ISIS Report 8/11/03
GM Crops Harm Wildlife
The UKs farm scale evaluations have shown conclusively that the
herbicide regime linked with GM spring oilseed rape and beet is damaging to
biodiversity. Lim Li Ching
for this report are available in the ISIS members site.
Full details here
The three-year farm scale evaluations (FSEs), results of which were
published on 16 October in the Royal Societys house journal, examined
three spring-sown GM crops oilseed rape, beet and maize. They were
undoubtedly the largest experiments of their kind, involving over 200 plots.
The FSEs were a compromise from the start. They did not focus on the
many other key questions regarding environmental safety gene flow,
transgenic contamination, creation of superweeds and
superpests, but looked only at the impact of managing GM
herbicide-tolerant (GMHT) crops on farmland biodiversity.
About 60 to70 fields each were planted to beet, maize and spring oilseed
rape. Each field was split, with half planted with a conventional variety
managed according to the farmers normal practice, and the other half sown
with a GMHT variety. The GM beet was tolerant to glyphosate, the GM maize and
oilseed rape were tolerant to glufosinate ammonium. These allow farmers to
indiscriminately spray the crops with herbicides, killing weeds and not the
But killing weeds adversely affects biodiversity. Weeds provide food and
habitat for countless animal species, including threatened birds. Populations
of the skylark, corn bunting and other birds have declined over the past 30
years, partly due to intensive agricultural practices that suppress weeds.
The FSEs thus recorded levels of weeds and invertebrates in the fields
and surrounding field margins. The researchers concentrated on the plants and
more-or-less sedentary herbivores and detritivores that react rapidly to any
major change in field management. Selected groups of other organisms with wider
foraging ranges (e.g. carabid beetles, bees, butterflies) were studied for
comparison. The key question was: would the changes in management associated
with GM crops exacerbate the trends perpetuated by conventional agriculture, of
reduced weed levels and wider impacts on farmland biodiversity?
The verdict on GMHT spring oilseed rape and beet
In general, the GMHT crops received less herbicide-active ingredient per
crop, with later and fewer applications than the conventional varieties, and
this, GM corporations have long claimed, means that GM crops could benefit the
environment. But the FSEs found otherwise. Overall results showed that GMHT
oilseed rape and beet would reduce farmland biodiversity, as the stronger
broad-spectrum herbicides used with GM crops control a wider range of weeds
In beet and oilseed rape, after the first application of broad-spectrum
herbicide, weed densities were lower in the GMHT crop, reversing initial higher
densities. The biomass (weight of weeds collected from a fixed area) in GMHT
beet and oilseed rape was one-sixth and about one-third, respectively, of that
in conventional plots.
The effects on weed diversity were transient and mostly small, but the
researchers concurred that, "it is only a matter of time before resistant
plants become widespread". Then diversity is likely to drop, as evolved
herbicide tolerance increases the dominance of a few species.
While reduction or removal of the visible flora temporarily reduces the
food available to farmland animals, the key to longer-term impacts is the
seed rain (seeds falling from weeds) and its contribution to the
seedbank (weed seeds left in soil). The GMHT beet and oilseed rape fields had
one-third and one-fifth, respectively, of the seed rain of conventional fields.
The reduced seed rains had demonstrable effects on the seedbanks in the
following year: densities in GMHT fields were about 20% lower than in
Although in the short term, any resulting decline is buffered by
existing seedbanks, and the loss of one years seed return itself did not
produce a large difference in future weed populations, relatively small
differences could sum to produce a large effect if sustained over several crop
rotations. The unavoidable conclusion was that GMHT crops would have a large
impact on weed populations in the longer term.
When the researchers looked closely at 12 individual weed species, which
are frequent and abundant in British agriculture, and important in the diet of
farmland birds, they found that biomass in the GMHT fields was significantly
reduced for five species in beet and oilseed rape. Subsequent survival was
significantly lowered for eight species in GMHT beet and six in GMHT oilseed
rape. In general, reproductive rates were lower (by about 50%) for most
species; and for many species (19 out of 24 cases), seed densities were lower
in the seedbank after GMHT cropping.
They concluded, "These differences compounded over time would result in
large decreases in population densities of arable weeds". And, "With a few
exceptions, weed species in beet and spring oilseed rape were negatively
affected by the GMHT treatment".
Correspondingly, the abundance of invertebrates on the soil surface is
generally lower in GMHT beet and oilseed rape. Such invertebrates are food for
mammals, birds and other invertebrates, and many are important for controlling
pests or recycling nutrients within the soil. The distribution of invertebrates
is affected by weeds in the field, and hence mirrors that of weed levels.
Specifically, there were less carabids that feed on weed seeds in GMHT
beet and oilseed rape. However, collembolan detritivore counts were larger
under GMHT crop management, most likely due to additional detritus produced
following efficient and later application of herbicides in the GM crops. While
Collembola are part of the diet of some farmland birds, the long-term effects
are uncertain. If GMHT crops lead to long-term decline in weed abundance, there
would be less biomass to produce detritus and subsequent reduction of the
effect on Collembola.
The FSEs also examined epigeal (species that spend most of their life on
plant and soil surfaces) and aerial (those whose main activity in the crop
involves a substantial proportion of time spent in flight) species. These
invertebrates play important roles in pollination and recycling of detritus;
many are dependent on flowering weeds and flowering crops for nectar or pollen,
or have larvae that feed directly on plants.
Most taxa were insensitive to management regimes. However, actively
foraging taxa, such as bees and butterflies, showed lower abundances in GM
fields. The abundances of all bees, honeybees and bumblebees in GMHT beet crops
were 55%, 27% and 58%, respectively, of those in conventional crops. Similarly,
there were 22% less butterflies in GMHT oilseed rape than in conventional.
Butterfly numbers were also lower in GMHT beet, especially in August when the
abundance was 68% of that in conventional fields. These smaller counts were
associated with lower abundance of flowering weeds.
Within-field findings are mirrored in the field margins. Field margins
can support a high diversity of plant species and are important for
conservation within farmed landscapes. They are habitat for numerous
invertebrates, a food resource for mammals, and a refuge for beneficial
parasitoids and predators. Margins provide resources for birds and may be the
only source of nectar and pollen in arable landscapes through much of the
However, field margins receive direct and indirect applications of
chemicals. Scorching of vegetation by herbicide-spray drift was on average 1.6%
on verges beside conventional crops and 3.7% beside GMHT crops. Less plant
cover (by 25%), which produced fewer flowers (by 44%) and less seed (by 39%),
were found on tilled margins of GMHT halves of spring oilseed rape fields. The
tilled margins of GMHT halves of beet also had less flowering and seeding (34%
and 39% lower, respectively).
All this had pronounced knock-on effects on butterflies. There were 24%
fewer butterflies in margins of GMHT oilseed rape. The likely cause is the
lower nectar supply. If sufficient forage is available elsewhere, then
populations of this mobile group will be buffered, but not if forage reductions
occur over large contiguous areas. Of the butterfly species common to arable
ecosystems, those with lower dispersal ability are likely to be most
Similar effects may be expected for other flower- and nectar-feeding
groups such as solitary bees, moths, hoverflies and other flies, as well as
less frequent nectar feeders such as beetles and wasps. Effects on such a range
of species groups could have implications for the pollination of arable plants.
The FSEs also looked at the effects on invertebrate trophic (or
functional) groups. Where the weeds were less abundant in GMHT beet and oilseed
rape, there were fewer herbivores, pollinators and natural enemies (predators
and parasitoids). Detritivores increased under GMHT management across all crops
due to the greater input, later in the season, of dead weeds on which they
feed. This shift in resources from the herbivore to the detritivore food web
resulted in a general trend of greater increases in the ratio of detritivores
to herbivores under GMHT than under conventional cropping. The reduced number
of pollinators may influence seed production of insect-pollinated weeds,
amplifying direct effects of herbicide on the weed flora.
All these negative impacts of GMHT beet and oilseed rape on biodiversity
are so conclusive that several NGOs demanded an immediate ban on GM crops. The
Royal Society for the Protection of Birds agreed that the risks are too great
for wildlife and called for the two GM crops to be banned. Many farmland birds
rely on seeds from weeds for their survival and GMHT beet and oilseed rape may
be the final nail in the coffin for some species.
In trying to downplay the negative impacts, some alleged that the
effects are not due to the GM crops per se, but to the herbicide regime,
and hence can be somehow managed away. However, the GM crops are
inextricably linked with the proprietary herbicides they are engineered to
tolerate, and it is the GMHT practice - the modified plant and the herbicide as
a package that has been damaging to the environment. Moreover, the
FSEs herbicide regime was recommended by the GM seed companies, so
presumably is realistic under commercial conditions.
Maize trials questionable
The effect of growing the third GMHT crop - maize seemed to be
positive, with higher weed density throughout the season, as well as higher
late-season biomass and seed rain. This had a corresponding effect on
invertebrates, with higher abundance on the soil surface, specifically of
carabids, and more butterflies during some months. There was greater plant
cover and flowering in field margins of the GMHT field, but no butterfly
differences were observed.
However, the apparent harmlessness of the GMHT maize is primarily
accounted for by the relative toxicity of the herbicide atrazine used on most
of the conventional maize, which resulted in lower weed densities. In contrast,
the GMHT maize allowed farmers to spray with a different, albeit weaker,
herbicide, leading to more weeds. Compared to the conventional, the
biodiversity measurements in GMHT maize thus looked relatively good.
A week before the publication of the FSE results, the EU announced a
ban on atrazine in agriculture. This means that atrazine would have to be
phased out in Britain within 18 months and that it would probably be withdrawn
from use before GM maize - if it mustered approval - was grown commercially.
This effectively invalidates the maize trails, which no longer reflect the real
conditions under which non-GM crops will be grown.
The researchers were only confident that their findings represent what
would actually happen, "unless the management regimes altered somewhat, for
example if... atrazine was no longer allowed on maize crops...". They
acknowledged that the results might need to be recalibrated and
that extra field research might be needed to gather new data on whatever regime
replaces atrazine in conventional maize.
But, theres more to this story than has been alluded to by the
media or admitted by the researchers (see "Cynical & dishonest science"
in GM maize trials).
The Advisory Committee on Releases to the Environment (ACRE) will now
consider the FSE results and advise the UK government on their implications.
ACRE will likely suffer some well-deserved embarrassment, as it had blithely
approved, in 1997, the GM oilseed rape tested in the FSEs, saying that it "did
not pose a risk in terms of human health and environmental safety for the
United Kingdom". On their recommendation, the UK Government had agreed to
marketing of the oilseed rape, but this was prevented because other European
countries opposed it.
If ACREs advice had been followed, farmers could have been growing
this damaging crop for the last five years. It was only public opposition that
forced more research on environmental effects.
And the public have made their opinion on GM crops clear. The GM
Nation? debate found widespread unease about GM crops and scepticism about
its benefits. An overwhelming 86% of the 37 000 people who responded said they
would not be happy to eat GM food, and 54% said they never want to see GM crops
grown in the UK.
Additionally, a report into the economics of GM crops by the Prime
Ministers Strategy Unit forecast found that the overall economic benefit
to the UK, at least in the short term, was "likely to be limited".
The GM Science Review report, flawed as it is, also failed to give
blanket approval for GM crops and instead highlighted the gaps and
uncertainties in our knowledge.
Moreover, while the FSEs showed up the damaging effects of GMHT crops,
they were still narrow, and say nothing about impacts on human or animal health
or agronomic performance. They also failed to ask any questions about the
transgenic nature of the crops, choosing instead to focus only on a secondary
effect, the impact of changing patterns of herbicide use. But neither did the
FSEs compare the GMHT crops with ecologically-managed crops that use no
herbicides, nor did they study effects on below-ground biodiversity (and thus
soil fertility). They say nothing about gene flow, coexistence with other forms
of agriculture and liability if anything goes wrong.
The UK government simply has no case for approving the commercial
growing of GM crops.
for this report are available in the ISIS members site.
Full details here