研究者詳細 - 久保田　康裕

論文 - 久保田　康裕

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Dispersal process driving subtropical forest reassembly: evidence from functional and phylogenetic analysis

Kusumoto B.

Ecological Research ( Ecological Research ) 31 ( 5 ) 645 - 654 2016年09月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Understanding the mechanisms of secondary succession related to forest management practices is receiving increasing attention in community ecology and biodiversity conservation. Abiotic and biotic filtering are deterministic processes driving community reassembly. A functional trait or phylogeny-based approach predicts that environmental filtering induced by clearcut-logging results in functional/phylogenetic clustering in younger forests, while biotic filtering (competitive exclusion) promotes functional/phylogenetic overdispersion in old-growth forests. From this perspective, we examined the patterns of functional/phylogenetic structures using tree community data (147 species x 170 plots). These data were chronosequenced from clearcut secondary forests to old-growth subtropical forests in the Ryukyu Archipelago, with species' trait data (leaf and stem) and species level phylogeny. To detect clustering or overdispersion in the functional and phylogenetic structures, we calculated the standardized effect size of mean nearest trait distance and mean nearest phylogenetic distance within the plots. Functional or phylogenetic clustering was relatively weak in secondary forests, and their directional change with increasing forest age was not generally detected. Mean nearest trait/phylogenetic distance for most plots fell within the range of random expectation. The results suggest that abiotic/biotic filtering related to functional traits or phylogenetic relatedness plays a diminished role in shaping species assembly during secondary succession in the subtropical forest. Our findings of functional and phylogenetic properties might shed light on the importance of dispersal (stochastic) processes in the regional species pool during community reassembly after anthropogenic disturbance. It will also contribute to the development of coordinated schemes that maintain potential species assembly processes in the subtropical forest.

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Crown asymmetry in high latitude forests: disentangling the directional effects of tree competition and solar radiation

Aakala T.

Oikos ( Oikos ) 125 ( 7 ) 1035 - 1043 2016年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Light foraging by trees is a fundamental process shaping forest communities. In heterogeneous light environments this behavior is expressed as plasticity of tree growth and the development of structural asymmetries. We studied the relative influence of neighborhood structure and directional solar radiation on horizontal asymmetry of tree crowns in late-successional high latitude (67-68 degrees N) forests in northern Fennoscandia. We described crown asymmetries as crown vectors (i.e. horizontal vectors from stem center to crown center), which we obtained from canopy maps based on crown perimeter measurements in the field. To disentangle the influence of the two main determinants, inter-tree competition and directionality of above-canopy solar radiation at high latitudes, we applied circular statistical models, utilizing cylindrical distributions, to these data consisting of orientations and intensities of crown asymmetry. At the individual tree level, our model predicted crown asymmetry vectors from the current stand structure, and the predictions became better when the intensity of asymmetry (i.e. crown vector length) was higher. Competition was the main determinant of crown asymmetry for 2/3 of trees, and the model predictions improved when we incorporated the directionality of solar radiation. At the stand-level, these asymmetries had resulted in a small increment of the projected canopy area and an increased regularity of spatial structure. Our circular statistical modelling approach provided a quantitative evaluation of the relative importance of directionality of solar radiation and neighborhood stand structure, showing how both of these factors play a role in formation of crown asymmetries in high latitude forests. This approach further demonstrated the applicability of circular statistical modeling in ecological studies where the response variable has both orientation and intensity.

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Climatic and geographic correlates of global forest tree species-abundance distributions and community evenness

Ulrich W.

Journal of Vegetation Science ( Journal of Vegetation Science ) 27 ( 2 ) 295 - 305 2016年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

QuestionsSpecies-abundance distributions (SADs) have long been at the centre of ecological interest because they summarize various patterns of community assembly in condensed form. Here we link observed patterns of SAD shape and evenness to latitude and climatic conditions to infer global trends in abundance distributions. LocationGlobal. MethodsWe compiled data on tree species abundances and climate covariates from 605 sites worldwide. We applied linear regression modelling and nonlinear least squares fitting of log-series and lognormal abundance distributions to species rank-order log-abundance plots to assess latitudinal and climatic gradients in abundance distributions and Pielou evenness. ResultsWe observed significant latitudinal trends in SAD shape and evenness, even after accounting for richness and spatial effects. Evenness tended to increase towards lower latitudes and was positively correlated with actual evapotranspiration and negatively with climatic variability. We observed an excess of log-series SADs at lower latitudes and an increase in lognormal distributions towards northern latitudes. Accordingly, the proportion of species less abundant than expected from a log-series distribution decreased towards the tropics. ConclusionsWe speculate that the observed latitudinal trends are caused by respective gradients in the importance of dispersal for local tree communityassembly. This interpretation implies the hypothesis that tropical communities tend to be more open and input-driven in comparison to temperate communities.

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Non-neutrality in forest communities: evolutionary and ecological determinants of tree species abundance distributions

Yasuhiro Kubota, Buntarou Kusumoto, Takayuki Shiono, Werner Ulrich, Franck Jabot

OIKOS ( WILEY ) 125 ( 2 ) 237 - 244 2016年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

The unified neutral theory of biodiversity and biogeography provides a promising framework that can be used to integrate stochastic and ecological processes operating in ecological communities. Based on a mechanistic non-neutral model that incorporates density-dependent mortality, we evaluated the deviation from a neutral pattern in tree species abundance distributions and explored the signatures of historical and ecological processes that have shaped forest biomes. We compiled a dataset documenting species abundance distributions in 1168 plots encompassing 16 973 tree species across tropical, temperate, and boreal forests. We tested whether deviations from neutrality of species abundance distributions vary with climatic and historical conditions, and whether these patterns differ among regions. Non-neutrality in species abundance distributions was ubiquitous in tropical, temperate, and boreal forests, and regional differences in patterns of non-neutrality were significant between biomes. Species abundance evenness/unevenness caused by negative density-dependent or abiotic filtering effects had no clear macro-scale climatic drivers, although temperature was non-linearly correlated with species abundance unevenness on a global scale. These findings were not significantly biased by heterogeneity of plot data (the differences of plot area, measurement size, species richness, and the number of individuals sampled). Therefore, our results suggest that environmental filtering is not universally increasing from warm tropical to cold boreal forests, but might affect differently tree species assembly between and within biomes. Ecological processes generating particularly dominant species in local communities might be idiosyncratic or region-specific and may be associated with geography and climate. Our study illustrates that stochastic dynamical models enable the analysis of the interplay of historical and ecological processes that influence community assemblies and the dynamics of biodiversity.

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Geographical patterns of butterfly species diversity in the subtropical Ryukyu Islands: The importance of a unidirectional filter between two source islands

Hirao T.

Journal of Biogeography ( Journal of Biogeography ) 42 ( 8 ) 1418 - 1430 2015年08月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

AimTo examine the roles of geohistorical and ecological factors in the development of butterfly assemblages on continental islands with multiple source pools. LocationThe Ryukyu Islands, Japan. This arc of continental islands is located between two source islands, Kyushu and Taiwan, and contains two major straits, the Tokara and Kerama gaps. MethodsA total of 489 butterfly species were identified on 59 islands, including the two source islands. The influences on species richness and rarity of latitude, area, elevation, and distances from the nearest source and from the nearest larger island were analysed using generalized linear models. The relationships between differences in area, elevation, and distance and dissimilarity between island butterfly faunas were evaluated by multiple regressions on distance matrices. The relationships between area, elevation, and distance from the source and dissimilarity to the source fauna were examined using linear models. The dissimilarity was based on the SOrensen index and its nestedness and turnover components. ResultsLatitude, area and isolation determined species richness and rarity, whereas differences in elevation and distance regulated species turnover between islands. The gaps between islands were associated with nestedness between island faunas. Area consistently had a negative relationship with the total dissimilarity to source fauna. The overall dissimilarity to Kyushu decreased with the distance from Kyushu, whereas dissimilarity to Taiwan increased with distance from Taiwan. Main conclusionsBoth environmental filtering and dispersal limitation determine the geographical patterns of butterfly assemblages in the Ryukyus. The present study focuses on the unique pattern wherein migration from Kyushu is facilitated on islands farther from Kyushu, while migration from Taiwan is inhibited on islands farther from Taiwan. The two source islands have contrasting roles that affect butterfly distributions unidirectionally. This study highlights the importance of resolving dissimilarity into nestedness and turnover components to elucidate the formation of island biota.

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Climatic drivers of trait assembly in woody plants in Japan

Shiono T.

Journal of Biogeography ( Journal of Biogeography ) 42 ( 6 ) 1176 - 1186 2015年06月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

AimA trait-based biogeographical approach can be used to shed light on species-sorting mechanisms that are driven by the interactions between species traits and abiotic conditions along large-scale gradients. We tested the hypothesis that geographical patterns of woody plant assemblages are driven largely by environmental filtering, in relation to climate harshness and seasonality, acting on key functional traits. LocationJapanese archipelago. MethodsUsing a large-scale grid-based dataset of 773 woody species and five functional traits measured in the field, spanning the Japanese archipelago, we analysed the influence of climate harshness (absolute minimum temperature and precipitation of driest month) and climate seasonality (temperature and precipitation seasonality, and the length of period suitable for photosynthesis) on three aspects of community trait structure: community mean trait values, functional richness and functional divergence. To confirm whether the influence of climate-based species sorting on functional structure was stronger than the impact of dispersal limitation, we used null models that did or did not account for the difference in regional species pools as a result of vicariance. ResultsWhile climate harshness and historical dispersal limitation had a some influence on trait structure, temperature seasonality played a significant role. Greater seasonality was associated with functional similarity in wood density and leaf nitrogen concentration, but also contributed to increased diversity in leaf thickness, specific leaf area and maximum height. Main conclusionsOur results demonstrate the importance of climate harshness and seasonality in shaping the geographical variation of functional trait structures in woody plant assemblages, while we found that species richness decreases with increasing climate harshness. Climate seasonality results in the convergence and divergence of co-occurring traits across different vegetation zones. This suggests that seasonal environmental variability acts not only as a filter of species traits but also as a driver creating a greater difference in functional strategies among woody plant species.

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Role of climate and geohistorical factors in driving plant richness patterns and endemicity on the east Asian continental islands

Yasuhiro Kubota, Takayuki Shiono, Buntarou Kusumoto

ECOGRAPHY ( WILEY-BLACKWELL ) 38 ( 6 ) 639 - 648 2015年06月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

We investigated the roles of climate, geography, and geology in plant diversity and endemicity on the east Asian continental islands, by testing predictions from contrasting hypotheses considering current climate, habitat stability, and isolation as major drivers of plant richness and endemicity. We created a fine-resolution map of vascular plant richness (5614 species) with 10 x 10 km grid cells. Using this large dataset and regression models, we explored correlations between species richness/number of endemics and temperature, precipitation, Quaternary temperature/precipitation changes, Quaternary alluvial development and volcanic disturbances (presence of alluvial plains and of pyroclastic flows), distance from the continent, and elevation. We applied these analyses to the vascular plant assemblage as a whole and separately to trees, herbs, and ferns. Temperature and precipitation were associated with the richness of vascular plants overall and of their endemics. Quaternary temperature change was negatively associated with the richness of vascular plants overall and of their endemics. The presence of pyroclastic flows and of lowland alluvial plains was negatively associated with those. Distance from the continent and elevation were positively associated with endemic species richness, especially those of trees and herbs. While current climate was an important predictor of species richness (especially of ferns), geographical isolation and habitat stability were the main predictors of the endemic species richness of trees and herbs. The relative importance of current climate and historical factors may be related to the dispersal ability of functional groups. Our results illustrate that the diverse geographical conditions reflecting the characteristics of the island led to the various historical effects on biodiversity patterns. The highly endemic flora on the east Asian islands resulted from species accumulation and in situ diversification, suggesting that the climate and historical hypotheses are not mutually exclusive, but can be reconciled as the interplay between recent ecological and evolutionary processes.

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Functional response of plant communities to clearcutting: Management impacts differ between forest vegetation zones

Kusumoto B.

Journal of Applied Ecology ( Journal of Applied Ecology ) 52 ( 1 ) 171 - 180 2015年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Understanding of the ecological impacts of logging practices on biodiversity and associated ecosystem processes is essential for developing sustainable forest management approaches. We documented the impacts of clearcutting on the functional structure of tree and herbaceous communities in hemiboreal, cool-temperate, warm-temperate and subtropical forests in the Japanese archipelago and identified forest vegetation that is vulnerable to deterioration of important ecosystem functions. We combined species data for leaf, stem, flower and fruit traits related to productivity, nutrient cycling and habitat quality for wildlife with phytosociological vegetation data from unmanaged and previously clearcut forests, then calculated functional structure indices [community mean (CM) of trait values, functional richness (FRic) and functional divergence (RaoQ)] of plant communities. For tree species, functional structure indices of specific leaf area (SLA), leaf carbon and nitrogen concentrations, maximum height, wood density and flower size differed between unmanaged and clearcut forests, while for herb species, only maximum height differed between the two forest types. Functional structure indices showed divergent patterns across forest vegetation zones. In hemiboreal, cool-temperate and warm-temperate forests, the CMs of SLA and leaf nitrogen concentration were greater and that of leaf carbon concentration was smaller in clearcut than in unmanaged forests. Although clearcut forests had greater species richness than unmanaged forests, FRic and/or RaoQ of maximum height were smaller in clearcut forests. In hemiboreal and cool-temperate forests, FRic and RaoQ of SLA were also smaller in clearcut forests. In contrast, subtropical forests showed no differences in species richness and functional structures between unmanaged and clearcut forests.Synthesis and applications. Functional redundancy of plant communities differs among traits and among forest vegetation zones. After intensive logging, hemiboreal, cool-temperate and warm-temperate forests were more vulnerable to the loss of ecosystem functions related to leaf and stem traits of tree species than were subtropical forests, which appeared relatively resilient. Locally adaptive management to maintain multiple ecosystem functions should be developed based on the degree of functional complementarity among plant species in forest communities. Functional redundancy of plant communities differs among traits and among forest vegetation zones. After intensive logging, hemiboreal, cool-temperate and warm-temperate forests were more vulnerable to the loss of ecosystem functions related to leaf and stem traits of tree species than were subtropical forests, which appeared relatively resilient. Locally adaptive management to maintain multiple ecosystem functions should be developed based on the degree of functional complementarity among plant species in forest communities.

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Beta diversity of woody plants in the Japanese archipelago: The roles of geohistorical and ecological processes

Kubota Y.

Journal of Biogeography ( Journal of Biogeography ) 41 ( 7 ) 1267 - 1276 2014年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Aim We addressed the roles of geohistorical and ecological factors on beta diversity patterns of woody plants in the Japanese archipelago. We scrutinized the contribution of recent diversification in shaping the woody plant diversity of insular areas in East Asia. Location The Japanese archipelago. Methods The distribution data of 1030 woody plant species were compiled for 65 localities in the archipelago. First, the relationships between geohistorical (straits, distance and area) and ecological (topographical heterogeneity, minimum temperature and annual precipitation) variables and taxonomic and phylogenetic beta diversity were tested using regression models. Second, geographical patterns of phylogenetic beta diversity were compared with those of taxonomic beta diversity using ordination and randomization tests. These analyses were applied to the woody plants overall and their functional groups defined by life-form (coniferous, deciduous broad-leaved and evergreen broad-leaved groups). Results Distance and minimum temperature showed significant positive relationships with both measures of beta diversity across the woody plants overall and the functional groups. The contributions of geographical barriers, topographical heterogeneity and annual precipitation varied among groups. Ordinations by phylogenetic beta diversity produced patterns that were consistent with those generated by taxonomic beta diversity, showing three clusters of localities in relation to geographical barriers, except in the coniferous group. The regression slopes of phylogenetic beta diversity versus distance were significantly smaller than those of taxonomic beta diversity versus distance across all groups. Main conclusions In the Japanese archipelago, the combination of geographical isolation and environmental filtering in response to geohistorical perturbations and environmental gradients has configured the beta diversity patterns of woody plants. The recent diversification of phylogenetically close relatives probably caused the spatial variations that exist in woody plant diversity. The archipelago functions as a refugium for relict taxa and as a hotspot for neoendemics, contributing to the broad-scale diversity bias favouring East Asia.

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Determinant factors influencing the spatial distributions of subtropical lianas are correlated with components of functional trait spectra

Kusumoto B.

Ecological Research ( Ecological Research ) 28 ( 1 ) 9 - 19 2013年01月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Lianas are important vegetation components that control structure and function, especially in tropical and subtropical forests. To explore the spatial assembly mechanisms of a subtropical liana community, we tested the following hypotheses: spatial distributions of subtropical lianas are determined by forest structures and topographic features, which are surrogates for host/light availability and edaphic/water conditions, respectively, and these effects are mediated through species functional traits. We examined the spatial distribution of lianas in two plots (areas 9 and 16 ha) representing landscapes in an intact forest and a secondary forest, and analyzed spatial distribution pattern at the species level using a simple, spatially explicit model. We also examined the correlations between determinant factors for species distribution and species functional traits, including climbing habits, leaf traits and wood density. The spatial distribution of lianas was controlled mainly by topographic gradient. Most species had preferences for concave topographies, i.e., valley habitats. Any covariates related to the host (or to light) had little influence on the distribution of most liana species. Distributional responses to topography were different among species, and associated significantly with leaf nitrogen content and climbing habit, but not with wood density. The correlation between variation in habitat preferences and leaf economic spectrum suggests that an environmental filter for physiological response to topography is the important mechanism shaping the spatial patterns of this subtropical liana community.

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(2013) 生物多様性の維持機構の解明に中立理論が果たす役割

久保田康裕

生物科学 64 242 - 249 2013年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Circular distributions of fallen logs as an indicator of forest disturbance regimes

Toshihiro Abe, Yasuhiro Kubota, Kenichiro Shimatani, Tuomas Aakala, Timo Kuuluvainen

ECOLOGICAL INDICATORS ( ELSEVIER SCIENCE BV ) 18 559 - 566 2012年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

We present a retrospective method for studying forest disturbance regimes, and especially the role of windthrows, based on circular statistical models of directions of fallen logs. This approach was applied to fallen log data from three areas of pristine Picea abies-dominated boreal forests in northern Europe. The data consisted of 5 plots from each of the three areas, totaling 15 plots and covering an area of 24 ha. The disturbance history of the plots, which varied from area to area, was known from previous detailed studies. We selected and fitted the most suitable circular model for each plot, based on goodness-of-fit and the Akaike information criterion. For uneven-aged forests, the symmetric von Mises distribution, was best fitted, while for the even-aged forest the sine-skewed wrapped Cauchy distribution was selected. The degree of concentration around the mean direction of fallen trees was strongest for the late-successional even-aged forest most exposed to windthrow, while an uneven-aged forest with drought-driven mortality had the lowest concentration and the greatest variance over the mean directions. For the third area, characterized by an uneven age structure and tree mortality driven by heart-rot fungi in old trees in interaction with wind, an intermediate between these two were derived. Our results suggested the utility of circular distributions of fallen logs and their statistical models for retrospective assessments of forest disturbance regimes. (C) 2012 Elsevier Ltd. All rights reserved.

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Dynamics of species diversity in a Japanese warm-temperate secondary forest

Yamada T.

Ecosphere ( Ecosphere ) 2 ( 7 ) 2011年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

To examine the dynamics of species diversity during secondary succession, growth, death and recruitment of trees were monitored for 39 years (1966 to 2005) in two plots (P-1 and P-3, 40m x 40m each) in a Japanese warm-temperate secondary forest recovering from clearcutting that occurred in the 1910s. Typhoons in the early 1990s seriously damaged P-1 and moderately damaged P-3. We examined how species diversity of trees changed through succession for three size classes: large (diameter at breast height, dbh >= 4.5 cm), medium (4.5 cm >= dbh >= 1.0 cm), and small (dbh < 1.0 cm). Before the typhoons occurred, species diversity and evenness generally increased over time in all size classes in both plots, except for medium trees in P-1. After the typhoons, species diversity increased over time without exception, and this usually involved increases in both species evenness and number. We found that recruitment always contributed to increases in species diversity but mortality did not. Recruitment increased species diversity because the recruitment rate of rare species was higher than that of abundant species. This reflected delayed recruitment of late successional species before the typhoons and the mass recruitment of early successional species after the typhoons. Abundance of the most dominant tree species of the large class in P-1 was greatly reduced due to mortality caused by the typhoon, resulting in an increase in species diversity in the large tree community. Gap formation by the typhoons also caused mass recruitment into the small and medium size classes, including many rare species, leading to increased species diversity in the small and medium tree communities. Through these processes, the typhoons enhanced species diversity in this Japanese warm-temperate forest. Synthesis: This is the first study on the dynamics of species diversity based on long-term monitoring of a single site in a Japanese warm-temperate forest. This direct monitoring revealed the species dynamics plus the significant impact of rare events, typhoons, on the species diversity.

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Approaches for forest disturbance studies: natural variability and tree regeneration

Ahto Kangur, Toshiya Yoshida, Yasuhiro Kubota, Marek Metslaid

JOURNAL OF FOREST RESEARCH ( SPRINGER TOKYO ) 16 ( 3 ) 153 - 154 2011年06月 [ 査読有り ]

掲載種別: 研究論文（その他学術会議資料等）

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

FUJII Shinjiro, KUBOTA Yasuhiro, ENOKI Tsutomu

Journal of forest research 15 ( 5 ) 289 - 298 2010年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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