Growth of first and second-rotation stands of Pinus radiata D. Don on dune-sand soils at Rennick. First progress report.  R. O. Squire, D. W. Flinn, P. Hopmans and P. W. Farrell.  January 1979.  55 pp. (unpubl.)

SUMMARY

By the turn of the century, softwood plantations composed predominantly of Pinus radiata will provide about 70 percent of Australia’s wood requirements, so it is of major importance that the growth and health of these plantations is maintained. Although first rotation (1R) plantations of P. radiata have been remarkably productive in Australia, there is evidence from South Australia that second rotation (2R) growth on dune-sands is in many instances substantially less than 1R-growth. The implications of this evidence for the extensive areas of P. radiata growing on coarse textured, infertile soils are serious.

Two concurrent studies are in progress at Rennick in south-west Victoria. The objective of the first study is to provide accurate information on the growth of successive rotations of P. radiata on sites embracing the widest possible range of 1R-site qualities. The objectives of the second study are: to provide interim evidence on the likely direction and magnitude of growth changes; to identify possible reasons for these changes should they occur; and to guide the development of silvicultural treatments to maintain or possibly increase growth over successive rotations.

In study I, 1R-stands of low and high side quality were examined by stem analysis to determine total volume and height growth as functions of age. Total volume measurements showed that growth on the study sites range from about 520 to 730 m³/ha at age 25 years, or from about low IV to II respectively on the South Australian site quality scale.

These stands were clear felled between October 1974 and February 1975. The unburnt sites were pit-planted during July 1975, with seedlings grown from 1R-seeds collected from plot trees and raised by cultural practices similar to those for the first rotation. As these 2R-stands develop, volume and height growth will be progressively compared with the original crop. Calculations of confidence limits indicate that it will be possible to detect differences between rotations in cumulative volume growth of 13 to 29 percent by age seven years and 9 to 12 percent by age 15 years.

Study II is based on plots located on 1R-sites which matches closely as possible the 2R-plots of Study I. P. radiata was established on these 1R-sites at the same time, and using techniques comparable with those used for Study I, except that the felled eucalypts were burnt prior to planting.

Results dealt with in this report covered the period July 1975 - November 1976 and show that early growth on unburnt 2R-plots has been markedly superior to that on burnt 1R-plots. Trees on 2R-plots achieved more than twice the height growth and nearly three times the basal area growth of those on 1R-plots during the first 16 months after planting. These differences were largely established during the December 1975 - March 1976 period, and were strongly related to differences in uptake of water and nitrogen which were both low enough on 1R-plots to severely restrict growth. Soil moisture availability during this period was lowest on 1R-plots due largely to the interrelated effects of higher weed competition (mainly bracken) and the absence of a mulch of litter and logging residue. This probably accounted in large part for the differences in water uptake and may have indirectly influenced N uptake by increasing mineralisation of organic N. These early results indicate that establishment practices aimed at conserving logging residue and litter remaining after the first rotation could be crucial to the maintenance and or improvement of wood production of successive rotations of P. radiata on infertile dune-sands.

Also published:

Squire, R.O., Flinn, D.W. and Farrell, P.W. (1979)  Productivity of first and second-rotation stands of radiata pine on sandy soils. 1. Site factors affecting early growth.  Aust. For. 42 (4): 226-35.