POLLINATORS POLLINATION AND FOOD PRODUCTION

THE ASSESSMENT REPORT ON POLLINATORS, POLLINATION AND FOOD PRODUCTION
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2. DRIVERS OF CHANGE OF POLLINATORS,
POLLINATION NETWORKS AND POLLINATION
2013; Kremen and Miles, 2012; Nicholls and Altieri, 2013;
for definitions and more details see the glossary). A large
meta-analysis found that more than 70% higher total bee
abundance and 50% higher total species richness of
wild bees could result from diversified farming systems
(Kennedy et al., 2013). Such differences were found for
Mediterranean and temperate regions, with benefits being
less accentuated in the tropics (Kennedy et al., 2013).
Increased numbers of wild pollinators in organic fields was
shown to correlate strongly with pollination success; for
example, a study on canola seed set in Canada revealed
3 to 6 times lower seed set on conventional and GMO
canola fields using insecticides and herbicides than on
organic sites of similar field size (Morandin and Winston,
2005). Strawberry (Fragaria × ananassa) pollination was
found to be higher at farms 2-4 years after conversion to
organic farming (Andersson et al., 2012) (see more details
in Chapter 6).
Effectiveness of organic management depends on the
landscape context, the crop type, the management of
the organic farms, soil conservation and the species
considered (Arnhold et al., 2014; Brittain et al., 2010).
Effects of local-scale conditions such as diversity in crops
and management type may strongly interact in managed
fields. Meta-analyses by Kennedy et al. (2013) found
that both field-scale diversity and organic farming have
distinct, positive impacts on wild bee abundance. Results
suggested that higher vegetation diversity in conventional
crop fields may increase pollinator abundance to the same
extent as organically managed fields with low vegetation
diversity (see also Winfree et al., 2008). However, organic
management might produce richer bee communities than
conventional management independently from the level of
field diversification (Kennedy et al., 2013). Characteristics
of agricultural disturbance may not always be mitigated
by organic management, depending on the underlying
mechanisms affecting pollinator populations (e.g., Forrest et
al. (2015) found differences in diversity, but not in functional
diversity of bees comparing organic and conventional fields,
which functional diversity was lower in both farm types than
in natural land cover types).
At the field scale organic management can enhance both
continuity of wild plant distribution and flowering, providing
continuous flower resources for pollinators. Rollin et al.
(2013) and Sarthou et al. (2013) have demonstrated that
in entomophilous crops where flower resources are very
important but of short duration, wild flower diversity in
the field (i.e. weeds with flowers) is more important for
favouring diversity of wild bees, and is promoted by organic
farming. Therefore insect-pollinated plants might occur
more evenly in organic fields and receive disproportionately
higher pollination benefit from organic farming due to higher
pollinator densities (Gabriel and Tscharntke, 2007).
Benefits for biodiversity can be observed on organic farms
at both farm and landscape scales; for example, greater
bee, hoverfly and butterfly diversity was found in landscapes
with a larger proportion of organic fields (Holzschuh et al.,
2008; Gabriel et al., 2013; Rundlöf et al., 2008). Nonintensive
field management using less chemicals and/
or having more diversified farming system, e.g., organic
farming, has positive effects more often in homogeneous
rather than heterogeneous landscapes (Rundlöf and Smith,
2006; Tuck et al., 2014), however isolated organic farms
may not provide any measurable benefit to local populations
of pollinators and pollination (Brittain et al., 2010). Moreover
a recent study argues that observed differences in
biodiversity between organic and conventional fields may
be explained by greater cost-effectiveness of conservation
efforts in low-productivity agricultural systems or on nonagricultural
land, rather than organic management per se
(Gabriel et al., 2013). However, Lüscher et al. (2014) showed
a strong influence of local organic agricultural management
on wild bees and a minor and inconsistent effect of the
surrounding landscape, after accounting for the effect of
geographic location. There might also be interacting effects
of farming system and landscape heterogeneity on pollinator
community composition and pollinator trait diversity.
Decreasing landscape heterogeneity resulted in overall
decline of species richness of hoverflies and wild bees,
while taxonomic breadth only declined on conventionally
managed farms (Andersson et al., 2013).
Not all studies found increased pollinator species richness/
abundance or increased diversity of plants on organic
farms. On 205 farms in Europe and Africa, Schneider et al.
(2014) found that at farm scale, the diversity of bees was
affected by the presence of non-productive land cover
types rather than by the farming system (organic or not).
Moreover, management type (organic vs. conventional) does
not always match with plant or crop diversity. Conventional
farms can be as diverse as organic ones (e.g., in Sweden –
Andersson et al., 2005), while there are very large organic
monocultures too (e.g., in South Africa – see Carvalheiro
et al., 2012). In Europe, great differences exist in the
implementation of organic farming or diversified agricultural
management methods among EU-countries, resulting in a
wide span of landscapes ranging from less intensively used
and heterogeneous landscapes on the one hand to highly
productive and monotonous landscapes on the other hand
(Kleijn et al., 2006). Overall, there is a need for more careful
experimental design to separate clearly the type of impacts
that occur from organic and conventional agriculture
(Roulston and Goodell, 2011).
Nevertheless, we can conclude that the creation or
maintenance of more diverse agricultural landscapes may
result in more diverse pollinator communities and enhanced
crop and wild plant pollination. Local diversification
and reduced intensity of land management will support