Douglas-fir is vulnerable to exceptional and recurrent drought episodes and recovers less well on less fertile sites

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Abstract

Context

Since the 2003 drought and heat wave, there have been many reports of Douglas-fir decline and dieback in France. Given the climate change that is predicted, more frequent drought episodes could induce recurrent decline processes. The nature and background of this threat requires a careful assessment.

Aims

The objectives of this study were: (1) to test the hypothesis that the major climate hazard that accounts for the decline in Douglas-fir growth is drought, and (2) to identify the main vulnerability factors involved.

Methods

Decline and recovery of radial growth were quantified of Douglas-fir in two particularly affected regions with a dendroecological approach; 899 trees were sampled on 58 plots. Mean climate data, ecological and dendrometric stand characteristics were tested in order to identify potential vulnerability factors

Results

A clear relationship was evidenced between growth and soil water deficit. A severe decline of radial growth was induced by the 2003 drought and was maintained during subsequent years due to recurrent drought episodes. Growth recovery at the stand level was enhanced by soil nutrient fertility.

Conclusion

Radial growth of Douglas-fir is clearly driven by the intensity of drought. In a context of climate change, an adaptive silvicultural strategy is required in order to cope with more frequent drought events. To mitigate the frequency and the intensity of water shortage episodes, site selection must take into account not only local climate characteristic but also soil properties like maximum extractable water content. Soil nitrogen fertility was found to play a key role for an efficient recovery of radial growth after drought episodes and thus must be preserved.

Handling Editor: Matthias Dobbertin

Contribution of the co-authors

Anne-Sophie Sergent has contributed to designing the experiment, writing the paper, analysing data. Philippe Rozenberg was co-supervisor of the work and has contributed to data analysing and proofread the paper. Nathalie Bréda was the coordinator of ANR-06-VULN-004, co-supervisor of the work and contributed to experimental design, running the data analysis, computing the water balance and writing the paper.