Sap flux – a real time assessment of health status in Norway spruce

ABSTRACT

Top dieback of Norway spruce (Picea abies), triggered by drought in 2004–2006, has been observed in Southeast Norway and trees died within four years after appearance of the first symptoms. The aim of our study was to use sap flux measurements as a diagnostic method for assessment of tree vitality. We used the heat field deformation method to monitor the sap flux density (SFD) in four pairs of healthy and declining trees in situ. To provide retrospective information on hydraulic performance of the trees we took samples for wood anatomical analysis. After felling the trees we used the modified differential translucence method (MDT) as a proxy for the SFD measurements. Healthy trees had three times higher SFD values as declining trees. In some healthy trees we detected decreasing SFD with time. The MDT method agreed with the SFD measurements. In conclusion, we detected sap flux dysfunction in declining trees and showed that the SFD reduction may occur during a short period, prior to occurrence of any visual symptoms. We suggest incorporating the SFD measurements into the repertoire of diagnostic tools in forest pathology.

KEYWORDS:

• Decline
• heat field deformation
• modified differential translucence
• Picea abies
• Sap flow
• sapwood
• spruce dieback

Acknowledgements

We wish to thank Markéta Štĕnová for excellent technical help.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The research has been funded by the Research Council of Norway [project Dieback in Norway spruce, no. 199403], the Norwegian Forest Owners’ Research Fund (Skogtiltaksfondet), Norwegian County Forest Offices, and the project Indicators of trees vitality, reg. no. CZ.1.07/2.3.00/20.0265, European Social Fund and the state budget of the Czech Republic.