Book review: The New Wild: Why invasive species will be nature's salvation by Fred Pearce
Icon Books 2015 
In
1910 New Zealand's great botanist Leonard Cochayne described the
dramatic change in plant communities which had occurred since the first
visit of Captain Cook to the country in 1769 (1). Some 560 new species
from Europe, Africa and elsewhere had by become established by then,
with half of them common throughout the country from the coasts to the
highest mountains:
At first thought, the idea of 560
different sorts of plants- some of them the most aggressive weeds in
Europe- having not only been loosed to do their will, but also having
established a secure footing, would lead to the conclusion that, if not
the flora of New Zealand, at any rate the primitive vegetation was
doomed. No conclusion could be more incorrect. Were it not that man has
changed, and is changing, the face of nature by means of his farming
operations, his grazing animals, his fires, his drains, and his
intensive exploitation of rain forest and flax swamp, the host of
foreign plant invaders would be powerless- the indigenous plants,
attuned to the special life conditions f their native land, would laugh
these aliens to scorn. Why, even now, when the introduced plants have
man as their potent ally, 66 percent of the species are rare or local,
40 percent being so rare as to be negligible, while merely 34 percent
can be classed as extremely common, common, or fairly common, these
being taken together. But these percentages do not emphasise the real
state of affairs, for many of the commoner plants are confined to sides
of toads, neglected building sites, and rubbish heaps- in short, to
"waste ground" as it is called- and there are many other species
restricted to cultivated land. In fact, probably only about 100 species
are established on land where the vegetation would be exposed to
modification only by grazing, fire, and other causes due to the indirect
action of man.The warfare, indeed, between the plant inhabitants
of primitive New Zealand and the alien invaders is waged almost
entirely under conditions where man takes a powerful hand, for, except
for certain rock, stony debris, and water-plant formations, no primitive
plant community has been desecrated by a single foreign invader. This
is a very different version of the story from that even yet current in
biological literature, where it is affirmed ad nauseum that the New
Zealand vegetation is powerless when it comes into competition with the
European plants, which by natural selection have become the very elite
of the weed world.
Cochayne's observations made over a
hundred years ago are almost identical to those made forcefully in Fred
Pearce's provocative new book which takes to task invasion biology-
the view that non-native species are generally "invasive", constituting
one of the greatest threats to biodiversity and ecosystem health, and
need to be controlled and where possible eradicated completely- almost
at any cost.
The European Commission on the Environment describe Alien Invasive Species (AILs)
as "a major threat to native plants and animals in Europe, causing
damage worth billions of euros to the European economy every year." Bird Life International call for
a far more extensive policy than that currently proposed, listing over
200 invasive species as of "high priority for urgent risk assessment" in
addition to the 37 that are currently listed for control; while the WWF quote the World Conservation Union as saying
the
impacts of alien invasive species are immense, insidious, and usually
irreversible. They may be as damaging to native species and ecosystems
on a global scale as the loss and degradation of habitats.Hundreds
of extinctions have been caused by invasive alien species. The
ecological cost is the irretrievable loss of native species and
ecosystems.
Pearce, winner the UK's environment
journalist of the year in 2001 and author of other books on climate
change, population and sustainability, comprehensively rejects these
assessments. Exactly as Cochayne describes above, "invasives" are more
accurately thought of as opportunists which generally only move into
ecosystems that have already been severely degraded by other human
activities, and are able to thrive on our pollution where nothing else
can. For example, the infamous Zebra mussels that spread through Lake
Erie at such a rate in the 1980s were moving into an ecological desert
so atrophied that everything else had already died- and apparently did a
fairly good job of cleaning it up. In time, the previously endangered
lake sturgeon, bass and migrating ducks moved back to feed on the
mussels.
This is a typical pattern with so-called "alien
invasions" which are generally the consequence rather than cause of
previous disturbance. Another infamous "invasive exotic", Kudzu,
from Japan- which became known as "the vine that ate the South" because
of its rapacious spread through the southern US- had previously been
widely planted as an ornamental, and for animal fodder and erosion
control. It only got out of hand as a result of other land-use changes:
The vine hasn’t changed. It is still revered in Japan. What has changed
in America is the land and people’s expectations of the land. Kudzu’s
foliage is no longer needed to feed grazing farm animals, which now live
in feedlots. The pastures are abandoned. No longer kept in check by
grazing, kudzu now grows where it is not wanted, spreading unchecked
almost anywhere south of the Mason–Dixon line. It is the enemy. The
pastures are being turned into woodland, where kudzu is a problem.
The
reality is that out of tens of thousands of introduced species-
including most of our food plants and garden ornamentals- only a tiny
minority ever become problematic or a threat to "native" vegetation in
this way. Often, for all the trouble they cause, they also can do a lot
of good; the costs they are claimed to incur are often wildly
exaggerated based on simplistic extrapolations (2), and these could well
be exceeded in some cases by the costs of control, which mainly are
doomed to failure anyway. Nor is it true that they are generally likely
to cause extinctions- Pearce concludes that this is based more of the
assumption that "exotics are bad" than supported by rigorous evidence.
While there have certainly been cases of loss of biodiversity on remote islands,
where local species have little options to extend their range, there
are plenty of counter examples where introduced species have increased
biodiversity. The problem is that "invaders" are simply not valued in
the same way that "natives" are:
In
fact we seem to have gone a long way from any interest in biodiversity.
The interest is entirely to do with protecting natives and avoiding
change....alien species don’t
count and are not counted. They do not exist as part of nature. They
have no place. They are un-nature, if not anti-nature. They should be
gone. Under this definition, biodiversity in the 21st century can only
go down. Extinction could cut the number of species, but introductions
could never increase it. Thus the inconvenient fact that alien species
actually increase real biodiversity in many places is simply defined
away. Big Brother in Nineteen Eighty-four would be proud. Franz Kafka
would be proud. Joseph Heller would have added an ecological chapter to
Catch-22, if he had known. It sounded more like an ideology than good
science.
A lot of the problem has to do with
conflating "invasive" with "exotic/non-native", but just as most
"exotic" novel species are not invasive, so there are also "native
invasives". Bracken fern Pteridium aquilinum, brambles Rubus fruticosus, and gorse Ulex europaeus, all
"native" to the UK but invasive as vigorous weeds or early colonisers
of disturbed ground if they come across the right conditions.
More
than that, and fundamentally to the whole debate, the line between what
is considered "native" and "non-native" is not just blurry but
scientifically meaningless. "Everything is visiting. Nothing is native"
observes Pearce. What specific combination of plants have ended up
living together in different areas at any given time is largely a
function of chance. Some species made it across to Britain when there
was a land bridge, some got stuck across the water when the sea levels
rose again. In trying to maintain "native" vegetation we are necessarily
picking a particular period in time from which to judge what can stay
and what must go.
Rhododendron ponticum, a major target
of conservation control in Britain because of its ability to prevent
regeneration of woodland, had been "native" here before the last
ice-age. Does this discount it on the basis that plant communities here
have since evolved without it? The difficulty is that many other species
are in the same category, but are not persecuted as invasive in the
same way. Ken Thompson, author of another recent book on the same topic
(2) points out that Fritillaria meleagris is generally considered a full-blooded British native, but was first recorded in the wild here only in 1736; while R. ponticum
first introduced to Britain in 1753, is still an "invasive exotic." To
further complicate matters, it is really a hybrid of three other Rhododendron species, which has evolved uniquely in the UK and is not found anywhere else! What, then, can it mean to call it anything but a native? Rhododendron
probably only became so widely spread anyway as a direct result of
being extensively sown throughout British woodlands to provide cover for
game.
(Conversely, Thompson gives the example of the
quintessentially "English" oak which, having spent more than 99% of
the last 2million years in Iberia, might more properly called Spanish.)
While
there are specific cases of co-evolution between two species, they tend
to be more exceptions than rules, and it is relatively rare for any
group of species to be entirely dependent on their specific
co-evolutionary companions- it turns out that ecosystems can usually
function perfectly well, and often with increased diversity, with a
mixture of old friends alongside new neighbours. Pearce points out that
Darwin did not see co-evolution as a principle driver of evolution, and
quotes ecologist and invasion biology critic Mark Davis who states 'nativeness is not a sign of evolutionary fitness’.
Darwin was clear that the individual species is the primary unit of
natural selection, not the "ecosystem"- a nebulous and controversial
concept in itself. Much of the ideology surrounding the desire to keep
nature in an idealized state of pristine "natural balance", frozen at an
arbitrary period of time (generally pre-Columbus) has less to do with
Darwin than, as Daniel Botkin has argued, with the much older
Judeo-Christian belief in the Great Chain of Being and guilt over the
Fall from Eden (4).
Nature is always changing,
and is proving in many respects far more resilient and adaptive than it
is often portrayed. While most conservation efforts focus on
extermination of plants that happen to make it onto the "invasive
species" lists, entire new ecosystems, and often highly diverse
regenerating secondary forests are emerging all around us. Perversely,
such habitats are not deemed worthy of conservationists' efforts to
protect them- despite increasing evidence that even most so-called
"pristine" habitats were subject to significant anthropogenic change in
pre-history (5). Pearce sees this as a blinkered and narrow view and a
sad lost opportunity. It is this "New Wild" that he feels we should now
turn our attention to, since in the rapidly changing world of the Anthropocene,
there is very little, if any, "pristine" wild left. With more
ecologists like Davis speaking out from this perspective of a "new
ecology"(6), science has already moved on to a large degree from earlier
conceptions of ecosystem balance. Now it is time for public
understanding of this science, and conservation policy, to catch up.
Pearce
has written an engaging book that should be a valuable contribution to
this often confusing debate. If he falls short in any area, it is
perhaps the cursory passing over of the threat posed by novel pathogens,
which are increasing due to global trade of plant material with
potentially devastating consequences to trees and shrubs (7). In
general though he is careful not to fall into the trap of claiming there
is no issue at all with introducing new species which might be at the
very least weedy or have unintended consequences. Some newcomers can
cause serious problems, more for humans than for "nature" though,and
noone wants rampant weeds in their gardens. Plants should be
investigated on a case-by-case basis, not assumed to be inherently bad
or noxious on the basis of the largely spurious notion of nativeness:
the vast majority are benign. This raises another issue, as pointed out
by Thompson: the public's goodwill, without which even the most
favourable eradication or control efforts cannot in any case succeed.
The public do not intuitively divide plants into native or non-native,
but assess them on their characteristics of usefulness or aesthetics,
which is exactly why plants are frequently assumed to have been native
for a long time when, like the fritillary they are relative recent
arrivals, and vice-a-versa. It is not just environmental issues at stake
here, but the public's trust in the integrity of science.
More
than just a critique of conservation, Pearce also presents a damning
indictment of science. With honorable exceptions, few scientists have
spoken up against the tendency of NGOs and policy makers to rely heavily
on just one or two studies which have either been misrepresented or
have little real evidence to back them up, and costly and often damaging
alien eradication programs have been allowed to continue unnecessarily,
often for decades.
As is clear from Cochayne's book written at the
beginning of the last century, there was never any very solid science
behind invasion biology, and it is time for this to be more widely
understood and debated in the public realm.
Also appeared on on theculturalwilderness
References
- Cochayne, L. 1910 New Zealand Plants and their Story
- see Pimentel, D. et al 2000 Agriculture, Ecosystems and Environment 84 (2001) 1–20
Economic and environmental threats of alien plant,animal, and microbe invasions Agriculture,
Ecosystems and Environment 84 (2001) 1–20. Pearce claims the widely
cited figure of $1.4 trillion being the annual coast to the global
economy from invasive species is an extrapolation to the entire world
from just six major economies, and the biggest three causes of these
costs coming from rats, weeds and plant pathogens in agriculture; among
other problems Pearce points out, no accounting is allowed for possible
benefits to the economy from aliens (such as cleaning water pollution
in the Lake Erie by the Zebra mussel mentioned above). - Thompson, K. Where do Camels Belong?
- Botkin, D. The Moon in the Nautilus Shell
-
Bowman, David MJS, et al. "The human dimension of fire regimes on Earth." Journal of biogeography 38.12 (2011): 2223-2236.
- see for example Brown, J. and Sax, D. An Essay on Some Topics Concerning Invasive Species Austral Ecology (2004) 29 , 530–536:
The
rare, restricted species are disappearing and the common widespread
species are becoming even more abundant and widely dispersed. This
hasbeen referred to as the homogenization or cosmopolitanization of the
world’s biota (Brown 1995; McKinney&Lockwood 1999).Is this
decrease in global biodiversity a bad thing? Is the net increase in
local species richness due to invasions a good thing? Is high species
richness desirable? We do not believe that these are scientific
questions.Science can elucidate the causes and consequences of these
changes in biodiversity, but ultimately deciding what is good or bad is a
moral and social issue. Few people would question whether the dozens of
exotic flower and vegetable species in their gardens are desirable. The
value judgements may change, however, if some of those same species
were to become naturalized and spread into wild areas or to become
serious weeds in agricultural fields. - Rackham, O. 2014 The Ash Tree Little Toller Books, Dorset
