Tree recovery during the aftermath of an outbreak episode of the Hungarian spruce scale in southern Sweden

ABSTRACT

In 2010, the first, and so far only, infestation of the Hungarian spruce scale (Physokermes inopinatus) and accompanying sooty mould occurred in Scania, southernmost Sweden. About 1000 ha of Norway spruce (Picea abies) were affected, and the trees suffered from the sucking of the insects as well as from the dense sooty mould that covered the needles. Salvage cuttings were carried out in many of the massively attacked forest stands, both in response to the fear that the trees otherwise would die, e.g. from secondary bark beetle attacks and to prevent spreading of the infestation. The aim of this study was to provide basic, quantitative knowledge on the aftermath response of trees that were heavily infested, but not exposed to salvage cutting. Growth characteristics, in terms of needle weight, shoot length and tree-ring size were measured on infested and uninfested trees to compare and contrast the spruce growth before, during and after the scale outbreak. The infestation resulted in dwarf annual shoots, stunted needles and thin tree rings. The needle weight returned to normal the following year, whereas shoot length and tree rings required one growing season before full recovery.

KEYWORDS:

• Physokermes inopinatus
• Picea abies
• needle weight
• shoot length
• tree ring

Acknowledgements

We thank Anders Jonshagen for help with shoot sampling, Tobias Lindblom for technical support and Fredrik Lagergren for support on forest inventory measurements, forest owners Henrik Tham and Erik Stiernswärd for access to sample sites and forest manager Jesper Runge for additional site information. We acknowledge the E-OBS data set from the EU-FP6 project ENSEMBLES (http://ensembles-eu.metoffice.com) and the data providers in the ECA&D project (http://www.ecad.eu).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The study is a contribution to the Strategic Research Area Biodiversity and Ecosystem Services in a Changing Climate (BECC), and the work was supported by the Tranemåla Foundation and the Swedish Research Council Formas (Svenska Forskningsrådet Formas) (2010-822).