Report from the Sub-comittee on the environment and health

Repeated spraying changes
<strong>the</strong> flora
Spray drift
Herbicides and nutrients
change <strong>the</strong> flora
Reestablishment of <strong>the</strong>
flora is difficult
5.2 Effect on <strong>the</strong> flora in cultivated and uncultivated
terrestrial ecosystems
Trials have shown that repeated and effective spraying of herbicides year
after year reduces <strong>the</strong> number of wild plants in cultivated areas. In semicultivated
areas, herbicides have been applied occasionally – usually in
<strong>the</strong> form of products against dicotyledonous species with a view to
promoting grass species and increasing <strong>the</strong> fodder value of grazing/hay
production. Artificial fertiliser has also often been applied to increase
fodder production on <strong>the</strong> area. This has also been done on land with
section 3 status under <strong>the</strong> Nature Protection Act, which does not fully
protect against adverse effects of <strong>the</strong> use of herbicides and fertilisers
since <strong>the</strong> law simply “freezes” existing practice.
During spraying, <strong>the</strong>re is spray drift to <strong>the</strong> surrounding areas, although
this can be reduced with modern spraying equipment. 10-20 years ago,
direct herbicide-spraying with an end nozzle on <strong>the</strong> spray boom was
recommended and practised in many places. Spray drift in connection
with normal use of herbicides is a particular problem for edge biotopes
because of <strong>the</strong>ir relatively large edge area in relation to <strong>the</strong> total area. For
<strong>the</strong> same reason, most of <strong>the</strong> small biotopes bordering on rotation fields
are seriously affected by eutrophication, caused particularly by artificial
fertiliser spread centrifugally on adjacent fields.
As a result of <strong>the</strong> widespread load of herbicides and nutrients, <strong>the</strong>
composition of <strong>the</strong> vegetation in <strong>the</strong>se types of biotope has developed
towards high-growing grass and herbaceous vegetation with low species
content and completely dominated by such species as great nettle, wild
chervil, common couch grass, cocksfoot grass, tall meadow oat, corn
thistle, grey magwort and goosegrass. These species tolerate most
herbicides relatively well and can use <strong>the</strong> ample supply of nutrients for
rapid and high growth, <strong>the</strong>reby shading out most competitors. In such
disturbed biotopes, one typically finds increased plant production and
plant biomass per unit of area. In all, <strong>the</strong>re are thus fewer species and less
locally and regionally characteristic vegetation, while species with high
nutritional requirements predominate.
In work on reinstatement of <strong>the</strong> natural environment, it has been
considered whe<strong>the</strong>r <strong>the</strong> original but lost natural values can be recreated
by blocking <strong>the</strong> negative, direct and indirect input of herbicides and
fertilisers. Experience with this is disappointing – in practice, <strong>the</strong>re is
substantial ‘ecological inertia’ acting against reversion to former types of
vegetation, mainly due to two factors:
• A tendency towards long-term maintenance of <strong>the</strong> high-level nutrient
status of <strong>the</strong> biotopes in almost every type of soil except <strong>the</strong> most
sandy and dry. This maintains <strong>the</strong> competitive high-growing type of
vegetation, which effectively prevents remigration of original species.
• The species’ poor and often short-lived seed pool and poor dispersal
abilities make reestablishment difficult. There are usually big
distances, few and poor dispersal paths or actual barriers to dispersal,
all working against remigration.
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