Læs hele rapporten som pdf-fil. - Naturrådet

NATURRÅDET / TEMARAPPORT / NATUR OG LANDBRUG
70
Landscapes and biodiversity
Historically, agriculture created a patchwork of
habitats that is richer in biodiv e r s i ty than the original
natural landscape in Europe. Over centuries
the number of plant species increased as the natural
mixed deciduous woodland landscapes were
opened up and became more diverse through
human intervention. In recent decades, how e v e r ,
agricultural land use has become more and more
intensive and is now one of the main causes for
an increasingly rapid extinction of plant and animal
species. In many parts of Europe more than
a third, in some areas even over half of all know n
species are either already extinct or at serious risk
(ECNC 1999). This dramatic loss in Eu r o p e a n
biodiversity is due to the elimination of and the
i n t e r ference with not only natural, but also with
semi-natural habitats and biotopes, many of which
have been in agricultural use for centuries.
Agricultural structural changes resulted both in a
loss of sites and structural elements of the
European countryside, as well as in changes in the
water and nutrient regime of its ecosy s t e m s .
Traditional, low-input farming systems, on which
many wild plant and animal communities are
crucially depended, are often no longer economically
viable and have been abandoned. In
Germany, almost 700 of the approximately 2700
vascular plant species have to be considered threatened.
Agriculture has been involved in more
than 500 cases where the causes for decline have
been identified. On the other hand, nature cons
e r vation cannot succeed without fa r m i n g
( Bundesamt für Naturschutz 1996). For exa m p l e ,
studies have shown that more than 80% of the
rare and declining bird species in Europe rely
on agricultural land, in particular extensiv e l y
managed grasslands (Figure 4).
Visible and invisible changes
Agriculture has been responsible for a variety of
c h a n ges, which have contributed to species
decline. There are obvious changes in the landscape
in areas where hedges have been removed
or where drainage has taken place, or where
land consolidation has created a more uniform
farming landscape. Also changes in traditional
farming systems, like wood pastures in the Spanish
dehesas, or the replacement of old olive groves
and orchards by modern plantations, have an
enormous influence on species div e r s i ty (Ba l d o c k
1990, v. Meyer 1993). These are examples of
the more visible changes, but probably much
more significant are the invisible changes such as
pollution or eutrophication of habitats and biotopes.
Such processes cannot be perceived directly,
but they fundamentally alter the nutrient conditions
and ecological balances of large areas. Most
European plant species are associated with nitrogen-poor
environments. However, the trend in
agricultural farming systems has been towards
intensification, thus increasing the nutrient input
to those habitats. The result is that threatened species
are mostly those that depend on low - n u t r i e n t
biotopes, and this is true for various kinds of
habitats (Ellenberg 1989).
Eutrophication of arable land
Eutrophication is clearly one of the main causes
for species decline. In the EU Member States,
since 1950 average application rates of mineral
nitrogen fertilizer increased fourfold from less
than 25 kilogrammes of nitrogen per hectare
(kgN/ha) to over 100 kgN/ha today. These figures,
however, relate only to the average national
application rate of mineral fertiliser. What matters,
however, is total nutrient input, including in
particular animal manure, and the surplus of
regional nitrogen balances. German studies show
that for the whole of West Germany the total
n i t r o gen input from mineral fertilizer and animal
manure increased from about 25 kgN/ha to
more than 150 kgN/ha since 1950. Over the
same period nitrogen withdrawal through harvested
crops increased only from about 20
kgN/ha to 40 kgN/ha. This means that the nitrogen
surplus emitted annually from the agricultural
system increased twenty-twofold from 5 to 110
kgN/ha (Köster & Severin 1988). Similar figures
have been calculated for other countries, and
regional “hot spots” show even much higher surpluses.