I just finished reading a very good article from The Guardian's
Environment section. (The Guardian, IMO, does the best job of reporting
on environmental issues of any major newspaper currently) The article
described an emerging trend in some U.S. cities to make biodiversity and
the the enhancement of urban wildlife a prominent concern in decisions
surrounding the kinds of trees planted on city land, such as streets,
parks and even schools. While it might seem like an obvious criteria,
the fact is that over the past several decades most urban planners, and
most private residents living in the city, have given little to no
regard to such concerns when choosing what variety of trees to plant for
ornamental purposes. In many cases, the primary factor has been a
tree's aesthetic appeal.
There has been a remarkable level of disregard, when it comes to
urban landscapes, to the interrelationship between tree species and
urban wildlife. Consider this fact:
Of the Audubon Society's list of the 20 common birds in decline here
in America, all of them have seen their populations decline by
at least 50% just since 1970. Of 800 bird species, about 17% are in decline.
Much of that population decline is the result of habitat loss. The
mistake we often make, however, is thinking of habitat loss strictly as a
function of urban development, as in the Joni Mitchell song
They paved paradise, put up a parking lot
While the physical loss of habitat cannot be discounted as a factor in the decline in wildlife populations,
the composition of tree species in what habitat that is left also plays a huge role in the ability of birds and other wildlife to survive and thrive in the urban environment.
This point is driven home by taking the single example of one bird
species many of you are probably familiar with, the Carolina Chickadee.
A single pair of Carolina Chickadees, according to Professor and
Chair of the Department of Entomology and Wildlife Ecology at the
University of Delaware Douglas Tallamy, must capture 6,000 to 9,000
caterpillars and take them back to their nest in order to raise a
typical brood of 6 nestlings. Those caterpillars, in turn, depend upon
specific host trees during their life cycles. And when it comes to
trees, it should come as no surprise that all varieties are not created
equal. An oak tree may support as many as 537 different caterpillar
species. In contrast, the Ginkgo (Maidenhair) tree, which is native to
China and widely used by cities and homeowners around the country as an
ornamental specimen, hosts only 3 caterpillar species. That
consideration carried far less weight in planting decisions than did its
appearance and the fact that it can grow in even poor soil conditions
with little care.
In thinking about urban biodiversity, it seems intuitively logical
that native trees and shrubs would support more native wildlife than
non-native species. But, it is more nuanced that that even. The Tulip
tree is native to North America, and is another species that has been
widely planted over the years as an urban ornamental tree. It grows
fairly quickly, reaching a height of some 160 ft. Yet compared to the
oak tree mentioned above, a Tulip tree supports only about 21 species of
caterpillars.
The most basic requirements of wildlife, in the end, are the same as
for humans. They need food and they need shelter. In that respect,
trees matter. Landscaping matters. It is not the number of trees, or
the fact that you landscape your home alone that matters.
What you plant
is often more important than the act of planting in and of itself. If
we value biodiversitity...if we are serious about addressing the decline
in bird populations and sustaining wildlife in our urban environments,
we must move considerations of their needs for both food and shelter
higher up on the list of criteria used in making such planting
decisions. And this consciousness needs to become institutionalized at
both the city level and, individually, as homeowners.
Another of the problems associated with using non-native landscaping
in the urban environment is that, to paraphrase a popular civic a motto,
"What happens in Vegas doesn't always stay in Vegas." Some
non-natives, though certainly not all, refuse to stay put in the urban
settings they are first introduced to. Think about English Ivy, or
Kudzu, or even certain trees. As the Jeff Goldblum character in
"Jurassic Park" warned early on in the film, "Nature finds a way."
Mostly, it finds a way to reproduce and spread. As these non-native
plants escape the confines of their urban gardens and landscapes, they
spread into more "natural" ecosystems, often displacing native
vegetation and forest species to the detriment of wildlife by reducing
vital food sources and breeding habitat.
There is an intrinsic irony with respect to non-native plants that is
parochial in nature. A home owner might think that he/she is actually
increasing the biodiversity
of their immediate environment by planting a non-native species on
their lot. After all...this is a plant that doesn't ordinarily grow
here, so if I plant it, I have made the environment, by definition, more
"diverse." That's not the case, however. Lacking natural competitors
or pathogens, many of these non-natives often have the ability to crowd
out native species and alter the environment. From a global
perspective, the rapid spread of non-native species is having the effect
of actually
decreasing biodiversity, and is leading us
inexorably towards a global homogenization of plant and wildlife
diversity. I have seen it referred to as a global march towards the
McPlanet...where no matter where you travel, one encounters the same
plants and animals.
Even within a large urban environment, however, there is also an
unmistakable socio-economic component to biodiversity. The more
affluent a neighborhood, it turns out, the more diversity exists. Upon
reflection, that's hardly surprising. More affluent neighborhoods are
characterized by more discretionary income that is used for landscaping.
If you were a bird or an urban mammal, where would you rather reside
and rear your young?
Here?
home in Eastmoreland, Portland, OR...avg income $87,645
Or here?
Eastside, Portland, OR, referred to as "Felony Flats", avg income $32,000
One of the more interesting web based developments that has arisen is
the marriage between two distinct databases in order to analyze the
links between urban tree species and biodiversity. From
Yale Environment 360:
A new study in the journal Landscape and Urban Planning also
looks at better ways of understanding urban wildlife and habitat in
combination. The study uses birds as bio-indicators for other wildlife
types because they are easier to count than shy, often nocturnal,
mammals, and because they are more broadly familiar to the public.
The study proposes a marriage of i-Tree and eBird, two current
methods for keeping track of the natural world. Designed by the U.S.
Forest Service, i-Tree is software used by organizations around the
world to record data on urban tree cover, from single trees to entire
forests. Its counterpart, eBird, from Cornell Lab of Ornithology, is a
checklist system enabling thousands of birders around the world to log
their observations into a central database. The combination of the two
enables researchers to assess not just which trees characterize a
neighborhood, but how good they are as bird habitat, and which birds are
using them.
One can only hope that urban planners and city agencies involved in
environmental decisions regarding street trees and open spaces will make
use of such information in the future. On a more individual level,
what can be done to educate homeowners about how their landscaping
choices impact biodiversity? That is, perhaps, a more vexing question.
People like pretty, eye catching specimens. And they really, really
like easy. Are native trees any harder to cultivate than non-natives?
Not really, in most cases. Sure, there are some non-natives that are
more tolerant of salt, if you live in the snow belt, or which accomodate
more neglect and inattention.
But if you are like me, you will come to the conclusion that the
trade off is not really worth it. Perhaps you enjoy birds, and even put
out feeders to try to attract them. And perhaps, like me, you have
been disappointed by the variety of birds that come to your
feeder...even discontinued feeding them for that reason. These
birds...indeed, all urban wildlife, require more than simply a handout
in the form of birdseed. They need an ecosystem. They need native
food. They need insects and caterpillars, which in turn depend upon
specific host plants. Maybe you plant flowers, hoping to attract
butterflies...and have also been disappointed at the low turnout.
Butterflies need more than just nectar from blossoms. They need host
plants during their larval stage...and often times those host plants
aren't the most attractive plants for landscaping.
As more and more cities spray roadsides to control weeds, many of
those host plants are disappearing. Learn what butterflies are native
to your area and google them. Learn what plants they require over
their entire life cycle.
You may not want to plant wild fennel, for example, in your front
yard...but perhaps you have an "out of sight, out of mind" strip on the
side where it would provide beneficial habitat without marring the
aesthetics of your landscaping vision.
But if we, as individuals, and as urban citizens, value wildlife and
hope to stem the loss of biodiversity here, we must take into
consideration what we plant and why we plant it. Forget that Ginkgo
tree, or that Norfolk Island Pine. or that Amur Maple. Instead of
planting an evergreen shrub like juniper, consider a fruiting shrub.
See a vacant lot in your neighborhood? How about seeding it with an
inexpensive can of wildflower seeds? Call your local city's department
in charge of tree planting/environmental services, and urge them to
consider native trees that support wildlife instead of choosing the most
"neglect tolerant" tree out there.
We can do this.
More reading:
http://www.theguardian.com/...
/https://public-media.si-cdn.com/filer/7f/af/7faf3de4-f6bf-4423-a4e3-5b3e29eb117b/cogongrass-imperata-cylindrica-in-bloom-in-early.jpeg)
DORLING KINDERSLEY VIA GETTY IMAGES
ERICH SCHMIDT VIA GETTY IMAGES
LINJERRY VIA GETTY IMAGES
