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Résumé :
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Beech woodland can be restored by direct planting of beech (Fagus sylvatica L.) seedlings in abandoned areas, but this method is generally avoided in forestry because of the growth difficulties of beech in full light conditions. This study tested a method that consists in planting beech seedlings in full-light conditions with Silver birch or Scots pine as nurse trees. A total of 65 two-year-old beech seedlings surrounded by either 3, 4, 5 or 6 pine or birch seedlings or without competitors were planted in bare-soil open-field conditions in central France. Tree growth and light availability were monitored at the end of each of the 3 years, and soil moisture was also measured the last year. At the end of the experiment, aerial biomass measurements were made on the beeches. Results showed that relative beech growth in terms of diameter was reduced by the local neighbourhood and that this reduction was particularly noticeable in the pine treatments where there was extensive pine seedling development. In contrast, relative beech height did not exhibit any significant variations among the treatments. Light availability was decreased by the neighbourhood, especially in the pine treatments. Light reduction was more pronounced in the last two years and in the middle or lower parts of the canopy of the subject beech. Soil water content was lower under the pine canopies than under the birch canopies, and was positively correlated to beech relative diameter growth. SLA, height-to-diameter ratio and crown length-to-crown width ratio increased with increasing competition from the neighbours. There were treatment effects on beech biomass partitioning: the branch biomass-to-total biomass ratio was lower in the pine treatment than in the birch treatment, whereas stem-to-total biomass ratio was lower in the birch treatment. This study showed that nurse trees tend to reduce beech growth but improve form. However, further studies are needed to quantify the effects of the neighbourhood on the growth of competitive herbaceous vegetation and on changes in the microclimatic conditions.
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