Spruce Beetle Monitoring in Thuringia
The spruce beetle, the eight-toothed bark beetle (Ips typographus) and the six-toothed spruce beetle (Pityogenes chalcographus) are the most significant biological vermin to the common spruce. Spruce beetles are bark breeders meaning their larvae feed off the bark’s water-carrying layer, thereby causing the development of gaps within these lifelines which may cause the tree to die off.
Damage caused by spruce beetles can be tremendous. Take the record year of 2003 for example, when spruce beetles were the cause of over 450,000 cubic meters of damaged wood. Apart from timber losing its value due to the damage dealt there are also costs in regards to the rehabilitation of the area, e.g. removing the affected spruces.
Possible damages are influenced by weather patterns, seeing spruce beetles only spawn at a certain temperature on the one hand while spruces on the other are able to defend themselves against a spruce beetle infestation through the exudation of resin if supplied with enough water. Spruce beetles therefore prefer warm and dry summers.
The six-toothed spruce beetle for example is able to reproduce in three generations during just one summer season given beneficiary weather conditions. After feeding and regenerating for a period of fourteen days the parent generation fly out again to spread what is called a sibling spawns. This can result in up to 10,000 new pairs deriving from just one original pair, its children and grandchildren.
The only way to fight the vermin is by removing infested trees from the forest as soon as possible thereby stopping the breeding cycle. There are two crucial factors regarding this forestry measure:
- monitoring of the population of spruce beetles in order to localize infested trees in time and
- recognizing infested trees in time in order to remove them from the forest before the spawn can fly out.
To this day it is the local foresters’ obligation to recognize infested trees on the spot. This approach is very time-consuming and consequently very expensive. It also carries the risk of not localizing every single hotbed of infestation. These are also reasons for the Forestry Administration of the Free State of Thuringia to participate in the EUFODOS project, with the objective to receiving a faster, more efficient approach in detecting hotspots of infestation.
Monitoring of the spruce beetle population is a crucial factor for both the foresters’ on-the-spot search as well as the detection via satellite images. Monitoring will on the one hand help narrowing down the period of intensive observation while on the other it enables the localization of hotspots, especially when taking into account that the spawns fly out and accordingly infect spruces at various times throughout Thuringia. This is due to temperature, hence the altitude of an area having an impact on the swarms flying out.
The Forestry Administration of the Free State of Thuringia has two approaches of monitoring the development of the spruce beetle population:
- The spruce beetles’ flight is monitored using bark beetle traps.
- Using meteorological data the spruce beetles’ current developmental state is modeled.
The spruce beetles’ flight is observed at 56 control points allocated throughout the whole area of the Free State of Thuringia, each usually consisting of two bark beetle traps placed in a distance of up to 500 meters from one another (Figure 1: deployment of bark beetle traps state of the art of bug).
These control points, set up in spruce inventories, carry the bark beetle traps (Figure 2: bark beetle trap 2) which hold attractants luring the spruce beetles. The traps are emptied on a weekly basis in order to determine the number of entrapped spruce beetles which is then submitted to a central unit.
The second approach, established by the Institute of Soil Science, Technical University Vienna, enables the modeling of a generation’s current developmental states, e.g. the appointed dates for egg deposition, damage dealt by the larvae, the next spawn flying out, etc. (Figure 4: example of calculating the development of spruce beetles) by incorporating meteorological data. The information gathered is used to determine the population development.
EUFODOS aims at using this approach of monitoring the population development based on punctual data in order to optimize the recording instants of satellite images for a comprehensive monitoring.