Stump sprout dynamics of Quercus serrata Thunb. and Q. acutissima Carruth. four years after cutting in an abandoned coppice forest in western Japan

The concern regarding the re-establishment of coppice forests has increased with respect to biodiversity conservation, bioenergy, and ecological services. To successfully restore the oak dominated coppices, understanding the factors affecting sprout regeneration is necessary because stump sprouts are the essential source of natural oak regeneration. In the present study, therefore, we sought to determine the stump sprout dynamics of the two widely distributed oaks in Japan, Quercus serrata and Q. acutissima, in relation to stump size, sprout characteristics, topographic factors, and canopy closure over a 4-year period following cutting in abandoned coppices. The study plot (40 × 90 m) was established in a coppice forest abandoned since the 1960s in western Japan. In winter 2013, canopy trees within and outside the plot were cut, then we collected the data of sprout origin position, sprout survival, sprout diameter, and length from 2014 to 2017. Four years after cutting, the proportion of surviving stumps decreased to 37% (n = 98) and 56% (n = 61) in Q. serrata and Q. acutissima, respectively. In both species, the Bayesian logistic mixed model showed that stump survival was not significantly affected by stump size and the examined environmental factors. The number of living sprouts per stump differed between Q. serrata (8.7 ± 6.7) and Q. acutissima (5.1 ± 4.6) after four years (P = 0.01). The number of sprouts per stump in both species tended to increase with stump diameter and was greater in convex area, but only significant for Q. acutissima. Dominant sprouts of Q. acutissima exhibited greater diameter and length than those of Q. serrata, and the relative growth rate of sprouts in both species decreased with time after cutting. Dominant sprouts originating from a higher position on the stump grew better than those closer to the ground level. Sprout growth was negatively affected by sprout number per clump and positively affected by dead sprout number per stump, but only significant for Q. serrata. Light availability positively, although modestly, influenced sprout growth. Our data suggest that relying only on stump sprouts to restore the abandoned coppice stands dominated by the two species is insufficient because their stump survival rate was relatively low. Within the observed range of stump diameter, it may not be a factor responsible for the regeneration failure in the two species. Artificial thinning of small and suppressed sprouts may promote the growth of the remaining dominant sprouts.