English to Japanese Science Environment & Ecology Urban ecology

Spontaneous vegetation: "...defined as all plants that develop without intentional horticultural input, is a characteristic element of the urban environment. It grows at no financial cost, is authentic and is always appropriate to site conditions.” (Kühn, N. "Intentions for the Unintentional: Spontaneous Vegetation as the Basis for Innovative Planting Design in Urban Areas", 2006), “the de facto native vegetation of the city.” (Del Tredici, P. "Wild urban plants of the northeast", 2010).

Essentially all vegetation that grows in vacant lots, brownfields, cracks in the pavement and on brick walls and buildings.
So far the only reasonable thing I've come up with is
a) 自発的植生, found at http://zouen.yu-yake.com/ji/jihatutekisyokusei.html and http://www.airies.or.jp/publication/earth/pdf/12_1-09.pdf or
b) 自然発生植生 as found in http://jglobal.jst.go.jp/public/20090422/200902233370452187

The context is obviously academic, the term has been used a lot in (urban) ecology but is also found in urban environmental geography. My aim is not only to find a good translation but also use the Japanese term(s) for a literature review.

Thanks for your help!