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

ON THE THERMAL INFLUENCE
OF FORESTS '
The opportunity of an experiment on a comparatively large
scale, and under conditions of comparative isolation, can occur
but rarely in such a science as Meteorology. Hence Mr. Milne
Home's proposal for the plantation of Malta seemed to offer an
exceptional opportunity for progress. Many of the conditions
are favourable to the simplicity of the result ; and it seemed
natural that, if a searching and systematic series of observa-
tions were to be immediately set afoot, and continued during
the course of the plantation and the growth of the wood, some
light would be thrown on the still doubtful question of the
climatic influence of forests.
Mr. Milne Home expects, as I gather, a threefold result : —
1st, an increased and better regulated supply of available
water • 2nd, an increased rainfall ; and, 3rd, a more equable
climate, with more temperate summer heat and winter cold. 2
As to the first of these expectations, I suppose there can be no
doubt that it is justified by facts ; but it may not be unneces-
sary to guard against any confusion of the first with the
second. Not only does the presence of growing timber increase
and regulate the supply of running and spring water inde-
pendently of any change in the amount of rainfall, but as
Boussingault found at Marmato, 3 denudation of forest is
sufficient to decrease that supply, even when the rainfall has
increased instead of diminished in amount. The second and
third effects stand apart, therefore, from any question as to the
utility of Mr. Milne Home's important proposal; they are
both, perhaps, worthy of discussion at the present time, but I
1 Read before the Royal Society, Edinburgh, 19th May 1873, and
reprinted from the Proceedings R.S.E.
2 Jour. Scot. Met. Soc, New Ser. xxvi. 35. 3 Quoted by Mr. Milne Home.
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