Kirk. — Growth-periods of New Zealand Trees. 429 



Art. XL VII. — On Growth-periods of New Zealand Trees, especially 

 Nothofagus fusca and the Totara (Podocarpus totara). 



By H. B. Kirk, M.A., F.N. Z.Inst., Professor of Biology, Victoria 



University College. 



[Read before the New Zealand Science Congress, Palmerston North. 29th January, 1921 ; 

 received by Editor, 14th February, 1921 ; issued separately, 12th August, 1921.] 



Most of the information available as to the diameter-increase in New 

 Zealand trees is expressed in terms of the diameter achieved by a tree 

 during its whole life, little regard being paid to its growth at different 

 periods of its life. Examination of several of our trees, however, shows 

 that there is a well-marked period of youth, during which growth is 

 slow ; a prime, during which growth is, relatively at all events (and often 

 absolutely), rapid ; and a period of senescence, during which growth is 

 slower than in youth. I was much impressed by this when marking 

 the section of a big totara (Podocarpus totara) in the Biology Museum of 

 Victoria University College. The Forestry Commission of 1913 published 

 a photograph of this section in its report, together with a diagram showing 

 the relative position of the twenty-five-year points marked on the radius, 

 but did not otherwise call attention to the widely varying rate of growth 

 at different periods. This varying rate is shown by the figures in Table A 

 of this article, and by the graphic representation which shows the increase 

 in diameter for each period of twenty-five years. It will be seen that in 

 the first 100 years — the youth of the tree — a diameter of only 350 mm. 

 (13-8 in.) was achieved. At 200 years the diameter had reached 1,180 mm. 

 (46-49 in.). The period of most rapid growth (of the arbitrary periods 

 marked) was that from 200 years to 225 years, bringing the diameter up 

 to 1,528 mm. (5 ft.). From this time growth became slower until it was 

 less than during the youth of the tree. At the age of 396 years, when the 

 tree was felled, its diameter was 2,528 mm. (8-3 ft.). It has been assumed 

 that only one growth-ring was formed in each year, and I believe the 

 assumption is justified. 



I have not examined other totara-trunks with the same attention, but. 

 have found that the slow early growth, the rapid growth of the prime, and 

 the slower growth of age are constant features. The bearing of this upon the 

 conservation of totara that have passed their first hundred years is obvious. 



In February, 1920, I was for a few days at Paradise, at the head of 

 Lake Wakatipu, where milling was being carried on in the beech forest, 

 and trees were being felled to supply material for the bridge over the 

 Reece. A number of trees of Nothofagus fusca had been felled, and 

 examination of these showed a well-marked youth and prime, and that 

 later growth had been at a slower rate, though the rate did not decline 

 uniformly. The oldest of these trees showed 213 rings, but it is probable 

 that none had reached full age. Standing trees of much greater diameter 

 were probably older, but they were generally hollow. I counted carefully 

 the rings on four of the sound trees, and measured the diameter-growth for 

 each period of five years. In Table A these results are shown for periods 

 of twenty-five years, to correspond with those chosen for the totara. These 

 figures, with the graphic representation, show the slowest growth during 

 the first twenty-five years, relatively rapid growth during the next seventy- 

 five, followed by a growth-rate slower than the maximum, but never coming 

 to be so slow as that of the youth period. I do not suppose that the 

 period of old age had been entered upon by any of these trees. The 



