Report from the Sub-comittee on the environment and health

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plant communities, <strong>the</strong> effects of mechlorprop have been investigated in
concentrations corresponding to those found in rainwater. The study
covers sensitive species – particularly <strong>the</strong> crucifers – but no effects have
been found (Solveig Mathiassen, DIAS, personal communication). One
can assess possible effects by combining data for <strong>the</strong> deposition of
pesticides with effect data.
5.2.1 Conclusions
Toge<strong>the</strong>r with crop rotation and o<strong>the</strong>r cultivation measures, <strong>the</strong> use of
herbicides has considerably reduced <strong>the</strong> flora in farmland under
cultivation. Accidental spray drift can have adverse effects on plants in
hedgerows and small biotopes. In particular circumstances, herbicides in
rainwater can presumably cause damage to plants outside <strong>the</strong> cultivated
area.
The following specific conclusions can be drawn:
• The number and frequency of plant species in an average field have
halved in <strong>the</strong> last 20-25 years. From an agricultural point of view, this
has been a desirable development, but it has adverse consequences for
<strong>the</strong> natural species. The main reason for <strong>the</strong> decline is <strong>the</strong> use of
herbicides, but changes in cultivation practice have also had a major
effect.
• Herbicide drift can affect <strong>the</strong> flora in hedgerows, small biotopes and
nature areas.
• In Denmark, pesticides have been detected in rainwater, but effects in
plants have not yet been detected. However, American studies have
shown that even small doses of some herbicides can harm particular
plant species. The studies in question are limited in numbers and
cover only a few pesticides.
• There is a lack of systematic studies of how pesticides in large,
connected areas affect wild plants and associated animals in
hedgerows, ditches and o<strong>the</strong>r small biotopes, and neighbouring nature
areas.
• The impact on <strong>the</strong> flora caused by long-distance transport and
deposition of herbicides in Denmark is not known. We know <strong>from</strong> a
Dutch study that effects are probable, but studies of both <strong>the</strong> effects
and <strong>the</strong> atmospheric transport are needed in order to determine <strong>the</strong>m
more exactly.
• There is also a lack of specific studies of <strong>the</strong> effect of herbicide use on
ground flora in forests, but <strong>the</strong>re is no doubt that even <strong>the</strong> limited use
of herbicides in forestry has a great and adverse effect on <strong>the</strong> original
ground flora. Many woodland plant species have a very slow
recolonisation rate (0-1 metre per year), which makes <strong>the</strong>m very
sensitive to herbicides, even if herbicides are used only in connection
with clear cutting and establishment.
• There have been no systematic studies of <strong>the</strong> combined effect of
fertilisers, pesticides and crop rotation on <strong>the</strong> flora in areas near fields.