Monday, August 9, 2010

Novel Ecosystems and the face of the Anthropangaea

This article says it all- from the importance of genetic diversity to recognizing that sometimes landscapes with very few native species can provide real value. There is a battle brewing among the scientific community that asks,
"What will the future of forests on the human dominated Anthropangaea look like?"

Article found in Nature Magazine...
A small group of ecologists is looking beyond the pristine to study the scrubby, feral
and untended. Emma Marris learns to appreciate ‘novel ecosystems’.
Joe Mascaro, a PhD student in a T-shirt and
floral print shorts, is soaking in the diversity
of the Hawaiian jungle. Above, a green canopy
blocks out most of the sky. Aerial roots
wend their way down past tropical trunks, tree
ferns and moss-covered prop roots to an understorey
of ferns and seedlings. The jungle is lush,
humid and thick with mosquitoes. It is also as
cosmopolitan as London’s Heathrow airport.
This forest on Big Island features mango
trees from India (Mangifera indica); Cecropia
obtusifolia, a tree with huge star-shaped leaves
from Mexico, Central America and Colombia;
rose apples (Syzygium jambos) from southeast
Asia; tasty strawberry guava (Psidium cattleianum)
from the threatened Atlantic coast of
Brazil; and a smattering of Queensland maples
(Flindersia brayleyana) from Australia. It also
has candlenuts (Aleurites moluccana), a species
that humans have moved around so much
that its origins have become obscure. There is
at least some native Hawaiian representation
in the form of hala, or screwpine (Pandanus
tectorius), which is pictured on the crest of
Punahou School, where US President Barack
Obama studied. There are no Hawaiian birds
here though. Mascaro sees plenty of feral pigs,
descendants of those brought by settlers from
other parts of Polynesia or from farther afield.
The soil is black and rich. Mascaro likes it here.
Most ecologists and conservationists
would describe this forest in scientific jargon
as ‘degraded’, ‘heavily invaded’ or perhaps
‘anthropogenic’. Less formally, they might
term it a ‘trash ecosystem’. After all, what is it
but a bunch of weeds, dominated by aggressive
invaders, and almost all introduced by
humans? It might as well be a city dump.
A few ecologists, however, are taking a second
look at such places, trying to see them
without the common assumption that pristine
ecosystems are ‘good’ and anything else
is ‘bad’. The non-judgemental term is ‘novel
ecosystem’. A novel ecosystem is one that has
been heavily influenced by humans but is not
under human management. A working tree
plantation doesn’t qualify; one abandoned
decades ago would. A forest dominated by
non-native species counts, like Mascaro’s
mango forest, even if humans never cut it
down, burned it or even visited it.
No one is sure how much of Earth is covered
by novel ecosystems. To help with this article,
Nature asked Erle Ellis at the University of
Maryland, Baltimore County, who produces
maps of ways that humans use Earth, to take
a stab at quantifying it. Defining novel ecosystems
as “lands without agricultural or urban
use embedded within agricultural and urban
regions”, Ellis estimates that at least 35% of the
globe is covered with them (see map, overleaf).
Their share of the planet will probably expand,
and many ecologists think that these novel ecosystems
are worthy of study and, in some cases,
For one thing, some novel ecosystems seem
to provide a habitat for native species — sometimes
crucial habitat, if all that the species originally
had is gone. They also often do a good
job of providing ‘ecosystem services’, those
things that nature does that benefit humanity,
such as filtering water in wetlands, controlling
erosion on hillsides, sequestering carbon from
the atmosphere and building soil. Provision of
ecosystem services is a popular argument for
preserving intact ecosystems, but many of its
advocates blanch a little when it comes to making
the same case for these ‘weedy’ areas.
Mascaro actually prefers novel ecosystems
to some native ones that are so vulnerable to
damage by humans that they require intense
management to maintain in their ‘pristine’
state. He sees the latter as museum-piece parks.
“Do we value the fact that nature contains a list
of things that were there 1,000 years ago, or do
we value it because it has its own processes that
are not under human control?” Mascaro asks.
For him, the value is in the processes.
Watching such processes unfold has scientific
merit to many researchers. Novel ecosystems
are often ideal natural experiments for
studying things such as community assembly
— how species find their way to a place and
which species become permanent residents
— and evolution of species in response to one
another. In essence, it takes a dynamic ecosystem
to study ecosystem dynamics, and these
novel ecosystems are the planet’s fastest movers.
Mascaro bets that all the rules of thumb and
general relationships developed over the years
by ecologists working in ‘intact’ or ‘historical’
ecosystems will probably also apply in these
new assemblages, but no one knows for sure,
because no one has studied them much.
There are some questions about the ways in
which things might be different in novel ecosystems.
Will landscape types remain the same,
with forests replacing forests and grasslands
replacing grasslands? Will novel ecosystems
evolve faster? Will they be dominated by one
species, as many who study invasive species
fear? Will species composition oscillate wildly
for decades or even longer? “We can’t know
except to observe it,” says Mascaro.
Havens of biodiversity?
One of the first researchers to see the importance
of the scrubby parts of Earth was Ariel
Lugo, a forest-service ecologist in Puerto
Rico. In 1979, Lugo was managing researchers
who were measuring the ground covered
by trees within pine plantations that were not
being actively managed. His technicians came
back to headquarters sweaty and discouraged.
“They said that they couldn’t measure the trees
without clearing all the new undergrowth,”
says Lugo. “They said it was impenetrable. I
thought they were wimps.”
The idea that ecosystems dominated by
pine, an invasive species, were so thick that his
workers couldn’t even walk through them went
against a central assumption of ecology: that
native forests will be the lushest. Millennia of
co-evolution should have created an ecosystem
in which almost every niche is filled, converting
the available energy into trees and other species
in the most efficient way. Conservationists
also generally assume that native ecosystems
contribute best to ecosystem services.
Lugo went to see for himself. Sure enough,
the pine plantations were bursting with vigour,
far more so than nearby native-only forests
of the same age. Lugo did a systematic study
of the pine plantations and some mahogany
ones, and found that the plantation understoreys
were nearly as species rich, had greater
above-ground biomass (the sheer weight of all
the living things) and used nutrients more efficiently
than the native forest understoreys. He
submitted his results to the journal Ecological
Monographs1. Reviewers were horrified. In the
end, it took almost a decade to get the paper
past peer review.
Since then, Lugo has found many novel ecosystems
in Puerto Rico and elsewhere that are
much more diverse than native forests, but that
are largely ignored by ecologists. “That diversity
doesn’t count because they are the wrong
species,” says Lugo, shaking his head. He’s
found alien trees that, by creating a shaded canopy
on parched, degraded pastureland, make
possible the establishment of native trees that
could never cope with such an environment on
their own. As a result he now finds it difficult
to despise invasive trees as he thinks his colleagues
do, and even embraces the change. “My
parents and their parents saw one Puerto Rico,”
he says, “and I am going to see another Puerto
Rico, and my children will see another.”
Lugo wasn’t the only researcher thinking
along these lines, but it was not until 2006 that
the new approach gained a manifesto — and a
name. Lugo and 17 other researchers published
a paper called “Novel ecosystems: theoretical
and management aspects of the new ecological
world order”2 suggesting that such systems were
worth scientific attention. To demonstrate the
depth of resistance to the idea, the published
paper quoted referees’ comments on the submitted
manuscript: “One reviewer commented
that the examples are ecological disasters, where
biodiversity has been decimated and ecosystem
functions are in tatters, and that ‘it is hard to
make lemonade out of these lemons’.” But Lugo
and his colleagues saw it in a different light: “We
are heading towards a situation where there are
more lemons than lemonade,” they wrote, “and
we need to recognize this and determine what
to do with the lemons.”
The amount of land taken up by novel ecosystems, defined as unused lands
embedded within agricultural and urban landscapes.
Lemons can have their own value, says restoration
ecologist Richard Hobbs, lead author of
the paper and now at the University of Western
Australia in Crawley. Some novel ecosystems,
he says, are “alternative stable states”, relatively
entrenched ecosystems that would be very difficult
to drag back to historical conditions.
Around the time the paper came out, Mascaro
became interested in Lugo’s work and set
out to see if his results could be replicated on
the windward side of Hawaii’s Big Island. Were
the many novel ecosystems on the islands nurturing
any native species? Were they providing
ecosystem services? He studied 46 forests
growing on lava flows of varying ages at various
altitudes and dominated by a variety of species,
including albizia (Falcataria moluccana),
a fast-growing tree from southeast Asia, and
Australian ironwood (Casuarina equisetifolia).
He found that, on average, the forests had as
many species as native forests. But by and large
they weren’t incubating natives as they seemed
to in Puerto Rico3.
Part of the reason for the difference may lie in
the uniqueness of Hawaiian flora, which evolved
in isolation for up to 30 million years4. Not many
plants got to Hawaii in the first place, so competition
and predation pressures weren’t very
fierce. Without having to worry about being
eaten by anything larger than an insect, raspberries
and roses lost their thorns and mints lost
their minty defence chemicals. When people
introduced plants from other parts of the world ,
along with their attendant herbivores, Hawaiian
plants couldn’t compete.
Futuristic perspective
But Mascaro’s results didn’t put
him off the novel-ecosystem
concept. For one, he found
that in many measures of forest
productivity, such as nutrient
cycling and biomass, novel forests
matched or out-produced
the native forests. They might
not be ‘natural’ in the eyes of
purists, but they are behaving
exactly as they should . “These
ecosystems, like it or not, are
going to be driving most of
the natural processes on Earth,” he said at the
2008 Ecological Society of America meeting
in Milwaukee, Wisconsin. It’s a message that
Peter Kareiva, chief scientist at the Nature Conservancy
in Seattle, Washington, wants to see
move from the academic world to the world
of conservation management. “You hear conservationists
talk about what they want to save,
what they want to stop,” he says. “They should
talk about what they want the world to look like
in 50 years.” Studies of novel ecosystems could
help conservationists to “face the facts and be
strategic”, Kareiva says, rather than trying to
beat back the unceasing tide of change.
Kareiva is a great fan of the ecosystem-services
argument for preserving nature. But he
admits that the problem of what to do when
novel ecosystems provide better services than
the native ones is “a question we don’t talk
about that much”. Nevertheless, he is willing to
imagine a world in which, for example, exotic
strains of the reed Phragmites are allowed to
thrive in US wetlands because they provide a
great habitat for birds, rather
than be torn out in an expensive
and potentially fruitless attempt
to return native vegetation to
Ecosystem-service arguments
are powerful enough to
get some ecologists to abandon,
or at least put to one side, their
deep distrust of novel ecosystems.
Like many of his peers,
Shahid Naeem, an ecologist at
Columbia University in New
York, says he “would love to get rid of every
invasive species on the planet and put all the
native species back in their place”. Yet he’s willing
to see what can be made of novel ecosystems
as he feels an imperative to improve conditions
for the billions of humans on Earth.
The idea that novel ecosystems provide
welcome diversity has also gained traction.
Thinking on ‘invasive species’ has mellowed
significantly since the field was first established
in the 1950s. Newer work by the likes of Mark
Davis at Macalester College in Saint Paul,
Minnesota, and Dov Sax at Brown University
in Providence, Rhode Island, has shown that
the vast majority of species that humans move
around can slot into new ecosystems without
driving anything else extinct, and that the common
vision of invasive plants forming dense
monocultural stands that take over everything
else in their path is actually the exception. Yet
the newcomers in novel systems can still be a
genuine worry.
Peter Vitousek, an expert on Hawaiian
biodiversity at Stanford University in California,
would put albizia forests in the category
of dangerous invaders, because they wipe out
stands of the native ‘ōhi‘a tree (Metrosideros
polymorpha). He acknowledges the services
that novel ecosystems provide and that “they
may even support native biological diversity in
some important circumstances”. But, he adds,
“as with many good ideas, [tolerance of novel
ecosystems] can be taken to an extreme at which
it is no longer useful. I think most of the albizia-
dominated stands of Hawaii represent that
extreme.” His point is well illustrated where one
of Mascaro’s albizia forests abuts a native ‘ōhi‘a
forest. The albizia trees on the boundary actually
lean out towards the ‘ōhi‘a — growing sideways
to escape the shade of the next row in, encroaching
on the natives’ sunlight and looking poised
to usurp them. It is a menacing spectacle, and an
apt symbol for their tireless expansion.
Mascaro grants the point. “I can understand
where a manager wants to bulldoze an
albizia forest if they are worried that it is going
to exterminate an ecosystem type that is the
last on Earth,” he says. “If we want to debate
whether to use or conserve novel ecosystems,
we will always have to deal with the risk they
pose to other systems. But at the moment, we’re
scarcely debating it at all.”
Novel ecosystems are likely to cause at least
some extinctions. For example, species that
have evolved dependent relationships with
other species are less likely to do well in a world
in which the pot is stirred and everything is
redistributed. Hawaiian honeycreepers, beautiful
birds that often feed only on one type of
flower, are not doing well; several are already
extinct. So for those who care about slowing
or stopping the rate of such extinctions, novel
ecosystems are a net negative .
James Gibbs, an ecologist at the State
University of New York in Syracuse, subscribes
to this view. “I think celebrating [novel ecosystems]
as equivalent or improved is not appropriate.”
As an example, he points to Clear Lake
in Northern California, where the number of
fish species has risen from 12 to 25 since 1800.
Sounds like a success story. But, says Gibbs,
species that were found only in that lake were
replaced with fish that are common elsewhere
— so there was a net loss in biodiversity. A similar
caveat may hold for the genetic diversity
hidden within a species. Forests dominated by
the offspring of a handful of exotic colonizers
could be less genetically diverse than forests
that have sat there for thousands of years.
A question of values
In the end, the question of novel ecosystems,
like so many questions in ecology and conservation,
boils down to what
should be valued most in
nature. For people who value
processes, such as Mascaro,
novel ecosystems are great
hubs of active evolution. For
those who value ecosystem
services, any novel ecosystem
could be better or worse than
what came before depending on
how it operates. For those who
care about global extinctions or about preserving
historical ecosystems, they are bad news.
Gibbs says he values the exquisite complexity
of ecosystems that have evolved together over
thousands or millions of years. “Why are we
worried about the extinction of languages, the
roots of music, all these weird cuisines?” he
asks. “There is something about diversity and
our need to steward it. It is the subtlety and the
nuance and complexity that makes life interesting.”
Novel ecosystems seem, to him, to lack
this value, to be samey and artificial, “sort of
like eating at McDonalds” .
To Kareiva, though, that attitude is “one of
the reasons the conservation movement is failing.
To think there is some kind of garden of
Eden pristine ecosystem. There is none! That
view is just going to get us nowhere.”
Indeed, the Garden of Eden view, in which
ecosystems are static, is no longer widely held.
Th is means that novel ecosystems, far from
being a new phenomenon, simply represent
the latest changes on a dynamic Earth. Gradual
climatic changes and sheer randomness mean
that some species wander around continents
over vast timescales, fleeing glaciers, splitting
up and reforming . This is why Davis and some
others do not like the ‘novel’ label. “Ecosystems
are always new, from one year to the next,” says
Davis. “Ecosystems are always encountering
new species — it might be not
from another country but from
100 metres upstream. Much
more accurate would be to refer
to these as ‘rapidly changing’
ecosystems — but I guess that
is not catchy enough.”
Standing in his Hawaiian
forest, Mascaro is all too aware
of change — and it is something
he values, even if humans did
have a hand in the process. He never swore allegiance
to preserving ecosystems as they were
before humans arrived, as many conservationists
of an older generation did. “People come
up to me and say ‘it sounds like you’ve given
up,’” says Mascaro. “I want to say ‘I never took
up arms, my man’. This isn’t about conceding
defeat; it is about a new approach.” ■
Emma Marris writes for Nature from
Columbia, Missouri.
1. Lugo, A. Ecol. Monogr. 62, 2–41 (1992).
2. Hobbs, R. J. et al. Global Ecol. Biogeogr. 15, 1–7 (2006).
3. Mascaro, J., Becklund, K. K., Hughes, R. F. & Schnitzer, S. A.
Forest Ecol. Manage/ 256, 593–606 (2008).
4. Ziegler, A. Hawaiian Natural History, Ecology and Evolution
157 (University of Hawaii Press, 2002).
See Editorial, page 435.
“There is no garden
of Eden pristine
ecosystem. That
view is just going to
get us nowhere.”

Vol 460|16 July 2009
NEWS FEATURE NATURE|23 © 2009 Macmillan Publishers Limited. All rights reserved
Vol 460|16 July 2009