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Applied Plant Biology

Benkenstrasse 254a
CH-4108 Witterswil
+41 (0)61 485 50 70


Mortality of beech and spruce is strongly increased by drought stress. In beech, a good indicator for drought stress is the minimum site water balance, the daily accumulated difference between rainfall and potential evapotranspiration. For spruce, a good indicator is the proportion between actual and potential evapotranspiration during the first 80 days of the vegetation period. For both trees it was best to average these indicators over several previous years: for beech over two, for spruce over three years. In spruce, mortality is even higher when drought stress is combined with increased nitrogen deposition as well as potassium and magnesium deficiency. The drought effect on spruce mortality is much stronger when nitrogen deposition is high or when the foliar potassium concentrations are low (high ratio between N and K). Also low magnesium concentrations go along with increased mortality in spruce. For oaks, mortality is correlated with potassium deficiency.

Beech mortality Beech mortality
  Mortality of beech increases with drought stress expressed as minimum site water balance
  summed over the two previous years. Additionally, beech trees die more often, where foliar
  phosphorus concentrations are low.

Spruce mortality Spruce mortality
  For spruce, the relationship between mortality and drought stress is highly dependent on
  nitrogen deposition (left), or on deficient concentrations of potassium and magnesium (right).

Oak mortaliy
  Mortality of oaks increases with decreasing
  foliar potassium concentration.