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Success of clonal tree plantations depends on genotype as well as phenotypic plasticity, which determines acclimation potential of individual trees to different environmental conditions. Short-term...

Although Chamaecyparis obtusa reduces soil pH and cation levels, limited information is available regarding their alterations after clear-cutting. We examined the soil pH and base cations on the upslopes and downslopes of individual trees and stumps of C. obtusa at two distances (0.5 m and 1.0 m) and three depths (0–5, 5–10, and 10–30 cm) in intact- and cut-tree plots. The soil pH was higher in the cut-tree plot than in the intact-tree plot, indicating the recovery of soil pH after clear-cutting. The recovery was more evident in the surface soils (0–5 cm) of downslope areas (0.5 m) than in other soil depths, which implies that the recovery of soil pH was caused by the lack of H+ supply from stumps after clear-cutting. The results of H+ (in H2O: water-soluble and KCl: exchangeable) suggested a lack of soluble H+ in the cut-tree plot. Soil Ca2+ and Mg2+ levels in the surface soil (0–5 cm) were 1.86-fold and 1.93-fold higher in the cut-tree plot than in the intact-tree plot, respectively, implying that the recovery of divalent cations after clear-cutting was caused by a reduction in cation loss through cation exchange with H+ derived from the stemflow. Collectively, soil pH and divalent cations were recovered after clear-cutting because the stemflow had ceased.

Tree age derived from annual-ring counts provides fundamental information on forest stands and individual trees in temperate forests. However, discontinuous growth in the trunk may cause inaccuracies in annual-ring counts, and the effect of radial growth rate and interspecific differences on discontinuous ring formation have not been evaluated in the same forest stand. We investigated the occurrence of discontinuous rings at the base of 435 tree trunk disks of 16 evergreen and 15 deciduous hardwood tree species growing in a temperate forest of Japan. The effects of tree age and radial growth rate on frequency of discontinuous rings and their interspecific differences were evaluated by a generalized linear mixed-effect model. Discontinuous rings were observed in 29 of the 31 species in 330 individuals, which is about 75% of the total number of individuals examined. The number of discontinuous rings proportionally decreased with the growth rate and increased with the tree age. On the other hand, the effects of the growth rate were different among species. The majority of species at the study site contained frequent discontinuous rings in the trunk base. Annual-ring counts from a single core would lead to underestimation of tree ages in this case. Stem disks or increment cores taken in multiple directions at ground level would be useful for accurate estimation of tree age in temperate hardwood forests.

The responses of forest production and nitrogen (N) utilization to belowground resource availability may be stronger in Moso bamboo forests than in woody forests because the former have higher N and water demands than the latter. The aim of this study was to clarify the different effects of mountain slope-induced belowground resource limitation on forest production between a Moso bamboo forest and a Japanese cedar forest. We compared the changes in biomass, net primary production, net primary production allocation, N utilization, N content per organ, and N use efficiency in response to soil resource availability at five different slope positions in each forest type. In the bamboo forest, the aboveground net primary production decreased upslope and the belowground net primary production allocation increased with decreasing upslope soil water availability. In contrast, leaf N content of the bamboo forest increased upslope, and N use efficiency decreased upslope with an increasing upslope soil N mineralization rate. Although a greater N use efficiency has often been reported at higher slope positions due to lower N availability, this phenomenon was observed at lower slope position in the bamboo forest. The soil N supply might exceed the soil N demand at higher slope positions, resulting in lower N use efficiency. The responses observed in the bamboo forest were absent in the Japanese cedar forest. The higher demand for belowground resources and environmental plasticity explained the higher productivity of the bamboo forest.

Changes in dominant plant species can influence the net primary production (NPP) via changes in species traits, including nitrogen use efficiency (NUE) and belowground allocation enhancing N uptake, as well as soil N availability. We investigated changes in above- and belowground NPP, N uptake, and NUE in response to changes in soil N in natural forests and plantations, with and without changes in species compositions among the environmental gradient, respectively. In plantations, NPP increased with increasing availability of soil N in the presence of constant NUE and the proportion of belowground NPP to total NPP. However, in natural forests, aboveground, belowground, and total NPP were high for the available middle range soil N. Belowground NPP and the proportion of belowground NPP to total NPP in natural forests was positively related to aboveground NPP. Both belowground NPP and soil N mineralization rates explained stand N uptake rates. These results indicated that belowground allocation might facilitate aboveground NPP with enhancement of N uptake by root allocation. Stand NUE decreased with soil N availability in natural forests and was stable in plantations, and resulted in lower production in natural forests and higher production in plantations under high soil N availability. The community weighted mean (CWM) of N resorption efficiency was positively related to NUE. The CWM of juvenile root growth, as reported previously for planted juveniles, was positively related to belowground NPP allocation. In addition, the ranges of CWMs were broader in natural forests than in plantations. This suggested that the different changes in NPP in response to changes in soil N between natural forests and plantations was due to the changes in leaf and root species traits via changing in species composition among sites. In conclusion, the present study showed that the changes in species specific traits in root growth and leaf N strongly affected the relationship between soil N availability and stand carbon and N dynamics.

Significance Identifying and explaining regional differences in tropical forest dynamics, structure, diversity, and composition are critical for anticipating region-specific responses to global environmental change. Floristic classifications are of fundamental importance for these efforts. Here we provide a global tropical forest classification that is explicitly based on community evolutionary similarity, resulting in identification of five major tropical forest regions and their relationships: (i) Indo-Pacific, (ii) Subtropical, (iii) African, (iv) American, and (v) Dry forests. African and American forests are grouped, reflecting their former western Gondwanan connection, while Indo-Pacific forests range from eastern Africa and Madagascar to Australia and the Pacific. The connection between northern-hemisphere Asian and American forests is confirmed, while Dry forests are identified as a single tropical biome., Knowledge about the biogeographic affinities of the world’s tropical forests helps to better understand regional differences in forest structure, diversity, composition, and dynamics. Such understanding will enable anticipation of region-specific responses to global environmental change. Modern phylogenies, in combination with broad coverage of species inventory data, now allow for global biogeographic analyses that take species evolutionary distance into account. Here we present a classification of the world’s tropical forests based on their phylogenetic similarity. We identify five principal floristic regions and their floristic relationships: (i) Indo-Pacific, (ii) Subtropical, (iii) African, (iv) American, and (v) Dry forests. Our results do not support the traditional neo- versus paleotropical forest division but instead separate the combined American and African forests from their Indo-Pacific counterparts. We also find indications for the existence of a global dry forest region, with representatives in America, Africa, Madagascar, and India. Additionally, a northern-hemisphere Subtropical forest region was identified with representatives in Asia and America, providing support for a link between Asian and American northern-hemisphere forests.

To test the effects of invasion by strawberry guava trees (Psidium cattleianum) on the forest soil ecosystem, we compared soil properties between pairs of adjacent native and P. cattleianum stands. We set up six study sites that had developed under different mean annual precipitation levels in the Ko'olau Mountains on the island of O'ahu, Hawai'i. Accumulated litter mass and soil pH decreased with precipitation in the native stands. Invasion by P. cattleianum increased the amount of litter and reduced the differences in soil water content and pH among the sites. We compared the decomposition process using the Tea Bag Index, which is determined by the difference in dry mass of commercially available green and rooibos teas in nylon mesh bags before and after 90 days of burial. Psidium cattleianum increased the initial litter decomposition rate irrespective of precipitation and other soil properties. On the other hand, P. cattleianum increased the long-term litter stabilization factor of the Tea Bag Index in wetter sites. The accumulation of litter was likely caused by indirect effects of P. cattleianum through the alteration of soil moisture properties. In summary, this study shows that invasion by P. cattleianum could alter the soil properties in both wet and mesic sites, suggesting the possibility of change in composition and/or function of decomposers.

Nitrogen (N) is the primary limiting nutrient for forest production. Therefore, understanding how environmental factors affect N transformation rates is essential for the provision of sustainable ecosystem services. Because these factors are interlinked, it is important to consider direct and indirect structural relationships to better understand the factors contributing to N transformations. In this study, we analyzed the structural cause–effect relationships surrounding N transformations by structural equation modeling using a database containing net and gross N transformation rates and related soil chemical properties from 38 sites across the Japanese archipelago. The average net N mineralization and nitrification rates in the Japanese forest soils were 0.62 ± 0.68 and 0.59 ± 0.65 mg N kg−1 d−1, respectively, and gross N mineralization and nitrification rates were 4.22 ± 3.59 and 0.98 ± 0.68 mg N kg−1 d−1, respectively. Compared with previous large scale studies, net and gross N transformation rates in Japanese forest soils were considerably diverse despite their relatively small land area and were representative of temperate forest ecosystems. Structural equation modeling analysis showed that net N transformations were directly affected by gross N transformations, which in turn were significantly and directly affected by soil organic matter contents. Soil organic matter was significantly affected by organic layer amount, tree species and soil group. The effect of soil group was the greatest among these factors, suggesting that soil organic matter contents in Japanese forest soils were mainly influenced by soil parent materials. This was especially evident for Andosols, which are derived from volcanic sediments and contain large amounts of soil organic matter leading to high N transformation rates in the Japanese forest soils. Among the factors related to organic layers and mineral soil layers, soil organic matter content and organic layer amount, which represent substrate availability, had significant effects on gross and net N transformation rates. However, by refining the scale of the dataset using soil groups/soil parent materials, the influence of substrate quality and soil chemical properties on N transformations was suggested. From the current dataset, it was indicated that soil parent materials were the most important factor controlling the pattern of N transformations in the soil of Japanese forest ecosystems. This conclusion should be repeatedly refined considering the spatial distribution of factors such as climatic conditions and forest types with additional site datasets obtained from future surveys.

Sika deer (Cervus nippon) sometimes cause extensive damage to planted tree seedlings. To evaluate the effects of culling on the spatial distribution patterns of sika deer and browse damage to planted seedlings, we compared the data collected before and after experimental culling in a cool, temperate, mixed forest on Kyushu Island, Japan. Experimental culling, conducted in an area of 1 km2, removed five, four and two sika deer in April, June and October 2011, respectively. During the year before culling, the spatial pattern of the number of sika deer caught on camera corresponded to the predicted sika deer density. Sika deer immediately browsed planted seedlings after the initial planting. The cumulative number of browsed seedlings increased over time, especially in winter. The spatial pattern of the cumulative number of sika deer caught on camera corresponded to that of browsed seedlings at the year’s end. During the year when culling was conducted, the number of sika deer caught on camera decreased around the center of the study site where the culling was conducted and the number of browsed seedlings decreased. During the year following culling, the cumulative number of browsed seedlings was very similar to that in the year before the culling, while the same low number of sika deer was caught on camera. These results indicate that the effects of deer culling resulted in decreased levels of sika deer appearance and browse damage for more than 1 year and for several months, respectively.

Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from -9 to +26 °C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained

In temperate forest ecosystems, accelerated freeze–thaw cycles caused by winter climate change are expected to affect nitrogen (N) cycling in soils. Net N mineralization and nitrification rates were investigated via incubations of sieved soils transplanted from ten temperate forest ecosystems to two northern Japan sites with natural snowfall gradients. This was done to address: 1) how freeze–thaw cycles affect N mineralization and nitrification in temperate forest soils; 2) whether freeze–thaw cycles change the soil N transformation rates in the following growing season; and 3) which soil characteristics affect the response of the N transformation rates to freeze–thaw cycles. The effect of freeze–thaw cycles on inorganic N and dissolved organic carbon productions differed among soils, that is, some soils produced more inorganic N and dissolved organic carbon in the conditions imposed by freeze thaw cycles than in the non-frozen treatment but the others did not. The response to the freeze–thaw cycles was explained by soil microbial activity (gross N mineralization and nitrification rate) and soil fertility (inorganic N pools in the early spring and water soluble ions). Freeze–thaw cycles significantly increased N transformation rates in the following growing season, suggesting that winter climate change might also affect nutrient availability for vegetation and soil microbes in the growing season. The magnitude and frequency of freeze–thaw cycles were considered to be important indicators of N transformation rates during the growing season, suggesting that the higher intensity of freeze–thaw cycles in the original locations of soils changed the microbial communities and functions with high tolerance to freeze–thaw cycles; this resulted in greater N transformation rates in the following growing season. Microbial activity, soil fertility and climate patterns in the original locations of soils are believed to have an effect on the response to winter climate change and to cause large variability of soil response of N transformation rates to freeze–thaw cycles in both the dormant and growing seasons.

We compared stand structure and plant species occurrence on the shoulders of 3-, 10- and 20-year-old roads in a subtropical evergreen broad-leaved forest to document temporal changes in edge effects of forest roads. We recorded 154 vascular species in the study plots, including 3 non-native species. We used generalized linear mixed models to analyze changes in forest structure and plant species composition in relationship to the distance from forest roads. The spatial patterns in stand structure at different distances from roads differed with road age. The large canopy openness on the edge of 3-year-old roads decreased with time after the construction. A progressive decrease in tree height on roadsides was observed after the road construction, suggesting tall trees could not withstand the dry and windy roadside environment. The edge effect on the canopy tended to be larger at higher elevation sites. The spatio-temporal pattern of species occurrence based on distance from roads differed by species. Typical pioneer species such as Schima wallichii and Eurya japonica increased along the edge, while less aggressive pioneer species and understory species decreased. As time passed after the road construction, some climax and understory species decreased at the forest edge, while other climax and understory species increased. The modeling methods proposed in this study could be applied to different roadside and edge study sites.

Biogenic volatile organic compounds (BVOCs) are known to play an important role in atmospheric chemistry due to their high reactivity and high emission rates. Therefore, in recent decades, many efforts have been made to estimate the emission rates, composition and allocation of the BVOCs. Monoterpenes (MNTs) and sesquiterpenes (SQTs) are major groups of BVOCs and mainly emitted from coniferous trees. There is quite a few reports discussing the seasonality of basal emission rate, which is a normalized emission rate at a set of standard conditions (e.g. temperature, light intensity), of the BVOCs. Three field measurements were conducted using branch enclosure techniques to determine MNTs and SQTs emission measured from mature trees of Cryptomeria japonica and Chamaecyparis obtusa , which are the most dominant trees in Japan and account for about 40–50% of Japanese forest in leaf amount throughout the four seasons in southern Japan in 2010. The results are compared with the measurements for the same compound classes obtained at a suburban area of Tokyo, Japan in 2009. The seasonal variation in the basal emissions of MNTs from both tree species at Shiiba did not show significant seasonal changes. For both tree species, the variations in the basal emission of MNTs differ in the two sites, while those of SQTs showed relatively similar variations. Chemical composition of SQTs showed clear and continued seasonal variations, while MNTs did not show any clear seasonal variation for these tree species at both sites. It can be hypothesized that the emissions of BVOC classes (e.g. MNTs and SQTs) depend on leaf age. In this paper, we discuss about the seasonal variations in the basal emission rates and chemical compositions of BVOCs obtained from the two dominant coniferous tree species in Japan based on nine field measurement campaigns conducted at two different sites.

Plant stoichiometry has been used to diagnose phosphorus (P) limitation caused by increased atmospheric nitrogen (N) deposition. Spatial variability of N/P stoichiometry within a forested watershed has not yet been evaluated. This study conducted synoptic sampling of leaf matter in 27 plots within a temperate forested watershed on low P availability rock (serpentine bedrock) with a moderately high atmospheric N deposition (16 kg N ha−1 year−1) to assess the effects of spatial topographic variation on N/P stoichiometry. Leaf N and P concentrations and N/P ratios of Japanese cypress were assessed, and their spatial variations were evaluated across a catchment. Average leaf P concentration was low (0.66 ± 0.16 mg g−1) across the sites, while leaf N concentration was high (13.0 ± 1.5 mg g−1); subsequently, N/P ratios were high (21 ± 5). In addition, the aboveground biomass growth of Japanese cypress positively correlated with litter P, implying the P limitation of Japanese cypress at the study site. Leaf P concentrations responded to the index of convexity (IC) values more than those of N. Subsequently, the N/P ratio correlated with IC, suggesting that N/P ratios are susceptible to topographic features. This could be partly caused by smaller spatial variability of N availability compared with P, owing to increased atmospheric N deposition. Thus, topography should be taken into consideration when diagnosing P limitation caused by N deposition.

We measured the aboveground biomass, biomass increment and litterfall production of a 140-year-old, abandoned Cryptomeria japonica plantation in order to infer the effects of topography on biomass production. The plantation was unsuccessful and the naturally regenerated broad-leaved trees contributed 93.4% (374.2 Mg ha−1) of the total aboveground biomass (400.2 Mg ha−1). Comparing between different slope positions, aboveground biomass decreased downslope corresponding to the decrease in broad-leaved tree biomass. The biomass of C. japonica did not vary with slope position. Biomass increment and litterfall production of the broad-leaved trees also decreased downslope. However, litterfall production per unit biomass and aboveground net primary production per unit biomass increased downslope. Results of a path analysis showed that biomass increment of C. japonica decreased with increasing topographical convexity, whereas biomass and litterfall production of broad-leaved tree increased. Litterfall production of broad-leaved tree decreased with increasing biomass of C. japonica, suggesting that, despite their small biomass, the presence of residual C. japonica may have negative effects on the distribution and productivity of the broad-leaved trees. Our results indicated that total aboveground biomass of the study site was comparable to that of old-growth C. japonica plantations. We inferred that the variation in aboveground biomass of the broad-leaved trees was largely determined by the topography, while their productivity was affected by interactions with planted C. japonica.

Defining the spatial arrangement and length of the cutting cycle in a logged area is crucial for reconciling potential conflicts between timber yields and maintenance of ecosystem services in natural forests. In this study, we investigated long-term impacts of clear-fell logging on timber production and tree species diversity in a subtropical forest on the Ryukyu Islands, using an individual-based simulation model. We assumed six logging scenarios defined by combinations of forest type and regeneration processes, which acted as surrogates for spatial scales of clear-fell logging. These scenarios were simulated under cutting cycles ranging from 20 to 150 years. Short-cutting cycles resulted in dominance by the sprouting species Castanopsis sieboldii. The compositional shift was accelerated by the lack of seed dispersal from surrounding forest areas. The simulations demonstrated that a sustainable logging regime maintaining both yield and tree species diversity requires a cutting cycle longer than 50 years. The simulation results also suggest that the trade-off between the recovery of tree species diversity and timber production is favored more in stands surrounded by mature forest than in isolated stands or stands surrounded by immature forest. Ecological risk assessments based on model simulations provide an alternative to current forest management practices that rely on empirical knowledge.

Subtropical forests in the Ryukyu Islands have been degraded by silvicultural practices, and thus their structural attributes are being shifted to other states dominated by a few tree species. This study clarified the mechanisms of the change, and examined the effect of clear logging on the resilience of a subtropical forest. Sprouting regeneration and typhoon disturbance were introduced into an individual-based model, SEIB-DGVM, for describing stand development and succession. The regeneration dynamics from young secondary to old-growth stands were reproduced fairly well with the model. Sprouting recruitment produced high stem density at the beginning of stand development, which caused a self-thinning trajectory following the −3/2 power law. In the late development stage after 70 years, tree species diversity fluctuated because of the regenerative response of sprouting species and the facilitatory effect of typhoon disturbance on the coexistence of subordinate species. The death of canopy trees because of typhoon disturbances reduced the dominance of Castanopsis sieboldii, and depressed its dominance in the understory. Consequently, the understory species could establish by virtue of fallen canopy trees, and tree species diversity increased at the stand level. Clear logging experiments in the model revealed that species diversity deteriorated, especially in the stand dominated by sprouting species. Resilience of subtropical forests was determined by initial species composition before clear logging. Our simulation results suggest that repeated logging drives subtropical forests with high species diversity to a stand monopolized by C. sieboldii.

Effects of sika deer (Cervus nippon) and dwarf bamboo (“sasa;” Sasamorpha borealis) on seedling emergence and survival were investigated in cool-temperate mixed forests in the Kyushu mountain range, Japan. We compared the effects of sika deer between two sites with different sika deer densities. One site (no-sasa forest) has sparse cover of S. borealis and a high density of sika deer, and the other site (sasa forest) has dense cover of S. borealis with a low density of sika deer. In the no-sasa forest, more seedlings emerged and the survival rate of the seedlings was higher compared with the sasa forest. Compared with the sasa forest, the canopy in the no-sasa forest was more open, the organic layer was shallower and drier, the mean daily soil temperature was higher, and soil temperature fluctuated more widely. Those environmental parameters did not differ between unfenced and fenced plots. The comparison between the sasa and no-sasa forests suggested that removal of S. borealis by sika deer had an indirect positive effect on seedling emergence and survival. However, the fenced-plot experiments indicated that sika deer inhibited seedling emergence and survival. These contradictory conclusions could result from the much larger negative effects of S. borealis on seedling emergence and survival compared with the effects of sika deer browsing.

We examined variations in stand structure and tree growth of a mangrove forest along two gradients: from the river mouth to upper stream and from the riverside to inland, along the Nakara River, Iriomote Island, Japan. Bruguiera gymnorrhiza (L.) Lamk. occurred throughout the intertidal area, though Rhizophora stylosa Griff. and Kandelia candel (L) Druce did not occur upstream. Basal area and maximum tree height of B. gymnorrhiza decreased downstream. The growth rate in stem diameter of B. gymnorrhiza decreased downstream in relation with the soil salinity. The basal area and the maximum tree height of B. gymnorrhiza increased with the distance from the riverside. R. stylosa increased in stem diameter and growth rate toward the riverside.

We investigated factors affecting the distribution of naturally regenerated broad-leaved trees in a 140-year-old Cryptomeria japonica plantation. We used path analysis to examine the relationship among microtopography, the biomass of planted trees, and the biomasses of canopy and subcanopy trees of broad-leaved species. The study plot was divided into three topographic types (ridge, slope, and valley), and we discuss how the different topographic types are affected. For all topographic types, the biomass of canopy trees of broad-leaved species decreased with convexity. For slope and valley topographies, the biomass of subcanopy trees of broad-leaved species also decreased with convexity. For ridge topography, the biomass of subcanopy trees of broad-leaved species increased with the biomass of planted trees, and decreased with the biomass of canopy trees of broad-leaved species. These results suggest the effects of microtopography on the biomass of subcanopy trees were much larger than the effects of canopy trees for slope and valley topographies, while the effects of microtopography were smaller for ridge topography.

We investigated spatial distribution of lianas, and examined relationships between distribution and topography in a secondary forest on the northern part of the main island of Okinawa, south-west Japan. All lianas with a stem diameter exceeding 2 cm at a point 1.3 m from the root were inventoried, and stem diameter and root position were measured within a small watershed (16.0625 ha). Geographical information systems (GIS) were used to divide the watershed into 257 cells in total, each cell being 25 m × 25 m. Three topographic parameters were measured in each cell: slope angle, slope aspect and relief. In total, 930 stems from 20 species of lianas were recorded. Distribution of all liana stems and 14 of 15 species analysed were biased toward concave sites. Abundance of total lianas was higher in concave sites than in convex sites. Our results suggest that distribution and abundance of lianas are strongly affected by topography, and that lianas tend to be distributed in sites with more water and nutrients, which are formed by relief in the Okinawa forest. Factors affecting stem density differed among species.

Annual amounts of litterfall and nitrogen input by litterfall were measured in a subtropical evergreen broad-leaved forest to examine the contribution of a liana species, Mucuna macrocarpa Wall., to the spatial heterogeneity of litterfall production and nitrogen input. The total litterfall in the study plot was 7.1 t ha−1 year−1. The amount of litterfall varied with topography and was greatest at the valley bottom and decreased toward the ridges. Macuna macrocarpa litterfall was absent on the ridges although it accounted for the largest percentage, 32%, of total leaf litter production in the valley. Nitrogen input by litterfall was 69 kg ha−1 year−1 in the plot. Nitrogen input by litterfall was also largest at the valley bottom and decreased toward the ridges. Leaf litter of M. macrocarpa had approximately twice the nitrogen concentration of litterfall of other species. Macuna macrocarpa accounted for 42% of nitrogen input by leaf litter in the valley. The abundance and the high nitrogen concentration of M. macrocarpa intensified differences in the amount of litterfall and nitrogen input by litterfall between valleys and ridges. It was concluded that a liana species, M. macrocarpa, can contribute to the spatial heterogeneity of litterfall and may subsequently affect nutrient cycling in a subtropical evergreen broad-leaved forest on Okinawa Island.

沖縄島北部の亜熱帯常緑広葉樹林の樹木の分布パターンにおける地形依存性の変化をさまざまなスケールで検討した。地形の傾斜と起伏は，地形を評価する方形区のサイズの変化に応じて変化するとともに，その空間的なパターンも変化したが，異なるスケール間には有意な正の相関があった。樹木各種が分布する方形区の傾斜および起伏の中央値の順位はスケールが変わってもあまり変化しなかった。一方，種ごとの分布パターンのスケール間比較を行った結果では，空間スケールの違いによって一部異なる分布傾向が認識されることが示された。イタジイはどの空間スケールでも凸状地に偏った分布が認められたが，35 m×35 mのスケールでは谷や尾根のどちらにも広く分布し，その大きな谷や尾根の中にある5 m×5 m程度の小さな凸状地に集中する分布が検出された。イジュはいずれのスケールでも，イタジイが分布する地形に比べ急傾斜の凹状地に分布する傾向が検出された。イタジイは個体サイズが大きくなるほど，傾斜がより緩く，より凸状の斜面に偏る分布傾向が認められたが，イジュでは個体サイズと分布する地形との間に明瞭な関係はみられなかった。以上のような樹木の地形依存的な分布パターンには，樹木個体群が地形に対応した結果により生じたものに加え，調査地の地形構造の特性を反映した結果により生じた可能性もある。

Field tree measurement to collect ground truth data is labor intensive. To make it efficient to collect the field data in a large scale, Unmanned Aerial Vehicle is introduced in this study. An automated photogrammetric technique called Structure from Motion (SfM) is used to create 3D data out of photos collected by UAV. Tree structure created by SfM is compared with the 3D data obtained by several Terrestrial Laser Scanners to see the difference in vertical forest structure. Canopy structure is mainly captured by UAV-SfM and there is more point density around tree canopy than 3D data obtained by airborne laser. The point density of UAV around tree canopy is equivalent to that of TLS data, but tree trunk underneath the canopy cannot be reconstructed well, because the trunk is obscured by tree canopy and it is not visible on photos.

Dynamical patterns of mineral elements during decomposition processes were investigated for seven common canopy species in a subtropical evergreen broad-leaved forest by means of litterbag technique over 2 years. The species studied are representative for the vegetation in the study area and differed significantly in chemical qualities of their litter. No significant relationships were found between decomposition rate (percentage dry mass remaining and decomposition constant k) and initial element concentrations. However, there were significant correlations between the percentage of dry mass remaining and the mineral element concentrations in the remaining litter for most cases. The rank of the element mobility in decomposition process was as follows: Na = K > Mg ≧ Ca > N ≧ Mn ≧ Zn ≧ P > Cu ≫ Al ≫ Fe. Concentrations of K and Na decreased in all species as decomposition proceeded. Calcium and Mg also decreased in concentration but with a temporal increase in the initial phase of decomposition, while the concentrations of other elements (Zn, Cu, Al, and Fe) increased for all species with exception of Mn which revealed a different pattern in different species. In most species, microelements (Cu, Al, and Fe) significantly increased in absolute amounts at the end of the litterbag incubation, which could be ascribed to a large extent to the mechanism of abiotic fixation to humic substances rather than biological immobilization.

Spatial variation in canopy structure induces highly variable patterns of light availability for juveniles and understorey trees (Nicotra et al. 1999, Oberbauer et al. 1988, Tang et al. 1999). In the heterogeneous light environment, plasticity in resource use is essential for survival of juveniles and hence maintenance of populations (Valladares et al. 2000). One of the most striking characteristics of plants in their response to a given resource availability is their capacity to change morphological traits (Kiippers 1994). Previous studies have attempted to understand the significance of morphological adaptations in their contribution to competitive ability, focusing on crown form (Kohyama 1987, Sterck et al. 2003), branching pattern (King 1998), shoot architecture (Canham 1988) and leaf shape (King & Maindonald 1999, Takenaka 1994, Yamada et al. 2000). Several studies have investigated the changes in morphology of saplings or seedlings growing under different light availability across canopy gaps (Ackerly & Bazzaz 1995, King 1994, Valladares & Pearcy 1998). However, the phenotypic plasticity in morphology of saplings adapting to the fluctuation of light availability has been investigated less (Blundell & Peart 2001, Poorter & Werger 1999). We evaluated the morphological plasticity of Shorea parvistipulata (Dipterocarpaceae, a canopy species) saplings growing under different levels of canopy openness in the Kubah National Park, Sarawak, Malaysia (13 7'N, 110009'E). The mean annual precipitation is extremely high, 6000-7000 mm (Hazebroek & Marshidi 2000). The mean daily temperature during the period between February to July in 1999 was 26.7 C. The study site is covered by mixed dipterocarp forest. All saplings of Shorea parvistipulata in a 30 x 30-m study plot were investigated in March 1998 and March 1999. The saplings of S. parvistipulata showed two forms: unbranched and branched. Dependence of tree morphology, such as leaf shape and crown form, on life stage has been reported in previous studies (Osada & Takeda 2003, Yamada & Suzuki 1996). There were 80 saplings in the study plot in March 1998; 61 were unbranched (76%) and 19 were branched (24%). Fortysix unbranched (75%) and 18 branched saplings (95%) survived to the end of the research period. To quantify the light environment, hemispherical photographs were taken with a fish-eye lens (Nikon 8 mm F2.8, Tokyo, Japan) directly above each sapling, and at the corners of a 5 x 5-m grid at 1.5 m height within the study plot. The canopy openness above surviving saplings was significantly greater than the average condition on the forest floor (Figure 1). The canopy openness for the saplings that died during the study period was lower than that for the surviving saplings (medians 3.74% and 4.59%, respectively, U-test, U= 242.5, P 0.3 5). Branched saplings were taller than unbranched saplings (medians were 63.4 cm and 35.6 cm, respectively, U-test, U= 60.5, P 0.21). Logistic regression analysis was used to quantify the probability of a sapling dying (X2 = 13.6, df= 2, P < 0.005) versus size and light availability. For 1Corresponding author. Email: enoki@agr.u-ryukyu.ac.jp

We examined the spatial distribution of saplings in relation to topography and stand structure in a subtropical evergreen broad-leaved forest in the northern part of Okinawa Island, Japan. The distributions of most species were influenced mainly by topography but also by canopy openness. Species were arranged along a topographical gradient from concave areas with low canopy openness to convex areas with high canopy openness. Canopy species were arranged along a gradient from unstable fertile areas to stable infertile areas. Species occurring mostly in convex areas had a narrower distribution range than those in concave sites. Thus, habitat heterogeneity provided by topography and stand structure appears to be important factors for maintaining high species diversity in the understory of this subtropical evergreen broad-leaved forest.

Decomposition of typhoon-generated and normal leaf litter and their release patterns for eight nutrient elements were investigated over 3 yr using the litterbag technique in a subtropical evergreen broad-leaved forest on Okinawa Island, Japan. Two common tree species, Castanopsis sieboldii and Schima wallichii, representative of the vegetation and differing in their foliar traits, were selected. The elements analyzed were N, P, K, Ca, Mg, Na, Al, Fe and Mn. Dry mass loss at the end of study varied in the order: typhoon green leaves > typhoon yellow leaves > normal leaves falling for both species. For the same litter type, Schima decomposed faster than Castanopsis. Dry mass remaining after 2 yr of decomposition was positively correlated with initial C:N and C:P ratios. There was a wide range in patterns of nutrient concentration, from a net accumulation to a rapid loss in decomposition. Leaf litter generated by typhoons decomposed more rapidly than did the normal litter, with rapid losses for N and P. Analysis of initial quality for the different litter types showed that the C:P ratios were extremely high (range 896 − 2467) but the P:N ratios were < 0.05 (range 0.02 − 0.04), indicating a likely P-limitation for this forest. On average 32% less N and 60% less P was retranslocated from the typhoon-generated green leaves than from the normal litter for the two species, Castanopsis and Schima. An estimated 2.13 g m–2 yr–1 more N and 0.07 g m–2 yr–1 more P was transferred to the soil as result of typhoon disturbances, which were as high as 52% of N and 74% of P inputted from leaf litter annually in a normal year. Typhoon-driven maintenance of rapid P cycling appears to be an important mechanism by which growth of this Okinawan subtropical forest is maintained.

The spatial distribution of trees in relation to topography was investigated using two topographic indices, slope steepness and slope configuration, in a 4-ha plot in a subtropical evergreen forest in the northern part of Okinawa Island, Japan. Most species showed an aggregated distribution and patch size was related to various microtopographical features, including small ridges and valleys. In a cluster analysis based on the dissimilarity of each species’ distribution, the species were divided into three major clusters. A significant correlation between the dissimilarity and the distance between each species on the axis of the two topographic indices indicated that species association was, in part, explained by the topographic indices. I suggest that species distributed on steep and concave slopes regenerate depending on disturbances such as landslides on unstable topography, whereas species distributed on ridges and upper slopes regenerate depending on the canopy gap. A number of species that were less abundant in the 4-ha plot occurred in the riparian area near a stream, where the density of more abundant species was low. The results of this study support the existence of habitat niche divergence related to topography in a subtropical evergreen broad-leaved forest.

The aim of this work was to analyze the pattern and chemical composition of litterfall and to investigate relationships between the contents of nutrient elements in senescent and fresh mature leaves of two dominant species: Castanopsis sieboldii and Schima wallichii , in two forest sites differing in edaphic condition on the northern Okinawa Island, Japan. In this subtropical forest, the mean annual rates of litterfall (including premature litter generated by windstorm) were 684 and 737 g m −2 yr −1 at site A and B, respectively. The leaf litter contributed 67% of annual total litterfall. The peak leaf fall occurred in March. Woody litter showed no particular pattern, and its peak fall varied with windstorm. The mean annual nutrient inputs by fine litterfall were, respectively, N 80.1, P 3.2, K 25.8, Ca 58.6 and Mg 17.1 kg ha −2 yr −1 at site A; and N 80.6, P 2.9, K 20.7, Ca 65.9 and Mg 17.8kg ha −2 yr −1 at site B. A marked seasonal variability was observed in the concentrations of N, P and K, with no important differences for Ca and Mg, in leaf litter for the two dominants. N, P and K were retranslocated to other tree organs and Ca, Mg, Mn and Al were accumulated in mature leaves. The comparison between leaf litter and fresh mature leaves suggests that the analysis of leaf litter cannot substitute for that of living leaves to evaluate the nutritional status of the species studied for essential elements N, P and K. However, the index of nutrient use efficiency in litterfall can be used as an indicator of soil nutrient conditions. We found site-dependent and between-species differences in nutrient content and nutrient remobilization. The nutrient cycling in this subtropical forest follows a pattern similar to tropical forests, with inefficient within-stand use of N and more efficient cycling of P. Es war Ziel dieser Arbeit das Muster und die chemische Zusammensetzung der Blattstreu zu analysieren, sowie die Beziehungen zwischen den Nahrstoffinhalten in seneszenten und frischen, voll entwickelten Blattern von zwei dominanten Arten zu untersuchen: Castanopsis sieboldii und Schima wallichii in zwei Waldarealen der nordlichen Okinawa Insel, Japan, die sich in den edaphischen Bedingungen unterschieden. In dem subtropischen Wald betrugen die jahrlichen Streufallraten 684 g m −2 a −2 auf der Flache A und 737 g m −2 a −2 auf der Flache B. Die Blattstreu stellte einen Anteil von 67% des gesamten jahrlichen Streufalls. Das Maximum des Blattfalls fand im Marz statt. Die verholzte Streu folgte keinem bestimmten Muster und ihr maximaler Fall variierte mit dem Wind. Der mittlere jahrliche Nahrstoffeintrag durch feine Streu betrug fur N 80.1, P 3.2, K 25.8, Ca 58.6 und Mg 17,1 kg ha −2 a −1 auf der Flache A und fur N 80.6, P 2.9, K 20.7, Ca 65.9 und Mg 17.8 kg ha −2 a −1 auf der Flache B. Bei der Blattstreu der beiden Dominanten wurde eine bedeutende, saisonale Variabilitat in den Konzentrationen von N, P und K beobachtet, wahrend Ca und Mg keine wichtigen Unterschiede aufwiesen. N, P und K wurden in andere Baumorgane verlagert und Ca, Mg, Mn und Al wurden in den voll entwickelten Blattern akkumuliert. Der Vergleich zwischen Blattstreu und frischen, voll entwickelten Blattern legt die Vermutung nahe, dass die Analyse der Blattstreu die der lebenden Blatter nicht ersetzen kann, um den Nahrstoffstatus der untersuchten Arten bezuglich der essenziellen Elemente N, P und K zu bewerten. Der Index der Nahrstoffnutzungseffektivitat im Streufall kann als Indikator fur die Bodennahrstoffbedingungen genutzt werden. Wir fanden probeflachenabhangige und interspezifische Unterschiede im Nahrstoffgehalt und in der Nahrstoffremobilisierung. Der Nahrstoffzyklus folgt einem Muster, das dem tropischer Walder gleicht, mit ineffizienter Nutzung von N und effizienterem Kreislauf des P innerhalb des Bestandes.

Various remote sensing technologies are utilized to monitor tropical forest for REDD project. In developing countries, the accuracy of field measurement does not satisfy the quality required for the validation of satellite remotely sensed data. Therefore, we introduce the most portable laser sensor, SICK LMS511, to measure trees in the field of tropical forest and the semi-automatic process to derive tree parameters from the 3D point cloud is established to provide accurate forest inventory data. From the accuracy assessment of the portable laser system provided 3.61 cm of root mean square error (RMSE) of stem diameter and 0.50 m of RMSE of tree height measurement. The portable terrestrial laser sensor can be the standard technique to create forest inventory data for the field validation of satellite remote sensing.

The effects of litter quality and site characteristics on the decomposition process were investigated using a litterbag method. Pine needle litters with differing nitrogen concentrations (0.8, 0.6 and 0.4%) were placed on the upper and lower slopes of a Pinus thunbergii Parl. plantation. After both 3 and 6 months, the mass of decomposing litter with the lower nitrogen concentration was larger than the litter with higher nitrogen concentrations. After 9 months, there were no significant differences in the litter mass remaining, regardless of the initial nitrogen concentration. Moisture content in the litter was always higher on the lower slope, although the mass of litter was smaller. Nitrogen concentration of the decomposing litter increased linearly with accumulated mass loss. The increase in nitrogen concentration of decomposing litter was greater on the lower slope, but this increase did not differ between initial nitrogen concentrations. The nitrogen release from the decomposing litter with higher initial nitrogen concentration was larger than the release from litter bags with lower nitrogen concentrations. This result suggests that there may be positive feedback between soil nutrient availability, litter quality and nutrient release from decomposing litter at the intraspecific level.

Patterns of litterfall and nutrient input in a subtropical evergreen broad-leaved forest in northern Okinawa, Japan, were studied during May, 1996–April, 1999. The mean annual rate of litterfall in the five sampling plots ranged from 6.84 to 8.93 Mg ha−1 yr−1, of which 63.3–68.5% were leaves; 22.4–29.1% woody parts (including branches < 5.0 cm in diameter and bark); 2.8–5.0% sexual organs and 4.6–6.3% miscellaneous material. Significant differences were found among plots and among years. Significantly monthly differences pronounced seasonal patterns in litterfall were observed. Total litterfall and leaf litter showed negative correlations with relative basal area of the dominant species,Castanopsis sieboldii; and showed positive correlations with mean height of the stands. The dominant species,C. sieboldii produced an average of 2.36 Mg ha−1 yr−1 of leaf litter, which covered 30.5% of the annual litter production, and the nutrient input from those litterfall contributed 32.3, 28.3, 30.2, 22.2, 32.5, and 30.5% of total N, P, K, Ca, Mg, and Na, respectively. Nutrient use efficiency in litter production was high, especially for P and K compared with other broad-leaved forests in Japan indicating that P and K may be limiting in Okinawan evergreen broad-leaved forest.

To examine the relative importance of nutrient resorption in increasing the nutrient-use efficiency of Pinus thunbergii Parl., we investigated the nitrogen contents of green and senescent needles of P. thunbergii trees growing at five positions along a slope (LS, lower slope; TR, transitional site; MS, middle slope; US, upper slope; RG, ridge) and found that soil nitrogen availability tended to decrease upslope. Nitrogen concentration in green and senescent needles decreased upslope. Nitrogen resorption efficiencies (percentage change in nitrogen content between green and senescent needles) increased upslope from 43 to 77% with decreasing soil nitrogen availability. Nitrogen resorption efficiency was related to green needle dry mass per unit length, but there was no clear correlation between nitrogen resorption efficiency and nitrogen content in green needles. We concluded that the increase in nitrogen resorption efficiency of P. thunbergii enhanced the nitrogen-use efficiency as a response to the low nitrogen availability.