Otto, L. F. (1999). Some Results of the Long Term Monitoring of Bark Beetles in the Ore Mountains. In B. Forster, M. Knizek, & W. Grodzki (Eds.), Methodology of Forest Insect and Disease Survey in Central Europe. Proceedings (pp. 118-123). Swiss Feder

Forster, B.; Knizek, M.; Grodzki, W. (eds.) 1999: Methodology of Forest Insect and Disease Survey in Central Europe.

Proceedings ofthe Second Workshop ofthe IUFRO WP 7.03.10, April20-23, 1999, Sion-Chateauneuf, Switzerland.

Birmensdorf, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) 118-123.

SOME RESULTS OF THE LONG TERM MONITORING OF BARK BEETLES IN THE ORE MOUNTAINS

L.-F. Otto, Fachbereich Waldbau/Waldschutz

Sachsische Landesanstalt fiir Forsten, D- 01827 Graupa, Bonnewitzerstr. 34

Introduction

In Saxony, the forests are dominated by Norway spruce (Picea abies [L.] Karst. ). 41% of the total forest area are composed of spruce stands. These stands consist of only one species mostly and all trees have the same age. Therefore, the most important aim of forestry is the stabilisation of these stands by silvicultural methods. The described situation in mind, the spruce bark beetle (Ips typographus L.) is the most important insect pest in Saxony.

In Saxony, a outbreak of this species did not take place in the last 10 years (see Figure 1). The possible reasons for that are:

• No occurence of bigger damages caused by snow or windfelling (no significant influence of the gale "Wiebke").

• Significant decrease of air pollution in the last years.

• Normal weather conditions (temperature and rainfall with no significant changes).

• Implementation of the integrated pest control system in a sufficient quality by foresters.

The Ore mountains are the centre of the bark beetle occurence in Saxony. On the one hand, instable spruce stands of homogenous structure are concentrated in this region. On the other hand, abiotic factors can play an important role. Therefore, this region is also a centre for investigations and observations of the behavior of bark beetles. In 1991, a small scale monitoring system was established with the objective to monitor the annual density and the population development over several years. The system is used together with the Institute of Forest Protection in Tharandt.

Methods

Figure 1 shows the area of observation. Three district forest offices were chosen for the monitoring. There are concentrated in the eastern part of the Ore mountains in different altitudes.

• Faests Qe JT10lrtains

Cl:lserved clstrict faest offices

• Faest staticns rncritDri1g trap systems 11 Faest meteaclcgcal station

Mlf!ostal>1 : 1000000

Fig. 1: Area of observation

In every district forest office, typical stands were chosen for the monitoring. The established monitoring system in front of these stands include 2 up to 20 pheromon traps. These trap systems serve also for the protection of the stands as a part of the integrated pest control system as well as for the testing of new baits and traps. For the monitoring and the assessment of the results presented, only the standard trap ("Theysohn") with a standard bait

("Pheroprax") was used. The captured beetles were collected and counted weekly. In Table 1, the environmental conditions for the stands are described with typical parameters.

Tab. 1: Environmental conditions for the observed stands

District forest Forest Stand Altitude Age Number of Exposition

office station [m] [years] traps

Tharandt Grillenburg 341 a3 380 90 8 w

Naunhof 847 a4 400 115 13

s

Barenfels Barenfels 315 a2 550 90 8 - 10 NE

Oberbarenburg 403 all 740 105 2 SE

Oberbarenburg 407 a6 750 126 5 SW

Altenberg Hirschsprung 425 a2 675 94 12 - 20

s

Detailed information on the volume of infested trees in the observed district forest offices came from the Saxon system for forest pest and diseases survey (see poster).

Meteorological data were collected by the state owned meteorological station of Marienberg in the middle part of the Ore mountains and by a forest meteorological station in a old spruce stand in the district forest office Heinzebank (see Figure 1). The latter works since 1994.

Results

Damage development

The volume of infested trees is a suitable parameter to describe the population development.

Figure 2 shows the change of this parameter in the last 20 years for the eastern Ore mountains.

volume of infested trees [m")

30000 25000 20000 15000 10000 5000

• 2. generation

m

Fig. 2: Volume of infested trees in the eastern Ore mountains since 1978

From 1980 to 1984 a outbreak took place. The main reason for this gradation was the level of air pollution in that time. The damage observed in the year 1983 with 25.500 m³ is

comparable with the volume of infested trees in the whole of Saxony in 1995. In the year 1995 damages caused by bark beetles reached a maximum. The years after 1987 were characterized by little changes in the damage. However, this figure shows that the damage increased significantly compared with the years before.

In Figure 3, the annual volume of infested trees in the whole of Saxony and in the observation area is compared. The development of these both units correlates with each other. But in the observation area an increasing trend can be observed. In 1991, the percentage of infested trees in the eastern Ore mountains amounts to 2% in relation to the whole of the country. The value of the latter increased from 6.5% in 1995 to 20.6% in 1998.

volume cl infested trees [m>)

30000 25000 20000 15000 10000 5000 0

Saxony

1991 1992 1993 1994 1995 1996 1997 1998

volume cl irlested trees [m>)

2500 2000 1500 1000 500

year

1991 1992 1993 1994 1995 1996 1997 1998

beelles per trap

all used slims) Gapu'ed beelles 7000

axJO 5000 4000 3000 2000 1000

1991 1992 1993 1994 1995 1996 1997 1998

rainfall

in relalial to 1he lcrgtirre average 2.00 [%)

180 180 140 120

100 -Ht--___,il*-__

=--..._,.__...,

80 00 40 20

0 +--K.U-.--"""-,-

1991 1992 1993 1994 1995 1995 1997 1998

-1 -2

-4

EQ)

Wl 400 2Xl

1001 1992 19Q3 1994 1995 19a) 1997 1998

Fig. 3: Volume of infested trees in Saxony and in the observation area and the number of captured beetles since 1991 and the weather conditions in that time

Another distinction between the annual registered damages in Saxony compared to the observation area is the situation in 1995 and 1996. In Saxony, the maximum volume of infested trees was registered in 1995. In the observation area, the damage increased also in 1996. The possible reasons for this difference were the meterological and air pollution

conditions in the winter 1995/96. This winter was characterized by severe damages caused by

ice-break and heavy damages caused by the combination of

so2

In 1992, 1994 and 1998, the volume of infested trees increased significantly compared with the year before. The contrary trend could be observed in 1993 and 1997.

Weather conditions

Weather conditions influence the host - parasite relation between L typographus and spruce in two ways. Especially high temperatures have a positive influence on the development of the beetle population. They are a precondition for a long swarm period as well as for a fast development from the egg to the beetle. On the other hand, the vitality of trees decreases as consequence of low precipitation.

In Figure 3, some characteristical meteorological parameters can be seen for the observation period. The parameters are divided in two periods. In Mai/June, the ftrst swarm flight of beetles after overwintering take place. The young beetles descended from this ftrst generation fly in July/ August. This will be registered as a second swarm period.

In 1992 and 1998, the rainfall in the period Mai/June reached only 76% and 80% of the long time average. In the other years and in the period July/ August, the precipitation was equal or higher compared to the long time average.

The dry springs in 1992 and 1998 were connected with high temperatures. The average temperature during the ftrst swarm period was 1.4 degree higher as the long time average for this period in 1992 and 0.7 degree higher in 1998. In these years, the volume of infested trees and the number of captured beetles has grown rapidly compared to the years before. This development could be seen in a diagramm in Figure 3. A similar development could be observed in 1994. In that year the conditions for bark beetles were optimal in the second swarm period. The rainfall from May until August was normal (108% of the long time average) but the mean temperature in July/ August was 2. 7 degree higher as the long time average.

On the other hand, the volume of infested trees decreased in 1993 and 1997. These years were characterized by normal precipitation and only slight differences between the mean

temperatures and the long time average in the swarm periods.

A diagramm in Figure 3 shows the number of hours with a mean temperature between 16.5 to 30 degree. This is exactly the temperature in which the swarm activity of L typographus takes place (Lobinger 1994). The graph shows that in 1994 the highest number ofhours with good swarm conditions was measured in the last 5 years. In 1996, 1997 and 1998, the numbers of hours with good swarm conditions were equal during the ftrst period but the mean

temperature in Mail June ranged from 1.4 degree below the long time average in 1996 to 0. 7 degree above the long time average in 1998. This shows the difficulties to use mean

temperatures for the interpretation of biological processes.

Number of bark beetles captured in pheromone traps

The annual captures per trap are shown for the selected stands in Figure 4. The results show following trends:

• Related to the different stands, the number of captured beetles per trap showed a big variation between the different years. For instance in 1993, the differences among the stands observed were small. The captures varied from 1200 to 2200 beetles per trap. In 1995, a high variation from 2500 to 14300 beetles per trap could be observed among the different stands.

• The traps in higher altitudes (over 700 m a.s.l.) show the lowest captures and only little changes between different years.

• The trend for the mean captures per year from the 6 observed trap systems is the same as the trend for the volume infested trees per year in the observation area. It could be seen in a diagram in Figure 3.

number of captured

beetles/trap stands:

16000

14000 12000 10000

8000 6000

4000 2000

1::1 Barenfels Abt. 315 a2 C Barenfels Abt. 403 a11

m Barenfels Abt. 407 a6 mAitenberg Abt. 425 a2 EiiiTharandtAbt. 341 a3

•TharandtAbt.: 847 a4

0

1991 1992 1993 1994 1995 1996 1997

year

1998

Fig. 4: Annual captures per trap for the selected stands

After investigations in 12 forest districts in Nordic countries during three years, Weslien et al.

(1989) found a strong correlation between the mean of captured beetles in trap systems (five groups with three traps) and the log-transformed tree mortality. The tree mortality (number of killed trees per km of suitable forest edge) increased at an exponential rate compared to the captures. Hiibertz et al. (1991) confirmed this result with their study in 8 Danish forest districts under non epidemic conditions.

Figure 5 shows the relation between the number of captured beetles per trap in the trap systems and the volume of infested trees in the district forest office Barenfels. These are the results for the 8 years from 1991 to 1998. Also in this case, a exponential correlation seems to exist between the number of captured beetles and the volume of infested trees.

volume of infested trees [m3]

1600 1400 1200 1000 BOO

600 400 200

.·· ,.

... ·· .··

D./ 0

/ D .._... • •. ·•••·•

1;1·· :11( •• • XSaFoA Biirenfels Abt. 403 a11

••• •• •••••••• ••••••• eSaFoA Biirenfels Abt.: 315 a2 .•• •• D ···:: .•.•.

...

beeHes/trap/year

Fig. 5: Relation between the number of captured beetles per trap in trap systems and the volume of

The exponential form of the relation means that traps capture a higher proportion of beetles population at a lower density level than at a high density level. This effect is not only important for using traps as a monitoring system but also for using them as a tool for pest control.

Figure 5 shows also that the relation between the captures and the volume of infested trees can be described for all observed stands with the same kind of function (exponential function) but the parameters of the function are different. This means that a defmed number of captured beetles in different stands has a different importance for the estimation of the actual bark beetle density in a larger region. If we want to use pheromon traps as a monitoring system we need detailed information on the stand typical relation between number of captured beetles and the volume of infested tress. The stand typical parameters can be found with long time observations. Another way can be the development of a mathematical model. This model has to describe the stand typical conditions (altitude, exposition, susceptibility to bark beetle attack etc.) with different function parameters.

Summary

Since 1991, our institute observed the swarm activity from 1 typographus in the eastern Ore mountains. This time was a non epidemic period. The damage depended on the annual weather conditions.

For monitoring, we can use the information on the volume of infested tress and the number of captured beetles in trap systems. However, we achieve the information on damages only after the swarm periods. Trap systems give actual data for instance on the begin of flight of the beetles, on the flight of the young beetles and so on. This information is important for foresters to realise the integrated pest control.

If we want to estimate the actual situation in a large area we need detailed information on the trap systems locally used. Compared to meteorological data, a prognosis can be possible. A first step is to compare the number of captured beetles with the results of the same stand for the same periods in the years before using the same traps and baits.

References

HUbertz, H., J.R. Larsen and B. Bejer: Monitoring Spruce Bark Beetle (lps typographus (L.)) populations under non-epidemic conditions. Scand. J. For. Res.; 6 (1991) 217-226

Lobinger G.: Air temperature as a limiting factor for flight activity of two species of Spruce bark beetles, lps typographus L. and Pityogenes chalcographus L. (Col., Scolytidae). Anz. Schlidlingskde., Pflanzenschutz, Umweltschutz; 67 (1994) 14-17 [in German]

Weslien, J., E. Annila, A. Bakke, B. Bejer, H.H. Eidmann, K. Narvestad, A. Niku1a and H.P. Ravn: Estimating risks for Spruce Bark Beetle (Jps typographus (L.)) damage using pheromone-baited traps and trees. Scand. J.

For. Res.; 4 (1989) 87-98