FIGHT FOR LIFE

Evening Post, Volume CXXIII, Issue 58, 10 March 1937, Page 4

FIGHT FOR LIFE

THE EIMU'S FATE

LAW OF THE JUNGLE

EXOTfO TREES USED

(By "Bushlover.")

During the earlier part of its life, a young rimu requires shade; then for a period it tolerates shade; then comes a time when it requires light.

If the native forest plant-life amid which the young rimu is born gives the rimu the shade which it requires, or tolerates, during the first and second periods, well and good. But when the growing rimu demands light, and the faster-growing native plants round it give only denser shade, trouble begins for the rimu.

Is this the reason why, in certain New Zealand forests, search discloses few or no rimus above a certain height (the height where light-demand begins) and below the height of millable trees? SHADE-TOLERANCY AND GROWTHKATE. Field work in the Akatarawa-Whaka-tikei forests, Hutt basin, reveals a sufficiency of young rimus up to four feet in height, "but between these, and trees of millable size, there is, except for odd specimens, nothing." Why? Because the sheltering growth round the small rimus became a suppressive growth to the larger sapling rimu, which therefore died. Or, in technical language, "the shade tolerancy period" of the rimu was "evidently exhausted during the time" required by the rimu to reach the height of three or four feet. The quoted words are taken from an article in the "New Zealand Journal of Forestry" (Te Kura Ngahere) issued on the authority of the New Zealand Institute of Foresters. The writer is the, Chief Forestry Officer of the Wellington Water Board, Mr. A. N. Perham; and as his field of operations is the Water Board's Akatarawa-Whaka-tikei commercial forest, the findings are of both local and national interest. What he writes concerning the chances of rimu to sow itself and regenerate itself in Nature recalls the article in the same journal by Mr. C. T. Sando on kauri dissemination and regeneration on the North Auckland spurs and on other parts of the kauri area. The national importance of the regeneration of kauri, beech, rimu, and other native timber trees does not need stressing. In the Water Board's forest, too dense shading by broadleaved native competitors is suppressing not only rimu, but such timber species as kahikatea or white pine, totara, matai, and miro. Mr. Perham adds that his statement concerning the gap in the rimu (above four feet of height) is true also, "with certain modifications as to height," of kahikatea, totara, matai, and miro. TIMBER TREES SUPPRESSED IN INFANCY. Mr. Perham finds that regeneration of these podocarps "is suppressed in its infancy; and the forest, so far as its timber components are concerned, is over-mature and stagnant," because probably of "the extremely slow growth-rate of the podacarps, and the dense shading effect of the evergreen broad-leaved species which form the secondary storey of the forest. Through this latter, the young podocarps arc unable to penetrate and attain to their ultimate light requirements during their period of shade tolerancy." If the native podocarps are too slowgrowing to escape from their surrounding nurse-plants before their nurseplants become then- destroyers, are there other timber species that will be sufficiently quick-growing to make use of the shading ■ plants, and yet to spring up into the light at the right moment? Searching for a timber tree with sufficient shade-tolerance, combined with sufficient speed of growth, upward and lightward, the Water Board Administration has experimented with exotic timber trees. Among lovers of the native .forest, the introduction of exotic trees into native forests meets with criticism. The criticism would be much more valuable if its would deal with the question of suppression of native timber trees by native undergrowth, and if it would indicate some purely indigenous remedy, as, for instance, silvicultural treatment (within reasonable cost) that might enable the native timber trees to overcome their regenerative disabilities. COMMERCIAL TEST. The position of a commercial forest, in which the aim is growth of new trees that must not only survive competition but be quick-growing enough to produce timber within an economic period, is of course" quite different from the position of a national park or a scenic reserve or a strictly protection forest. The Water Board's area is about 80,000 acres, and, of this, the section treated as commercial forest is about 12,000 acres. When the sawmiller in the Akatar-awa-Whakatikei forest drags his logs out of a given area, the Forestry Officer and his staff plant their exotic trees, and the race with the native second growth, to fill the blanks created by the sawmiller, begins. By the third year after the sawmiller ' has finished the area, the competitive native second growth (principally kotukutuku, makomako, pate) is fairly in its stride, "and by the seventh to eighth year has, in many cases, reached a height of twenty feet. From this stage, the growth-rate slows up progressively and culminates at heights of from approximately thirty to forty feet. Hence, success in the establishment of the exotics resolves itself into getting them to a height approaching twenty feet by the seventh year." Mr. Perham quotes figures of height of his exotics to indicate that this growth-rate may be attained: The exotics include Lawson's cypress, Californian redwood, Cryptomeria japonica, western red cedar, Douglas fir, deodar, Monterey cypress, western hemlock, and Oregon alder. Mr. Perham concludes: "Whether the ultimate result of this piece of work will be success or failure, time alone can demonstrate, but so far as the result may be determined at present, the prospect of ensuring a rotational crop of timber appears to be exceedingly bright."