Many studies comparing organic and conventional
farming were poorly designed. Large numbers of studies
had low numbers of replicates or failed to include in the
design factors other than farming system (see Appendices
1 and 2), for example landscape structure, soil type and
farm history. It is questionable whether studies performed
at the plot scale are relevant at all to the wider
question of whether organic farming enhances biodiversity.
The population dynamics of many organisms
operate at much larger scales than a few square metres.
We recommend that future studies focus on the socioeconomic
units at which decisions about farm management
are made, i.e. at the scale of single farms or larger.
Criteria for the selection or farms or fields to be studied
are important. If matched farm pairs are used there is
a risk of producing a reduced difference between the
farming practices. This is because it is difficult to match
organic farms to the most intensively managed conventional
farms in large-scale homogeneous landscapes.
Similarly, it may not be possible to match conventional
farms to the most varied organic farms in small-scale
landscapes. On the other hand, if average conventional
and organic farms are compared without taking the
landscape into account, any difference between the systems
can often be attributed to landscape differences
rather than farming system.