Effects of advance regeneration and germinated seedlings on forest recovery after clearcutting of Chamaecyparis obtusa plantations in Southern Kyushu,Southwestern Japan

We clarified the effect of advance regeneration on natural forest recovery after clearcutting of conifer plantations over the mid-term observation period (12–14 years to allow formation of the forest canopy). We established understory-intact plot (UI-plot), where advance regeneration (AR; DBH more than 1 cm before clearcutting) were retained, and understory-cleared plot (UC-plot), where all ARs were removed at felling of conifer crops. We surveyed individual density, species richness, and tree height with reference to different regeneration origins 1 year after and 12 or 14 years after clearcutting. Then, we compared the structural changes in UI-plot with that in UC-plot. The resprouted AR in UC-plot has provided the same effect as the retained AR in UI-plot in forming their height distribution patterns and stratification over a mid-term recovery process. We also found that individual density and species richness attributed by the individuals of newly established seedlings after clearcutting (SE), have contributed to the stand development in the both plots. Furthermore, SE was found to have a large contribution to forest recovery in terms of tree density and species number, while its significance for the recovery of gravity-dispersal, lucidophyllous trees was limited. We concluded that the advantage of AR retention is limited to the fast recovery of forest structure at the early stage after clearcutting, and mostly disappeared over a mid-term observation period as far as abundant advance regeneration was sufficiently accumulated and surrounding seed sources were effectively secured.

     

Dynamics of an old evergreen coppice in southwestern Japan with special focus on a typical coppice species (Castanopsis cuspidata) and a climax species (Distylium racemosum)

We investigated stand dynamics of an abandoned evergreen coppice (c.a. 100 years old) over the course of 21 years in south Kyushu, Japan. The study stand showed a change in species composition from being dominated by Castanopsis cuspidata to Distylium racemosum, that is, from a typical coppice species to a typical climax species of the region. However, the relative dominance of Castanopsis spp. appeared to remain very high in the study stand compared to that in the Aya Research Site, a typical old-growth forest in the region, due to abundant C. cuspidata canopy trees of coppice origin. This suggests that the species composition of the study stand remained distinct from that of climax forests in the region. On the other hand, D. racemosum did not show a significant change in diameter at breast height (DBH) class frequency distribution from 1996 to 2017, probably due to the slow growth of this species. However, generalized linear models (GLMs) were used to identify the factors affecting better DBH growth of this species in the gap, indicating the potential for further development of the population structure when small trees are released from suppression of canopy trees. This suggests, inversely, that the development of the D. racemosum population was heavily suppressed by abundant C. cuspidata canopy trees of coppice origin that survived to the age of nearly 100 years. Further, large typhoons are suggested to cause severe canopy disturbances that remove canopy trees of C. cuspidata, which might be important for promoting further forest succession, even for a nearly 100-year-old evergreen old coppice.

     

Restoration of semi-natural forest after clearcutting of conifer plantations in Japan

We reviewed recent studies on the restoration of semi-natural forests after clearcutting of conifer plantations with specific reference to the importance of setting restoration goals, general and specific factors influencing restoration, and the prediction and judgment of successful restoration. For the restoration of semi-natural forests following the clearcutting of conifer plantations, recovery levels and appropriate restoration methods cannot be considered separately from the aims of restoration to provide ecosystem services. Restoration needs to be based on the setting of goals that correspond to the type and degree of ecosystem services targeted. When we aim to restore vegetation dominated by late-seral canopy trees within as short a period after the clearcutting of conifer plantations as possible, advanced regeneration in the pre-logged plantation is the most important and reliable source of post-logging regeneration, just as it is in the recovery of disturbed non-plantation forests. Advanced regeneration is not always present in plantations. Seedling establishment by seed rain from adjacent natural forest patches after a disturbance can contribute to late-seral or canopy species; however, the range of the edge effect is generally short, and the degree of the edge effect depends on the natural forest type and is more pronounced in deciduous forests, such as those in cool-temperate climates, or in forests with a complex forest structure. Thus, advanced regeneration is a better predictor of short-term forest recovery than measures based on seed rain from adjacent seed sources. However, restoration achieved only through advanced regeneration can simplify the species composition, and the recolonization processes of gradual species accession from seeds should be considered in the long-term context of restoration.