Kazuo Yabe

Perceptions of urban stream corridors within the greenway system of Sapporo, Japan

Abstract Many rivers and streams have disappeared through flood control, drainage works and urban development in Sapporo, Japan. Also, accessibility to and naturalness of the streams have deteriorated. Newer river and stream corridor improvement technologies such as nature-oriented construction, and public involvement methods are emphasized in the Sapporo General Green Space Plan. The purpose of this study is to make clear the perceptions of stream corridors and to show some factors which are important for integrating them into the Urban Greenway Plan. After consideration of landforms, stream corridor land uses and location, five stream corridors which have been improved in the Sapporo urban areas were selected. Neighborhood residents’ perceptions of the stream corridors were surveyed using a questionnaire, and a census of the vegetation along the stream banks was also taken. The results showed that improvement of the stream corridors in question had been supported by nearby residents. After the factor analysis, five important factors of stream corridor perception, namely, “recreational use,” “participation,” “nature and scenery,” “sanitary maintenance,” and “water safety” were identified. Based on these factors, stream corridor features including vegetation that may affect preference were discussed as variables for integrating the stream corridors into the Greenway Plan. Furthermore, using the factor scores, respondents were classified into three groups: the Passive Group, the Recreation Interested Group, and the Participation Oriented Group. Corresponding to these groups, a number of programs facilitating participation in or support of greenway planning are suggested. In conclusion, it is suggested that (1) enhancing the ecological environment; (2) creating a recreational circulation system; and (3) making full use of the natural and cultural characteristics of the local areas are important to the integration of stream corridors in urban greenways.

Key variables controlling the vegetation of a cool‐temperate mire in northern Japan

Abstract. In the cool-temperate Bibi Mire, Hokkaido, Japan, valley fens and flood-plain fens have quite different vegetation. The main variables controlling the vegetation were all hydrological: mean water level, water level fluctuation and surface water flow. Chemical factors such as electrical conductivity, dissolved oxygen and related peat decomposition were less important. The pH was about neutral and has little effect. The flood-plain fen developed under fluctuating water table conditions. The dominant species are Calamagrostis langsdotffii and Carex pseudocuraica. When temporal inundation occurs in the rainy or typhoon seasons, the submergence stimulates bud germination of the stoloniferous C. pseudocuraica, which can rapidly elongate its stolons upward. Some large floating peat mats occurred in the flood-plain fen zone. On these mats some Alnus japonica saplings establish and patches of alder forest can arise. Here the water level was higher than in the peripheral alder forest zone. The valley fen is dominated by Carex lasiocarpa var. occultans and/or C. limosa. It is formed under stable water table conditions in the inundated parts of the mire -where the non-inundated wet areas are dominated by alder trees. In the area where the surface water is flowing, these two fen sedges grow in deeper water since the high oxygen content is considered to compensate the flooding stress.

Comparisons of nutrient recovery and specific leaf area variation between Carex lasiocarpa var. occultans and Carex thunbergii var. appendiculata with reference to nutrient conditions and shading by Phragmites australis

The distribution of two sedge species was studied in two mires which differ in abiotic environments and in distribution of Phragmites australis. Carex lasiocarpa var. occultans dominated in nutrient-poor valley mire, and Carex thunbergii var. appendiculata dominated in nutrient-rich flood plain subject to water fluctuations. Phragmites australis grew well in nutrient-rich conditions. The distribution of C. lasiocarpa showed a strong negative correlation with P. australis coverage, whereas C. thunbergii coverage was not affected by P. australis. The leaf area per dry leaf mass (specific leaf area: SLA) of C. thunbergii increased with shading by P. australis, but that of C. lasiocarpa was stable. The SLA flexibility of C. thunbergii to light interception might enable this species to invade P. australis patches in nutrient-rich environments. The residual nutrient ratio of nitrogen and phosphorus (the ratio of the residual nutrient content at the end of the growing season to peak nutrient content) in the vegetative ramet of C. thunbergii was 1.7 times higher than that of C. lasiocarpa. This low residual ratio may indicate effective nutrient recovery to storage organs. The effective nutrient recovery in C. lasiocarpa might enable this species to grow even in nutrient-poor environments. However, it may be difficult for C. lasiocarpa to expand its habitat to nutrient-rich areas where P. australis dominates as it is not shade tolerant.

Base mineral inflow in a remnant cool-temperate mire ecosystem

Kiushitou (42°28′ N, 141°9′ E) is a lowland mire located in a residential area of northern Japan. We examined the 2-D distribution of hydrochemical variables and their seasonal changes in relation to plant communities in an attempt to conserve the Sphagnum fen (Sphagnum subfulvum). This mire is gently sloping and the upper area consists of alder and ash forests, while the lower area is covered with fen communities. The grassy fen, Moliniopsis japonica, occurs throughout the lower area, whereas the Sphagnum fen is restricted to the southwest part of the mire. anova and canonical correspondence analysis revealed that the occurrence of Sphagnum fen is negatively correlated with Mg, Ca and electrical conductivity (EC). These variables indicated that water in the upper forest area contained a high concentration of minerals from the neighboring residential area. Seasonal changes in EC values revealed that the watercourse from a spring point in an upper corner to the lowest drainage ditch was divided into two, southwest and northeast, courses. Because the northeast-course spring water joins mineral-rich water flowing from a point at the upper margin, the northeast part of the lower area contains considerable Ca and Mg. In contrast, the mineral-poor spring water flowing into the southwest part of the mire ensures the survival of the Sphagnum fen. Thus, when we stop the supply of mineral-rich water from the upper margin the area of the Sphagnum fen will expand into the northeast part of the mire. Two-dimensional details of the hydrochemical regime clarify the impact of mineral inflow and the expansion mechanisms of these minerals.

Effects of nutrient loadings from catchments on Asajino mire, a small coastal ombrotrophic mire in northernmost Japan

The relationship between water chemistry and vegetation was studied in a coastal ombrotrophic mire in northern Hokkaido, Japan. The distributions of Sphagnum and Phragmites communities were separated clearly by the pH and ion concentration of the peat surface-pore water. The drainage ditches along the road across the center of the mire had a high pH and ion concentration, as did the peat water in the western part of the mire. It was found that fields used for livestock farming on a hill to the west of the mire leached materials into the mire through drainage ditches, surface runoff, and probably also through ground water, and thus influenced the water chemistry of the mire. Management of the water, including that in the catchment of the mire, should be introduced before biological buffering capacity against excess nutrient loading caused by human activity is exceeded and the mire loses its ombrotrophic status.

Reduced soil contributes to the anomalous occupation of dwarf communities in N-richer habitats in a cool-temperate mire

Spatial patterns of the oxidation–reduction potential (Eh) of soil, water level and chemistry were examined in the fen area of the Tohfutsu mire, northern Japan, where horse pasturage has been carried out throughout the growing season every year. The fen vegetation consisted mosaically of communities mono- or codominated by Eleocharis kamtschatica, Iris setosa and Carex lyngbyei. The highest concentration of total dissolved nitrogen of soil water was observed in the dwarf community dominated by E. kamtschatica with smaller biomass, whereas the nutrient level was lower in the community monodominated by C. lyngbyei with larger biomass. Principal component analysis denoted well that Eh, N, K, and pH contributed to the differentiation of these communities significantly. During the growing season that was investigated, the highest nitrogen concentration was observed in midsummer, when plants are expected to absorb nutrients intensely, indicating that the supply of dissolved nitrogen far exceeded the nutrient uptake of plants. Multiple habitats with reduced soil were formed by submergence and by an excess of nitrogen due to pasturage, and the soil reduction indirectly inhibited the incursion of species with large biomass at such sites. It was demonstrated that soil Eh contributed to the anomalous pattern of vegetation where the supply of available nitrogen exceeds the uptake by plants.

Effects of Urbanization on the Flora of Open Space in Sapporo City

札幌市の11緑地の植物相を主成分分析法によって解析した。第1軸は孤立化指標 (周辺の森林率 孤立後の時間) と負相関を持ち, 森林植物の種数とも負相関を持った。孤立化は市街地拡大の指標でもあるため, この軸は緑地の都市化によって森林植物が減少することを抽出した。第2軸は, 緑地内の撹乱地の増加により雑草種が増加するという人為的な影響を抽出した。都市化によって消失する森林植物は30種の草本と14種の木本であった。また鳥散布型の木本は孤立化によって消失しやすく, 周辺100m以内の森林率が孤立化に影響を与えやすかった。さらに, 30種の草本が林床性であることから, 断片化 (小面積化) の影響が大きいものと思われる。