Diversifying crop rotations with temporary grasslands - Université de ...

2000). The majority of arable weeds are annual species (therophytes, Raunkiær, 1905) that
survive the unfavourable season and the yearly soil tillage in arable fields as seeds. However,
weeds may also show strong differences in their ecological niches defined by the
requirements for light and nutrients, the tolerance to competition and to physical and chemical
disturbances. Several species are mainly found in certain crop types, soil types and climatic
conditions (specialists) while others are rather generalists.
Distribution and status:
Today, a quite high number of weed species is found in various regions in temperate climates
all around the world. Some species show increasing population dynamics and expanding
geographical areas (‘invasive species’) while others are decreasing and locally or globally
threatened to extinction and therefore included in Red Lists (Sutcliffe and Kay, 2000). Note
that both categories may include ‘native’ and ‘exotic’ species (see ‘Origin’)!
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