Collected works > Edinburgh edition, 1894-98 - Works of Robert Louis Stevenson > Volume 28, 1898 - Appendix

INFLUENCE OF FORESTS
wood is never allowed enough time to overtake the rapid
changes of the more sensitive air. Hence, so far as we can see
at present, trees appear to be simply bad conductors, and to
have no more influence upon the temperature of their sur-
roundings than is fully accounted for by the consequent
tardiness of their thermal variations.
Observations bearing on the second of the three points have
been made by Becquerel in France, by La Cour in Jutland
and Iceland, and by Rivoli at Posen. The results are perfectly
congruous. Becquerers observations * were made under wood,
and about a hundred yards outside in open ground, at three
stations in the district of Montargis, Loiret. There was a
difference of more than one degree Fahrenheit between the
mean annual temperatures in favour of the open ground. The
mean summer temperature in the wood was from two to three
degrees lower than the mean summer temperature outside.
The mean maxima in the wood were also lower than those
without by a little more than two degrees. Herr La Cour 2
found the daily range consistently smaller inside the wood than
outside. As far as regards the mean winter temperatures,
there is an excess in favour of the forest, but so trifling in
amount as to be unworthy of much consideration. Libri found
that the minimum winter temperatures were not sensibly lower
at Florence, after the Apennines had been denuded of forest,
than they had been before. 3 The disheartening contradictori-
ness of his observations on this subject led Herr Rivoli to the
following ingenious and satisfactory comparison. 4 Arranging
his results according to the wind that blew on the day of
observation, he set against each other the variation of the
temperature under wood from that without, and the variation
1 Gomptes Rendus, 1867 and 1869. 2 See his paper.
3 Annates de C'himie et de Physique, xlv., 1830. A more detailed com-
parison of the climates in question would be a most interesting and
important contribution to the subject.
4 Reviewed in the Austrian Meteorological Magazine, vol. iv. p. 543.
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