survey of trees conducted by Friends of the Don East (FODE) in east
Toronto neighbourhoods has turned up some interesting and disturbing
information about the condition of our urban forest.
The "Trees Count" study examined private and public trees
on several streets in Cabbagetown, Riverdale, Leaside and East York.
was conducted last summer, with the financial support of the Toronto
Atmospheric Fund, to test the usefulness of a tree inventory process
called Neighbourwoods© which is specifically designed to allow
volunteers to determine the health of trees in residential neighbourhoods
and help communities develop strategic plans to protect and enhance
their urban forests.
The results have led Friends of the Don East to develop plans to
greatly enlarge the inventory work in 2003.
The teams of volunteers examined nearly 400 trees during four weekends
in August and September. Two or three streets from each of the four
neighbour-hoods were included in the study, and nearly 30 pieces
of information were collected for each tree.
Homeowners allowed the teams access to privately-owned trees in
most of the backyards in the targeted areas. Trees on city property
along the street were also examined, but they formed only 36% of
the total. The study found that nearly two-thirds of the trees in
the neighbourhoods are on private property. This confirms experience
in other cities and shows that homeowners have a very large part
to play in the overall health of the urban forest.
Norway Maples made up 34% of all the trees in the sample. A close
relative, the Silver Maple, was the second most common species,
accounting for a little over 6%. Siberian Elms ranked close behind
in third place. Fourth place was occupied by White Mulberry and
fifth by a third maple species, the Manitoba Maple.
of species which represent
more than 5% of the total trees in the survey
Although 45 different tree species were found in the survey, 70%
of the trees were from only eleven species, suggesting that biodiversity
is quite poor in Toronto's urban forests. The fact that close to
half the trees (46%) were maples is disturbing for several reasons.
In the first place, both Manitoba Maple and Norway Maple are non-native.
The Norway Maple is a popular choice partly because it comes in
a variety of leaf colours including the dark red Crimson King cultivar.
It is also better able than many species at withstanding air pollution,
compacted soils and other poor growing conditions that face trees
planted along city streets.
of municipally-owned trees
versus privately owned trees
of native and non-native trees
of trees in each of six diameter classes
- 15.5 cm
- 30.5 cm
- 45.5 cm
- 60.5 cm
- 76.5 cm
of trees by height classes
to 11 metres
than 11 metres 65%
of native and non-native trees
by each diameter class
Norway Maples are also highly invasive and they have become
a very serious problem in stream valleys where they are squeezing
out native tree species. They shade out saplings as well as
woodland wildflowers, sedges and other groundcover normally
found in native forests, and this makes the soils more susceptible
to erosion. This highly prolific species has already taken over
large areas of Toronto's ravines.
Secondly, such overwhelming dependence on a single family of
trees makes Toronto's urban forest particularly susceptible
to being decimated by diseases or environmental problems affecting
maples. The city had bitter experience of this in the last century
when Dutch Elm disease wiped out virtually all of Toronto's
stately elm trees, leaving many streets completely barren.
Thirdly, the survey found that maples are an even more dominant
part of east Toronto's forest when their size is taken into
account as well as their numbers. The Silver and Norway maples
formed the overwhelming majority of the largest trees, and together
they comprised over 80% of the total leaf area.
The leaves of trees intercept and remove air pollutants, provide
air conditioning by evaporating water, and provide protection
from sun and wind.
While all trees make important contributions to air quality
and local climate, the greatest benefits come from the biggest
trees because they have the largest leaf area. Investing nearly
all these critical functions in one or two species is obviously
Fourthly, large trees are also the oldest and represent the
trees that most likely will have to be removed in the near future.
Toronto neighbourhoods that today are graced by large numbers
of magnificent large maples may quickly find themselves with
drastically fewer trees if action is not taken in time to renew
their urban forest. For example, nearly one quarter of all the
trees examined already show structural defects that make them
The Trees Count survey was conducted with exactly these problems
in mind. While the inventory looked at less than 400 trees,
the results strongly suggest that east Toronto communities need
more information about their trees in order to appropriately
plan for the future of their urban forests. FODE hopes to continue
the tree inventory work this summer and to concentrate on one
or two large neighbourhoods in order to develop a complete picture
of the status of their urban forests.
Besides their obvious environmental benefits, trees form a substantial
part of the value of a house. Approximately 15% of the house
and lot price may be related to its trees, and some real estate
appraisers think this number is closer to 30%, especially for
large mature trees.
Much of this value is aesthetic and could not be determined
from the data collected. However, the analysis did allow calculation
of the replacement value of each tree based on its size, species,
condition and location using the approach of the Council of
Tree and Landscape Appraisers.
benefits of trees go up exponentially as their size
and total leaf area increases.
this conservative valuation concluded that the average tree
in the survey was worth over $2100.
Oaks averaged more than $5000 each, with Black Walnuts and Red Oaks
In addition to inventorying trees, the volunteers who conducted
the survey also identifed 129 locations where there was room to
plant additional trees.
We must preserve suitable locations to plant new trees. There are
increasing pressures to pave over or build over lands that could
support trees and other vegetation. When front lawns are replaced
with parking pads, the opportunity to plant trees in that location
This preservation of plantable spots is the third "P"
in an effective urban forest program. The other two are protecting
existing trees and planting new ones.
Most tree programs only emphasize the last "P", but it
can't be accomplished effectively without determined efforts to
provide and preserve plantable locations.
And while we are waiting for new trees to grow, we need to make
every effort to protect the trees we already have. One large tree
provides climatic, energy and environmental benefits equal to hundreds
of new saplings.
This is proven by the average leaf area of the trees in the study
- a stunning 4300 square metres.
The study also identified 83 potential heritage trees and found
four regionally rare trees - two very large White Oaks, and two
The key finding, however, is that the urban canopy in the study
areas is dominated by Norway Maples, a non-native invasive species
with negative impacts on natural areas, particularly Toronto's ravines.
In addition, the maturity of many trees, while contributing to neighbour-hood
aesthetic and real estate values, and relief during heat waves,
means that many parts of Toronto will soon face potentially significant
FODE believes that these key conclusions suggest both a huge near-term
requirement to plant replacement trees and a corresponding opportunity
to reduce the extensive presence of Norway maples and improve the
diversity of the existing canopy with more native species.
The Trees Count inventory was conducted by volunteers. They utilized
the Neighbourwoods© program developed at the University of
Toronto by Andy Kenney and Danijela Puric-Mladenovic, who subsequently
crunched the numbers and produced a detailed 108-page summary report.
The graphs accompanying this article are taken from that report.
See full report. The
appendix provides detailed data on each of the trees examined in
Count 2002: Summary Report (512 KB in PDF format)
You Can Get Involved
Trees Count is specifically designed to be used by community groups
and non-expert volunteers. Friends of the Don East has drawn conclusions
from the experience and is seeking additional funding to support
more extensive tree inventory work this summer in neighbourhoods
along the Don Valley. If you would like to get involved, please
contact FODE at (416) 466-9153 or send an email to firstname.lastname@example.org.
The 2003 survey is expected to begin in May or June.