EFFECT OF THINNING ON THE DISTRIBUTION AND BIOMASS OF FOLIAGE IN THE CROWN OF RADIATA PINE

Replicated plots in a 15-year-old plantation of radiata pine (Pinus radiata D. Don) of basal area approximately 40 m 2 /ha were thinned from below to approximately 11, 18, 23, and 28 m'-/ha respectively. The plots were re-thinned periodically thereafter to these same basal areas; one replicate of plots was retained relatively unthinned. Regression equations relating needle dry weight to branch cross-sectional area were developed and used to examine the distribu­ tion of foliage of various ages within the crowns. In the upper crown (70-80% height decile and above), the percentage of 1-year foliage increased acropetally from 52 to 75% whereas that of 2-year and 3-year and older foliage decreased slightly (28 to 22%) and markedly (20 to 3%) respectively. In the middle and lower crown, i.e., all deciles below the 70-80% decile, the distribution of foliage across age classes was approximately constant at 37% (1-year), 28% (2-year), and 36% (3-year and older). The combined biomass of 1- and 2-year leaves within the whole crown averaged 73% of total leaf biomass under all thinning regimes. Though stand density had little effect on proportionate distribution of foliage by position in the crown or leaf age, the total amounts of foliage varied greatly. Total foliage biomass ranged from 4.9 to 11.3 tonnes/ha and annual foliage production from 2.4 to 4.3 tonnes/ha in stands of mean stand density ranging from 15m 2 /ha (biomass) or 21 m 2 /ha (annual production) to 46 m 2 /ha.