Thinning effect on understory community and photosynthetic characteristics in a subtropical Pinus massoniana plantation

Thinning forest stands changes biotic and abiotic conditions, subsequently altering understory communities including their photosynthetic characteristics. We investigated the effects of thinning (25% basal area decrease) in a subtropical Pinus massoniana Lamb. plantation at two post-thinning times: 0.5 years (PT 0.5 ) and 2.5 years (PT 2.5 ). Thinning (PT 0.5 and PT 2.5 ) significantly increased understory density (+104.9% and +142.4%, respectively), aboveground biomass (+191.1% and +239.2%, respectively), the Shannon–Wiener index, and the Pielou index and decreased the Simpson index (p < 0.05). Species richness significantly increased at PT 0.5 and decreased at PT 2.5 (p < 0.05). Photosynthetic characteristics of new and old leaves of three dominant species (Woodwardia japonica (Linn. f.) Sm., Dryopteris championii (Benth.) C. Chr., and Dicranopteris dichotoma (Thunb.) Bernh.) showed different variations at 0.5 and 2.5 years after thinning, depending on their various adaptive strategies. Generally, thinning improved leaf carbon fixation capacity of these dominant plants (except W. japonica old leaves). Leaf photosynthetic characteristics of these species exhibited some common changes with respect to leaf morphological attributes and chlorophyll content. Thinning increased new-leaf length (or width) and reduced old-leaf chlorophyll b concentration at PT 0.5 but reduced new-leaf length, specific leaf area, and all-leaf chlorophyll concentration at PT 2.5 . In conclusion, thinning is a useful tool for increasing understory abundance and carbon fixation capacity of some fern species.