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

genetically modified crop varieties e.g. with herbicide resistances. The selective control of
weed plants that are similar to the cultivated crop is most challenging, especially in the case
of monocultures and simple crop successions.
Aesthetics:
‘Weed’ plants may be perceived as aesthetically unattractive, which may be one reason for
classifying them as unwanted. On the other hand, several ‘weed’ species may also be
appreciated due to a ‘nice’ or interesting appearance and colourful flowers increasing the
attractiveness of agricultural landscapes. Moreover, other plants without special attractiveness
are generally not considered as weeds if they are growing in more natural habitats. The appeal
of a plant is thus also no good criterion to classify a species as a weed (‘One man’s flower is
another man’s weed’).
Origin:
A big number of the arable weed species currently found in Europe have been introduced
since longer or shorter times. This fact is reflected in one of the French words for weed,
‘ adventice’ that comes from the Latin ‘adventicius’, meaning ‘foreign’. Many weed species
probably originate form the steppes in the Persian region (south of the Caspian Sea) (as do
many cereal crops) and came to Europe since the development of agriculture about 7000 years
ago. These species are called ‘archaeophytes’ and include species such as Centaurea cyanus.
Archaeophytes may be distinguished from ‘neophytes’, which came to Europe after the 15th
century. Some weed species may also have their origins in Europe (‘native’ species or
‘apophytes’), living probably in rather small habitats with regular natural disturbances such as
river banks.
Ecological requirements and habitats:
Most arable weeds are characterized by fast growth and high reproductive output (big number
of small seeds or fast vegetative spread), that may quickly invade after disturbances.
Therefore, they may be called ‘ruderals’ or ‘r-selected’ species. This aspect is stressed by the
weed definition used by Baker (1974): ‘ a plant is a weed if, in any specified geographical
area, its populations grow entirely or predominantly in situations markedly disturbed by man
(without, of course, being deliberately cultivated plants)’. Most weeds are well adapted to
frequently disturbed habitats such as arable crops, gardens or construction sites, but some
species may also be found in more natural habitats ("facultative weeds", Sutcliffe and Kay,
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