are so good, that out of 1,500 new trees, we lost
only a couple in this year. For anyone who knows
how tough it is to establish street trees during an
extended drought, that's quite an accomplishment!
What tree species are your
best performers? What are your
species diversity guidelines?
SA: Many types of tree grow quite well here in
Eugene, although our extended summer drought
(June-September) can be challenging for species that
require summer rain. Some of our top performers as
street trees include: European hornbeams (Carpinus
betulus), parrotias (Parrotia persica), ginkgos (Ginkgo
biloba), oaks (Quercus spp.), maples (Acer spp.) (espe-
cially bigleaf maple/Acer macrophyllum), tupelos
(Nyssa spp.), Lavelle hawthorns (Crataegus × lavallei),
and catalpas (Catalpa spp.). The jury is still out on
Chinese pistache (Pistacia chinensis) trees (some have
fared quite well, others have not; we're not sure why).
Trees that don't do that well as street trees here
include: sweet gums (Liquidambar spp.), pin oaks
(Quercus palustris), honey locusts (Gleditsia tri-
acanthos), and fast-growing American elm cul-
tivars (Ulmus americana). These trees seem
to do better in areas with a colder, more
definitive dormant season than we have.
In terms of species diversity guidelines, we try to
meet or exceed the 10/20/30 rule (which dictates
that a single species not exceed 10% of a popula-
tion, that a single genus not exceed 20%, and that
a family not exceed 30% of a population). Overall,
our street tree population is well within these
guidelines, although it can be challenging to meet
the 10/20/30 goal on smaller scale sites. We also
try to promote intraspecific genetic diversity, func-
tional diversity, and age diversity wherever possible.
We do have a bit of an age diversity issue in our
downtown core, where there are lots of senes-
cent bigleaf maples and relatively few middle-aged
trees. We are working to address this liability. >>
A beloved street tree, Oregon
white oak (Quercus garryana), with
creative sidewalk placement.
Photo by Eric DeBord
32 CityTREES
