TY  - JOUR
A1  - Dobbertin, Matthias
A1  - Eilmann, Britta
A1  - Bleuler, Peter
A1  - Giuggiola, Arnaud
A1  - Graf Pannatier, Elisabeth
A1  - Landolt, Werner
A1  - Schleppi, Patrick
A1  - Rigling, Andreas
T1  - Effect of irrigation on needle morphology, shoot and stem growth in a drought-exposed Pinus sylvestris forest
JF  - Tree Physiology
N2  - In Valais, Switzerland, Scots pines (Pinus sylvestris L.) are declining, mainly following drought. To assess the impact of drought on tree growth and survival, an irrigation experiment was initiated in 2003 in a mature pine forest, approximately doubling the annual precipitation. Tree crown transparency (lack of foliage) and leaf area index (LAI) were annually assessed. Seven irrigated and six control trees were felled in 2006, and needles, stem discs and branches were taken for growth analysis. Irrigation in 2004 and 2005, both with below-average precipitation, increased needle size, area and mass, stem growth and, with a 1-year delay, shoot length. This led to a relative decrease in tree crown transparency (−14%) and to an increase in stand LAI (+20%). Irrigation increased needle length by 70%, shoot length by 100% and ring width by 120%, regardless of crown transparency. Crown transparency correlated positively with mean needle size, shoot length and ring width and negatively with specific leaf area. Trees with high crown transparency (low growth, short needles) experienced similar increases in needle mass and growth with irrigation than trees with low transparency (high growth, long needles), indicating that seemingly declining trees were able to ‘recover’ when water supply became sufficient. A simple drought index before and during the irrigation explained most of the variation found in the parameters for both irrigated and control trees.
Y1  - 2010
U6  - http://dx.doi.org/10.1093/treephys/tpp123
SN  - 1758-4469 (Online)
SN  - 0829-318X (Print)
VL  - 30
IS  - 3
SP  - 346
EP  - 360
PB  - Oxford University Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Rigling, Andreas
A1  - Eilmann, Britta
A1  - Koechli, Roger
A1  - Dobbertin, Matthias
T1  - Mistletoe-induced crown degradation in Scots pine in a xeric environment
N2  - Increasing Scots pine (Pinus sylvestris L.) mortality has been recently observed in the dry inner valleys of the European Alps. Besides drought, infection with pine mistletoe (Viscum album ssp. austriacum) seems to play an important role in the mortality dynamics of Scots pines, but how mistletoes promote pine decline remains unclear. To verify whether pine mistletoe infection weakens the host via crown degradation, as observed for dwarf mistletoes, we studied the negative effects of pine mistletoe infestation on the photosynthetic tissues and branch growth of pairs of infested and non-infested branches. Pine mistletoe infection leads to crown degradation in its host by reducing the length, the radial increment, the ramification, the needle length and the number of needle years of the infested branches. This massive loss in photosynthetic tissue results in a reduction in primary production and a subsequent decrease in carbohydrate availability. The significant reduction in needle length due to mistletoe infection is an indication for a lower water and nutrient availability in infested branches. Thus, mistletoe infection might lead to a decrease in the availability of water and carbohydrates, the two most important growth factors, which are already shortened due to the chronic drought situation in the area. Therefore, pine mistletoe increases the risk of drought-induced mortality of its host when growing in a xeric environment.
Y1  - 2010
U6  - http://dx.doi.org/10.1093/treephys/tpq038
SN  - 1758-4469  (Online)
SN  - 0829-318X (Print)
VL  - 30
IS  - 7
SP  - 845
EP  - 832
PB  - Oxford University Press
CY  - Oxford
ER  -