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Although successional changes in the functional diversity (FD) of plant communities have been reported in earlier studies, the processes driving these changes remain unclear. Based on the datasets of a long-term tree census conducted during a secondary succession, we comprehensively investigated the FD and its rate of change during a secondary succession in cool, temperate secondary forests in Chichibu, Central Japan. Data from more than 30-years of observations in plots of secondary forest stands with a wide range of stand ages were used to test changes in species diversity, community-weighted means (CWMs) of each trait, FD, and their change rates. Although species diversity decreased constantly with stand age, the FD (Rao's Q) of all traits decreased significantly at the mid-successional stage, corresponding to the stem-exclusion stage. Changes in CWMs of traits indicated the directional shifts of species composition from resource-acquisitive to resource-conservative along succession, especially at the stem exclusion stage. Although the FD of each trait changed differently with succession, that of several resource-conserving traits decreased significantly at the stem exclusion stage. Based on long-term multiple chronosequence resampling, we found that stem exclusion significantly decreased the FD along a secondary succession in cool temperate forests. This sheds light on the critical role of the stem exclusion stage in shaping plant community traits, indicating the importance of this stage in forest management strategies. • We used long-term tree census data from secondary forest succession. • Analyzing functional diversity change over time using long-term and multiple chronosequence resampling techniques. • Finding the decrease in functional diversity as forests advance through the stem exclusion stage. • Highlights the crucial role of stem exclusion phase in shaping plant trait diversity. [ABSTRACT FROM AUTHOR]

Highlights • Storm disturbance 55 years ago does not affect current wood decay fungal communities. • Disturbance and wood decay type have significant impacts on bryophyte communities. • Disturbance and wood decay type have significant effects on seedling density. • Bryophyte species affect tree seedling density. Abstract Storm disturbance has a huge impact on subalpine forest ecosystems. Evaluating the long-term effects and mechanisms of storm disturbance is of great significance for conservation of subalpine forests as frequency and intensity of storms are increasing because of the climate change. Species of subalpine conifer tree genera such as Picea and Tsuga need coarse woody debris (CWD) such as logs and stumps for seedling colonization; thus, their establishment is greatly affected by the condition of CWD, which largely depends on the activity of fungal decomposer communities and saproxylic bryophyte communities. Because the process of CWD decay and associated ecological succession is known to take several decades in subalpine forests, we hypothesized that storm disturbance has long-lasting effects on fungal communities, their wood decay function, saproxylic bryophyte communities, and seedling establishment. To test this hypothesis, we surveyed fungal, bryophyte, and seedling communities at forest sites that had been disturbed by a large typhoon 55 years ago and compared them with those of surrounding undisturbed coniferous forest in central Japan. Contrary to our hypothesis, Illumina sequencing for the fungal ITS1 region in rDNA obtained from wood samples did not show that past disturbance had an obvious effect on current fungal communities. Also, the frequencies of occurrence of various wood decay types were not significantly different between disturbed and undisturbed plots. However, disturbance affected bryophyte communities, which had strong effects on the seedling densities of Picea jezoensis var. hondoensis , Tsuga diversifolia , and Betula spp. These results suggest that the previous typhoon disturbance in the focal area had long-lasting effects on biotic interactions and seedling regeneration on CWD, but these effects might not be attributable to the impacts of disturbance on CWD fungal communities and their wood decay function. [ABSTRACT FROM AUTHOR]

Highlights • Forests were investigated over 50 years after a severe windthrow. • Salvage logging noticeably reduced the amount of dead wood carbon stock. • Unsalvaged stands had a larger amount of dead wood than undisturbed stands. • Unsalvaged stands stored similar amounts of total woody carbon as undisturbed stands. • Thus, dead wood potentially offset the reduced live woody biomass. Abstract Windthrow disturbances often produce large amounts of dead woody materials in a forest. However, post-disturbance, salvage logging greatly reduces the amount of dead woody materials, and thus, carbon stocks. Because the dead woody materials can persist as coarse woody debris (CWD) for a very long time in cool climatic areas, such as boreal and subalpine forests, salvage logging might have long-term effects on the carbon stocks of disturbed forests. In this study, we examined the effects of windthrow by a super typhoon in 1959 and subsequent salvage logging on the carbon stock of subalpine forests more than a half-century after the disturbance in central Japan. We sampled disturbed and not salvaged (unsalvaged) stands versus disturbed and salvaged stands within 10 years of the disturbance (salvaged) in addition to undisturbed stands (undisturbed). The volume of CWD was higher in the unsalvaged stands versus the other two types of forests. Specifically, the volume of classes with intermediate decay was very high, contributing to greater carbon stocks of CWD in the unsalvaged stands. Although the carbon stock of living trees was higher in the undisturbed stands compared to the disturbed stands (unsalvaged and salvaged), the total carbon stock (live + dead) of the unsalvaged stands (104 Mg C ha−1) was almost equivalent to that of the undisturbed stands (99 Mg C ha−1) and was much higher than that of the salvaged stands (72 Mg C ha−1). This study demonstrates that CWD produced by a typhoon acts as a large carbon stock for more than a half-century, potentially offsetting the loss of live woody biomass in disturbed forests. [ABSTRACT FROM AUTHOR]

Given that forest dieback due to emerging pests is increasing under global warming, understanding the relationships between pests, climate, and forest biodiversity is an urgent priority. In Japan, mass attacks of an ambrosia beetle, vectoring a pathogenic fungus, cause oak wilt outbreaks in recent decades. Here, the associations of oak wilt and climate with wood-inhabiting fungal communities in apparently healthy Quercus serrata trunks were investigated using DNA metabarcoding in seven sites along a climatic gradient in Japan. Amplicon sequencing of the fungal internal transcribed spacer 1 region generated 1,339,958 sequence reads containing 879 fungal operational taxonomic units (OTUs) in 234 wood samples. OTU compositions were significantly different between sites with and without oak wilt. OTU richness increased with temperature and precipitation at sites where oak wilt was present, but this relationship was not observed at sites without oak wilt, possibly due to interaction between oak wilt and climate. • Oak wilt disease is correlated with fungal communities in living oak trees. • OTU richness increased with temperature and precipitation at sites with oak wilt. • OTU richness was not correlated with macroclimate at sites without oak wilt. • Oak wilt was correlated with absence of some white-rot decomposer fungi. • Precipitation had a negative correlation with the species richness of brown-rot fungi. [ABSTRACT FROM AUTHOR]

• We incorporated regeneration on downed logs into LANDIS-II forest landscape model. • We revealed the long-term effects of post windthrow management on forest recovery. • Birch-dominated forests regenerated and persisted over 100 years at scarified sites. • Salvaging after a first windthrow delayed biomass recovery after a second one. • CWD-dependent species hardly recover after multiple windthrows in case of salvaging. Post-windthrow management delays forest biomass recovery by altering the situation of disturbance legacies and can change the species composition. Although the short-term effects of post-windthrow management have been well studied, we do not have enough knowledge about the long-term effects of post-windthrow management on species composition and biomass recovery. Those effects associated with an increase in the windthrow frequency are also unknown. Although forest landscape models can effectively evaluate these effects, conventional models do not represent the regeneration process on downed logs, which is essential for simulating forest succession. We focused on hemiboreal forests in northern Japan and aimed to (1) incorporate the regeneration process on downed logs into LANDIS-II, which is one of the most used forest landscape models; (2) evaluate the long-term effects of post-windthrow management on tree species composition and aboveground biomass recovery; and (3) evaluate the associated long-term effects of interactions between post-windthrow management and increased windthrow frequency. We incorporated the regeneration process on downed logs into LANDIS-II by regulating the probability of the establishment of species that depend on dead wood, such as spruce, according to the availability of well-decayed dead wood. The incorporation of this process resulted in simulations of trends in species composition and aboveground biomass recovery after post-windthrow management that were more accurate than those produced by the original model. In the modified LANDIS-II simulation, reductions in dead wood and advanced seedlings due to salvage logging had little effect on the tree species composition or aboveground biomass recovery; however, the complete destruction of advanced seedlings by scarification induced a delay in aboveground biomass recovery and a shift to birch-dominated forests that continued for 100 years. In addition, the reduction in dead wood due to salvage logging decreased the number of seedlings, especially of dead wood-dependent species, that established after windthrow. When the windthrow frequency doubled, this decrease in seedlings induced a delay in aboveground biomass recovery, and a substantial decrease in dead wood-dependent species biomass occurred after a subsequent windthrow event. However, after the second windthrow event and following scarification, the forest recovered in the same way as after the first windthrow because the destruction of advanced seedlings and understory plants, namely, dwarf bamboo (Sasa spp.), by scarification reset the site conditions. To conserve the species composition and aboveground biomass of hemiboreal forests under climate change, which is expected to increase windthrow frequency, salvage logging and scarification should be avoided. [ABSTRACT FROM AUTHOR]

• Analysis on a 30-years observation data along a chronosequence of secondary forest. • Net biomass change has accelerated prior to 1980s, but has decelerated after 1980s. • Nitrogen and CO 2 rather than climatic factors might contribute to the acceleration. • Water stress, air pollutants and deer herbivory might contribute to the deceleration. Secondary forests are a huge carbon sink in terrestrial ecosystems, but it remains unclear whether growth of secondary forests has accelerated or decelerated due to global environmental changes, especially in East Asia. In this study, we analysed 30 years of data at 26 permanent plots along a secondary succession of temperate forest in central Japan to test whether the aboveground biomass (AGB) growth of secondary forest has accelerated or decelerated. The AGB–age relationship has clearly shifted upwards from the 1980s to the 2010s. The observed annual net AGB change (ΔAGB) was higher than that expected from the AGB–age relationship. These results indicate that ΔAGB has accelerated. However, the observed ΔAGB adjusted for the effects of stand age has gradually decreased from the 1980s to the 2010s. This indicates that ΔAGB of the secondary forest had accelerated prior to the 1980s, and decelerated after the 1980s. The decrease in ΔAGB after the 1980s was due to decreased biomass gain in the 1990s and increased mortality after the 1990s. Climatic factors are not considered the driver of the acceleration of ΔAGB because mean annual temperature and annual precipitation at the study site was relatively stable before 1980. However, mean annual temperature has increased since the 1980s and annual precipitation was low in the 1990s, which would result in increased drought stress and may have contributed to the decrease in biomass gain in the 1990s. Other abiotic and biotic stresses may also have contributed to the increased mortality after the 2000s. This study revealed a long-term transition from an acceleration phase to a deceleration phase of forest growth, indicating that forest growth changes relating anthropogenic environmental changes since mid-20th century are not necessarily unidirectional. [ABSTRACT FROM AUTHOR]

• We revealed long-term effects of salvaging after windthrows on total carbon stocks. • The total carbon stock almost recovered 64 years after the windthrow and salvaging. • Broadleaves and CWD generated after the windthrow have offset CWD lost by salvaging. • Well-decayed CWD and the organic layer carbon stock were low in salvaged forests. To mitigate the negative effects of climate change, it is necessary to conserve carbon stocks in forests. Typhoons fell many standing trees and generate a substantial amount of coarse woody debris (CWD). In boreal forests, CWD contributes to maintaining carbon stocks for a long time after a disturbance because the decomposition rate of CWD is relatively low. We know that salvage logging after a disturbance tremendously decreases the forest carbon stock over the short term after logging but know little about its long-term effects. We targeted a catastrophic windthrow caused by a super typhoon in 1954 in boreal forests in northern Japan and estimated the long-term effects of salvage logging after the windthrow on the above- and belowground carbon stocks by comparing old-growth forests with low damage from the super typhoon in 1954 or any subsequent typhoons (OG), forests damaged by the typhoon with remaining CWD (i.e., windthrow, WT), and forests damaged by the typhoon followed by salvage logging (WT + SL). The CWD carbon stock of decay class 5 (i.e., the most decayed CWD) in WT was significantly larger than that in OG and WT + SL, suggesting that the CWD in decay class 5 in WT had been generated by the typhoon 64 years ago, and the negative effect of salvage logging on the carbon stock still remains apparent in the CWD carbon stock of decay class 5. The carbon stock of the organic (O) layer in WT was larger than that in WT + SL, probably because of three factors: (1) the slower decomposition rate of fallen leaves and twigs of conifers than broadleaves, as conifer litter is abundant in WT; (2) greater carbon transition from the CWD to the O layer in WT; and (3) the occurrence of a lower decomposition rate in the O layer in WT. However, the total carbon stock in WT + SL has almost recovered to the level of that in WT within the last 64 years. The carbon stocks of broadleaves that grew rapidly after the disturbance and the newly accumulated dead trees generated throughout the stand developmental process might contribute to the recovery of carbon stock in WT + SL. These results indicate that salvage logging affects the allocation of carbon in the forest even after 64 years after a catastrophic windthrow, although there was no large difference in total carbon stock. [ABSTRACT FROM AUTHOR]