Report from the Sub-comittee on the environment and health

The importance of <strong>the</strong>
+scenario for <strong>the</strong> seed
pool and plant density
Impacts on <strong>the</strong> wild flora
in hedgerows and small
biotopes
The wild flora in natural
areas
In <strong>the</strong> +scenario, both <strong>the</strong> herbicide dosage and <strong>the</strong> treatment frequency
index would probably be somewhat reduced compared with present good
farming practice. At <strong>the</strong> same time, increased use of mechanical weed
control would partially compensate for <strong>the</strong> reduced effectiveness of <strong>the</strong>
chemical control. On average, <strong>the</strong> consequence would probably be, at
most, a 10-20% larger total seed pool than in present production.
Spray drift of herbicides affects <strong>the</strong> flora in biotopes close to <strong>the</strong> field,
such as hedges, field borders and ditches, and along watercourses and
ponds. Within a few metres of <strong>the</strong> edges of <strong>the</strong> field, lethal effects can be
observed in a number of plant species. The dose and thus <strong>the</strong> effect
normally decrease rapidly with distance <strong>from</strong> <strong>the</strong> field, which means that
only sub-lethal effects on plant growth and seed production are normally
seen outside <strong>the</strong> local zone around <strong>the</strong> field. The magnitude of <strong>the</strong> effect
depends on <strong>the</strong> sensitivity of <strong>the</strong> plant species, <strong>the</strong> composition of <strong>the</strong>
plant community and <strong>the</strong> condition of <strong>the</strong> vegetation. Several studies
have shown effects of spray drift over a distance of up to 50 metres <strong>from</strong>
<strong>the</strong> sprayed area (Marrs et al., 1989, 1993; Davis et al., 1993, 1994).
However, most of <strong>the</strong> flora were only affected in an area between 0 and 5
m <strong>from</strong> <strong>the</strong> field. However, <strong>the</strong>re is a lack of experimental data on effects
of herbicides in low doses on wild plant species, and <strong>the</strong> extent of spray
drift and its effect on wild flora have not been systematically studied in
Denmark. Both <strong>the</strong> 0-scenario and <strong>the</strong> +scenario would reduce <strong>the</strong>
consumption of herbicides and thus <strong>the</strong> risk of spray drift to land close to
<strong>the</strong> field. This would considerably reduce <strong>the</strong> load, whe<strong>the</strong>r spraying was
discontinued altoge<strong>the</strong>r or was only carried out occasionally. However,
owing to <strong>the</strong> lack of data, it is not possible to quantify <strong>the</strong> beneficial
effect on <strong>the</strong> vegetation. The areas affected would be reduced in step
with <strong>the</strong> herbicide consumption. In <strong>the</strong> 0+scenario, <strong>the</strong> impact would be
reduced to <strong>the</strong> few localities in which pesticides were still used. In <strong>the</strong> 0scenario,
<strong>the</strong>re would no longer be any impact on <strong>the</strong> neighbouring areas.
Besides being affected by herbicides, areas close to <strong>the</strong> field are normally
seriously affected by nutrients supplied <strong>from</strong> <strong>the</strong> field, which contribute
to a change in <strong>the</strong> composition of <strong>the</strong> flora towards a greater content of
grasses and <strong>the</strong> loss of annual and sensitive perennial herbaceous plants.
The established, nutrient-demanding vegetation of species of grass and
tall perennials, such as creeping thistle, common nettle and cow-parsley,
counteracts immigration of o<strong>the</strong>r species. Species with short-lived seeds,
such as cornflower, anemone and scabious, often die out, making
reestablishment <strong>from</strong> <strong>the</strong> seed pool impossible. All in all, this means that,
in many places, a reduced herbicide load on <strong>the</strong> neighbouring areas
would not result directly in changes in <strong>the</strong> plant communities in <strong>the</strong>
direction of greater diversity unless <strong>the</strong>re were a significantly reduced
supply of nutrients and, at <strong>the</strong> same time, physical measures, such as
mowing and thinning, which open <strong>the</strong> vegetation to invasion <strong>from</strong>
outside or to germination of seeds in <strong>the</strong> seed pool.
The diffuse dispersal of herbicides <strong>from</strong> cultivated land must generally
be regarded as having little effect on <strong>the</strong> flora in natural areas except
where <strong>the</strong>se are directly adjacent to cultivated land. Reduced use of
herbicides on cultivated land would <strong>the</strong>refore have little effect on <strong>the</strong>
composition of <strong>the</strong> flora, which depends to a far greater extent on <strong>the</strong>
management of <strong>the</strong> area and <strong>the</strong> supply of nutrients. There are a few
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