Download Biodiversity on Nafferton Farm There are three principal influences

Biodiversity on Nafferton Farm
There are three principal influences affecting biodiversity on Nafferton Farm:1) Length of time of crop growth and cover
2) The organic half has greater crop diversity and the extra crops are dicotyledons
3) Weeds are not generally present in the conventional crops
Invertebrates
In general there is far more invertebrate activity in organic fields than in conventional but
the difference is the activity on the crop and weeds, not on the soil-surface. The mixture of
crop diversity and weeds in organic fields provides habitat for a number of plant-eating
invertebrate groups and for their predators and parasites. Organic grass/clover has a more
diverse invertebrate fauna than conventional grass.
Conventional oilseed rape has a lot more invertebrates than conventional cereals.
The number of invertebrates are influenced specifically by the following:1) Length of time of crop growth and cover:
Conventional arable crops (winter wheat, winter barley, oilseed rape) are sown in autumn
and provide cover throughout winter.
Organic arable crops (spring wheat, spring barley undersown with grass/clover, spring
beans, potatoes, other vegetables such as swede or leek) are spring sown so that fields
have no cover in spring, generally until the end of May.
2) The organic half has greater crop diversity (see above) and the extra crops are
dicotyledons:
Dicotyledons have a lot more invertebrates than cereals, and oilseed rape has many more
invertebrates than cereals. Beans and Brassicas are dicotyledons, which increase the
number of insects such as flea beetles (Chrysomelidae), weevils (Curculionidae) and leaf
beetles (Chrysomelidae), which then leads to an increase in groups such as parasitic wasps
(Hymenoptera).
3) Weeds are not generally present in the conventional crops:
Weeds such as charlock (wild mustard), fathen and knotweed have their own invertebrates
and the flowers of charlock (and oilseed rape) attract parasitic wasps and hoverflies.
How management differences affect invertebrate groups:
Ground beetles (Carabidae).
Crop type is a principal influence on the collection of different types of ground beetles in a
field.
The other difference is that small beetles prefer open, bare ground with limited vegetation
whilst larger species need more vegetation cover. Therefore, smaller species are much
more abundant on the organic arable than on conventional, which are dominated by larger
species, especially Pterostichus melanarius.
However, all ground beetle species are very active and most fly. Therefore, most species
occur on both sides of the farm and there is little difference in species richness between
the two halves of the farm.
Rove beetles (Staphylinidae).
These are even more active than ground beetles, they all fly. Again distribution is affected
by management, with a lot more small species on organic arable fields. However, they are
greatly affected by productivity and generally there are more in conventional arable than
organic but there is probably more species in arable.
Ladybirds (Coccinellidae).
The distribution of ladybirds on the farm is affected by migration; in 2006 and 2010
considerable numbers came in from the east. However, nearly all ladybirds are found in
the organic fields; they generally like weedy fields.
Flea and leaf beetles (Chrysomelidae) and weevils (Curculionidae).
Species of these groups are phytophagous and feed on both crops and weeds and
therefore are far more abundant on the organic crops. However, oilseed rape has a
number of species of both groups.
Soldier beetles (Cantharidae) and lacewings (Neuroptera).
Both these natural enemies prefer weedy fields and are far more abundant on organic
fields.
Hoverflies (Syrphidae).
Generally influenced by nectar sources, these flies are most abundant in organic fields with
flowering weeds.
Parasitic wasps (Hymenoptera : Parasitica).
A group influenced by both food sources, of which aphids are a major part, and by being
attracted to flowers.
They are most abundant on the conventional half on oilseed rape and on the organic half
in fields with flowering weeds.
Sawflies (Hymenoptera : Symphyla).
These phytophagous insects are more abundant in the organic fields where plant diversity
is higher.
Spiders (Araneae).
Money spiders (Linyphiidae) generally prefer grassy vegetation and are more abundant in
the denser conventional cereals than in the open organic.
However, wolf spiders (Lycosidae) and other web spinning spiders are more abundant in
organic fields.
Birds
The main management effects are on wintering birds.
The presence of stubble, especially wheat and bean, on the organic half of the farm helps
seed eating birds such as linnet, skylark and stock dove, with far more activity on the
organic fields compared to conventional. On the conventional half, oilseed rape is used by
far more birds than cereals. Organic grass/clover is preferred by a number of species, such
as blackbird and chaffinch, to conventional grass.
Non-crop habitat is also important for birds. Fields with margins of tall herbaceous
vegetation, usually with thistles, nettles and tall grasses, are used more by seed-eating
birds than fields with tall hedges and woodland. There are some species preferring
woodland edges, e.g. woodpigeons and crows.
The change from conventional to organic management appears to have benefited about 25
bird species.
Species preferring organic stubble to cereals include linnet, skylark, stock dove, grey
partridge, yellowhammer, reed bunting, goldfinch, pied wagtail and mistle thrush and soilinvertebrate feeders rook and jackdaw.
Species preferring grass/clover to grass include blackbird, chaffinch, meadow pipit, blue
tit, dunnock and redwing.
Woodpigeons are most active in oilseed rape fields.