要　旨　埼玉県幸手市内でのタンポポ分布調査によるタンポポ地図を作成するとともに，各種タンポポの 生育地の土壌条件（pH，電気伝導度，土壌硬度，A層の状態，土壌有機物量および土壌水分量）を測定した．タンポポの生育には土壌条件が深くかかわり，外来タンポポは在来タンポポより幅広い土壌適性域を有することがわかった．幸手市では1951年から1991年にかけて，水田地帯で大規模な土地改良事業が実施され，さらに農道が舗装化され　化学肥料も多量に使われるようになった．この結果，タンポポの群落が細分化されるとともに土壌環境が変化した．このようにして，本市は水田地帯でありながら，在来タンポポの生育に対する土壌環境は外来タンポポに対するよりはるかに悪化した．従って，在来タンポポの減少は都市化のみでなく，土地改良も大きな影響をもっていることが明らかになった．

キーワード：在来タンポポ，外来タンポポ，タンポポ地図，土壌

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Distribution of native and introduced dandelions, and the relationship between dandelions and soil condition in Satte-shi, Saitama.

Tadashi FUKUDA
Tokorozawa-Midorigaoka High School. 2-695-1 Mikajima, Tokorozawa-shi, Saitama 369-1164
Hiroshi HASEGAWA
3-19-23 Mihara, Asaka-shi, Saitama 351-0025
Etsuo OSAJI
Nerima-ku Board of Education. 6-12-1 Toyotamakita , Nerima-ku, Tokyo 176-0012

Abstract
　　The natural environment for the settlement of dandelions was studied in Satte-city, Saitama Prefecture. The distributions of both native and introduced dandelions were surveyed. The soil conditions (pH, electric conductivity, hardness, percentages of organic substances, water content and also state of A-layer) were measured at many points where dandelions settle.
　　It was proved that the settlement of dandelions was deeply affected by the soil conditions. Introduced dandelions can settle in wider range of soil conditions than native ones.
　　Since 1951 to 1991 the extensive re-adjustment of rice-field was performed in this city and the populations of dandelions became smaller.
　　Also the chemical fertilizer acculated, and roads in the rice-field were paved.
　　As the result, the soil conditions for the settlement of native dandelions have become severely worse than for the settlement of introduced ones.