Removal of phosphorous in logs when harvesting Eucalyptus delegatensis and Pinus radiata forests on short and long rotations

Summary

The quantity of phosphorus (P) accumulated in the wood and bark of tree stems, and which is removed from the forest by harvesting, has been estimated for native Eucalyptus delegatensis stands and Pinus radiata plantations on the southern tablelands of New South Wales. The rates at which P is accumulated and removed in logs are compared for the two species grown on either short (20 yr) or longer (40 yr for P. radiata, 60 yr for E. delegatensis) rotations.

The comparison showed that in stands which are older than about 7 years, 3–5 times more P is removed from the forest when harvesting a unit weight of P. radiata log (wood and bark) because this species contains more sapwood (which persists for 17–25 years before being transformed to heartwood) than E. delegatensis (7 years of sapwood), and the concentration of P is much greater in sapwood than in heartwood. The concentration of P is more than three (and can be ten) times greater in the heartwood of P. radiata than it is in E. delegatensis.

Shortening of rotations will increase the amount of P removed per unit of wood harvested for both species. If E. delegatensis were to be managed on short rotations of about 7 years when all or most of the harvest is sapwood, then there may be little difference in the quantity of P removed per unit of wood between this species and P. radiata of the same age.

Harvesting of boles from P. radiata grown on a rotation of 20 years compared with that of E. delegatensis grown on a rotation of 57 years can increase the amount of P removed from the forest by a factor of almost 6. Since both the amount of P in the soils and the natural inputs of P are small, we conclude that fertilisation is likely to be necessary in order to sustain reasonable productivity in many Australian plantations of radiata pine.