Gap dynamics is a universal model of small scale forest regeneration, but in cold climate a canopy gap may expose seedlings to environmental stress that, combined with higher light incidence, may lead to photoinhibition. Considering Hokkaido’s climate, this could be important to forest regeneration and species distribution, and thus it should be investigated.

The influences of environmental conditions, under canopy and in a wide canopy gap, on the photosynthesis of Abies sachalinensis and Betula ermanii seedlings were studied by making photosynthetic light curves, measuring chlorophyll fluorescence, environmental indicators, and gathering meteorological data, at the Uryu Experimental Forest in Hokkaido.

Seedlings of both species were photoinhibited in both sites in May and June, but in the open canopy site this state lasted until August. Abies growing in the closed canopy site showed stronger photoinhibition in spring, than those on the open canopy site, but recovered quickly after the canopy’s new leaves flushed. The degree of photoinhibition was statistically correlated with low-temperature and site. Although photoinhibited, Betula showed higher photosynthetic rates than Abies at the open canopy site. The results may point to trade-offs between stress mitigation and photosynthetic capacity in different light environments.