Resilience of stand structure and tree species diversity in subtropical forest degraded by clear logging

Abstract

Subtropical forests in the Ryukyu Islands have been degraded by silvicultural practices, and thus their structural attributes are being shifted to other states dominated by a few tree species. This study clarified the mechanisms of the change, and examined the effect of clear logging on the resilience of a subtropical forest. Sprouting regeneration and typhoon disturbance were introduced into an individual-based model, SEIB-DGVM, for describing stand development and succession. The regeneration dynamics from young secondary to oldgrowth stands were reproduced fairly well with the model. Sprouting recruitment produced high stem density at the beginning of stand development, which caused a selfthinning trajectory following the -3/2 power law. In the late development stage after 70 years, tree species diversity fluctuated because of the regenerative response of sprouting species and the facilitatory effect of typhoon disturbance on the coexistence of subordinate species. The death of canopy trees because of typhoon disturbances reduced the dominance of Castanopsis sieboldii, and depressed its dominance in the understory. Consequently, the understory species could establish by virtue of fallen canopy trees, and tree species diversity increased at the stand level. Clear logging experiments in the model revealed that species diversity deteriorated, especially in the stand dominated by sprouting species. Resilience of subtropical forests was determined by initial species composition before clear logging. Our simulation results suggest that repeated logging drives subtropical forests with high species diversity to a stand monopolized by C. sieboldii.

Using tree functional diversity to evaluate management impacts in a subtropical forest

“…The differences in the community weighted mean for a functional trait between forest types with different management histories is informative for considering the shifts of the dominant trait value in a community (Baraloto et al 2012). Greater leaf thickness and wood density found in managed forests suggest that clear-cutting and plantation establishment may have affected growth dynamics in the forests (Fujii et al 2009). Forest practices often promote the dominance of pioneer species with low wood density and high specific leaf area and leaf nitrogen concentration (Baraloto et al 2012, Carreño-Rocabado et al 2012, but the subtropical forest demonstrated a converse trend.…”

Long-term ecological impacts of clear-fell logging on tree species diversity in a subtropical forest, southern Japan

“…In this study, 46 tree species with different subtropical forest ecological niches were considered in describing the stand development processes (Fujii et al 2009). Species traits were characterized in terms of the maximum tree height, maximum crown width, wood density, and sprouting rate.…”

“…At the end of the simulation period, the impacts of the cutting cycle on tree species richness, the dominance of Castanopsis sieboldii and tree species diversity was quantified. We focused on the dynamics of C. sieboldii after clearlogging because this species is the most dominant, characterizing the forest structure and dynamics in subtropical forests (Kubota et al 2005;Fujii et al 2009). …”

“…To clarify the compositional shifts in response to clear-cutting, we applied a spatially explicit individual-based dynamic global vegetation model (SEIB-DGVM) developed by Sato et al (2007). This model accounts for sprouting regeneration and typhoon disturbance, and captures essential features of stand development including self-thinning processes following the -3/2 power law, as well as the facilitating effect of typhoon disturbance on the coexistence of subordinate species (Fujii et al 2009). This simulation model can quantify the impact of clear-fell logging on a subtropical forest, and could provide valuable information on alternative forest management options.…”

Understory thinning reduces wood-production efficiency and tree species diversity in subtropical forest in southern Japan

“…We applied a spatially explicit individual-based dynamic global vegetation model (SEIB-DGVM) developed by Sato et al (2007). This model takes into account sprouting regeneration and typhoon disturbance, and captures the essential features of stand development, including a selfthinning process that follows the -3/2 power law, as well as the facilitating effect of typhoon disturbance on the coexistence of subordinate species (Fujii et al 2009). This simulation model can quantify the ecological/economical constraints of logging regimes and forest prescriptions, and could provide valuable information on alternative options for forest management (Fujii et al 2010).…”