Please note that this blog no longer accepts comments (there was
too much spam coming in!). If you're reading this blog and want to
respond then please use the contact form on the site.
You can also follow me on twitter.
Belatedly, here is my Mind and Matter column from the Wall Street
Journal on 24 March 2012.
In her remarkable new book "The Rambunctious Garden," Emma Marris explores
a paradox that is increasingly vexing the science of ecology,
namely that the only way to have a pristine wilderness is to manage
it intensively. Left unmanaged, a natural habitat will become
dominated by certain species, often invasive aliens introduced by
human beings. "A historically faithful ecosystem is necessarily a
heavily managed ecosystem," she writes. "The ecosystems that look
the most pristine are perhaps the least likely to be truly
In the Netherlands, for example, cattle are being used to
re-create a simulacrum of a Pleistocene woodland, because their
aurochs ancestors would have been vital in keeping forest patchy.
To keep African national parks from deforestation, elephant control
is sometimes needed. To let aspen, willow and beaver return to
Yellowstone, it was necessary to reintroduce the wolf, which
reduced elk numbers. To preserve Mojave Desert tortoises, it is
essential to control native ravens, whose numbers have been boosted
by distant landfill sites.
Some ecosystems are enriched and made more productive by
invasive species. In terms of "ecosystem services"-the provision of
clean water, the absorption of carbon, the creation of soil, the
prevention of erosion-Hawaiian forests dominated by alien tree
species can perform better than the pristine habitats they replace.
Though many invasive aliens are notorious for the harm they bring
(pythons in Florida, cane toads in Australia, brown tree snakes in
Guam), many others enhance the local nature scene.
Where I live, in the U.K., American gray squirrels are
exterminating native red squirrels with the help of a parapox virus
and a better ability to digest acorns. Aesthetically, this is a
pity: The red is nicer to look at and part of local culture. But
ecologically, one has to admit that the gray is better at filling
the squirrel niche in our broadleaf woodland. Reds are really a
pine-adapted species that had responded to a broadleaf vacancy
after the most recent ice age.
Ms. Marris's book goes further, challenging the very idea of a
balance of nature. In the first half of the 20th century,
ecologists came to believe in equilibrium-that natural systems
tended toward a steady state. So, for example, a bare patch of
ground would be colonized by a succession of species-annual weeds,
then grasses, then shrubs, then trees-until it reached its "climax"
state. Conservation, therefore, was a matter of restoring this
Academic ecologists have abandoned such a static way of thinking
for something much more dynamic. For a start, they now appreciate
that climate has always changed, and with it, ecology. Twenty
thousand years ago the spot where I live was under a mile of ice.
Then it was tundra, then birch forest, then pine forest, then
alder, linden, elm and ash, then most recently oak, but beech was
Which is its climax? We now know that oak seedlings rarely
thrive under mature oaks (which rain caterpillars on them), so the
oak climax was just a passing phase.
Yet even as academic ecologists have abandoned balance-of-nature
thinking, it still dominates practical conservation management. Ms.
Marris quotes the ecologist Daniel Botkin: "If you ask an ecologist
if nature never changes, he will almost always say no. But if you
ask that same ecologist to design a policy, it is almost always a
balance-of-nature policy": preserve this rare species, maintain
this habitat structure, freeze in time this ecological moment,
return this degraded land to a particular state, whatever the
weather and whatever the novel arrivals of exotic species. Just as
in our management of the economy, we think of states, not
So what's a good conservationist to do? Ms. Marris sets you
free: "In a nutshell: Give up romantic notions of a stable Eden, be
honest about goals and costs, keep land from mindless development
and try just about everything."