Mizue Ohashi

Foraging activity and dietary spectrum of wood ants (Formica rufa group) and their role in nutrient fluxes in boreal forests

Abstract 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.

Modeling CO2 exchange over a Bornean tropical rain forest using measured vertical and horizontal variations in leaf‐level physiological parameters and leaf area densities

Southeast Asian tropical rain forests are among the worlds most important biomes in terms of global carbon cycling; nevertheless, the impact of environmental factors on the ecosystem CO 2 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 CO 2 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 (N a ) within the canopy could be one-dimensionally described as a linear function of height. N a 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 CO 2 flux calculated on the assumption that N a 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 CO 2 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.

The effect of red wood ant (Formica rufa group) mounds on root biomass, density, and nutrient concentrations in boreal managed forests

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 (<2 mm) and coarse (>2 mm) 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.

Estimation of radioactive 137-cesium transportation by litterfall, stemflow and throughfall in the forests of Fukushima.

Since the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011, large areas of the forests around Fukushima have become highly contaminated by radioactive nuclides. To predict the future dynamics of radioactive cesium ((137)Cs) in the forest catchment, it is important to measure each component of its movement within the forest. Two years after the accident, we estimated the annual transportation of (137)Cs from the forest canopy to the floor by litterfall, throughfall and stemflow. Seasonal variations in (137)Cs transportation and differences between forests types were also determined. The total amount of (137)Cs transported from the canopy to the floor in two deciduous and cedar plantation forests ranged between 3.9 and 11.0 kBq m(-2) year(-1). We also observed that (137)Cs transportation with litterfall increased in the defoliation period, simply because of the increased amount of litterfall. (137)Cs transportation with throughfall and stemflow increased in the rainy season, and (137)Cs flux by litterfall was higher in cedar plantation compared with that of mixed deciduous forest, while the opposite result was obtained for stemflow.

Distribution of ant species and mounds (Formica) in different-aged managed spruce stands in eastern Finland

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.

Organic mound-building ants : their impact on soil properties in temperate and boreal forests

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.

A new approach for the simultaneous tracking of multiple honeybees for analysis of hive behavior

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.

Effects of excising and washing treatments on the root respiration rates of Japanese cedar (Cryptomeria japonica) seedlings

Tree root respiration is an important component of the carbon balance in forest ecosystems; however, it is not clear whether root preparation treatments (such as excising and washing) affect root respiration measurements. Here, we aimed to compare the respiration rates of roots subjected to different treatments (i.e., washing with water vs. brushing without water, and excising vs. not excising) for 17-month-old seedlings of Cryptomeria japonica. Immediately after sampling an entire root system, the root respiration rate was measured on a mass basis using a closed static chamber system equipped with an infrared gas analyzer. We found that the respiration rates for roots that were excised 10–20 times were significantly higher than those for roots that were not excised. There was no significant difference in the root respiration rates between washing and brushing treatments. Our results indicate that large numbers of excisions (>10 times) could lead to bias in the measured changes in specific root respiration rates, and imply that differences between washing and brushing treatments do not affect the specific root respiration rate. We conclude that potential variation in recorded root respiration rates could be minimized by standardizing the root preparation technique, which should involve rapidly removing all loose soil and limiting the extent of root excision.

Vertical variations in wood CO2 efflux for live emergent trees in a Bornean tropical rainforest

Difficult access to 40-m-tall emergent trees in tropical rainforests has resulted in a lack of data related to vertical variations in wood CO2 efflux, even though significant variations in wood CO2 efflux are an important source of errors when estimating whole-tree total wood CO2 efflux. This study aimed to clarify vertical variations in wood CO2 efflux for emergent trees and to document the impact of the variations on the whole-tree estimates of stem and branch CO2 efflux. First, we measured wood CO2 efflux and factors related to tree morphology and environment for seven live emergent trees of two dipterocarp species at four to seven heights of up to ∼ 40 m for each tree using ladders and a crane. No systematic tendencies in vertical variations were observed for all the trees. Wood CO2 efflux was not affected by stem and air temperature, stem diameter, stem height or stem growth. The ratios of wood CO2 efflux at the treetop to that at breast height were larger in emergent trees with relatively smaller diameters at breast height. Second, we compared whole-tree stem CO2 efflux estimates using vertical measurements with those based on solely breast height measurements. We found similar whole-tree stem CO2 efflux estimates regardless of the patterns of vertical variations in CO2 efflux because the surface area in the canopy, where wood CO2 efflux often differed from that at breast height, was very small compared with that at low stem heights, resulting in little effect of the vertical variations on the estimate. Additionally, whole-tree branch CO2 efflux estimates using measured wood CO2 efflux in the canopy were considerably different from those measured using only breast height measurements. Uncertainties in wood CO2 efflux in the canopy did not cause any bias in stem CO2 efflux scaling, but affected branch CO2 efflux.

Waggle dance effect: dancing in autumn reduces the mass loss of a honeybee colony

SUMMARY 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.