Abstract
Sasa spp., monocarpic dwarf bamboos, are known to form recalcitrant understories, lower species diversity, and hinder forest development. Sasa borealis distributed throughout Korea showed a phenomenon of synchronized dieback after large-scale synchronized flowering nationwide around 2015. Therefore, we conducted this study to take advantage of the rare event and add prevailing activity of wild boars and culm removal to elucidate whether they promote the regeneration of a long-term suppressed forest. We set permanent plots in forests with different understory types, and tracked the vegetation change in 5 years with respect to species composition, tree regeneration, and S. borealis reestablishment. This study focused on comparison between plots established after mass flowering. In flowering stands, we found the species diversity increased significantly with increase in species evenness, but not with recruitment of new species. Furthermore, the seeds of mass-produced bamboo germinated, and the seedling abundance was found to increase considerably. In stands rooted by wild boar, species diversity increased through the recruitment of new species, including tree species. It increased the abundance of shrub and perennial herbs, while it suppressed the reestablishment of S. borealis. Although rooting effect was independently significant regardless of flowering, the synergistic effect of rooting and flowering on forest regeneration was outstanding. Wild boar seemed to function as a remover of dead culms and a breaker of remaining underground mats as well as a seed disperser. Consequently, the species composition became similar to the reference stands. However, culm cutting caused negative effects by facilitating S. borealis to re-occupy or resprout. Overall, as the wild boar population increases, the positive effect can be expected to enhance. At landscape scale, considering several factors such as flowering and non-flowering, and population size of wild boar, the long-term suppressed forests by S. borealis are projected to regenerate with mosaic forests.
Highlights
Only rooting effect was significant for the increase in richness (F = 32.088, p < 0.001, Figure 3b), and flowering alone did not increase the richness
We focused our interest on the very rare phenomenon of large-scale nationwide flowering of S. borealis in Korea [31] and studied its effect on subsequent forest regeneration
After thorough monitoring for 5 years after the dieback of S. borealis, we found the species diversity in the forests increased to a significant extent
Summary
Some plant species enable the formation of dense monospecific understory when ample light is exposed to the forest floor due to large-scale and repeated canopy disturbances. Royo and Carson defined it as ‘recalcitrant understory’ [1]. Such understory is promoted by changes in browsing and fire regime, and is extensively prevalent across several climate zones in temperate [2,3,4,5,6], tropical [7,8], and boreal forests [9]. The well-known species forming recalcitrant understory are ferns, bamboos, lianas, grasses, and Rhododendron spp., which expand rapidly via clonal strategy. It should be noted that the understory has negative impacts on forests, such as hindering forest regeneration [10,11], lowering species diversity [1,12,13,14], inhibiting the establishment and
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