Tatsuyuki Seino

Habitat differentiation among tree species with small-scale variation of humus depth and topography in a tropical heath forest of Central Kalimantan, Indonesia

Small-scale spatial association of the distribution for 55 abundant tree species with two environmental factors (humus depth and surface microtopography) was examined in two 1-ha plots of a heath (kerangas) forest in Central Kalimantan, Indonesia. More than 80% of the 55 species showed a significant habitat preference in humus depth and/ or relative elevation in at least one plot. In particular, ten species occurring in both plots showed a consistent significant preference for humus depth or relative elevation in the two plots. Using randomization tests, however, only five species significantly associated with humus depth and no species with relative elevation. These results suggest that edaphic and topographic factors, especially humus depth, contribute to determining local spatial distribution and floristic composition of abundant tree species in the forest.

Pattern of changes in species diversity, structure and dynamics of forest ecosystems along latitudinal gradients in East Asia

We examined effects of seasonality of climate and dominant life form (evergreen/deciduous, broad-leaf/coniferous) together with energy condition on species diversity, forest structure, forest dynamics, and productivity of forest ecosystems by comparing the patterns of changes in these ecosystem attributes along altitudinal gradients in tropical regions without seasonality and along a latitudinal gradient from tropical to temperate regions in humid East Asia. We used warmth index (temperature sum during growing season, WI) as an index of energy condition common to both altitudinal and latitudinal gradients. There were apparent differences in patterns of changes in the ecosystem attributes in relation to WI among four forest formations that were classified according to dominant life form and climatic zone (tropical/temperate). Many of the ecosystem attributes—Fisher’s alpha of species-diversity indices, maximum tree height and stem density, productivity [increment rate of aboveground biomass (AGB)], and population and biomass turnover rates—changed sharply with WI in tropical and temperate evergreen broad-leaved forests, but did not change linearly or changed only loosely with WI in temperate deciduous broad-leaved and evergreen coniferous forests. Values of these ecosystem attributes in temperate deciduous broad-leaved and evergreen coniferous forests were higher (stem density was lower) than those in tropical and temperate evergreen broad-leaved forests under colder conditions (WI below 100°C). Present results indicate that seasonality of climate and resultant change in dominant life form work to buffer the effects of energy reduction on ecosystem attributes along latitudinal gradients.

Effects of selective logging on tree species diversity and composition of Bornean tropical rain forests at different spatial scales

Reduced-impact logging (RIL) is known to be beneficial in biodiversity conservation, but its effects on tree diversity remain unknown. Pattern of tree diversity following disturbance usually varies with spatial scale of sampling (i.e., plot size). We examined the impacts of RIL on species richness and community composition of tree species at different spatial scales, and the scale (plot size) dependency of the two metrics; species richness versus community similarity. One 2-ha and three to four 0.2-ha plots were established in each of primary, RIL, and conventionally logged (CL) forest in Sabah, Malaysia. Species richness (the number of species per unit number of stems) was higher in the RIL than in the CL forest at both scales. The relationship between species richness and logging intensity varied with plot size. Species richness was greater in the RIL than in the primary forest at the 2-ha scale, while it was similar between the two forests at 0.2-ha scale. Similarly, species richness in the CL forest demonstrated a greater value at the 2-ha scale than at the 0.2-ha scale. Greater species richness in the two logged forests at the 2-ha scale is attributable to a greater probability of encountering the species-rich, small patches that are distributed heterogeneously. Community composition of the RIL forest more resembled that of the primary forest than that of the CL forest, regardless of plot size. Accordingly, species richness is a scale-dependent metric, while community similarity is a more robust metric to indicate the response of tree assemblage to anthropogenic disturbance.

Biotic homogenization and differentiation of soil faunal communities in the production forest landscape: taxonomic and functional perspectives

Biotic homogenization has been reported worldwide. Although simplification of communities across space is often significant at larger scales, it could also occur at the local scale by changing biotic interactions. This study aimed to elucidate local community processes driving biotic homogenization of soil faunal communities, and the possibility of biotic re-differentiation. We recorded species of oribatid mites in litter and soil layers along a gradient of forest conversion from monoculture larch plantation to primary forests in central Japan. We collected data for functional traits of the recorded species to quantify functional diversity. Then we quantified their taxonomic/functional turnover. Litter diversity was reduced in the larch-dominated stands, leading to habitat homogenization. Consequently, litter communities were biologically homogenized and differentiated in the plantations and in the natural forest, respectively. Turnover of functional traits for litter communities was lower and higher than expected by chance in the plantations and in the natural stand, respectively. This result suggests that the dominant assembly process shifts from limiting similarity to habitat filtering along the forest restoration gradient. However, support for such niche-based explanations was not observed for communities in the soil layer. In the monocultures, functional diversity expected from a given regional species pool significantly decreased for litter communities but not for those in the soil layer. Such discrepancy between communities in different layers suggests that communities more exposed to anthropogenic stresses are more vulnerable to the loss of their functional roles. Our study explains possible community processes behind the observed patterns of biological organization, which can be potentially useful in guiding approaches for restoring biodiversity.

Plastic changes of leaf mass per area and leaf nitrogen content in response to canopy openings in saplings of eight deciduous broad-leaved tree species

Leaf nitrogen content per area (Narea) is a good indicator of assimilative capacity of leaves of deciduous broad-leaved trees. This study examined the degrees of increase in Narea in response to canopy openings as leaf mass per area (LMA) and leaf nitrogen content per mass (Nmass) in saplings of eight deciduous broad-leaved tree species in Hokkaido, northern Japan. Five of the species were well-branched species with a large number of small leaves (lateral-growth type), and the other three species were less-branched species with a small number of large leaves (vertical-growth type). The degrees of increase in Narea were compared between the two crown types. In closed-canopy conditions, leaves of the vertical-growth species tended to have a lower LMA and higher Nmass than those of the lateral-growth species, which resulted in similar Narea for both. LMA increased in canopy openings in the eight species, and the degrees of increase were not largely different between the lateral- and vertical-growth species. On the contrary, Nmass was unchanged in canopy openings in the eight species. As a result, Narea of each species increased in canopy openings in proportion to the increase in LMA, and the degrees of increase in Narea were similar in the lateral- and vertical-growth species. Therefore, this study showed that the degrees of increase in Narea were not correlated with the crown architecture (i.e., the lateral- and vertical-growth types).

Concordance and discordance between taxonomic and functional homogenization: responses of soil mite assemblages to forest conversion.

The compositional characteristics of ecological assemblages are often simplified; this process is termed “biotic homogenization.” This process of biological reorganization occurs not only taxonomically but also functionally. Testing both aspects of homogenization is essential if ecosystem functioning supported by a diverse mosaic of functional traits in the landscape is concerned. Here, we aimed to infer the underlying processes of taxonomic/functional homogenization at the local scale, which is a scale that is meaningful for this research question. We recorded species of litter-dwelling oribatid mites along a gradient of forest conversion from a natural forest to a monoculture larch plantation in Japan (in total 11 stands), and collected data on the functional traits of the recorded species to quantify functional diversity. We calculated the taxonomic and functional β-diversity, an index of biotic homogenization. We found that both the taxonomic and functional β-diversity decreased with larch dominance (stand homogenization). After further deconstructing β-diversity into the components of turnover and nestedness, which reflect different processes of community organization, a significant decrease in the response to larch dominance was observed only for the functional turnover. As a result, there was a steeper decline in the functional β-diversity than the taxonomic β-diversity. This discordance between the taxonomic and functional response suggests that species replacement occurs between species that are functionally redundant under environmental homogenization, ultimately leading to the stronger homogenization of functional diversity. The insights gained from community organization of oribatid mites suggest that the functional characteristics of local assemblages, which support the functionality of ecosystems, are of more concern in human-dominated forest landscapes.

Functional Differentiation and Positive Feedback Enhancing Plant Biodiversity

Ecosystems are under the control of negative feedback due to resource competition, and it is difficult to explain the coexistence of many species in an ecosystem. By contrast, evolutionary history suggests that positive feedback between living organisms and environments contributes to increasing biodiversity. This paper presents a conceptual framework to interface these feedbacks, taking forests and tree communities as an example. One of the prevailing global patterns of biodiversity is the latitudinal gradient of tree species diversity in forests. A tenfold difference exists in species diversity between tropical lowland forests and either tropical high-altitude forests or temperate forests. We examined tree census data from permanent plots across various forest types in eastern Asia. Tree species diversity increased exponentially along a geographic gradient while ecosystem measures such as biomass, biomass turnover rate and asymptotic canopy height increased only linearly. Examination of a size-structure-based dynamic model of tree populations suggests that these ecosystem measures multiplicatively contribute to the extreme species diversity in tropical lowland rain forests. The same model also shows that any singular species with higher resource-use efficiency replaces all coexisting species under the constraint of functional tradeoff. Such replacement brings about increasing efficiency of ecosystems in resource exploitation, and in turn presents a greater opportunity for species coexistence. The non-linear relationship between whole ecosystem measures and species diversity develops through the process of positive feedback between the energetic efficiency of ecosystems and the functional differentiation among species, on evolutionary time scales.

Structure, floristics and diversity of tropical montane rain forests over ultramafic soils on Mount Kinabalu (Borneo) compared with those on non-ultramafic soils

We describe here the structure, floristics and diversity of tropical montane rain forests over ultramafic soils on Mount Kinabalu, Borneo, and compared them with those on non-ultramafic soils. We used 14 sample plots from 1580 to 3080 m elevation, six on ultramafic soils and eight on non-ultramafic soils, and identified all trees ≥4.8 cm diameter. The plot area ranged from 0.1 to 1 ha, the majority (nine plots) being 0.25 ha. Forests on ultramafic soils showed more stunted structure, especially at higher altitudes, than those on non-ultramafic soils and on ridges than on slopes. Species of Coniferae (Araucariaceae and Podocarpaceae) and Myrtaceae strongly dominated on ultramafic soils occupying 61–96% of basal area in each plot, compared with 22–63% on non-ultramafic soils. Among 287 species found in the 14 plots, only nine species (including four species endemic to Mount Kinabalu) were strictly restricted to ultramafic soils. Nonmetric multidimensional scaling demonstrated that elevational change in species composition was accelerated on ultramafic soils and on ridges. Tree species diversity was generally lower on ultramafic soils than on non-ultramafic soils at the comparative altitudes. Multiple regression analysis suggested that soil nutrients (phosphorus and nitrogen) could be the cause of vegetation differentiation between ultramafic and non-ultramafic soils, although the data on soil metals are lacking. Comparison of our results with those from other mountains with ultramafic soils in South-east Asia demonstrated the uniqueness of the montane rain forests over ultramafic soils on Mount Kinabalu.

Management Effects on Tree Species Diversity and Dipterocarp Regeneration

Unregulated selective logging has been common throughout the Southeast Asian tropical rain forests. Such logging usually damages more than 50 % of the original forest biomass and causes soil disturbances by the use of heavy machinery (Cannon et al. 1994; Pinard and Putz 1996; Bertault and Sist 1997; Sist et al. 1998). To mitigate the deleterious logging impacts, reduced-impact logging has been applied in some tropical production forests (Kleine and Heuveldop 1993; Lagan et al. 2007; Putz et al. 2008a). Reduced-impact logging is a modification of selective logging that is intended to minimize collateral damage to the residual stands. Such methods include pre-harvest inventory, mapping of all canopy trees, directional felling, liana cutting, and planning of skid trails, log decks, and roads (see Chap. 1). In comparison with unregulated conventional logging, reduced-impact logging is beneficial in maintaining not only future crop trees (Rockwell et al. 2007; Pena-Claros et al. 2008) and forest biomass (Johns et al. 1996; Pinard and Putz 1996; Bertault and Sist 1997; Sist et al. 1998; Putz et al. 2008b; Imai et al. 2009), but also biological diversity, such as dung beetles (Davis 2000), flying insects (Akutsu et al. 2007), soil fauna (see Chap. 4 by Hasegawa et al., this volume), and forest-dwelling vertebrates (see Chap. 5 by Samejima et al., this volume). Many other taxa, such as ants, arachnids, bats, birds, fishes, and animals, also are not adversely affected by reduced-impact logging (Azevedo-Ramos et al. 2006; Wunderle et al. 2006; Castro-Arellano et al. 2007; Felton et al. 2008; Presley et al. 2008; Dias et al. 2010; Bicknell and Peres 2010). However, the effects of reduced-impact logging on tree species diversity of tropical rain forests remain largely unknown, despite that the diversity of trees is fundamental to the structure and functions of the forests. The diversity of trees may also determine the diversity of other taxonomic groups because trees provide resources and habitat structures for dependent species. The aim of this study is to examine the effects of reduced-impact logging versus conventional logging on tree species diversity and composition in the lowland tropical rain forests in Deramakot and Tangkulap.

Effects of Temperature and Light Conditions on Growth of Current-Year Seedlings of Warm-Temperate Evergreen Tree Species and Cool-Temperate Deciduous Tree Species

It is suggested that global warming affects plant distribution along latitudinal and altitudinal gradients because vegetation changes with thermal conditions. Simulation studies predicted that global warming largely affects plant distribution (e.g., Morin et al., 2008). Actually, vegetation change during several decades has been observed (Penuelas et al., 2007; Lenoir et al., 2008). By contrast, some other studies did not observe vegetation changes (Holtmeier & Broll, 2007; Harsch et al., 2009). Interpretation of results of simulation models also needs caution because simulation results are different according to modeling methods even for same species (Thuiller, 2003). Therefore, there is still uncertainty of effects of global warming on plant distribution. Plant distribution is determined by integrated demographic processes such as seed dispersal, seed germination, growth and survival of individual plants. Since early demographic phase such as seedling establishment is more susceptible to environmental conditions than the adult phase (Kullman, 2002), it is important to clarify effects of temperature on seedling growth to predict effects of global warming on plant distribution. There are many experimental studies that examined effects of temperature on growth of tree seedlings (Danby & Hik, 2007; Hoch & Korner, 2009; Munier et al., 2010). For example, Yin et al. (2008) reported that seedling growth of Betula albo-sinensis increased in the warm condition with 0.51oC higher than the ambient air condition. Many experimental studies that examined effects of temperature were conducted at bright conditions (e.g. Danby & Hik, 2007; Way & Sage, 2008). However, most seedlings distribute in dark closed-canopy conditions in forests. Therefore, it is necessary to examine effects of temperature on seedling growth not only in bright conditions but also in dark conditions. Plants plastically change morphology according to light conditions. For example, relative biomass allocation to leaves is greater in dark conditions than in bright conditions,