We surveyed species composition in relation to substrates, and microsite characteristics of temperate conifer species in an old growth Chamaecyparis obtusa forest on Mt. Shiraga, Kochi, Japan. We established nine study quadrates on a gentle slope where masses of rock or dwarf bamboos are dominant on forest floor, and we measured the diameter at breast height of all trees that were more than 1.5 m in height and the height of all conifer seedlings (< 1.5 m in height) while recording their standing substrates: stump, fallen log, rock, mound, and ground. According to detrended correspondence analysis, the nine quadrates were roughly divided into a group dominated by Chamaecyparis obtusa and Tsuga sieboldii, and a group of mixed broad-leaved tree stands, implying that the former establish on a block slope and the later establish on the ground. Chamaecyparis obtusa seedlings significantly established on fallen logs and old stumps while larger trees (> 1.5 m in height) were found on stumps. Thirty percent of large Chamaecyparis obtuse trees were established at an elevated position above the ground, and half of them had stilt-like roots. Tsuga sieboldii seedlings were established on rocks and stumps, while the larger trees were found on stumps. Both seedlings and larger trees of Pinus parviflora established on stumps though there were few of these. Abies firma seedlings were more likely to be found on the ground, but intermediate-sized trees were missing, showing their limited regeneration. Thus the stumps and logs play an important role as microsites for establishing conifers, except Abies firma, in an environment in which masses of rock or dwarf bamboo are dominant on the forest floor.
Large animals such as sika deer are considered to have diverse impacts on the aboveground and belowground processes in terrestrial ecosystems. Previous studies on the ecological impacts of deer grazing have been mostly conducted in open ecosystems where the home ranges of the deer are not restricted; however, few studies have been conducted in closed ecosystems. The present study was carried out to investigate the impact of deer on soils and plants in Nakajima Island in Lake Toya, where sika deer populations are dense within the closed ecosystem. We used six deer fences on the island and examined the physical and chemical properties of soils along with the chemical properties of plants. The thickness of litter layer on the soil surface was smaller and the surface soil hardness was larger outside the fences than inside. In addition, the soil nitrogen characteristics inside and outside the fence varied with the locations, especially the grassland soil outside the fence had higher nitrate-N than the forests. Similarly, nitrogen concentrations in Japanese spurge leaves were significantly higher outside the fences in the grassland than inside. These results suggest that in Nakajima Island, increased density of deer variously changes the physical properties of the soils and the chemical properties of the soils and plants, and these changes vary based on deer abundance and vegetation type. Because ranges for the movement of deer are limited in Nakajima Island, the effects of high deer density could be observed over the island, and stabilized for long time.
Knowledge about carbon dynamics on the organic matter pooled in the forest soil was important as basic data to discuss the effect of the progress of global warming. In this study, one treatment area (0.23 ha) and one control area (0.24 ha) were set in a 35-year-old Cryptomeria japonica plantation of Tokyo University of Agriculture Okutama Forest in Okutama-machi, Nishitama-gun, Tokyo, in December 2012, and clear-cutting and ground clearance were done in the treatment area in March 2013. Fixed-point measurements of soil respiration rate (RS) were conducted regularly from January 2013 to December 2018 at 19 and 21 points in the treatment and the control areas, respectively. Volcanic ash soil distributes in the study site. From the comparison of RS estimated at 20℃ （RS20), the ratios of RS20 in the treatment area to the control area were increasing from 0.60 in 2013 to 0.74 (highest) in 2016, but decreased to 0.49 in 2018. The carbon stocks in the surface soil (0-5 cm deep) measured in 2018 were 24.6 t ha-1 at the treatment area and 23.2 t ha-1 at the control area. The total carbon emission for six years was estimated to be 50.3 tC ha-1 in the treatment area, which could not be explained by the decomposition of the organic matter pooled in the surface soil before harvesting. These results support the importance of the carbon pool of subsurface soil for consideration of soil carbon dynamics.
Spatial assessment of nitrogen content in canopy leaf is important to understand the spatial variability of nitrogen cycle in forest ecosystem, because leaf nitrogen closely relate to quality and quantity in litterfall, nutrient cycle and plant nutrient uptake. This study aims to develop and analyze the assessment method to estimate spatial distribution of nitrogen content in canopy leaf in natural forest with heterogeneous species composition and complexed canopy structure using unmanned aerial vehicle (UAV) with digital camera through Structure from Motion (SfM). The study was conducted in a natural cool-temperate mixed forest in Uryu experimental forest, Hokkaido University located in northern Hokkaido, Japan. Digital image for single leaf in dominated 8 tree species (2 evergreen coniferous and 6 deciduous broad-leaved species) and Sasa dwarf bamboo as understory vegetation were taken to analyze the relationship to leaf nitrogen content using various RGB indicators. There were significant correlations between RGB indicators and leaf nitrogen content in coniferous and broad-leaved tree (with Sasa understory), respectively. We developed a method to estimate the spatial distribution of each vegetation using the aerial digital images taken from UAV derived digital surface model (DSM) and their seasonal differences between leave on and off periods. Spatial distribution of nitrogen content in canopy leaf was mapped from the relationship between the RGB indicators and leaf nitrogen content on the vegetation map. From this result, spatial dynamics in nitrogen cycling of forest ecosystem can be visualized and mapped out to help to understand detail locational difference.
The following study was performed for the purpose of verifying how plant diversity changed by tree species conversion from coniferous plantation to broad-leaved forest. We investigated changes in the composition of plant species over a 30-year period in broad-leaved forest in the warm-temperate zone, which regrew after meteorological damage. The total number of species increased for three years after the disturbance, but subsequently decreased. To analyze the changes in species composition from an ecological perspective, the species were typed according to habitat classification. Lucidophyllous forest species increased throughout the study period. Non-forest type species increased rapidly in the early regrowth stage and then decreased. Overall, in the regrowth broad-leaved forest, the plant species increased markedly in the early regrowth stage due to a temporary increase in non-forest type species caused by disturbance, but these species then decreased with time. To conserve diversity in forest management, we must be aware that plant diversity in regrowth forests depends on non-forest type species.
Soil scarification is a natural regeneration practice in which both understory dwarf bamboo and surface soil are removed using civil engineering machinery. We provide a historical review of soil scarification practices in Hokkaido, the northernmost island of Japan. Soil scarification has been conducted widely in Hokkaido since the 1960s. It has been shown to be efficient for natural regeneration where Betula spp. are dominant. As a low-cost reforestation technique, soil scarification has recently received renewed attention regarding a large area of Abies sachalinensis plantation facing a final cutting period in Hokkaido. On the basis of past findings focusing on soil disturbance, scarification practices should strike a balance between maintaining soil physicochemical quality and entirely removing dwarf bamboo, Betula trees show better growth in scarified stands than in stands regenerated without scarification, and soil scarification may significantly reduce nutrient status. Previous reports on scarification-regenerated birch forests were derived mainly from young stands (<20 years old). Thus, it remains unclear how much timber of specific volume and size can eventually be harvested from scarification-regenerated birch forest. To achieve well-executed birch forest management, current scarification practices need to be improved depending on local conditions. Some issues still need to be addressed, for example, a countermeasure to tall forbs of concern in low-altitude areas and investigation of the causes of previously failed scarification practices.
Non-commercial thinning is known to produce aerial needle litter. The vertical position of litter mass is important for understanding material cycling in thinned forests because aerial litter decomposes more slowly than ground litter. The decomposition processes of aerial and ground litter and the physical falling of aerial litter to the ground determine the dynamics of remaining amount and vertical distribution of litter. Furthermore, decomposition in each position and aerial litter fall may depend on meteorological factors. We aimed to estimate the dynamics of remaining amount of litter by linking litter fall and decomposition rates and developed Bayesian models to clarify the effects of meteorological factors on these processes. We monitored decomposition and aerial litter fall of a Cryptomeria japonica needle litter for 42 months after thinning. The model results suggested that temperature was a determining factor for temporal variation in the litter decomposition rates, while precipitation was the main determining factor for temporal variation in the fall rate of aerial litter. Temperature and precipitation were positively correlated with decomposition and aerial litter fall, respectively. Our linked model suggested that aerial litter fall contributed only slightly to remaining amount of total litter during the 42 months after thinning, but affected the vertical distribution of litter considerably. The model also indicated that the above meteorological factors contribute notably to the dynamics of remaining amount of total litter and the vertical distribution. These results suggest that our model has the potential to be an effective tool for understanding material cycling in non-commercially thinned stands in temperate regions.
To elucidate uptake via the roots and the dynamics of cesium (Cs) in Japanese cedar (Cryptomeria japonica D. Don), we measured the stable cesium (133Cs), rubidium (Rb), and potassium (K) content in the needles and wood of Japanese cedar harvested from four sites: 1) Kawauchi; 2) Kamikawauchi; 3) Otama; and 4) Tadami in Fukushima Prefecture, Japan. The levels of deposition of radiocesium were different among sites. The contents of 133Cs, Rb, and K were higher in current needles and heartwood than in old needles and sapwood, respectively. In addition, 133Cs, Rb, and K content tended to be lower in the small than in the large trees. This result suggests that Cs would be accumulated in heartwood, particularly in mature trees. Proportional relationships were observed between 133Cs in old needles and heartwoods as well as sapwoods. Therefore, 133Cs in wood may be estimated from 133Cs in needles. 133Cs in needles and wood varied among sites, with higher levels observed in Tadami and Kamikawauchi. Exchangeable K in surface soil was slightly lower in Tadami and Kamikawauchi than in Kawauchi and Otama. Soil exchangeable 133Cs was the highest in Tadami. The 133Cs uptake via roots and the dynamics of 133Cs in Japanese cedar may be affected by soil exchangeable K and 133Cs.
We investigated the changes in soil physical and chemical properties at five plots, approximately 3 km apart from Mt. Shinmoe, with the volcanic ejecta and buried soil from a half year to one and a half year elapsed time from 2011 eruption of Mt. Shinmoe. The volcanic ejecta were composed by thin volcanic ash and thick pumice layer. The water-extractable ions and sulfur content in the volcanic ejecta were relatively smaller than those in the previous reports with other volcanos. The sulfate and ammonium were dominant for the water-soluble fraction. The clay content increased along with the time in any layer, indicating that clay migration had occurred. The thickness of the layer, total carbon and nitrogen content, cation exchangeable capacity and exchangeable cation content little fluctuate during this period. The sulfate and ammonium ion in the water-soluble fraction, sulfur content, and available phosphate seemed to decrease gradually, but the trend is obscure. Although the ejecta did not absorb phosphate up to 1 year after eruption, the ejecta one and half year after eruption was slightly able to absorb phosphate accompanying the increase in oxalate-extractable aluminum and Alp/Alo ratio. With regard to the nutrient load to the soil, because the contribution from thick pumice layer was greater than that from thin fine ash layer, we suggest that the contribution from pumice layer could be more important in the long-term change.
The 2011 Heisei Sanriku mega-tsunami destroyed most of the forests along the eastern Pacific coastline of Japan. The Forest Agency of Japan (FAJ) has played a positive role in the restoration of tsunami-damaged coastal forests by constructing tide embankments and planting trees. Seawater inundation and sea-sand deposition in and on topsoil generally lead to excessive Na^+ absorption and accumulation in plants, competitive inhibition of nutrient uptake by Na^+, and a decrease in suction potential caused by low osmotic pressure between the soil matrix and plant roots. During the disaster, excessive Na^+ absorption in topsoil, incremental changes in soil pH (H_2O), and deterioration in ground water drainage due to ground subsidence strongly affected rhizosphere microenvironments. These changes in turn caused severe damage, including needle discoloration, debilitation, droop, and finally death, to broad areas of the eastern Pacific coastal forests. Rehabilitation of tsunami-created saline soils in these forested lands requires the removal of sea salt, a difficult task as most Japanese forests have poor irrigation facilities. Efficient removal of sea salt from the soils must therefore rely on high-precipitation events, such as typhoons and the rainy season in Japan. Reforestation of seawater-inundated forests along the Pacific coastal areas affected by the tsunami will require continued soil chemistry monitoring and rehabilitation.
In this study, we aimed to obtain evidence of forest fires that had occurred in the mountainous region of Nikko, Tochigi, by using an analysis for detecting charcoal particles on the soil surface of Sasa grasslands on a historical topographic map drawn in 1915, in which there were no historical documents of forest fire. To test the efficacy of the charcoal particle analysis, we first conducted the analysis in places where forest fires had occurred in the past; we located these places by using old photographs of burnt forests, taken in 1905 in the Meiji era; literature survey for forest fires; and surveys for tree age structure. We found that these places are situated in the Sasa grasslands and the adjacent broad-leaved forest near the Yu-no-ko Lake on the map in 1915. The literature survey showed that the forest fires had occurred near these places about 120 years ago (1890s); this information corresponded with the tree age structure of birch and oak forests around these places that consisted of trees less than 120 years of age. Charcoal analysis used in these forests detected charcoal particles in all the forests, indicating the efficacy of the analysis. Then, charcoal particle analysis and surveys in other oak-white birch forests in the area where the Sasa grasslands were located in 1915 revealed the presence of charcoal particles in all the forests, and tree age structure showed that the forests consisted of trees that were, at most, 101 years of age. Therefore, we collected evidence that forest fires had occurred across the region in the Meiji era and that the existing forest vegetation on the Sasa grasslands and adjacent broad-leaved forests would have been established after the fires.
We investigated the relationship of vegetation to geomorphology in a V-shaped valley bottom of an incised meandering mountainous stream in a transition zone from fir-hemlock forests to cool-temperate deciduous broad-leaved forests in Kyushu, southwestern Japan. The bank of a channel reach (410 m in length) of a forth-order valley of Oyabu creek was divided into 32 units, and overstory vegetation, slope characteristics, flood frequency and other geomorphic features for 15 m width from the vegetation edge were surveyed. The bank vegetations of 32 units were classified into three types: Tsuga sieboldii forests (ridge type), Quercus crispula forests (secondary broad-leaved type) and Betula grossa forests (valley-bottom type). These types were related to slope forms, soil depth and slope inclination, but not to flooding frequency. These results suggested that the bank vegetation type classified by the overstory species composition in the V-shaped valley was influenced by hillslope processes rather than by the fluvial process of the main creek. The slope forms were related to the incised meander and geomorphic features such as the back slopes and the escarpments. These results suggested that river meander and geomorphic features may also have significant impacts on patch mosaic formation in a riparian strip in a V-shaped valley through the promotion of different bank slope characteristics through long-term lateral erosion processes.
Most of litter returned by non-commercial thinning was existed without contact onto the forest floor. We discussed nitrogen dynamics with decomposing litter after thinning with a focus on the site difference of litter existence in this study. The amount of nitrogen returned by thinning was 84kg ha^<-1> and 67% of them were existed in the air without contact onto the floor. Litterbag containing green needles was installed in the air and on the surface in forest floor, and decomposition rate and nitrogen supply with decomposing of green needles into the soil were investigated. Decomposition rate was not differed among treatments after one year installation but was higher in the surface than the air in two year after. Nitrogen concentration in the remaining green needles was increased from just after installation in both of treatment, and was statistically higher in the surface than in the air. After decomposition, amounts of nitrogen containing in the remaining green needles were gained by immobilization until six month after in the air and one year after in the surface. Nitrogen supply into the soil with green needle decomposition started early in the air compared in the ground. Contribution of nitrogen supply into the soil from green needles installed on the surface during two years was 64%. Because decomposition rate of green needles installed on the surface between one and two year after higer than those of in the air.