T. Curt et al., Predicting site index of Douglas-Fir plantations from ecological variablesin the Massif Central area of France, FOREST ECOL, 149(1-3), 2001, pp. 61-74
Douglas-Fir is the main species used in France for reforesting mid-elevatio
n regions, mostly on former heathlands and coppices. In order to clarify it
s auto-ecological Limits, and to provide forest managers with relevant info
rmation for planting, we studied its productivity in a wide range of site c
onditions. Based on data from 202 Douglas-Fir pure stands at mid-elevation
regions, site productivity was assessed using variance analysis with site t
ypes, site groups, and multiple regression analysis with ecological variabl
es. Site index, determined from stem analysis data, was used as a species s
pecific measure of site quality. Results show that Douglas-Fir site index i
s correlated to soil nutrient status, and secondarily to soil moisture regi
me. Mean stand productivity was generally high, but considerable variation
in site index was determined within a study area that was classified by for
est managers as uniform. Correlation between site classification and site i
ndex was confirmed, because it was based on synoptic factors that are simpl
e and robust indicators of site productivity. Other methods to assess site
quality, such as multiple regression on ecological variables and multivaria
te site groups, appear to be less explicative and robust for predicting sit
e index. The results allow forest managers to predict the site index at par
cel scale. Further investigation should be carried out in order to explain
the major causes of the unexplained variance of site index by ecological va
riables, especially genetic variation, and effect of age. (C) 2001 Elsevier
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