April 2019 - Parks & Recreation - 29

parks and forests. In our changing
climate, voracious pests and sneaky
diseases that gain a slight foothold
within parklands can spread like
wildfire before they can be noticed,
caught and quarantined. It's possible for common species, like those
ash trees, to be all but eliminated in
a decade or less.
Whether plant, animal, virus or
bacteria, all living organisms are
locked in a battle with the pathogens,
pests and parasites in their surrounding environment. Using the tools and
tricks that nature has equipped them
with keeps them in the game. One of
the oldest, strongest tools in this arsenal is the ability to adapt, then pass
along that element of survivability to
the next generation.
The founders of Pittsburgh's
parks left quite the legacy, not only
in the consideration that they gave
to the design and preservation
of parkland, but also the impressive diversity of the urban forests.
While it may be impossible to stop
pests and diseases from invading,
the Pittsburgh Parks Conservancy
aims to give park trees a fighting
chance by carrying on this important effort to increase biodiversity.
A Diminishing Gene Pool
Surrounding the popular community space of Schenley Plaza, near
the Carnegie Museum of Natural
History, is a stand of large, regal
London plane trees. These massive trees don't just offer shade on
sunny summer days. They ring an
alarm on a national level.
" When London plane trees were
first introduced to the United States,

PHOTO COURTESY OF PITTSBURGH PARKS CONSERVANCY

A Young Naturalist measures the diameter at breast height (DBH) of a tree, which
helps to estimate its volume, biomass
and carbon storage.

one nursery had a tree that did very
well, " says Parks Conservancy Director of Horticulture and Forestry
Phil Gruszka. " But they couldn't get
it to reproduce from seed, so they
started getting cuttings to grow out.
Then they released it to the trade and
named that cultivar 'Bloodgood.' "
Selected for its superior resistance to the fungus anthracnose, the
Bloodgood cultivar (a plant chosen
for its particular genetic makeup)
has been spread around now for
about 30 years, dominating nursery
stock of London planes. Plane trees
bought from nurseries have identical
genetic material to every other plane
tree. In short, they have not been
grown from seed from two parent
trees: They're clones. " Today, if I
wanted to replace a London plane, "
continues Gruszka, " I can only buy
the cultivar Bloodgood. "
However, a study conducted by
Gruszka and Dr. Cynthia Morton,
formerly of the Carnegie Museum
of Natural History, found some-

thing surprising about the Schenley
Plaza trees: They are all genetically
different. The trees, planted before
Bloodgood started to gain popularity, are much more diverse than the
current nursery stock. Of nearly
200 such trees that have been planted over the years in Pittsburgh's
parks, 100 are of a strong, diverse
population, toughened from years
of fighting off pests and disease.
Were these study findings true
only for London planes? Gruszka
and Morton widened their net to
test Pittsburgh's park tree diversity
against trees sold around the country. After polling nurseries from
various parts of the country, they
found that 10 common trees used
all over the United States were
clones - tree stock from major
nurseries across the country is diminishing the tree gene pool.
Creating Greater
Genetic Diversity
Because a large majority of trees

W W W. PA R K S A N D R E C R E AT I O N . O R G | A P R I L 2 0 1 9 |

Parks & Recreation

27
April 2019 - Parks & Recreation

Table of Contents for the Digital Edition of April 2019 - Parks & Recreation
