Warm-temperate Forest Research Articles

Managing forest complexity through application of disturbance–recovery knowledge in development of silvicultural systems and ecological rehabilitation in natural forest systems in Africa

How can we accommodate the diversity in tree species and sizes in mixed-species/size/age stands in the sustainable management of natural forests and woodlands in Africa for diverse timber and non-timber forest products and services, and during rehabilitation of degraded forests? The evergreen moist tropical to warm-temperate forests, from the equator to 34°S, generally function through relative shade tolerance. The tropical, strongly seasonal, drier deciduous woodlands generally function through adaptation to fire and/or grazing/browsing. Silvicultural systems, when implemented, are often not aligned with the ecological characteristics of the particular forest systems or the specific targeted species. This paper presents the concept of using the basic disturbance–recovery processes, with recovery development via stand development stages, as the basis for the development of silvicultural systems suitable for maintenance of forest complexity. Grain analysis and stem diameter distributions, analysed from resource inventories, are used to determine the specific shade- or fire-tolerance characteristics of key economical and ecological tree species. The gained knowledge of the ecosystem and species characteristics (including modes of regeneration, i.e. from seed or vegetative regrowth) and processes is used to simulate the ecological disturbance–recovery processes through the development of mixed silvicultural systems, such as a single-tree selection system, a group felling system and a coppice management system in the same forest. Very similar concepts are used to develop rehabilitation strategies to recover the processes towards regrowth stands of diverse species and structure: through stands of introduced plantations and invader tree species; and through early regrowth stages in deciduous woodlands and evergreen forests, after fire, slash-and-burn traditional agriculture, charcoal production or open-cast mining.

Belowground carbon pools and dynamics in China's warm temperate and sub-tropical deciduous forests

Abstract. We report the first estimates of pools and dynamics of microbes, roots, plant litter and soil organic carbon (SOC) in three dominant types of China's vast deciduous forest area: Betula platyphylla, Quercus liaotungensis, and Quercus aliena var. acuteserrata. Organic matter degradation rates overshadowed litter inputs as the main determinant of the soil carbon stocks. Across the three forests, rates of litter decomposition were also indicative for turnover rates of SOC. Litter and SOC decay was faster in the sub-tropical than in the warm-temperate forests. Among the latter, SOC turnover was highest in the forest producing the higher-quality litter. Microbial biomass was, as expected, correlated with SOC content. Microbial activity, in contrast, was highest at the sub-tropical forest, despite the lower SOC availability, lower fraction of labile SOC, and lower soil microbial biomass. These results may contribute to increased understanding of controls over belowground carbon cycling in deciduous forests.

Genetic structure and putative selective sweep in the pioneer tree, Zanthoxylum ailanthoides

Zanthoxylum ailanthoides Siebold & Zucc. is one of the most frequently encountered pioneer trees in Japanese warm-temperate evergreen oak forests. Our previous study in one region of Japan suggested high levels of population differentiation and putative natural selection acting on one of the nuclear loci analyzed. Here, we extend our analysis to study the genetic structure of 10 populations of Z. ailanthoides across Japan using 9 simple sequence repeat (SSR) loci for a better understanding of its genetic structure. First, the southernmost population (Kagoshima) in the samples was found to have the highest genetic diversity, suggesting there was a glacial refugium at or near the location of the population. Second, relatively strong genetic differentiation was found among populations, and there was a positive correlation between genetic distances and geographic distances (Mantel test; P < 0.001). Based on this information, we analyzed nucleotide variation at the putatively selected locus homologous to the gene encoding the ADP-glucose pyrophosphorylase large subunit (agpL). Despite the strong genetic differentiation among populations suggested by the SSR loci, the agpL locus was monomorphic in almost all populations analyzed. The results of this study strongly supported the possibility of a selective sweep at or near the agpL locus.

Pollen-based biome reconstructions for Latin America at 0, 6000 and 18 000 radiocarbon years ago

Abstract. The biomisation method is used to reconstruct Latin American vegetation at 6000±500 and 18 000±1000 radiocarbon years before present (14C yr BP) from pollen data. Tests using modern pollen data from 381 samples derived from 287 locations broadly reproduce potential natural vegetation. The strong temperature gradient associated with the Andes is recorded by a transition from high altitude cool grass/shrubland and cool mixed forest to mid-altitude cool temperate rain forest, to tropical dry, seasonal and rain forest at low altitudes. Reconstructed biomes from a number of sites do not match the potential vegetation due to local factors such as human impact, methodological artefacts and mechanisms of pollen representivity of the parent vegetation. At 6000±500 14C yr BP 255 samples are analysed from 127 sites. Differences between the modern and the 6000±500 14C yr BP reconstruction are comparatively small; change relative to the modern reconstruction are mainly to biomes characteristic of drier climate in the north of the region with a slight more mesic shift in the south. Cool temperate rain forest remains dominant in western South America. In northwestern South America a number of sites record transitions from tropical seasonal forest to tropical dry forest and tropical rain forest to tropical seasonal forest. Sites in Central America show a change in biome assignment, but to more mesic vegetation, indicative of greater plant available moisture, e.g. on the Yucatán peninsula sites record warm evergreen forest, replacing tropical dry forest and warm mixed forest presently recorded. At 18 000±1000 14C yr BP 61 samples from 34 sites record vegetation reflecting a generally cool and dry environment. Cool grass/shrubland is prevalent in southeast Brazil whereas Amazonian sites record tropical dry forest, warm temperate rain forest and tropical seasonal forest. Southernmost South America is dominated by cool grass/shrubland, a single site retains cool temperate rain forest indicating that forest was present at some locations at the LGM. Some sites in Central Mexico and lowland Colombia remain unchanged in the biome assignments of warm mixed forest and tropical dry forest respectively, although the affinities that these sites have to different biomes do change between 18 000±1000 14C yr BP and present. The "unresponsive" nature of these sites results from their location and the impact of local edaphic influence.

Explaining conifer dominance in Afrotemperate forests: Shade tolerance favours Podocarpus latifolius over angiosperm species

We contrasted the regeneration success of angiosperm canopy species with that of Podocarpus latifolius to test whether this conifer was sufficiently shade tolerant to be favoured on infrequently disturbed and well-shaded sites. Seedling and sapling population structures were measured in several habitats representing a light gradient in warm temperate forest in the Drakenberg mountains of South Africa. The angiosperm-dominated forest was well-shaded (∼5.5% PAR) and lacked ground vegetation. Seedlings of angiosperm canopy species were abundant but the absence of saplings indicated regeneration failure. In contrast, P. latifolius was represented by all size classes beneath the intact canopy indicating continuous regeneration in angiosperm-dominated forest. Angiosperm regeneration was similarly poor in forest gaps, which were dominated by grasses, ferns and vines. P. latifolius entered the advanced regeneration in gaps by establishing in shade before gap formation. The floor of the Podocarpus-dominated forest was less shaded (∼7.5% PAR) than angiosperm-dominated forest and dominated by grass, which suppressed most conifer regeneration. Gaps in Podocarpus forest were more than double the size of gaps in angiosperm forest and dominated by vines and understorey shrubs. There was no clear winner of the angiosperm–conifer contest in Podocarpus forest gaps. Consequently, gaps maintain limited angiosperm diversity in Podocarpus forest. Angiosperm canopy species regenerated continuously in the high light (∼11.5% PAR) thicket environment. Few seedlings of P. latifolius were recorded in the thicket environment. Our findings are consistent with the hypothesis that shaded and infrequently disturbed forest sites favour shade-tolerant conifers over relatively light-demanding angiosperm species. The outcome of the competitive interaction between angiosperm and conifer at the regeneration phase depends on the relative shade-tolerance of associated species.

Regeneration pattern analysis of Quercus liaotungensis in a temperate forest using two-dimensional wavelet analysis

This paper introduces the two-dimensional (2D) wavelet analysis as a general interrogative technique for the detection of spatial structure in lattice data. The 2D wavelet analysis detects components of hierarchical structure and displays the locational information of the components. Patches and gaps of different spatial scales in graphical presentation of wavelet coefficients can be linked to the local ecological processes that determine patterns at stand or landscape scales. Derived from the 2D wavelet transform function, the calculation of wavelet variance can reduce the four-dimensional data of wavelet coefficients to a two-dimensional wavelet variance function and quantify the contribution of the given scale to the overall pattern. We illustrate the use of the 2D wavelet analysis by analyzing two simulated patterns and identifying the regeneration pattern of the Quercus liaotungensis in a warm temperate forest in north China. Our results indicate that the recruitment of Q. liaotungensis occurs in an overlapping area between the patch of adult and canopy gap at scales of 45 m×45 m–70 m×70 m and 20 m×20 m–30 m×30 m. The regeneration pattern of Q. liaotungensis can be mainly ascribed to a trade-off between two ecological processes: recruitment around parent trees and the physiological light requirements of seedlings and saplings. Our results provide a general portrayal of the regeneration pattern for the dispersal-limited and shade-intolerant Quercus species. We find that the two-dimensional wavelet analysis efficiently characterizes the scale-specific pattern of Q. liaotungensis at different life-history stages.

Topography-specific emergence of fungal fruiting bodies in warm temperate evergreen broad-leaved forests on Yakushima Island, Japan

We conducted line route censuses of fungal fruiting bodies from August to September in 2005 and 2006 along ridges and valleys and compared the differences in the encounter rates of fungal fruiting bodies (= fruiting bodies seen per census kilometer) between types of topography and between fungal functional groups (i.e., ectomycorrhizal and saprobic fungi) in warm temperate evergreen broad-leaved forests on Yakushima Island, Japan. We found 251 fungal fruiting bodies (26 families, 50 genera, and 65 species) in total, including 51 bodies from Tricholomataceae, 41 from Russulaceae, 25 from Boletaceae, and 19 from Amanitaceae. The encounter rate of ectomycorrhizal fungi was greater at the ridge route (26.7unit/km) than at the valley route (8.7unit/km) and that of saprobic fungi was greater at the valley route (25.0unit/km) than at the ridge route (12.5unit/km). In addition, we conducted 7-year intermittent sampling and identified 40 families, 96 genera, and 142 species. The topography-specific emergence pattern of the intermittent sampling method was similar to that of the line census method. The fungal species composition in this study was possibly affected by a topographic gradient for both fungal functional groups through soil moisture, nutrient availability, and host tree distribution.

Distribution of Myxomycetes on coarse woody debris of Pinus densiflora at different decay stages in secondary forests of western Japan

The relationship between myxomycete species and the decay stage of wood of Pinus densiflora coarse woody debris was investigated in warm temperate secondary forests of western Japan. The number of species and species diversity of the myxomycete community reached the maximum on moderately decayed wood. The 25 dominant species recorded from 8 or more samples of the total 1530 samples were arranged in order of the succession index corresponding to the stage of decay. Species on slightly decayed hard pine wood were characterized by Stemonitis splendens, Enerthenema papillatum, and Physarum viride, whereas species of Cribrariaceae were found on brittle decayed soft wood increasing abundance according to the decay stages. Most of the species occurred where there was sufficient moisture preserved in the environment of the decaying wood, although S. splendens specifically emerged in low-moisture environments. Because the myxomycete species had preference to different decay stages of wood, it appears that they change sequentially during myxomycete community succession on dead pine wood according to the progression of decay.

Cross-taxon congruence in a trekking corridor of Sikkim Himalayas: Surrogate analysis for conservation planning

Summary The use of surrogate taxon in conservation planning has become an important tool in the recent years. Woody tree, bird and butterfly diversity indices were used to investigate their potential as surrogates in the Sikkim Himalayas. Woody trees, birds and butterflies were surveyed in 19 permanent plots/transects at open (canopy cover 40%) forest conditions along two sets of forest types [warm temperate broadleaf forest (1780–2350 m), and cool temperate sub-alpine forest (2350–3600 m)] in the Khangchendzonga Biosphere Reserve of Sikkim Himalayas, India, during 1998-1999. Cross-taxon congruence among the three taxonomic groups was investigated along a 26 km trekking corridor to examine the extent to which these group of organisms can function as surrogates for each other. Diversity indices (Shannon diversity index and Margalef species richness) of the three taxonomic groups were used to assess the congruence pattern in open and closed canopy conditions within warm temperate broadleaf forest and cool temperate sub-alpine forest and the altitudinal gradients (irrespective of forests conditions and types). Although the woody tree, bird and butterfly diversity indices showed differences between the open and closed canopy conditions, they were insignificant. But, when they were compared between the warm temperate broadleaf forest and cool temperate sub-alpine forest, all of these indices were significantly related showing higher values in the warm temperate broadleaf forest and the pattern along the altitudinal gradients was found in to be in a decreasing order. In addition, simple regression among the three taxonomic groups and their Pearson correlations further supplemented the congruence patterns suggesting their potential for surrogates usable as a conservation planning tool. These congruence patterns are discussed in context of regional and global studies to validate its applicability for conservation and tourism planning.

Development of microsatellite markers for Euchresta japonica and E. formosana (Leguminosae)

We isolated 13 microsatellite loci from Euchresta japonica, an endangered shrub species that grows in warm-temperate forests in East Asia. Of these 13 loci, only one was codominant and polymorphic with five alleles. Cross-species amplification in a related species, E. formosana, detected nine of these loci, all of which were codominant and polymorphic with 2 to 9 alleles. These markers will facilitate further studies on the genetic characteristics of these two Euchresta species.

SIMULATION AND ANALYSIS ON FUTURE CARBON BALANCE OF THREE DECIDUOUS FORESTS IN BEIJING MOUNTAIN AREA, WARM TEMPERATE ZONE OF CHINA

Aims Climate change is expected to cause changes of carbon cycling in forest ecosystems, and prediction research suggests there is dramatic spatial heterogeneity and uncertainty in responses of carbon balance of forest ecosystems to climate change. The goals of our research were to predict and analyze impacts of climate change on the carbon cycling of warm temperate forests in Beijing mountain area in the next 100 years and to understand the heterogeneity and uncertainty on the ecosystem scale with LPJ-GUESS model. Methods The ecosystem model was used to learn how forest ecosystem productivity and carbon bal-ance change in a long-term time scale and to learn about differences of carbon balance among various ecosystems by comparing ecosystem components of carbon balance. The dynamic vegetation model (LPJ-GUESS), used for the first time in China and driven by A2 and B2 greenhouse gas emission sce-narios of the Special Report on Emissions Scenarios (SRES) of IPCC, projected climate change impacts on carbon balance for three typical warm temperate forest ecosystems (oak, birch and Chinese pine forests) in the Dongling Mountain area of Beijing, China. Important findings Net ecosystem primary productivity (NPP) and heterotrophic respiration (Rh) will increase in the three forests, and the A2 scenario was associated with larger changes in NPP and Rh than the B2 scenario. Because of differences in species composition among the forests, increases in NPP and Rh were different and changes in net ecosystem exchange (NEE) were different among the forests: oakforest switched from a sink to a small source of carbon, birch forest remained as a smaller sink of carbon, and Chinese pine forest became a larger carbon sink over the next 100 years. Also, carbon biomass will generally increase in the forests by 2100. Comparing SRES A2 with B2, there was larger carbon storage in the relative lower emission scenario (B2). Projected differences in carbon balance among these forests in the same area were more dependent on species composition than climate factors (A2 and B2 scenarios) under future climate change.

Taxonomic revision and biogeography of the Tamarix-feeding Diorhabda elongata (Brullé, 1832) species group (Coleoptera: Chrysomelidae: Galerucinae: Galerucini) and analysis of their potential in biological control of Tamarisk

The primarily Palearctic Diorhabda elongata species group is established for five Tamarix-feeding sibling species(tamarisk beetles): D. elongata (Brullé, 1832), D. carinata (Faldermann, 1837), D. sublineata (Lucas, 1849) REVISEDSTATUS, D. carinulata (Desbrochers, 1870), and D. meridionalis Berti &amp; Rapilly, 1973 NEW STATUS. Diorhabdakoltzei ab. basicornis Laboissière, 1935 and D. e. deserticola Chen, 1961 are synonymized under D. carinulata NEWSYNONYMY. Illustrated keys utilize genitalia, including male endophallic sclerites and female vaginal palpi andinternal sternite VIII. Distribution, comparative biogeography, biology, and potential in biological control of Tamarix inNorth America are reviewed. Diorhabda elongata is circummediterranean, favoring Mediterranean and temperate forestsof Italy to western Turkey. Diorhabda carinata resides in warm temperate grasslands, deserts, and forests of southernUkraine south to Iraq and east to western China. Diorhabda sublineata occupies Mediterranean woodlands from Franceto North Africa and subtropical deserts east to Iraq. Diorhabda carinulata primarily inhabits cold temperate deserts ofMongolia and China west to Russia and south to montane grasslands and warm deserts in southern Iran. Diorhabdameridionalis primarily occupies maritime subtropical deserts of southern Pakistan and Iran to Syria. Northern climatypesof D. carinulata are effective in Tamarix biological control, especially in the Great Basin desert. Diorhabda elongata isprobably best suited to Mediterranean woodlands of northern California. Northern climatypes of D. carinata may be bestsuited for central U.S. grasslands. Diorhabda sublineata, D. meridionalis, and southern climatypes of D. carinata and D. carinulata may each be uniquely suited to areas of the southwestern U.S.

Topography-specific emergence of fungal fruiting bodies in warm temperate evergreen broad-leaved forests on Yakushima Island, Japan

We conducted line route censuses of fungal fruiting bodies from August to September in 2005 and 2006 along ridges and valleys and compared the differences in the encounter rates of fungal fruiting bodies (= fruiting bodies seen per census kilometer) between types of topography and between fungal functional groups (i.e., ectomycorrhizal and saprobic fungi) in warm temperate evergreen broad-leaved forests on Yakushima Island, Japan. We found 251 fungal fruiting bodies (26 families, 50 genera, and 65 species) in total, including 51 bodies from Tricholomataceae, 41 from Russulaceae, 25 from Boletaceae, and 19 from Amanitaceae. The encounter rate of ectomycorrhizal fungi was greater at the ridge route (26.7unit/km) than at the valley route (8.7unit/km) and that of saprobic fungi was greater at the valley route (25.0unit/km) than at the ridge route (12.5unit/km). In addition, we conducted 7-year intermittent sampling and identified 40 families, 96 genera, and 142 species. The topography-specific emergence pattern of the intermittent sampling method was similar to that of the line census method. The fungal species composition in this study was possibly affected by a topographic gradient for both fungal functional groups through soil moisture, nutrient availability, and host tree distribution.

Domestic goat grazing disturbance enhances tree seed removal and caching by small rodents in a warm-temperate deciduous forest in China

Context. Grazing by large herbivores may have a considerable influence on ground vegetation as well as on the species composition and abundance of granivors (e.g. small rodents) and this may affect forest regeneration. Very few studies have focussed on the effects of herbivore disturbance on forest regeneration by looking at the modified seed-hoarding behaviour of small rodents. Aims. To test the indirect effects that grazing disturbance by domestic animals has on seed dispersal through the modified seed-hoarding behaviour of small rodents. Methods. We looked at the differences in seed removal and caching of Liaodong oak (Quercus liaotungensis) by small rodents between a plot that was grazed and a plot that was ungrazed by domestic goats in a warm-temperate forest in northern China in 2006 (a non-mast-seeding year) and 2008 (a mast-seeding year). Key results. Seed removal and caching by small rodents were significantly higher in the grazed plots, especially in the mast-seeding year (2008). Significantly more seeds were buried in soil during the mast-seeding year (2008) compared with the non-mast-seeding year (2006). Conclusions. Grazing-induced disturbance might stimulate hoarding efforts by seed-caching rodents. Mast seeding benefits seed survival and forest regeneration. Implications. The presence of large herbivores is likely to benefit early seed dispersal in forests by increasing the hoarding activities of rodents.

Distribution of Myxomycetes on coarse woody debris of &lt;i&gt;Pinus densiflora&lt;/i&gt; at different decay stages in secondary forests of western Japan

The relationship between myxomycete species and the decay stage of wood of Pinus densiflora coarse woody debris was investigated in warm temperate secondary forests of western Japan. The number of species and species diversity of the myxomycete community reached the maximum on moderately decayed wood. The 25 dominant species recorded from 8 or more samples of the total 1530 samples were arranged in order of the succession index corresponding to the stage of decay. Species on slightly decayed hard pine wood were characterized by Stemonitis splendens, Enerthenema papillatum, and Physarum viride, whereas species of Cribrariaceae were found on brittle decayed soft wood increasing abundance according to the decay stages. Most of the species occurred where there was sufficient moisture preserved in the environment of the decaying wood, although S. splendens specifically emerged in low-moisture environments. Because the myxomycete species had preference to different decay stages of wood, it appears that they change sequentially during myxomycete community succession on dead pine wood according to the progression of decay.

Host trait preferences and distribution of vascular epiphytes in a warm-temperate forest

To illustrate the ecological factors and process leading to the observed diversity patterns of vascular epiphytes, we examined the effect and importance of host tree traits on epiphyte richness and spatial aggregation of epiphytes. The study was conducted in warm-temperate forest in Japan. The recorded host traits were diameter, height, species, habitat topography, and growth rate, and we analyzed the effects and importance of these traits on three species groups: total epiphytic species, epiphytic orchid species, and epiphytic pteridophyte species. Diameter and species of host trees had the greatest influence on epiphytes and their magnitudes were roughly similar in all species groups. Growth rate and topography were less important than host size and species. Growth rate had a negative effect on all three groups, and topography was important for pteridophytes. Epiphyte richness did not exhibit clear spatial aggregation. Our results suggest that size, stability, and quality of the host are equally important in determining epiphyte colonization.

When sleep or hide makes the difference in macroevolution

The article by Liow et al. (1) opens an interesting debate on the influence of ecological and life-history traits on macroevolutionary patterns. These authors attribute the greater duration of small mammals to the evolution of “sleep-or-hide” (SLOH) behaviors as a buffer against environmental changes. They base their conclusions on a database of extant micromammals that mostly inhabit deciduous forests, cold steppes, and grasslands from the Paleartic and Neartic biogeographical realms (see Fig. 1). In doing so, they disregard that mean annual temperatures during the Neogene were significantly higher (2), with tropical and warm-temperate forests covering most of Eurasia (3). Whereas many of the living micromammals selected by Liow et al. exhibit some kind of SLOH behavior, most of their living counterparts from warmer and tropical regions do not (4).

Seedling establishment of five evergreen tree species in relation to topography, sika deer (Cervus nippon yakushimae) and soil surface environments

We investigated the seedling survival of five evergreen tree species over 3 years inside and outside deer-exclusion fences in a warm temperate evergreen broad-leaved forest on Yakushima Island, Japan. Seedling survival was examined in relation to topography, herbivory by sika deer, and the soil surface environment (i.e., soil surface wetness, light conditions, slope inclination, and soil disturbance). The study species included Myrsine seguinii Lév., Syzygium buxifolium Hook. et Arn. (Group A: species distributed on the upper slope of the study site), Litsea accuminata (Bl.) Kurata, Schefflera octophylla (Lour.) Harms (Group B: species distributed on the lower slope), and Cleyera japonica Thunb. p.p. emend. Sieb. et Zucc. (Group C: species distributed on both slopes). The soil surface environment on the upper slope was drier, lighter, and more easily disturbed than the lower slope. Generalized linear model analyses indicated that seedling survival in fenced and unfenced quadrats was greater on the upper slope than on the lower slope for Group A and B species but not for Group C species. A micro-spatial scale analysis revealed that seedling survival was correlated with soil wetness, ground light conditions, and soil disturbance but not slope inclination. These results indicate that seedling survival was correlated with topography, sika deer herbivory, and the micro-spatial scale environment. Topography-related differences in seedling survival appear to adequately reflect the observed adult plant distributions for Group A and C species but not for Group B species.

Spatio-temporal patterns of forest carbon dioxide exchange based on global eddy covariance measurements

Spatio-temporal patterns and driving mechanisms of forest carbon dioxide (CO2) exchange are the key issues on terrestrial ecosystem carbon cycles, which are the basis for developing and validating ecosystem carbon cycle models, assessing and predicting the role of forests in global carbon balance. Eddy covariance (EC) technique, an important method for measuring energy and material exchanges between terrestrial ecosystems and the atmosphere, has made a great contribution to understanding CO2 exchanges in the biosphere during the past decade. Here, we synthesized published EC flux measurements at various forest sites in the global network of eddy flux tower sites (FLUXNET) and regional flux networks. Our objective was to explore spatio-temporal patterns and driving factors on forest carbon fluxes, i.e. net ecosystem productivity (NEP), gross primary productivity (GPP) and total ecosystem respiration (TER). Globally, forest NEP exhibited a significant latitudinal pattern jointly controlled by GPP and TER. The NEP decreased in an order of warm temperate forest > cold temperate and tropical rain forests > boreal and subalpine forests. Mean annual temperature (MAT) made a greater contribution to forest carbon fluxes than sum of annual precipitation (SAP). As MAT increased, the GPP increased linearly, whereas the TER increased exponentially, resulting in the NEP decreasing beyond an MAT threshold of 20°C. The GPP, TER and NEP varied substantially when the SAP was less than 1500 mm, but tended to increase with increasing SAP. Temporal dynamics in forest carbon fluxes and determinants depended upon time scales. NEP showed a significant interannual variability mainly driven by climate fluctuations and different responses of the GPP and TER to environmental forcing. In a longer term, forest carbon fluxes had a significant age effect. The ecosystem was a net carbon source right after clear-cutting, gradually switched to a net carbon sink when the relative stand age (i.e. ratio of actual stand age to the stand rotation age) approached 0.3, and maximized carbon sequestration capacity at pre-mature or mature stand stages. This temporal pattern of NEP was correlated with stand leaf area index and associated GPP. This study highlights the significance of spatio-temporal dynamics in the CO2 exchange in forest carbon cycling studies. It is also suggested that in addition to forest biomes, interannual variations and stand age effects of forest carbon fluxes should be considered in the global carbon balance.

Habitat niche specialization in an understory species in a warm temperate forest

AbstractRelationships between microhabitat variables; understory light conditions in summer and winter, altitude, slope inclination and topographic categories (valley, ridge, and slope) and the distribution of Aucuba japonica Thunb. (Cornaceae), a common understory shrub species in Japan were examined using non‐contagious 66, 20 × 20 m2 quadrats. The Morishita's Iδ suggested that A. japonica distributions were strongly heterogeneous among the quadrats. Therefore positive spatial autocorrelation of A. japonica at a within‐quadrat level (≤20 m) was obvious. Moran's I statistics showed a significant positive spatial autocorrelation in A. japonica abundance within the distance shorter than 60 m. But the partial Mantel tests suggested that the mass effect from neighboring quadrats would little explain A. japonica abundance in a quadrat. The partial Mantel tests also clearly showed that A. japonica distributions were strongly structured by topography and understory light conditions. Using Monte Carlo randomization tests, we found that A. japonica was aggregately distributed in quadrats in valley which were covered by deciduous canopies. Better understory light conditions in winter together with valley edaphic conditions may increase the abundance of A. japonica there. It is concluded that habitat niche specialization is important in structuring distribution of A. japonica in this forest community.