Initial evaluation of tree growth and silvicultural costs in low-density plantations of hybrid larch (Larix gmelinii var.japonicax L. kaempferi) established by seedlings and rooted-cuttings

In Hokkaido, northern Japan, more and more artificial stands of Japanese larch (Larix kaempferi) have been logged lately, because of their maturation and increasing demand for domestic timber due to the recent decrease of imported logs. Reforestation of these stands, however, tends to be delayed, since the relatively high costs for silviculture, such as planting, weeding and thinning, often discourage private land owners from regenerating the stands. To promote the reforestation and maintain the resource of this tree species in the region, silvicultural costs are expected to be lowered. The Fsub(1) hybrid of Kuril larch (L. gmelinii var. japonica) and Japanese larch exhibits various superior traits, i.e. rapid growth and high survival rate at the juvenile stage and straight stems. These traits are all desirable for low-density plantation which could contribute to the potential reduction in silvicultural costs of the species. Furthermore, as the rooted-cutting method has been established for propagation of the selected families of the Fsub(1) hybrid with high wood quality, future production of high quality timber are also expected. To evaluate the growth performances of the Fsub(1) hybrid planted at lower density and assess the costs of this new silvicultural system, we set up five experimental stands in the various regions of Hokkaido during the years between 2002 and 2004. Planting densities were 625, 1000 and 1333 trees/ha and two kinds of planting stock, i.e. seedlings and rooted-cuttings, were used. At the age of 5-year-old, trees originated from rooted-cuttings were taller than those from seedlings. Mean survival rates at this stage were 4% lower in the rooted-cuttings than seedlings. Silvicultural costs for the initial six years, i.e. costs for site preparation, purchase of seedlings/rooted-cuttings, planting, weeding and application of rodenticide, were reduced by 30-40% in the stands with lower planting density (1000 trees/ha) as compared with those with regular density (1900 trees/ha). Although the partial weeding by the striped-way allowed some broad-leaved trees to invade into the non-weeded areas, the cost for eliminating these trees were quite low and, consequently, the striped weeding contributed to reduce the total silvicultural cost in the initial stage of stand establishment.