (nos. 1, 2) than in the northern ones (nos. 3,4, 5) but the intensity of damage was about the same.
DISCUSSION
The results indicate that attack by the pine shoot beetle on trees with a DBH of less than 5cm is often low. The proportion of trees colonized by beetles, as well as the attack density,
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202 E. Annila and R. Heikkilä Scand. J. For. Res. 6 (1991)
ATTACK DENSITY/«q. m
Stand No. 1 Stand No. 2
100-
SO-
SO-
4 0 -
1 0 -
T
i «T..
RATE OF INCREASE
PRODUCTION (EXIT HOLES/sq. m)
400
300
200
100
1Í77 1971 1979
Y M C
1977 1978 1979
Y M T
Fig. 4. Attack density, rate of increase (no. of exit holes/parent beetles), and production of newbeetles in five different pine stands during three consecutive years. Standard error is indicated.
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Seand. I. For. Res. 6 (1991) Breeding efficiency in Tomicus piniperda 203
ATTACK DENSITY/«!, m
Stand No. 3 Stand No. 4
400
100
100
to
RATE OF INCREASE
PRODUCTION (EXIT HOLES/sq. m)
400
»00
200
100
Fig. 4 (continued)
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204 E. Annila and R. Heikkilä Scand. J. For. Res. 6 (1991)
ATTACK DENSITY/»q. m
Stand No. S
too
RATE OF INCREASE
PRODUCTION (EXIT HOLES/sq. m)
300-
200-
100- 1Êi
•
T
1•1S77 197S 1879
VwFig. 4 (continued)
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Scand. J. For. Res. 6 0991) Breeding efficiency in Tomicus piniperda 205
increased with increasing tree diameter. All trees with a diameter of more than 8 cmapparently become colonized. The results are in good agreement with the findings ofstudies carried out in Sweden (Langström, 1979).
The average attack density and beetle production per tree was low compared with theresults of some other studies (e.g. Doom & Luitjes 1971, Langström, 1979; 1986). One
.reason to the differences may be cool weather in summer 1977 and 1978. The meanmonthly temperatures in July and August in the study areas were between 1.5 to 2.5°Clower than the long-term average for the period 1931-1960 (Kuukausikatsaus, 1976-80). Innorthern Finland, the pine shoot beetle population is often suppressed by cold weather(Juutinen, 1978; Saarenmaa, 1983; 1985).
Intraspecific competition has been observed to decrease the production of pine shootbeetles if the attack density is high (Nuorteva, 1954, Eidmann & Nuorteva, 1968, Saaren-maa, 1983, Sauvard, 1989). Because the density in the present study remained far below
Table 2. Beetle production on the sample plots and the number of shoots killed by beetles.S.E. = standard error
Standno.(year)
No. of beetles
Fromstems
Experimental stands
1.197719781979
197719781979
3.197719781979
197719781979
197719781979
35 39527 27831 300
45 29927 49620 266
57 196' 17 77211 561
9 5304 7263 733
13 78430 64355 460
Additional stands
6.1979
1979
19791980
-
-
-
Per hafromstumps
26753505
20901 1281 573
20 17731 100
6 240
4 0253 0344 991
4 0353 1975 390
-
-
-
Totalno.
35 42128 03131 805
47 38928 62421 839
77 37348 87217 801
13 5557 7608 724
17 81933 84060 850
-
-
-
Perremainingtree
17.915.718.5
26.014.29.4
67.647.818.6
12.010.98.9
10.524.451.2
No. of shoots killedby beetles
Per ha
Mean
37 51444 08229 027
51 16336 09846 917
28 17915 0346 698
13 06010 2407 809
16 34027 15821 178
11 073
41243
28 56073 960
Per tree
Mean
11.917.213.1
24.615.122.5
22.010.72.0
7.211.13.2
4.316.319.2
8.9
27.3
13.534.5
S.E.
1.22.00.8
1.62.22.0
1.40.90.2
0.60.70.3
0.51.11.1
1.2
2.7
1.63.8
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206 E. Annila and R. Heikkilä Scand. J. For. Res. 6 (1991)
the critical level, 150 egg galleries per square metre, competition is not likely to have hadany decreasing effect on beetle production.
The attack density and beetle production are dependent on the felling date of the trees.Lângstrôm (1986) found that attack on trees felled in June or July was very low comparedwith those felled during early spring. Trees felled in late fall, as in the present study, canalso be less suitable as breeding material than trees felled during winter or spring.
Shoot damage was also low in all years. According to Lângstrôm (1979), pine shootbeetles may kill as many as 150 shoots per tree if trees with rough bark are left on theground after thinning. Nilsson (1974) stated that reduced growth of young pines is likely ifbeetles destroy more than 20 shoots per tree. When 200 shots per tree were artificiallypruned in a young Scots pine stand, the average reduction in volume growth was 16% and20% during the two following years (Ericsson et al. 1985). Lângstrôm (1980) reported an8% reduction in diameter (DBH) growth when 50% of the shoots were removed. Only aslight effect on tree growth was thus to be expected in the stands of the present study.
Not even repeated thinnings during several successive years seems to markedly increasethe population of the pine shoot beetle. Obviously, the initial beetle population in the studyareas was so high that the breeding material which became available after the firsttreatment was almost completely colonized. The proportion of breeding material occupiedby beetles is also dependent on the increase in the amount of material compared with thatof the previous year. Nuorteva (1964) found that the attack density of T. piniperda wasunusually low after heavy snow damage in pine forests. However, his material shows noincrease in density in the following year when there was no longer an excessive amount ofbreeding material present.-
Overall, the results of the present study show that the risk of serious shoot damage bypine shoot beetles after late autumn thinnings is generally low. The risk can be furtherreduced by strip barking, cutting the lower part of the trunks into short sections(Lângstrôm 1979) or removing the trees with a DBH of 7 cm or more from the stand beforethe emergence of the new beetle generation. Considering that damage caused by the rootrot fungus is regarded as chronic, but that of the pine shoot beetle temporary, thinningsduring summer should be avoided.
ACKNOWLEDGEMENTS
The authors wish to express their sincere thanks to Enso-Gutzeit Co. and Rauma-RepolaCo., for arranging the field studies.
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Ericsson, A., Hellqvist, C., Lângstrôm, B. , Larsson, S. & Tenow, O. 1985. Effects on growth ofsimulated and induced shoot pruning by Tomicus piniperda as related to carbohydrate andnitrogen dynamics in Scots pine. J. Appl. Ecology 22, 105-124.
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kvarstående träd (Breeding of pine shoot beetles in cleaning waste of Scots pine and subsequentshoot-damage on remaining trees). Sveriges Lantbruksuniversitet Skogsentomologiska rapporter1, 1-52.
Längström, B. 1980. Tillväxtreaktion hos unga tallar efter artificiell skottklippning för att simuleramärgborreangrepp (Growth response of young Scots pines to artificial shootpruning, simulatingpine shoot beetle attacks). Sveriges Lantbruksuniversitet Skogsentomologiska rapporter 2, 1-26.
Langström, B. 1986. Attack density and brood production of Tomicus piniperda in thinned Pinussylvestris stems as related to felling date and latitude in Sweden. Scand. J. For. Res. 1, 351-357.
Molin, N. 1957. Om Fomes annosus spridningsbiologi. Medd. Stat. Skogsf. Inst. 47 (3), 1-36.Nilsson, S. 1974. Tillväxtförluster hos tall vid angrepp av märgborrar (Increment losses caused by
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Nuorteva, M. 1964. Über den Einfluss der Menge des Brutmaterials auf die Vermehrlichkeit und dienaturlichen Feinde des Grossen Waldgärtners, Blastophagus piniperda L. (Col. Scolytidae). Ann.Ent. Fenn. 30, 1-17.
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Rennerfelt, E. 1952. Om angrepp av rotröta på tall. Medd. Stat. Skogsf. Inst. 4 (9), 1-49.Rishbeth, J. 1951 a. Observations on the biology of Fomes annosus with particular reference to East
Anglian pine plantations. Spore production, stump infection, and saprofytica activity in stumps.Ann. Bot. 15, 1-21.
Rishbeth, J. 1951 b. Butt rot by Fomes annosus Fr. in East Anglian conifer plantations and its relationto tree killing. Forestry 24, 114-120.
Saarenmaa, H. 1983. Modeling the spatial pattern and intraspecific competition in Tomicus piniperda(Coleoptera, Scolytidae). Comm. Inst. For. Fenn. 118, 1-40.
Saarenmaa, H. 1985. Within-tree population dynamics models for integrated management of Tomicuspiniperda (Coleoptera, Scolytidae). Commun. Inst. For. Fenn. 128, 1-56.
Sauvard, D. 1989. Capacités de multiplication de Tomicus piniperda L. (Col., Scolytidae). J. Appl.Ent. 108, 164-181.
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