2 The N.Z. Journal of Science and Technology. [Feb. 
introduced trees, usually as single trees grown in the open, he draws the 
conclusion that these trees are the only practicable ones for the economic 
production of timber. To prove his case he wants figures of volume- 
growth per acre of close forest, and he has none to offer. His standard of 
timber-production per tree is not the standard of scientific forestry, which 
is timber-production per acre of normal forest. Thus, in looking at the 
growth of the native trees and the introduced trees, a large discount has 
to come off the growth of the introduced trees, because most of them 
belong to the class known in forestry as “ light-demanders,” while the 
native trees as a whole belong to the class known as “ tolerant,” or 
“ shade-bearers.” This means -that two or three of the native trees may 
flourish in the light, and consequently the forest space, of one of the introduced 
trees. 
There is the evidence of an experienced bush-expert, Mr. Luxford, of 
Hamilton, that in one instance rimu natural regrowth (in the forest near 
Greymouth) has yielded a growth-figure per acre estimated at 30,000 super¬ 
ficial feet in 30 years.^ This works out to a forester’s timber-growth 
figure (“ acrim ”) of 167 cubic feet. So good a volume-growth is seen only 
occasionally in Europe, where a gross acrim of 150 cub. ft. is the maximum 
over any large area* 
The light and space in the forest required by various trees will be 
found discussed in the forestry text-books, but more especially in a par¬ 
ticularly good American Bulletin, Forest Service, No. 92, Light in 
Relation to Tree-growth, Washington, 1911. This pamphlet is strongly 
edited, the authors being Professor R. Zon, an eminent American forester, 
and Dr. H. S Graves, the head of the American Forest Service. It 
mentions that six European yew-trees ( Taxus haccata) will flourish in the 
light (forest space) required by one European birch— Betula alba. 
Again, I know by long experience that, even in the bright light of the 
latitude of the extreme north of New Zealand, if blue-gum be planted in 
forest clearings even a very small proportion of shade will stunt or quite 
stop its growth. At the same time., I have a photo taken in the New 
Zealand forest where rimu and other native trees are seen growing with 
full vigor in a light which my standard photometer showed was about 
one-sixtieth full daylight, apart from sunlight. Of course, photo-chemical 
rays are not the same as the rays utilized by growing vegetation, but in 
the solar spectrum the intensity of one may fairly be taken as an index 
of the intensity of the other. 
It is true that the growth of individual trees in the open is an indication 
of the growth of trees in dark close forest, and just to that extent the 
growth-figures discussed by Mr. Maxwell have value. In his first table, 
called E, he compares the growth of indigenous trees in New Zealand 
with the growth of foreign trees in foreign countries. Now, a practised 
forester perceives at once that the native New Zealand trees grow faster 
than the common timber-trees of Europe taking each in their own forests; 
and to prove his point he will refer to the standard yield tables of modern 
forest science, such as those of Weise, of which German-English translations 
have been published and which are partly reproduced in Professor Schlich’s 
Manual of Forestry. But Mr. Maxwell’s table E does not do this ; its 
authorities are merely the individual opinions of certain writers of more or 
less value, according to circumstances. 
