大橋 瑞江

Wood ants (Formica rufa group) are regarded as keystone species in boreal and mountain forests of Europe and Asia by their effect on ecosystem carbon (C) and nutrient pools and fluxes. To quantify the impact of their activity on boreal forest ecosystems, C, nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca) pools and fluxes in wood ant nests (WAN), and soil were assessed along a 5-, 30-, 60-, and 100-year-old Norway spruce (Picea abies L. Karsten) dominated successional gradient in eastern Finland. Amounts of C and nutrients in WAN increased with stand age, but contained less than 1% of total C and nutrient pools in these stands. The CO2-efflux from nests was also insignificant, as compared to CO2-efflux from the forest floor. Annually, the amount of C brought by wood ants into their nests as honeydew, prey and nest-building materials ranged from 2. 7 to 49. 3 kg ha-1 C, but this is only 0. 1-0. 7% of the combined net primary production of trees and understorey in boreal forests. The difference between wood ant nest C inputs and outputs was very small in the younger-aged stands, and increased in the older stands. Carbon accumulation rates in nests over a 100 year period are estimated to be less than 10 kg ha-1 a-1. In contrast to C, annual inputs of N, P, and K are larger compared to wood ant nest nutrient pool size, ranging from 3 to 6% of the annual tree stand and understorey uptake. This indicates a more rapid turnover and transport of N, P, and K out of WAN, and suggests that wood ants increase the cycling rate of these nutrients in boreal forests. © 2012 Springer Science+Business Media New York.

Information related to the growth of fine roots is important for understanding C allocation in trees and the mechanisms of C cycling in ecosystems. Observations using a camera or scanner embedded in the soil enabled us to obtain continuous images of fine-root-growth dynamics. However, these methods are still labor-intensive because the image analysis has to be conducted manually. We developed an automated method for tracking movement or elongation of fine roots using a sequence of scanner images. We also show how data obtained with these methods can be used for calculating fine-root behavior. Two A4-size scanners were buried in a mixed forest in Japan and images were taken continuously from within the soil. We preprocessed these images by extracting the fine-root area from the images and developed an automated calculation plug-in we named A-root for tracking growth movement of the tips of fine roots. A-root and manual-tracking results were compared using the same images. The results show the A-root and manual-tracking methods yielded similar levels of accuracy. The average growth rate of 17 fine roots tracked using the program was 0.16mm h-1. The observation of the direction of growth in fine roots showed the direction may be influenced by the original root's growth where the fine roots branched, distribution of soil particles, other roots, and the force of gravity. The A-root analysis also suggested there may be an interaction between speed of growth and changes in direction of growing fine roots. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Recent studies suggest that wood ants (Formica rufa group) mounds are point sources of carbon dioxide (CO 2), which increase the heterogeneity of soil carbon (C) emissions in forest ecosystems. However, little is known about the impact of anthropogenic activities, such as logging and subsequent forest succession, on these fluxes. In this study, we measured the CO 2 efflux and temperature of wood ant mounds and the surrounding forest floor in managed Finnish boreal forests of different ages (5, 30, 60, and 100 years old) to assess how the effluxes vary with stand age. We conducted efflux measurements from the mounds and the surrounding forest floor throughout the ants' active season (May-September) and during the onset of hibernation (October). The annual CO 2 efflux was then estimated using mound or forest floor temperatures, which were measured for one year. The average annual CO 2 efflux from the ant mounds was 10.2 (±5.8 SD) kg m -2 year -1, increasing from 3.9 (±0.3 SD) kg m -2 year -1 in the 5 year-old stands to 14.3 (±3.0 SD) kg m -2 year -1 in the 100 year-old stands. Temperatures was significantly higher in the ant mounds than in the forest floor, and the average temperature difference between mounds and forest floor increased with stand age, being the lowest in the 5 year-old (4.1 (±3.1 SD) °C) and highest in the 100 year-old stands (10.3 (±5.2 SD) °C). There were no statistical differences in the mound CO 2 efflux per volume among forest age classes, suggesting higher ant CO 2 efflux in the older stands likely come from larger ant populations in the bigger mounts. The different mound temperature regimes among stand age classes indicates that the activity of wood ants changes with forest succession, particularly after clear-cutting, which alters CO 2 efflux from the mounds. The impact of ant mounds on total CO 2 efflux from the soil, estimated from mound area and volume, respectively, increased with forest age, from 0.05 (±0.05 SD) % to 0.31 (±0.18 SD) % and from 0.05 (±0.06 SD) % to 0.90% (±1.11 SD). © 2012 Elsevier Ltd.

The relationships between red wood ants (Formica rufa group) and other ground-dwelling arthropods were studied in young managed forests stands in Eastern Finland. The main objectives were: (i) to test the influence of stand type (dominant tree species; age: sapling versus pole stage) and numbers of red wood ants on the occurrence of other ground-dwelling arthropods and (ii) to study the occurrence of red wood ants versus other arthropods on a distance gradient from ant mounds. We used pitfall traps set in 5-14-year-old sapling stands and 30-45-year-old pole-stage stands of Scots pine (Pinus sylvestris L.) and birch (Betula spp.) forests. Pitfall trap catches of red wood ants did not vary significantly between the forest stand types, although some groups of other arthropods showed clear responses to stand type (e.g. catches of other Formicinae and Gnaphosidae were higher in sapling stands than in pole-stage stands). The number of red wood ants clearly explained less of the variation in assemblages of other ground-dwelling arthropods than the forest stand type. Red wood ant numbers decreased significantly with distance from the mounds, but the other ground-dwelling arthropods were insensitive to this gradient or even showed a preference for proximity to ant mounds and high ant activity. The results obtained in the present study suggest that wood ants do not have strong effects on several other ground-dwelling arthropod groups in young managed forests other than in the immediate vicinity of their mounds. © 2012 The Authors. Agricultural and Forest Entomology © 2012 The Royal Entomological Society.

A honeybee informs her nestmates about the location of a profitable food source that she has visited by means of a waggle dance: a round dance and a figure-of-eight dance for a short- and long-distance food source, respectively. Consequently, the colony achieves an effective collection of food. However, it is still not fully understood how much effect the dance behavior has on the food collection, because most of the relevant experiments have been performed only in limited locations under limited experimental conditions. Here, we examined the efficacy of the waggle dances by physically preventing bees from dancing and then analyzing the changes in daily mass of the hive as an index of daily food collection. To eliminate place- and year-specific effects, the experiments were performed under fully natural conditions in three different cities in Japan from mid September to early October in three different years. Because the experiments were performed in autumn, all six of the tested colonies lost mass on most of the experimental days. When the dance was prevented, the daily reduction in mass change was greater than when the dance was allowed, i.e. the dance inhibited the reduction of the hive mass. This indicates that dance is effective for food collection. Furthermore, clear inhibition was observed on the first two days of the experiments; after that, inhibition was no longer evident. This result suggests that the bee colony adapted to the new environment. © 2012. Published by The Company of Biologists Ltd.

A honeybee informs her nestmates of the location of a flower by doing a waggle dance. The waggle dance encodes both the direction of and distance to the flower from the hive. To reveal how the waggle dance benefits the colony, we created a Markov model of bee foraging behavior and performed simulation experiments by incorporating the biological parameters that we obtained from our own observations of real bees as well as from the literature. When two feeders were each placed 400 m away from the hive in different directions, a virtual colony in which honeybees danced and correctly transferred information (a normal, real bee colony) made significantly greater numbers of successful visits to the feeders compared to a colony with inaccurate information transfer. Howerer, when five feeders were each located 400 m from the hive, the inaccurate information transfer colony performed better than the normal colony. These results suggest that dancing's ability to communicate accurate information depends on the number of feeders. Furthermore, because non-dancing colonies always made significantly fewer visits than those two colonies, we concluded that dancing behavior is beneficial for hives' ability to visit food sources.

Social insects interact extensively with their mates. To reveal the mechanism of their sociality, it is important to observe the behavior of each individual in a colony and to analyze their social contexts. Recently, digital video cameras have become less expensive despite increases in their performance, enabling researchers to record the behavior in various places easily. However, much labor and time is needed to analyze the social behavior manually from the video footage. In this study, we propose a new method to detect and track multiple bees moving on a flat surface. Our proposed method consists of three core processes: (i) detecting the bee candidate regions using a background subtraction method and binarization, (ii) identifying individuals by a combination of overlapping information in temporal changes of position and simple prediction of the candidate regions based on the bee's movement, and (iii) outputting the locations and trajectories of the identified bees. Our system succeeds in processing a video of sixteen bees moving freely on a flat arena for three minutes. More than 95% of the bees' central points were successfully extracted and their trajectories precisely traced. © 2012 IEEE.

The production and turnover of fine roots (diameter ≤2mm) contributes significantly to carbon cycling in forest ecosystems. We compiled an up-to-date global database covering 186 stands from the literature and estimated fine root production (FRP) and fine root turnover (FRT) for boreal, temperate and tropical forests in order to study the relationships between FRP or FRT and environmental and stand variables. FRP for all plants (trees+understorey) was 311±259 (n=39), 428±375 (n=71) and 596±478gm-2a-1 (n=32) in the boreal, temperate and tropical forests, respectively, and the corresponding annual FRT rates were 0.77±0.70, 1.21±1.04 and 1.44±0.76, respectively. When the FRP and FRT of trees were estimated separately for boreal and temperate forests the differences between the two biomes were insignificant. The mean FRP of trees for the two biomes combined was 306±240gm-2a-1 (n=86) and the annual FRT was 1.31±1.43. Fine root biomass (FRB) was the most significant factor explaining the variation in FRP, and more so at the tree level than at the stand level, explaining 53% of the variation in FRP for trees at the tree level. The corresponding proportions at the stand level were 21% for all plants and 12% for trees. Latitude, mean annual temperature and annual precipitation each explained <20% of the variation in FRP or FRT. Fine root production and FRT estimates are highly dependent on the species included in the sampling, the sampling depth and the methods used for estimating FRP or calculating FRT. The results indicate that the variation in FRP on a global scale can be explained to a higher degree if we focus on tree roots separately from the roots of the understorey vegetation and on FRP at the tree level instead of FRP at the stand level or on FRT. © 2011 Elsevier B.V.

Social activities are among the most striking of animal behaviors, and the clarification of their mechanisms is a major subject in ethology. Honeybees are a good model for revealing these mechanisms because they display various social behaviors, such as division of labor, in their colonies. Image processing is a precise and convenient tool for obtaining animal behavior data, but even recent methods are inadequate for the identification or description of honeybee behavior. This is because of the difficulty distinguishing between the large number of individuals in a small hive and their multiple movements. The present study developed a new computer-aided system, using a vector quantization method, for the identification and behavioral tracking of individual honeybees. The vector quantization method enabled separation of honeybee bodies in photographs recorded as a movie. This system succeeded in analyzing a huge number of frames quickly and can thus save both time and labor. Moreover, the system identified more than 72% of the bees in a hive and found and determined the active areas in the hive by extracting the trajectories of walking bees. In addition, useful behavioral data on the honeybee waggle dance were obtained using the present system. © INRA, DIB-AGIB and Springer Science+Business Media B.V., 2011.

1 The mutualism between wood ants of the Formica rufa group and aphids living in the canopy of trees is a widespread phenomenon in boreal forests, and it can affect tree growth. However, not all trees in the forest are involved in this interaction. 2 To assess the incidence of host trees involved in this ant-aphid mutualism and its spatial distribution in boreal forests, we inventoried sample plots with a radius of 10-15 m around wood ant mounds in 12 forest stands of two age classes (5-12-year-old sapling stands and 30-45-year-old pole stands) and two dominant tree species (Scots pine and silver birch) in Eastern Finland from 2007 to 2009. 3 The proportion of trees visited by ants out of all trees on the individual study plots were in the range 4-62%, and 1.5-39% of the trees on the plots were consistently visited by ants during all 3 years. The percentage of host trees increased with the ant mound base area on the plots. Trees visited by ants were larger and closer to the mound than trees not visited by ants. Within the group of visited trees, more ants were found on bigger trees and on trees close to the ant mounds. 4 Extrapolated from plot to stand level, we estimated that 0.5-6.6% of the trees were host trees in at least one of the three study years, and that only 0.01-2.3% of all the trees were consistently visited by ants during all 3 years. It is concluded that ant-aphid mutualism is a minor occurrence at the stand level. © 2011 The Authors. Agricultural and Forest Entomology © 2011 The Royal Entomological Society.

Fine roots form one of the most significant components contributing to carbon cycling in forest ecosystems. We study here the effect of variation in root diameter classes, sampling depth and the inclusion of understorey vegetation root biomass in fine root biomass (FRB) estimates. The FRB estimates for different forest biomes are updated using a database of 512 forest stands compiled from the literature. We also investigate the relationships between environmental or forest stand variables and fine root biomass (≤2mm in diameter) at the stand (gm-2) and tree level (g tree-1). The FRB estimates extrapolated for the whole rooting depth were 526±321gm-2, 775±474gm-2 and 776±518gm-2 for boreal, temperate and tropical forests, respectively, and were 26-67% higher than those based on the original sampling depths used. We found significant positive correlations between ≤1 and ≤2mm diameter roots and between ≤2 and ≤5mm roots. The FRB estimates, standardized to the ≤2mm diameter class, were 34-60% higher and 25-29% smaller than those standardized to the ≤1mm and ≤5mm diameter classes, respectively. The FRB of the understorey vegetation accounted for 31% of the total FRB in boreal forests and 20% in temperate forests. The results indicate that environmental factors (latitude, mean annual precipitation, elevation, temperature) or forest stand factors (life form, age, basal area, density) can not explain a significant amount of the variation in the total FRB and a maximum of 30% that in the FRB of trees at the stand level, whereas the mean basal area of the forest stand can explain 49% of the total FRB and 79% of the FRB of trees at the tree level. © 2010 Elsevier B.V.

To evaluate water treatment residue (WTR) as a soil substitute material, its physical properties were investigated and compared with decomposed granite soil (DGS). For comparison purposes, relative gas diffusivity (D/D0), saturated hydraulic conductivity (Ks), water retention curve, porosity and readily available water were measured for both the WTR and the DGS. The measured D/D0, Ks, water retention ability and porosity were higher for the WTR than for the DGS. These differences may be attributable to intra-aggregate and inter-aggregate pores created in the WTR through binding of silt and clay particles in the flocculation process. The behavior of water and gasses surrounding these pores may explain the physical properties of the WTR. The characteristics measured in this evaluation indicate that WTR has good potential for reuse as a soil substitute material. © 2010 Japanese Society of Soil Science and Plant Nutrition.

It is well established mat honeybees inform their nestmates of the location of flowers they have visited by a unique behavior called a "waggle dance". To evaluate the efficacy of this dance in terms of food collection, we constructed a Markov model for foraging behavior. The computer simulation showed that our model faithfully expressed actual bee behavior; revealed that a colony in which honeybees danced and correctly transferred information made 2.15 times more successful visits to food sources compared to a colony with non-accurate information transfer; and suggested that the waggle dance is effective only under particular conditions. © 2010 International Information Institute.

This study was undertaken to identify critical and practical factors explaining spatial variations in soil respiration and to estimate stand-scale soil respiration in an aseasonal tropical rainforest on Borneo Island. To this aim, we conducted soil respiration measurements at 25 points in a 40 m × 40 m subplot of a 4 ha study plot between 2002 and 2006, and examined the spatial variation in soil respiration averaged over the 4 years in relation to soil, root, and forest structural factors. In addition, we examined the spatial representativeness of soil respiration measured in the subplot using a specific scaling procedure. Consequently, we found significant positive correlation between the soil respiration and forest structural parameters such as the mean diameter at breast height (DBH), total basal area, and maximum DBH within 6 m of the measurement points. The most important factor was the mean DBH within 6 m of the measurement points, which had a significant linear relationship with soil respiration. Using the derived linear regression and an inventory dataset, we estimated the 4 ha plot-scale soil respiration. The 4 ha plot-scale estimation (6.0 μmol m-2 s-1) was nearly identical to the subplot-scale measurements (5.7 μmol m-2 s-1), which were roughly comparable to the nocturnal CO2 fluxes calculated using the eddy covariance technique. In addition, we discuss characteristics of the stand-scale soil respiration at this site by comparing with those of other forests reported in previous literature in terms of the soil C balance. Soil respiration at our site was noticeably greater, relative to the incident litterfall amount, than soil respiration in other tropical and temperate forests probably owing to the larger total belowground C allocation by emergent trees. Overall, this study suggests the arrangement of emergent trees with larger DBH and their belowground C allocation could be primary factors controlling spatial variations in soil respiration in the tropical rainforest. © 2009 Elsevier B.V. All rights reserved.

The honeybee can control its hive environment to survive drastic changes in the field environment. To study the control of multiple environmental factors by honeybees, in this experiment, we developed a continual and simultaneous monitoring system for the temperature, moisture, and carbon dioxide (CO2) concentration in a honeybee hive. Changes in hive weight, CO2 production rate, and honeybee behavior were also monitored to estimate energy costs and behavioral activity for the environmental regulation. Measurements were conducted in August 2008. We found that the honeybee hive has a microclimate different from the ambient climate, and that the difference was partly accompanied by changes in honeybee activity. Our results also suggest that hive tem-perature, humidity, and CO2 concentrations are controlled by different mechanisms. Additional monitoring of the hive environment and honeybee behavior for longer periods would enable us to understand the mechanisms of environmental control by honeybees, which is one of the behaviors that define honeybees as social insects. © 2009 The Psychonomic Society, Inc.

1. We monitored three different-sized wood ant (Formica aquilonia Yarrow) mounds over a 3-year period in Finnish boreal forests dominated by Norway spruce (Picea abies Karst.), to assess the seasonal temperature dependency of ant activity. Additionally, we also monitored Norway spruce trees around the mounds for descending honeydew foragers. 2. The amount of collected honeydew and prey and its composition, as well as the carbon (C), nitrogen (N), and phosphorus (P) in honeydew and invertebrate prey was also investigated. 3. The number of warm days (average temperature above 20 °C) and the amount of precipitation differed among the years. Ant activity at the mounds (but not on the trees) was highly correlated with air temperature throughout the ant-active season (May-September), but ant activity in spring and autumn was lower than in summer at similar temperatures. During all 3 years, honeydew played a major role in wood ant nutrition (78-92% of dry mass). Invertebrate prey was mainly Diptera (on average 26.2%), Coleoptera (12.5%), Aphidina (9.3%), and Arachnoida (8.5%). 4. The total amounts of C, N, and P input brought into the ant mounds in the form of food (both honeydew and prey) on the stand level were 12.6-39.0, 1.6-4.6 and 0.1-0.4 kg ha-1 year-1, respectively, which is equivalent to 2-6%, 12-33% and 27-58% of the fluxes in annual needle litterfall in typical boreal Norway spruce forests. Thus, wood ants can play a significant role in short term and local N and P cycling of boreal forest ecosystems. © 2009 The Royal Entomological Society.

Ant-aphid mutualisms, in which ants tend aphids, which in turn provide honeydew to the ants, are widespread and have been shown to affect plant growth. In boreal forests the effect of ant-aphid mutualism on tree growth can vary with stand age, because forest clear-cutting harms the ecologically most dominant ant partner in such mutualisms, wood ants (Formica rufa group). We studied whether the mutualism between wood ants and Cinara aphids affects the growth of boreal Norway spruces (Picea abies L. Karst.) in stands of different ages. In boreal forests, conifers, unlike deciduous trees, have only few defoliating insects, and therefore we expected the growth loss of conifers due to sap sucking by aphids not to be compensated by reduced insect herbivory due to predation by wood ants. The study was conducted in medium-fertile spruce-dominated stands in eastern Finland. We used stands of four different age classes (5, 30, 60 and 100 years) and selected ten spruces heavily visited and ten spruces lightly visited by ants around five medium-sized ant mounds in each stand age class. The access of ants was blocked on half of the trees in both groups. In the 5-year-old stands, the mean annual height growth of individual heavily visited seedlings was 16.3% greater than in the ones where ant traffic was blocked, but this difference was not significant. In the 30-year-old stands, the mean annual radial growth of the heavily visited spruces was 7.3% smaller than in trees where ant traffic was blocked, and this difference was significant. The mutualism had no significant effect on the radial growth in the 60- and 100-year-old stands. In the 60-year-old stands, however, the spruces that were visited heavily prior to the beginning of the study grew significantly less relative to their past growth than the initially lightly visited trees during the study. This suggests that the ant-aphid mutualism may have long-term effects on tree growth. The ant-aphid mutualism had no significant effect on the growth at the stand level. The results indicate that ant-aphid mutualism can have a significant effect on the growth of individual spruces, but the effect is negligible at ecosystem level. © 2008 Elsevier B.V. All rights reserved.

We describe a new and easy technique for placing and lifting root meshes to estimate fine root production in forest ecosystems. The method improves upon previously proposed mesh placement techniques by using a sharp stainless steel blade and two thin stainless steel sheets to insert mesh more easily and accurately in the soil, and utilizing a narrow garden spade to lift the soil block containing the mesh. The proposed technique takes significantly less time than the widely used ingrowth core method, causes minimal disturbance to the soil, and requires only simple equipment. The detailed documentation of the method provided herein should improve estimations of fine root production in forest ecosystems.

Although soil carbon dioxide (CO2) efflux from tropical forests may play an important role in global carbon (C) balance, our knowledge of the fluctuations and factors controlling soil CO2 efflux in the Asian tropics is still poor. This study characterizes the temporal and spatial variability in soil CO2 efflux in relation to temperature/moisture content and estimates annual efflux from the forest floor in an aseasonal intact tropical rainforest in Sarawak, Malaysia. Soil CO2 efflux varied widely in space; the range of variation averaged 17.4 μmol m-2 s-1 in total. While most CO2 flux rates were under 10 μmol m-2 s-1, exceptionally high fluxes were observed sporadically at several sampling points. Semivariogram analysis revealed little spatial dependence in soil CO2 efflux. Temperature explained nearly half of the spatial heterogeneity, but the effect varied with time. Seasonal variation in CO2 efflux had no fixed pattern, but was significantly correlated with soil moisture content. The correlation coefficient with soil moisture content (SMC) at 30 and 60 cm depth was higher than at 10 cm depths. The annual soil CO2 efflux, estimated from the relationship between CO2 efflux and SMC at 30 cm depth, was 165 mol m-2 year-1 (1,986 g C m-2 year-1). As this area is known to suffer severe drought every 4-5 years caused by the El Nino-Southern Oscillation, the results suggest that an unpredictable dry period might affect soil CO2 efflux, leading an annual variation in soil C balance. © 2008 Springer Science+Business Media B.V.

Mound-building ants (Formica spp.), as key species, have large impacts on organisms and ecosystem functions in boreal Eurasian forests. The density, sizes and locations of ant mounds determine the magnitude and the spatial distribution of ant activities in forest ecosystems. Clear-cutting can destroy wood ant colonies, and the species, abundance, dimensions and locations of ant mounds may change as forest stand structure changes with stand age. We compared ant species composition, ant mound numbers and dimensions, and the spatial distribution of mounds in Norway spruce [Picea abies (L.) Karst.] stands of different age (5, 30, 60 and 100 years) in eastern Finland. The mound density of Formica aquilonia Yarr. was greater in the two oldest stand age classes, while most mounds of Formica rufa L., Formica polyctena Först., Formica lugubris Zett., Formica exsecta Nyl. and Formica pressilabris Nyl. were found in the two youngest age classes. The mean volume, the volume per area and height/diameter ratio of F. aquilonia mounds increased with stand age. In the oldest stand age class, mounds were slightly smaller in well-lit locations than in shade and near stand edges than further from the edges indicating that new mounds are established in well-lit locations. Similarly, the longest slopes of the mounds faced south, indicating the importance of exposure to the sun. F. aquilonia mounds were concentrated near stand edges, and the spatial distribution of the mounds was aggregated in some stands. At the ecosystem level, the aggregation of ant mounds near stand edges may increase the edge productivity, as mounds concentrate resources to the edges and release nutrients after abandonment. © 2008 The Authors.

Ants are important components of most soil invertebrate communities, and can affect the flow of energy, nutrients and water through many terrestrial ecosystems. The vast majority of ant species build nests in the mineral soil, but a small group of ants in temperate and boreal forests of Eurasia and North America build large parts of their nests above-ground using organic materials collected from the surrounding soil. Many studies have shown that ants nesting in mineral soil can affect water infiltration rates, soil organic matter (OM) content, and nutrient cycling, but much less is known on how mound-building ants influence soil physical and chemical properties. In this paper we summarize what is known on the soil impacts of organic mound-building ants in temperate and boreal forests, and how these ants could be affected by ecosystem disturbance and future climate change. Much of this information comes from studies on Formica rufa group ants in Europe, which showed that CO2 emissions and concentrations of C, N, and P are usually higher in ant mounds than in the surrounding forest soil. However, ant mounds are a minor component of total soil C and nutrient pools, but they do increase spatial heterogeneity of soil water and available nutrients. Mound-building ants can also impact tree growth, which could change the quantity and quality of OM added to soil. Forest management, fire, and projected climate change, especially in boreal forests, could affect mound-building ant population dynamics, and indirectly, soil properties. © 2008 The Authors.

Wood ants (Formica rufa group) are dominating ecosystem elements of the boreal region due to their wide and abundant occurrence. They collect and concentrate organic material from the surrounding forest floor by building large above-ground mounds. These mounds have higher temperature and lower water content than the surrounding forest floor. We studied how these peculiar environmental conditions affected mass loss and carbon (C), nitrogen (N), phosphorus (P) and potassium (K) mineralisation of organic matter in boreal Norway spruce (Picea abies L. Karst.)-dominated mixed forest stands of four different age classes (5-, 30-, 60-, and 100-year-old) situated in eastern Finland using the litter bag technique. Norway spruce needle litter was incubated in inhabited and abandoned wood ant mounds as well as on the surrounding forest floor. We expected decomposition to be extremely slow due to the dryness of the mounds. Mass losses inside inhabited mounds were lower compared to the surrounding forest floor (on average 30 vs 50% after 2 years) but not as low as we expected, which might be a result of ant and microbial activity in the mounds. Decomposition in the abandoned mounds proceeded similarly as on the forest floor. Nutrient mineralisation proceeded more slowly in the ant mounds than on the surrounding forest floor. Mineralisation occurred for all studied nutrients in the ant mounds, except for N, which net amount remained stable during the years of the experiment. When wood ant mounds are abandoned and their porous and dry structure is no longer maintained by the ants, their decomposition is accelerated, and nutrients may be available for uptake by plants, although the nutrient mineralisation seems still to remain lower compared to the surrounding forest floor. However, eventually the mound material will be decomposed and nutrients mineralised, thus providing a nutrient hot spot increasing the heterogeneity of forest floor nutrient availability. © 2007 Springer-Verlag.

Organic mounds of the red wood ants (Formica rufa group; RWA) have been shown to be "hot spots" of carbon dioxide (CO2) efflux from the European forest soils. However, little information is available on the variability of CO2 effluxes from RWA mounds and on the factors regulating CO2 efflux. We assessed the seasonal and diurnal changes in CO2 effluxes, temperatures and volumetric water contents from mounds of Formica aquilona, the important RWA of the boreal forests in Finland. The daily average CO2 efflux from RWA mounds ranged 1.1-6.9 g CO2 m-2 h-1 during the active ant season (May-September), and from 0.2 to 1.1 g CO2 m-2 h-1 during their dormant period (October-April). Mound CO2 efflux from May to September was 3.6-6.0 times higher than from the surrounding forest floors, and most likely came from RWA respiration. Seasonal changes in mound CO2 effluxes were significantly correlated with mound temperature, but not with volumetric water content (7% on average). The high CO2 efflux associated with increased volumetric water content (up to 34%) after a RWA mound was abandoned indicated that these dry mound conditions restrict microbial decomposition of mound organic matter. CO2 effluxes were highest at night and lowest during the day, which is likely due to an increased ant activity or numbers in the mound at night. Diurnal changes in mound CO2 efflux were negatively correlated with air temperature, and positively correlated with the difference between the mound and air temperature. This suggests that thermal convection of warmer mound air to the colder outside air at night might be also a cause of the diurnal changes. We conclude that seasonal and diurnal variations in mound CO2 effluxes are dependent on RWA activities and fluctuation in RWA mound and outside temperatures. © 2007 Elsevier Ltd. All rights reserved.

Wood ants (Formica rufa group) are ubiquitous in European boreal forests and their large long-lived mound nests, which mainly consist of forest litter and resin, accumulate carbon (C) and nutrients. The C and nutrient dynamics of wood ant mounds in response to forest succession have received minor attention in boreal forests. We aimed to study whether the C, nitrogen (N) and phosphorus (P) concentrations and the bulk density of ant mounds differ from those of the surrounding forest soil, to estimate the C, N and P pools in ant mounds, and to test whether the concentrations and pools change with forest age. Norway spruce (Picea abies (L.) Karst.) stands on medium-fertile sites in 5-, 30-, 60- and 100-year stand age classes were studied in eastern Finland. Carbon and P concentrations in the above-ground mound material were higher than those in the surrounding organic layer. The C, N and extractable P concentrations were higher in the soil under the ant mounds than in the surrounding mineral soil (0-21 cm). The low bulk densities in the ant mounds and the soil below them could be a result of the porous structure of ant mounds and the soil-mixing activities of the ants. The C/N ratios were higher in the mounds than in the organic layer. Carbon concentrations in the ant mounds increased slightly with stand age. Carbon, N and P pools in the ant mounds increased considerably with stand age. Carbon, N and P pools in ant mounds were <1% of those in the surrounding forest soil. Nevertheless, the above- and belowground parts of the ant mounds contained more C, N and P per sampled area than the surrounding forest soil. Wood ants therefore increase the spatial heterogeneity in C and nutrient distribution at the ecosystem level. © 2007 Elsevier B.V. All rights reserved.

Although information regarding the spatial variability of soil respiration is important for understanding carbon cycling and developing a suitable sampling design for estimating average soil respiration, it remains relatively understudied compared to temporal changes. In this study, soil respiration was measured at 35 locations by season on a slope of Japanese cedar forest in order to examine temporal changes in the spatial distribution of soil respiration. Spatial variability of soil respiration varied between seasons, with the highest coefficient variation in winter (42%) and lowest in summer (26%). Semivariogram analysis and kriged maps revealed different patterns of spatial distribution in each season. Factors affecting the spatial variability were relief index (autumn), soil hardness of the A layer (winter), soil hardness at 50 cm depth (spring) and the altitude and relief index (summer). Annual soil respiration (average: 39 mol m-2 y-1) varied from 26 mol m-2 y-1 to 55 mol m-2 y-1 between the 35 locations and was higher in the upper part of the slope and lower in the lower part. The average Q10 value was 2.3, varying from 1.3 to 3.0 among the locations. These findings suggest that insufficient information on the spatial variability of soil respiration and imbalanced sampling could bias estimates of current and future carbon budgets. © 2007 Elsevier Ltd. All rights reserved.

Red wood ants (Formica rufa group, RWAs) are common insects in boreal forests in Fennoscandia, and they build large, long-lived mounds as their nests. RWA mounds are enriched with carbon and nutrients, but little information is available about how they affect root distribution and the nutrient uptake of trees. In this study, we investigated the biomass, biomass density, nutrient concentrations, and amounts of fine (<2mm) and coarse (>2mm) roots in RWA mounds, and compared them with those of surrounding forest soil in mixed coniferous stands of different age classes in Finland. Neither fine nor coarse root biomasses differed significantly between the aboveground parts of the mounds and the organic layer of the soil. Root biomass density was lower in mounds than in the organic layer. However, fine root biomass and biomass density were higher in the belowground parts of mounds than in the surrounding mineral soil. Macroelement (N, Ca, K, P, S, Mg) and Zn and Cu concentrations in roots in the mounds were significantly higher than those in the organic layer. Root biomass and biomass density did not differ between stands of different age classes. The results of this study indicate that RWA mounds increase heterogeneity in root distribution in forest ecosystems, and also increase the availability of nutrients for plants that extend their roots inside RWA mounds. © 2007 The Japanese Forest Society and Springer-Verlag Tokyo.

Little is known about the variability in carbon dioxide (CO2) emissions from soil (soil respiration) in tropical rainforests. We studied temporal and spatial fluctuations of soil respiration in an intact Asian tropical rainforest. The values of soil respiration were distributed lognormally with mean and median values of 5.32 and 4.65 μmol m-2 s-1, respectively. Soil respiration varied little over time though highly in space. CO2 hot spots (>10 μmol m-2 s-1) were found with extremely high values (15-25 μmol m-2 s-1). Each CO2 hot spot occurred sporadically at different times and locations. It is hypothesized that animal activities are responsible for the hot spots. The impact of CO2 hot spots on total soil respiration was 10%, which is comparable to the estimation of net C balance in tropical rainforests. Copyright 2007 by the American Geophysical Union.

Red wood ants (Formica rufa group) are important elements in boreal forest ecosystems, where they occur in high abundance and build large and long-lasting, above-ground mounds of organic material. However, little is known on their role in the carbon (C) cycling in boreal forests. We measured temperature and carbon dioxide (CO2) efflux from three different-sized wood ant mounds and the surrounding forest floor from May 2004 to April 2005 in Norway spruce [Picea abies (L.) Karst.] dominated forests in eastern Finland. Additionally, mound and forest floor temperatures were measured continuously and CO2 effluxes at 2-4-week-intervals. During the ants' active season (May-September), measurements were conducted in the morning, afternoon, evening and at night, while fluxes were measured once a day during the ants' inactive season. CO2 emissions from the mounds were up to nearly eight times higher than those from the surrounding forest floor during the active season of the ants, but no statistically significant differences were observed during the period from October to February. Both mound and forest floor CO2 fluxes were highly correlated to mound or forest floor temperature. Based on our measurements, we are able to estimate the annual CO2 efflux from ant mounds and the surrounding forest floor, based on nonlinear regression analyses using CO2 flux as dependant and mound or forest floor temperatures as independent variables. Although red wood ant mounds were found to be "hot spots" for CO2 efflux, that increase the spatial heterogeneity of C emissions within a forest ecosystem, their annual emissions were only 0.30% of that from the forest floor. Thus, our results indicate that red wood ant mounds do not directly contribute significantly to the overall C budget of the boreal forest ecosystem studied. © 2006 Elsevier Ltd. All rights reserved.

Southeast Asian tropical rain forests are among the world's most important biomes in terms of global carbon cycling; nevertheless, the impact of environmental factors on the ecosystem CO2 flux remains poorly understood. One-dimensional multilayer biosphere-atmosphere models such as soil-vegetation-atmosphere transfer (SVAT) models are promising tools for understanding how interactions between environmental factors and leaf-level physiological parameters might impact canopy-level CO2 exchange. To examine application of the SVAT model in tropical rain forests, which is expected to be difficult partly because of the complex canopy structure and large number of tree species, we measured vertical and horizontal variations in leaf-level physiological parameters and leaf area densities together with eddy covariance measurements using a canopy crane in a tropical rain forest in Sarawak, Malaysia. Despite differences in species and canopy positions, leaf nitrogen per unit area (Na) within the canopy could be one-dimensionally described as a linear function of height. Na also clearly explained the other leaf-level physiological parameters across species and canopy positions. Even though the leaf area density profile likely varies in this tropical forest, the SVAT model satisfactorily reproduced the eddy covariance measurements. Furthermore, the CO2 flux calculated on the assumption that Na measured in the upper canopy was distributed evenly throughout was almost the same as that taking the vertical gradient into consideration. These findings suggest that when reproducing the CO2 flux in tropical rain forests using the SVAT model, the leaf area density profile obtained from the leaf area index (LAI) measured at one point and leaf-level physiological properties measured across species in the upper canopy are sufficient. Copyright 2006 by the American Geophysical Union.

Although it is known that small changes in boreal soil carbon (C) fluxes may affect the global soil C balance, our knowledge of the variability in the origin and magnitude of boreal soil C fluxes is still limited. Red wood ant (RWA; Formica rufa group) mounds can be found in high densities in boreal forests, but little is known about how these mounds influence forest soil C dynamics. We developed a dynamic closed-loop chamber system to measure carbon dioxide (CO2) effluxes from a RWA mound and tested the results against measurements of forest floor C fluxes made with a commercial respirometer. The two methods yielded comparable results. CO2 efflux from a RWA mound as measured with the new system was significantly higher than that from the surrounding forest floor. The result suggests that RWA mounds are CO2 "hot spots" within a forest. More investigations would be necessary to evaluate the role of RWA mounds in ecosystem C dynamics. © 2005 Elsevier B.V. All rights reserved.

Red wood ant (Formica rufa group) mounds release high amounts of carbon dioxide (CO2). As red wood ants and other invertebrates living in mounds are poikilothermal organisms, their metabolism and therefore CO 2 emissions are affected by changes in temperature. Thus, seasonal or diurnal changes in air temperature could affect CO2 emissions from mounds. We found that seasonal mound CO2 emissions and air temperature were correlated, both peaking in mid-summer. In contrast, diurnal CO2 emissions and air temperature were inversely correlated, as we observed highest C fluxes during the night when air temperature was lowest. This CO2 emission pattern can likely be explained by higher metabolic rates of ants resulting from their clustering, and increased numbers of ants in the mound when outside air temperature drops at night. Changes in microbial decomposition of mound organic matter or thermal convection of warm CO 2-rich mound air to the colder surface at night likely do not play a major role in the diurnal C fluxes observed in our study. © Finnish Zoological and Botanical Publishing Board 2005.

We examined how the projected increase in atmospheric CO2 and concomitant shifts in air temperature and precipitation affect water and carbon fluxes in an Asian tropical rainforest, using a combination of field measurements, simplified hydrological and carbon models, and Global Climate Model (GCM) projections. The model links the canopy photosynthetic flux with transpiration via a bulk canopy conductance and semi-empirical models of intercellular CO2 concentration, with the transpiration rate determined from a hydrologic balance model. The primary forcing to the hydrologic model are current and projected rainfall statistics. A main novelty in this analysis is that the effect of increased air temperature on vapor pressure deficit (D) and the effects of shifts in precipitation statistics on net radiation are explicitly considered. The model is validated against field measurements conducted in a tropical rainforest in Sarawak, Malaysia under current climate conditions. On the basis of this model and projected shifts in climatic statistics by GCM, we compute the probability distribution of soil moisture and other hydrologic fluxes. Regardless of projected and computed shifts in soil moisture, radiation and mean air temperature, transpiration was not appreciably altered. Despite increases in atmospheric CO2 concentration (Ca) and unchanged transpiration, canopy photosynthesis does not significantly increase if Ci/Ca is assumed constant independent of D (where Ci is the bulk canopy intercellular CO2 concentration). However, photosynthesis increased by a factor of 1.5 if Ci/Ca decreased linearly with D as derived from Leuning stomatal conductance formulation [R. Leuning. Plant Cell Environ 1995;18:339-55]. How elevated atmospheric CO2 alters the relationship between Ci/Ca and D needs to be further investigated under elevated atmospheric CO2 given its consequence on photosynthesis (and concomitant carbon sink) projections. © 2004 Elsevier Ltd. All rights reserved.

Soil respiration was measured for 2 years in an artificial gap and in an undisturbed area in a Japanese cedar (Cryptomeria japonica D. Don) forest to estimate the contribution of root respiration to total soil respiration. Measurement plots were set up at the center of the gap, the edge of the gap, the edge of the surrounding stand and within the stand. Using a small gap (2.5 m × 2.5 m) enabled us to maintain the same soil temperature and soil moisture as found in the stand. Seasonal fluctuations in soil respiration, increasing in summer and decreasing in winter, corresponded to changes in the soil surface temperature. Soil respiration in the gap site did not differ significantly from those in the stand in the first year of gap formation. However, in the second year, the minimum CO2 flux was observed at the center of the gap and the maximum at the edge of the surrounding stand. Assuming that the differences between soil respiration in the center of the gap and that in the stand were equal to the root respiration, the root respiration rate was calculated from the relationship between the root respiration rates (Rr) and the soil surface temperature (Ts) by Ln(Rr) = 0.07Ts + 3.48. The average contribution of root respiration to total soil respiration, as estimated from the soil surface temperature in the stand by using the above equation, was 49%. After taking root decomposition into consideration, the contribution of root respiration to soil respiration increased from 49 to 57%.

Little information is available on the fluctuation of soil respiration in Japanese cedar forests (Cryptomeria japonica D. Don), a principal and highly productive plantation in Japan. We measured the seasonal change in soil respiration for three years in thinned and intact sections of a Japanese cedar forest to establish the relationship between soil respiration and environmental factors and to examine the effects of a common silvicultural practice, namely forest thinning. We measured soil respiration while regulating CO2 concentration and wind speed in a chamber using a portable open-flow chamber system. Soil respiration rates, ranging from 2570 to 3060 (g CO2) m-2 year-1 and 1830 to 2170 (g CO2) m-2 year-1 in the thinned and intact sections, respectively, increased in summer and decreased in winter. Soil respiration rates (R(s)) significantly correlated with soil surface temperature (T(s)). The relationship was approximately In (R(s))= a + b(T(s)), where a and b are constant values, varying from 0.067 to 0.106 and from 3.30 to 4.62, respectively. The Q10 values were 2.0 and 2.5 in the thinned and intact sections, respectively. Soil surface CO2 concentrations (0.8-3.9 g m-3), calculated from the soil respiration rates, were higher than ambient atmospheric CO2 concentrations. They tended to increase in summer and decrease in winter. Soil respiration rates in the thinned section were significantly higher than those of the intact section in the first and second years of the measurement, but not in the third year, namely the fifth year after thinning; an indication that thinning may have increased soil respiration from the forest floor temporarily.