TY - JOUR
T1 - Spatio-temporal variation of environmental signals inducing seed germination in temperate conifer plantations and natural hardwood forests in northern Japan
AU - Seiwa, K.
AU - Ando, M.
AU - Imaji, A.
AU - Tomita, M.
AU - Kanou, K.
N1 - Funding Information:
We thank two anonymous reviewers for insightful comments that greatly improved the manuscript. This work was supported by a grant from the Ministry of Education, Science, and Culture of Japan (No. 07660178, Seiwa).
PY - 2009/1/20
Y1 - 2009/1/20
N2 - To document the spatial and temporal variation of environmental signals inducing seed germination in temperate forests, we measured temporal patterns of environmental signals and seed germination of six pioneer tree species in unthinned and thinned stands of conifer forests (Cryptomeria japonica plantations) and in the understory and gaps of hardwood forests in Japan. We also conducted germination experiment in laboratory for the six pioneer species to test the effects of red:far-red (R:FR) light ratio and temperature fluctuations on the seed germination. In conifer forests, the photosynthetic photon flux density (PPFD), the R:FR ratio, and the amplitude of temperature fluctuations in thinned stands were 2, 1.5, and 3 times higher, respectively, than those of unthinned stands. The PPFD and R:FR ratios just above forest floor also increased after the removal of thick litter accumulation. As a result, higher seed germination was observed in thinned compared to unthinned stands for three photoblastic species, whereas little differences were observed for three non-photoblastic species. These findings suggest that thinning, which frequently reduces litter accumulation, can substantially affect the regeneration of pioneer species and the resultant species diversity in conifer plantations. None of the measured environmental signals changed seasonally in unthinned stands of conifer forests, but they all changed remarkably in the understory of the hardwood forests. In this system, all signals were high and nearly identical to those in the gaps in early spring prior to canopy closure. Thus, the percent germination of the three photoblastic species was enhanced by high R:FR ratios and/or large temperature fluctuations even beneath the canopy and was nearly equal to that in the thinned conifer stands where the environmental conditions were nearly identical to those in the gaps. However, all of the environmental signals decreased with the expansion of canopy leaves and reached minimums at canopy closure. Even in the thinned stands and the gaps, the PPFD and magnitude of temperature fluctuations decreased over time due to shading by growing herbs and/or emerging canopy leaves. In these temporally changing environments, the germination of all photoblastic species ceased simultaneously. This study clearly demonstrated that the environmental signals inducing seed germination of photoblastic pioneer species spatially and temporally change in temperate forests, particularly in deciduous hardwood forests. Furthermore, these signals, PPFD, R:FR ratio, and the amplitude of temperature fluctuations, appear to play a very important role in tree regeneration and subsequent species diversity.
AB - To document the spatial and temporal variation of environmental signals inducing seed germination in temperate forests, we measured temporal patterns of environmental signals and seed germination of six pioneer tree species in unthinned and thinned stands of conifer forests (Cryptomeria japonica plantations) and in the understory and gaps of hardwood forests in Japan. We also conducted germination experiment in laboratory for the six pioneer species to test the effects of red:far-red (R:FR) light ratio and temperature fluctuations on the seed germination. In conifer forests, the photosynthetic photon flux density (PPFD), the R:FR ratio, and the amplitude of temperature fluctuations in thinned stands were 2, 1.5, and 3 times higher, respectively, than those of unthinned stands. The PPFD and R:FR ratios just above forest floor also increased after the removal of thick litter accumulation. As a result, higher seed germination was observed in thinned compared to unthinned stands for three photoblastic species, whereas little differences were observed for three non-photoblastic species. These findings suggest that thinning, which frequently reduces litter accumulation, can substantially affect the regeneration of pioneer species and the resultant species diversity in conifer plantations. None of the measured environmental signals changed seasonally in unthinned stands of conifer forests, but they all changed remarkably in the understory of the hardwood forests. In this system, all signals were high and nearly identical to those in the gaps in early spring prior to canopy closure. Thus, the percent germination of the three photoblastic species was enhanced by high R:FR ratios and/or large temperature fluctuations even beneath the canopy and was nearly equal to that in the thinned conifer stands where the environmental conditions were nearly identical to those in the gaps. However, all of the environmental signals decreased with the expansion of canopy leaves and reached minimums at canopy closure. Even in the thinned stands and the gaps, the PPFD and magnitude of temperature fluctuations decreased over time due to shading by growing herbs and/or emerging canopy leaves. In these temporally changing environments, the germination of all photoblastic species ceased simultaneously. This study clearly demonstrated that the environmental signals inducing seed germination of photoblastic pioneer species spatially and temporally change in temperate forests, particularly in deciduous hardwood forests. Furthermore, these signals, PPFD, R:FR ratio, and the amplitude of temperature fluctuations, appear to play a very important role in tree regeneration and subsequent species diversity.
KW - Conifer plantation
KW - Germination timing
KW - Leaf phenology
KW - Litter accumulation
KW - PPFD
KW - Red to far-red ratio
KW - Species diversity
KW - Temperature fluctuations
UR - http://www.scopus.com/inward/record.url?scp=56449099216&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=56449099216&partnerID=8YFLogxK
U2 - 10.1016/j.foreco.2008.09.002
DO - 10.1016/j.foreco.2008.09.002
M3 - Article
AN - SCOPUS:56449099216
VL - 257
SP - 361
EP - 369
JO - Forest Ecology and Management
JF - Forest Ecology and Management
SN - 0378-1127
IS - 1
ER -