6 The N.Z. Journal of Science and Technology. [Feb. 
in the open. The good timber comes from the forest-grown tree ; the 
gum-tree in the open may be coarse timber only fit for firewood or fencing- 
posts. I have seen many such that would not pay the expense of cutting 
up for firewood. 
In the British Isles, where there are practically no natural forests, and 
where now new forests are to be made at an expense of £15,000,000 as a 
measure of war-insurance, exotic trees will no doubt be largely used. They 
may yield double or treble that of the native trees, so that there is only 
their riskiness against their general adoption. The subject will be found 
discussed in Transactions of the Royal Scottish Arhoricultural Society for July, 
1915. Dr. Henry there points out that four exotics—Douglas fir, Sitka 
spruce, giant thuya, and the European larch—may be expected to yield a 
200 acrim—viz., an average yield of 200 cub. ft. per acre per year. Now, 
the native trees in European forests do not, over any large area, have an 
acrim exceeding 150 (spruce forests of Saxony), while the general average 
probably does not exceed an acrim of 70 cub. ft. In spite of this, no 
European forester, not even those holding the most revolutionary ideas 
in forestry, has ever proposed to cut down the native forests and replace 
them by quicker-growing exotics. European foresters are proceeding 
cautiously and gradually, working in exotics here and there according to 
circumstances. New Zealand can do no more. 
There are people, however, who say it matters little to New Zealand 
what is the forest policy of other countries ; and one may consider that 
point of view, though it sounds shallow, because the New Zealand bush, 
for practical purposes, is the same as the South African bush, and that 
has been successfully managed on the European forest system for one- 
third of a century. 
Risk in planting Exotic Trees. —After the expense of planting exotic 
trees comes the risk. The introduced trees in New Zealand, and in every 
country, carry a heavy risk. We can introduce flowers, and fruits, and 
vegetables, and find out just what they are worth in a few years. The 
forester has to wait hundreds of years before he can know the exact value 
of introduced trees. He cannot spray or cultivate ; he is left entirely in 
the hands of Nature ; and at any time, perhaps after several centuries, 
Nature may turn on him and make his introduced trees worthless. This 
has actually happened with Pinus strobus in Europe and Pinus pinea in 
South Africa. Each did very well for about a couple of centuries ; now 
they are so badly attacked by fungoid diseases that as forest-trees they are 
worthless. England surpasses every country in the world in the number 
of its introduced trees, but the history of English arboriculture teems 
with promising introductions that have failed after some years. Thus 
foresters in every country go slow with exotics. 
When all is said, discussion about the rate of growth of native and 
introduced trees is mainly academical. In practice the difference is effaced 
by various economical circumstances. A native forest on soil of low value 
may produce little timber, but with no capital sunk on it there is no loss. 
Every plantation in a country of costly labour is heavily weighted. The 
wild forest in a state of nature is earning nothing—growth balances decay ; 
but as soon as it is skilfully worked it starts making a timber increment. 
Banish fire and grazing, and it is safe to say that for every tree cut, nature 
provides two or three to replace it. On the other hand, if Wellington 
wanted a suburban forest like those of Brussels or Paris, and were to set 
