(Ma 2006). In the most connected landscape,dispers-
al effectsseemed most important and resulted in a
lower regional diversity and more similar local
communities, associated with the dominance of a
number of competitive species which were argued
to disperse more easily in this landscape. In the
least connected landscape, species such as dande-
lions (Taraxacumspp.) andAegopodium podagraria
were more common, supporting the view that frag-
mentation of habitats may result in local commu-
nities being more dominated by weedier species
with high dispersal ability. The landscape with in-
termediate connectivity had the highest regional
diversity, resulting in the predicted hump-shaped
pattern of regional diversity in relation to connec-
tivity (see Fig. 9.2c).
Our results showing that organic farming had no
effect on diversity were at odds with generally held
notions, and also with the majority of other studies
(analysed by Bengtssonet al. 2005). Why was Sweden
different? The large variation in effect size among
studies in the literature, coupled with closer inspec-
tion of individual results, suggested that the effect of
farming system might be larger in more intensively
managed and more homogeneous landscapes than
in small-scaled mosaic landscapes with many semi-
natural habitats. This is in essence a test of the hy-
pothesis that at low dispersal the importance of local
sorting increases, while at intermediate dispersal the
landscape is more important (see above). If this is
true, an interaction between landscape and farming
system is expected in studies conducted along a suf-
ficiently long gradient of landscape heterogeneity.
Exactly this was found independently in southern
Sweden for butterflies (Rundlo ̈f and Smith 2006)
and bees (Rundlo ̈f 2007), and in central Germany
for arable weeds (Roschewitzet al. 2005) and bees
(Holzschuhet al. 2007). Such results are highly infor-
mative from a basic metacommunity perspective, but
if they are common they also pose problems when
implementing ameliorative measures such as agri-
environmental schemes: Should organic farming be
encouraged only in homogeneous and intensively
managed landscapes which have lower regional di-
versity, because this is where the largest gains in
diversity can be achieved?
In fact this may not be the case. The highest biodi-
versity is usually found in heterogeneous land-
scapes, but this is also where farming is presently
less profitable and farmland risks being abandoned
with current policies. Any scheme that results
in continued farming in these areas will counter
decreases in biodiversity and also have other socio-
economic benefits, and organic farming is one
such scheme. In the most homogeneous landscapes,
the increase in landscape quality that organic farm-
ing entails will mainly favour a few generalistic
species that are quite common in other parts of
the human-dominated landscape, such as villages
and urban areas. The fact that the effect appears
large is that the most intensively used land-
scapes are so extremely depauperated that any in-
crease in diversity will appear substantial. For
example, in many agricultural areas in The Nether-
lands, regional bumble bee diversity is in essence
only four species (Kleijn and Langevelde 2006),
whereas more than 10 species are regularly found
in agricultural and urban areas in southern and cen-
tral Sweden (Rundlo ̈f2007;Anderssonet al.2007;
J. Risberg, J. Bengtsson and B. Cederberg, unpub-
lished data).
In addition, there appears to be a positive effect
of the amount of organic farming in the landscape.
Rundlo ̈fet al. (2008) found that for butterflies there
was a higher local diversity in landscapes with a
high proportion of organic farming within a 1 km
radius, irrespective of farming system. This indi-
cates that, along these long gradients from homo-
geneous to mosaic landscapes, the landscape effect
on diversity can be substantial.
An important message for managers emerging
from these studies is that landscape effects on di-
versity or species composition of plants and insects
often may be found on the scale of management, in
agricultural landscapes usually individual farms.
In our studies in Sweden, landscape variables
measured at the 25 km^2 scale were not significant,
whereas heterogeneity at the farm and multiple-
field scales was (approx. 0.52km^2 ) (Weibullet al.
2000). This means that the choices of individual
landowners often can have a large influence on
diversity, and identifies the farmers as important
decision-makers for conservation. However, there
may be more immediate gains for farmers manag-
ing their land for higher diversity, to which we will
now turn.126 APPLICATIONS