Ryoko Hirata

Growth recovery of young hinoki (Chamaecyparis obtusa) subsequent to late weeding

The effects of late weeding treatment on the growth of young hinoki (Chamaecyparis obtusa) during the sixth growing season after planting were examined. Furthermore, the contribution toward hinoki growth recovery of crown productivity (NAR) and biomass allocation to crown (CAR) were determined. In the late weeding plot, no decline in height growth was observed subsequent to weeding, and growth in diameter at breast height (DBH) and crown projection area (CPA) began to recover subsequent to weeding; however, DBH and CPA were reduced and experienced a 1- to 1.5-year growth delay compared to values associated with the weeding plot at the end of the second year subsequent to weeding. Relative growth rate (RGR) and NAR in the late weeding plot recovered and possessed similar values to those of the weeding plot in the second year subsequent to weeding. CAR values of the late weeding plot were similar to those of the weeding plot both before and after weeding. These results suggested that the recovery of NAR rather than that of CAR was primarily responsible for the recovery of RGR. The present study demonstrated that hinoki were able to quickly acclimate to an environment dramatically altered by late weeding and recover growth rate within a short period of time. The present study also showed that delays in crown expansion associated with late weeding may have impeded subsequent matter production. Therefore, it was concluded that late weeding treatments should be employed only when the associated delays in growth are taken into account.

Thirty-year stand dynamics of an old evergreen coppice forest in Southern Kyushu, Southwestern Japan

ABSTRACT We investigated forest development processes for a period of 30 years (during 87–116-year-old) in an evergreen coppice stand in southern Japan that was highly dominated by Castanopsis sieboldii. Stand age changing developmental stages were verified and compared with the results of a previous case study of evergreen coppices mainly dominated by C. cuspidata, C. sieboldii and Quercus salicina in the same region. A survey plot was established in 1985, and tree height and diameter at breast height of all living stems were recorded. Stems of single-stem individuals and multi-stem individuals were distinguished based on observations of stem bases for each of the overstory and understory. Changes in stem density and species diversity were then evaluated. In the overstory, stem density declined between 92- and 116-year-old. On the other hand, stem density in the understory exhibited a distinct increase during the study period; however, it was primarily single-stem and multi-stem evergreen shrubs, such as Aucuba japonica, and multi-stem evergreen trees, such as C. sieboldii that contributed to this increase. The species diversity index (H’) also indicated the same trends. Therefore, it was concluded that the stand examined in the present study exhibited characteristics of the “understory re-initiation” stage after 92-year-old, and that stand development was delayed compared to development of stands examined in a previous study. These results indicated that the progress of stand development may differ depending on dominant species or forest environment even within evergreen coppices in the same region.

Effect of surface soil conservation by litter from shelterbelts on Chamaecyparis obtusa plantation

ABSTRACT We investigated forest floor cover, the amount of transported soil, and litter fall in a hinoki plantation adjacent to an evergreen broadleaf forest set as the shelterbelt on a ridge in order to evaluate the edge effect on surface soil conservation for the hinoki plantation by the litter from the shelterbelt. High values of broadleaf litter fall and forest floor cover, and a low value of transported soil, were observed closer to the edge. Generalized linear modeling suggested that transported soil was strongly affected by the forest floor cover, the percentage of which was largely dependent on the broadleaf litter fall, which was mainly determined by the distance from the edge. These results suggested that the direct supply of litter from the shelterbelt conserves the surface soil of the hinoki plantation around the forest edge.