Residence time determines the distribution of alien plants - Invasive Plants: Ecological and Agricultural Aspects - page 73

cessfully through the stage of casual occurrence and become naturalized, and
2) to become more distributed and invade over a larger range. The former is
documented by higher mean MRT found in naturalized than in casual species
(see also [25]), the latter by a significant positive relationships between meas-
ures of invasive species distribution and MRT.
In Europe, the effect of residence time is still obvious after several millen-
nia of plant invasions. Not surprisingly, it is less pronounced in archaeophytes
than in neophytes but statistically detectable, even though the data used to
reconstruct the history of invasions on a time scale of millennia must be nec-
essarily less precise and more biased than reconstructions based on herbaria
and published records that are available for neophytes.
Can we compare the effect of residence time between these two distinct
groups of European alien species, i.e., archaeophytes and neophytes (histori-
cal invaders versus recent newcomers)? Simple comparison along the lines of
the present paper would suggest investigation of the current distribution of
both groups. That archaeophytes are more common than neophytes has been
repeatedly documented using the Czech flora [29, 55] and the same can be
shown for Great Britain. Number of quadrats (hectads) from which the spe-
cies is reported from the period 1987-1999 in Preston et al. [36] is signifi-
cantly higher (F = 173.3; df = 1, 1751; P < 0.001) for archaeophytes (as clas-
sified in Preston et al. [37], n = 231) than for neophytes (n = 836). However,
this pattern cannot be interpreted as a consequence of different residence
times only. Archaeophytes, mostly weeds of arable land recruited from the
Mediterranean area, represent an ecologically distinct group with specific fea-
tures and differ from neophytes in many respects: life form and strategy and
habitat requirements in particular [55]. That they are more common than neo-
phytes is certainly, at least in part, associated with their long-term presence in
invaded regions - there is no reason to expect that the principles valid for
archaeophytes and neophytes separately, on two different time scales, do not
apply for the entire history of plant invasions in Europe. However, given the
pronounced difference in habitat affinities of both groups, to decouple the
effect that residence time might have had on archaeophytes and neophytes
from other factors, both groups should be compared in a habitat where their
occurrence overlaps, i.e., arable land. Such analysis is available and shows
that the historical associations are very subtle, yet clearly detectable at pres-
ent: Pyˇek et al. [43] found that archaeophytes are common in old crops intro-
duced with the beginning of agriculture, such as cereals, but poorly represent-
ed in relatively recently introduced crops (rape, maize), where neophytes are
most numerous. These patterns reflect the history of plant invasions in Central
Europe. Neolithic agriculture, introduced from the Near East in the 6th mil-
lennium BC, brought archaeophytes with crops and, by creating intense and
continuous propagule pressure and imposing new agricultural management,
facilitated their invasion. By contrast, the crops introduced during the past five
centuries and their specific agrotechnical management has supported spread-
ing of other weed species, mainly invaders from overseas. In addition,