Terumasa Takahashi

Carbon content of soil in urban parks in Tokyo, Japan

Because of difficulties in estimating the carbon fixation rate, we alternatively investigated the C content of the soil in 19 urban parks in the Tokyo metropolitan area. The C content of the soil under three vegetation types was measured: grassland/turf (“turf”); tree-planting area with plant management (with weeding and removal of fallen leaves) (“tree-planting area”); coppice or tree-planting area without plant management (“coppice”); bare land was used as control. Average C contents of turf, tree-planting area and coppice were about 82, 79 and 120 Mg–C ha−1, respectively, and were larger than the C content of trees in an urban park, as estimated in previous studies. The results indicate that the soils of urban parks function as a C sink.

Changes in Soil Chemical and Physical Characteristics in Japanese Cypress (Chamaecyparis obtusa Endl.) Stands by Mixture of Deciduous Broad-leaved Trees in the Northern Kanto Region of Japan

In order to clarify the effects of a mixture of deciduous broad-leaved trees on soil fertility, we investigated litter biomass accumulation, mineral soil chemical and physical characteristics, characteristics of nitrogen mineralization, and the mutual relationships between them in Japanese cypress (Chamaecyparis obtusa) stands mixed with deciduous broad-leaved trees at different ratios (mixture ratio; MR = 0, 16, 33, 43, 100% by basal area) in the northern Kanto region of Japan. Litter biomass in the forest floor and mineral soil was 19.1 Mg ha−1 in MR 0% and decreased approximately 60 % in MR 33%, MR 43% and MR100%. The permeability at 0–5 cm soil depth in MR100% was twice as much as that in MR 0%. Increases in soil permeability were likely due to larger soil pores in the higher MR with much accumulated deciduous broad-leaves. At 0–5 cm soil depth, the differences in carbon concentration among the plots were not clear. On the other hand, carbon concentrations at 5–10 cm depth increased from 90 g kg−1 to 147 g kg−1 with increases in MR from 0% to 100%. Concentrations of exchangeable bases increased two to four times with increases in MR from 0 to 100% at 0–10 cm depth. Soil pH (H2O) generally increased with increases in MR at each depth. The rates of net nitrogen mineralization at 0–5 cm depthin vitro increased from 25 to 87 mg kg−1 2 weeks−1 with increases in MR from 0 to 100%. However, increases in nitrification with increases in MR were not clear compared with nitrogen mineralization. These results indicated that a mixture of deciduous broad-leaved trees in a Japanese cypress stand was effective in preventing soil fertility decline.

Comparison of organic matter dynamics in soil between Japanese cedar (Cryptomeria japonica) forest and adjacent Japanese red pine (Pinus densiflora) forest established on flatland

In order to clarify the effects of tree species on organic matter dynamics in soil, we investigated the amount of forest floor material, leaf litter decomposition rate, soil chemical characteristics, soil respiration rate and cellulose decomposition rate in a Japanese cedar forest (cedar plot) and an adjacent Japanese red pine forest (pine plot) established on a flatland. The amount of forest floor material in the cedar plot was 34.5 Mg ha−1 which was greater than that in the pine plot. Because the leaf litter decomposition rate was higher in the pine plot than in the cedar plot, it is likely that the difference in the amount of forest floor material between the plots is caused by the difference in the leaf litter decomposition rate. The C concentrations of soil in the cedar plot were 1.2–2.1 times higher than those in the pine plot. Soil pH(H2O)s in the cedar plot were significantly higher than those in the pine plot. The soil respiration rates and the rates of mineralized C in the cedar plot byin vitro incubation were higher than those in the pine plot. From this result, it is assumed that soil organic matter in the cedar plot was decomposed relatively faster compared with the pine plot. Furthermore, microbial activities, which were reflected as cellulose decomposition rates in the cedar plot, were higher than those in the pine plot.

The effects of urbanization on chemical characteristics of forest soil in Tamagawa basin, Japan

In order to clarify the effects of urbanization on the chemical characteristics of forest soils, we investigated several surface soil chemical characteristics, including (1) carbon (C) concentration, (2) concentrations of exchangeable bases, (3) cation exchangeable capacity (CEC), and (4) soil pH of forests in the Tamagawa basin, Japan. We defined the road ratio as level of urbanization. Study sites were located in areas with varying levels of surrounding urbanization. Surface soil concentration of exchangeable bases (especially calcium and magnesium), percent base saturation, and pH (H2O) increased with an increasing road ratio; in other words, with increased urbanization, C and CEC were unrelated to road ratio. One reason for the observation of increasing exchangeable bases with increasing urbanization appears to be the deposition of dust. The increase in exchangeable bases concentration (and % base saturation) corresponds to increases in soil pH.

Allelopathic Activities of Tree Species

木本植物種の他感作用物質の有無や他感作用の程度・様式を把握する目的で, 関東地方に見られる木本種30種類について, 葉からの水抽出液と工タノール抽出液を用いた, レタスを検定植物とする発芽・生育試験を行った。発芽開始時間, 発芽速度, 最終発芽率, 幼根・胚軸の伸長量を求め, 種間比較を行った。いずれの樹種でも発芽速度の低下と幼根の伸長阻害が見られた。陽樹であるアカマツ・クロマツ・イイギリ・エゴノキは水抽出液, エタノール抽出液のいずれについても顕著な他感作用を示すことから, 他感作用物質を持つと考えられる。このような他感作用物質を持つ樹種を緑地へ植栽することによる, 雑草の発生や生育の抑制が期待される。

The relation between the population of the earthworm and types of vegetation or soil environment.

土壌改良資材として注目されているミミズに関する基礎的知見を得るために，植生の違いとミミズの生態の関係について調査した。様々な植生タイプの調査地で約1年間，ミミズの個体数を調査した。ヒノキやマツ由来のリターの多い調査地ではミミズはほとんど生息せず，スギや落葉広葉樹由来のリターが多い調査地では多くのミミズが生息していた。また，常緑樹の調査地では越冬しやすく，落葉樹や草本の調査地では越冬しにくいと推察された。同調査地の土壌性質の分析の結果，ミミズの少ない調査地土壌の交換性Ca含量が少ないことがわかった。また，ミミズの数と微生物活性および糸状菌数との間にトレードオフの関係が見られた。

The Efficiency of Forest Surface Soil Originated in Volcanic Ash as Planting Ground

火山灰起源の森林表土の植栽基盤としての有効性について検討するため, 比較的浅い表土 (表土 (浅)), 比較的深い表土 (表土 (深)), 心土, 比較的浅い表土と心土の混合土壌, 施肥した心土 (施肥土) で土壌の化学性と植栽された苗木の生育を比較した。施肥土の無機態窒素含有量と電気伝導度は施肥直後には他の土壌を上回ったが, 急激に減少し, 3ケ月後には他の土壌と同等になった。施肥土の苗木は1年目にはその他の土壌より良好に生育したが, 2年目にはほとんど生育しなかった。表土 (深) の苗木の生育は表土 (浅) よりも劣り, 心土とほぼ同等であった。表土 (浅) での苗木の葉の高い光合成速度と比較的低い呼吸速度が苗木の安定的な生育の原因と推察された。

The Effects of Mixing of Trzfolium repens and Cutting Height on Soil Chemistry and Vegetation Growth in Zoysia Turf.

芝生地へのシロツメクサの混植による粗放的管理方法について検討するために, ノシバのみで造成された芝生地と, ノシバとシロツメクサを混植した芝生地において, 刈り高を2.5cmと5.0cmの2段階に設定し, 土壌中の無機態窒素量, 土壌酸度, 刈り込み後のノシバ, シロツメクサの再生量と雑草の発生量を調査した。調査期間は1998年7月から10月である。シロツメクサの混植によって土壌中の無機態窒素量は増加した。土壌pH (H2O) はいずれの調査区でも6.0-6.8であった。刈り高2.5cm区では, ノシバ・シロツメクサ混植区のノシバの再生量は, ノシバ単植区よりも少なかった。刈り高5.0cm区では, ノシバ・シロツメクサ混植区のノシバの再生量がノシバ単植区よりも多かった。ノシバ・シロツメクサ混植区のシロツメクサの再生量は刈り高5.0cm区では一定に保たれたが, 刈り高2.5cm区では減少し続けた。雑草発生量は全植生の再生量の1割以下であり, 刈り高2.5cm区よりも刈り高5.0cm区で少なかった。以上の結果から, ノシバによる芝生地では, シロツメクサを混植し, 刈り高を5.0cm程度にすることでシロツメクサの施肥効果を維持しながら, 雑草の発生もある程度抑制できるといえよう。

Effects of Rainfall through the Canopy of Shrub on the Ion Supply to Soil

中低木植栽を通過した降雨が土壌へのイオン供給に及ぼす影響を明らかにするために, 降雨の樹冠通過に伴う水量と水質の変化を1998年5月から10月にかけて調査した。多くの場合, 降雨は樹冠によって40%以上遮断された。樹冠通過雨のpHは林外雨よりも高かった。降雨のイオン濃度は植栽の樹高が高いほど上昇し, 降雨量が多いと低下する傾向にあった。H+, アルカリ度, 無機態窒素を除くイオン濃度は樹冠通過によって上昇した。降雨によるK+, Ca2+, Mg2+, Cl-供給量は植栽によって2～5倍に増加した。ほとんどの場合, これらのイオンの70%以上が植物からの溶脱に由来していた。一部の植栽では無機態窒素とSO42- の葉面吸収の可能性が考えられた。

The Analysis of the Factor of Trail Erosion with Special Reference to the Trail-side Vegetation in Tanzawa Mountains

神奈川県の丹沢山地において, 周辺植生と登山道荒廃の程度等との関係について調査を行った。その結果, 傾斜度や登山道周辺植生の低木・草本層の違い, あるいは土性の違いによって, 侵食量・侵食幅・侵食深といった登山道荒廃の程度等に明らかな差異が認められた。特に, 草本層の植被率が低い所やイネ科の草地内など, 周辺植生の表土中に太い根が少なく, 植被率や植生高が低く人が脇にそれやすい地点では, 登山道幅の拡大が顕著にみられた。また, 登山道内の土性が, 透水性が悪く侵食されやすい壌土の地点では, 侵食深が拡大する傾向がみられた。逆に, ササ類が密に生育し, 表土中の太い根の量が多い地点では, 侵食幅の拡大はほとんどみられず, また透水性の良い砂壌土の地点では比較的侵食深の拡大は抑えられていた。