Reversible variations in some wood properties of Norway spruce (Picea abies Karst.), depending on the tree felling date
Ernst Zürcher, Christian Rogenmoser, Azadeh Soleimany Kartalaei and Diane Rambert
Traditional knowledge, in the form of so-called rural rules, indicates that the date of
tree felling has an important influence on wood quality. The main factor, after the season
of the year, is said to be the position of the moon. The object of the research presented
here was to study the variability of some user-related properties of wood, by analyzing
measurable parameters. The material stems from four different Swiss sites and is
representative of central European conditions. The study involved 576 trees — Norway
Spruce (Picea abies Karst.) and Sweet Chestnut (Castanea sativa Mill.) — felled on 48
dates throughout the fall and spring of 2003–2004 (always on Mondays or Thursdays).
Before the start of the experiment, one sample was taken on the same day from each of
the tested trees, to serve as reference. Wood properties analyzed are: water-loss,
shrinkage under controlled drying, air drying and oven drying density. The statistical
analysis of the complete data series reveals (in addition to a seasonal trend) a generally
weak, but highly significant role of the synodic and sidereal moon cycles and, to a lesser
extent, the tropical cycle.
The lunar-related differences are more marked for the middle months of the trial.
The most obvious variation in Spruce occurs between samples of trees felled immediately
before the Full Moon and the samples immediately following Full Moon. Smaller series of Spruce samples were tested on hygroscopicity, compression strength and calorimetry. Here too, the strong value shifts observed around
the Full Moon found a clear confirmation. The main variation factor for water uptake is
however the type of forest and the site, a naturally grown mountain forest producing a
clearly less hygroscopic wood. The results from this study bring some transparency and
objectivity into a mainly unexplored field of traditional knowledge, a field subject to
controversial discussions. Further research in chronobiology of wood could lead to an
ecological technique enhancing specific wood properties.