118
a. R. POTTS AND GI. P. VICKERMAN
were very numerous in winter wheat in 1970. Otherwise, insects, weeds
and diseases were generally controlled or were not thought to concern
the farming community.
The main reaction of farmers to the recent upsurge of diseases has
been (1) the use of more fungicides, and (2) the introduction of diseaseresistant varieties. An example of the former is that one agricultural
aircraft contractor sprayed 5000 ha with dithiocarbamates to control
yellow rust in one two-week period in 1972. The long-term ecological
effects of this are unknown.
Many new high-yielding and disease-resistant varieties have been
rapidly taken up by the farming community. Thus, the wheat Joss
Cambier accounted for 35% of the national winter wheat acreage in
1971/1972 and the spring barley Sultan accounted for 38% of the spring
barley crop in 1970. Both varieties had only been in use for about three
years. As with earlier varieties, however, their disease resistance has
soon broken down. But there are signs that the recent rapid swings in
and out of favour of varieties (Fig. 3) will eventually be replaced by
spatio-temporal mosaics of varieties. So far, however, there has been
no research on the relationship between intensity of cropping and breakdown time, nor on the most suitable spatial configuration of varieties.
As with many agricultural regimes there is clearly going to be advantage
in diversity, but it is not clear how the advantage will be different from
that which would accrue from the spreading of risks in a non-ecological
system.
111. CHANGES IN ECOLOGICAL DIVERSITY
Possibly the main aim of good husbandry is to eliminate the competitors of the crop to simplify the habitat and to approach true
monoculture. Thus, natural grassland has become by degrees the
cereal crop that we know today. Such modifications of the flora have
been accompanied by changes in the fauna. Some of these changes
have been measured by comparing the faunal diversity of typical
Downland grassland and modern cereal crops subjected to different
farming practices. Three methods were used : pitfall trapping, emergence
traps and the Dietrick vacuum insect collector.
A. T H E F A U N A L D I V E R S I T Y O F DOWNLAND,
S P R I N G A N D W I N T E R B A R L E Y
Four sites were investigated in 1969:
(1) Downland-typical Brachypodium pinnatum (L.) Beauv.-Festuca
ovina L. grassland on thin soils, more or less unmodified since the
a. R. POTTS AND GI. P. VICKERMAN
were very numerous in winter wheat in 1970. Otherwise, insects, weeds
and diseases were generally controlled or were not thought to concern
the farming community.
The main reaction of farmers to the recent upsurge of diseases has
been (1) the use of more fungicides, and (2) the introduction of diseaseresistant varieties. An example of the former is that one agricultural
aircraft contractor sprayed 5000 ha with dithiocarbamates to control
yellow rust in one two-week period in 1972. The long-term ecological
effects of this are unknown.
Many new high-yielding and disease-resistant varieties have been
rapidly taken up by the farming community. Thus, the wheat Joss
Cambier accounted for 35% of the national winter wheat acreage in
1971/1972 and the spring barley Sultan accounted for 38% of the spring
barley crop in 1970. Both varieties had only been in use for about three
years. As with earlier varieties, however, their disease resistance has
soon broken down. But there are signs that the recent rapid swings in
and out of favour of varieties (Fig. 3) will eventually be replaced by
spatio-temporal mosaics of varieties. So far, however, there has been
no research on the relationship between intensity of cropping and breakdown time, nor on the most suitable spatial configuration of varieties.
As with many agricultural regimes there is clearly going to be advantage
in diversity, but it is not clear how the advantage will be different from
that which would accrue from the spreading of risks in a non-ecological
system.
111. CHANGES IN ECOLOGICAL DIVERSITY
Possibly the main aim of good husbandry is to eliminate the competitors of the crop to simplify the habitat and to approach true
monoculture. Thus, natural grassland has become by degrees the
cereal crop that we know today. Such modifications of the flora have
been accompanied by changes in the fauna. Some of these changes
have been measured by comparing the faunal diversity of typical
Downland grassland and modern cereal crops subjected to different
farming practices. Three methods were used : pitfall trapping, emergence
traps and the Dietrick vacuum insect collector.
A. T H E F A U N A L D I V E R S I T Y O F DOWNLAND,
S P R I N G A N D W I N T E R B A R L E Y
Four sites were investigated in 1969:
(1) Downland-typical Brachypodium pinnatum (L.) Beauv.-Festuca
ovina L. grassland on thin soils, more or less unmodified since the