160 NATIVE FOREST AND PLANTATIONS OF INTRODUCED TREES. 
in northern Europe and about 35 in. in the tropics : 25 in. may be taken 
for the extra-tropics and the North Island of New Zealand. There is 
thus no area too dry for successful forestry in the North Island, and 
only perhaps Central Otago and some smaller areas in the South Island. 
The dull light which thins the timber “ stands ” of foggy England and 
northern Europe is equally absent from New Zealand. Thus in New 
Zealand, where there are mild summers and winters, and rarely a want 
of moisture, light is left as the sole limiting factor. If the imdividual 
native timber-trees of New Zealand have a timber-growth greater by 
40 or 80 per cent. than those of Europe, it is probable that the incre- 
ment of timber per acre is proportionately greater still, for in addition 
to the climatic reason there is the fact that the New Zealand timber-trees 
belong to the shade-bearing or tolerant class of trees. 
SHADE-BEARING AND LIGHT-DEMANDING ‘'l'REES. 
It is the ABC of forestry that all forest-trees are classified as being 
light-demanding (intolerant) or shade-bearing (tolerant). Lists are drawn 
up giving graduated scales for each class. For New Zealand trees this 
knowledge will come with the forestry of the future. In the meantime 
we know that trees in the New Zealand class of forest, the dense evergreen 
forest, are usually more or less shade-bearing; and observation shows 
that New Zealand trees are no exception to this rule. 
Shade-bearing trees, Ceferis paribus, produce more timber per acre 
per year than light-demanding trees. This is shown by a glance at the 
yield-curyes given in my “‘ Journal of a Forest Tour,’’ Spruce and 
Silver-fir grow side by side in the same forests. In pure ‘‘ stands ”’ 
Spruce at first shows the higher volume of timber per acre, but as 
maturity is approached this position is- reversed. The lght required 
for one Blue-gum may satisfy half a dozen Silver-firs, and the Blue-gum 
only produce three times as much timber as one Silver-fir !* 
In my. album of New Zealand forest views are two suggestive photos, 
The first photo shows the slow growth of a native tree taken away from 
its forest home—a Black-pine in the Botanic Gardens, Christchurch, that 
at forty years of age is ll ft. high. It has had ample light, garden 
cultivation, and shows no sign of disease or injury, but, as a shade- 
bearing tree, is a fish out of water. It is not one-eighth the size of light- 
demanding trees growing alongside it. 
The other photo shows the obverse of the picture—Rimu and Miro 
trees growing in the dense shade of the native forest at Buller Gorge. 
They are flourishing in shade so dense that a light-demanding tree would 
perish forthwith. By test with a photo light-meter I ascertained that 
these two young trees of Rimu and Miro were flourishing in a light only 
about one-sixtieth that of full hght in the open. The photo-active rays 
difier from the growth rays, but the one is an indication of the other, 
A light-demanding tree, such as the common Blue-gum, for instance, 
wants the full light of these latitudes. I know from experience in plant- 
ing it in cleared forest that when full light is cut off, only by a little, the 
Blue-gum shows a reduced growth. Be 
_ To quote an illustration from the great fir forests of Europe, Silver-fir 
is a shade-bearer with a heavy ‘‘stand’’ of timber at cropping-time. 
Whether we take first-class, second-class, or third-class forest, Spiedel’s 


* The American Forest Service Bulletin 92, « Light in Relation to Tree-growth,” 
may be consulted. It is by two eminent American foresters—Graves and Zon. 

