Management of compaction during harvest of Pinus plantations in Queensland: II. Preliminary evaluation of compaction effects on productivity

Two retrospective studies were conducted in the coarse-textured, coastal lowland soils of south-eastern Queensland to provide a preliminary assessment of compaction affects on the productivity of Pinus plantations. In the first study, stem wood volume of a 9-year-old plantation established on a site used as a log dump during clearfell harvest of the first rotation was reduced by 40.3%. There was a clear link between persistent compaction, reduced root development and reduced wood production. Standard site preparation and cultivation operations used at the time of second rotation establishment did not ameliorate compaction damage. A number of operational measures are suggested for minimising the impact of log dumps on plantation productivity. In the second study, dendro-chronological techniques were used to determine annual basal area increments (BAIs) of crop trees following thinning operations that resulted in rut compaction of various intensities. The methodology allowed both positive growth responses to thinning and adverse growth responses from compaction to be identified. BAI reduction was most prominent in larger trees adjacent to rut compaction exceeding 10 cm depth. For example, BAI of trees with a 27.5 cm under-bark diameter adjacent to ruts 15 and 35 cm deep was reduced by 17% and 29% respectively compared to increment of those adjacent to ruts 0 cm deep. The study provides support for proscribing rut compaction exceeding 10 cm in depth.