Tree Protection Notes

Wednesday, February 14, 2007

Oakville Tree Distribution by Size

What’s wrong with this picture?

53% of Oakville’s trees have trunk diameters below 7.7cm dbh or 3 inches. A large percentage of these are shrubs and hedges. Only 164,000 trees have trunks above 30cm or 12 inches. How long would it take with out current distribution to reach a more optimal configuration? (A silver maple for instance will typically reach 27cm after 15 years, 58cm after 30 years).

We can potentially obtain a minimum 40% canopy coverage target in around 45 years (our goal should be much higher), if we have a 2% mortality rate (which is low) and the loss of none of our existing healthy trees.

Increased development activity and land clearing for new development projects has led to public concern with the removal of mature trees.  How do we protect our existing large trees?

The town can do two things to address the problem: education and or legislation. These are highlighted in the report Oakville’s Urban Forest: our solution to our pollution http://www.oakville.ca/Media_Files/forestry/UFORE.pdf

Action item 3: The Urban Forest Strategic Management Plan (UFSMP) will develop a private urban forest stewardship education program.

ACTION ITEM 8: The Town should investigate the feasibility of an incentive program for private large stature trees in order to maximize filtration of criteria pollutants and GHG's.

ACTION ITEM 11: The Forestry Section should Chair an interdepartmental/interagency Technical Advisory Committee to develop through the UFSMP:

a) Urban forest canopy cover targets for Oakville and;

b) How key Town Departments can contribute to achieving these targets.

ACTION ITEM 14: Amend the Town's Official Plan, Part C, Section 10.4 to recognize the municipal urban forest as a component of the municipality's "infrastructure." This is intended to build on the Town's existing Tree Protection Policy (Corporate Policy # 01-03-08).

The development of tree protection legislation falls under Action Items 8, 11 and 14. Legislation should be designed to encourage private property owners to protect their large mature trees and to discourage developers from removing mature trees when building or expanding homes. There are a variety of possible approaches:

• directive by-laws which disallow the removal of specific size, number and species or healthy trees
• by-laws and ordinances which  prohibit the removal of a certain percentage of tree canopy from a property or require mitigation of removal by requiring the guarantee of return of tree canopy in 5 to 10 years – either on the property or on public space
• by-laws which prohibit the removal of trees during specific periods of time, e.g.  after the transfer of ownership or during nesting season
• by-laws which require the posted intention of tree removal allowing neighbors to make the case that their quality of life and or property values will be negatively impacted by such removal
• by-laws which restrict the removal of trees from specific locations based on their impact on ecology or hydrology
• by-laws which prohibit the removal of trees that provide shade over impermeable surfaces (e.g. parking lots, roadways, etc.) during summer months

These are but a few examples and a place to start, (see additional material).

Oakville’s Urban Forest: our solution to our pollution

Report Conclusions related to the development of a private property tree protection bylaw:

1. aim for species, size and age diversity (reduces the impact of pests)

o        currently size and age are not well distributed

2. Increase the number of healthy trees

o        particularly important in industrial areas of the Town and new developments

3. Sustain and increase existing tree cover

o        education, tree protection and incentive programs

4. Sustain large, health trees (greatest per tree effects)
5. Use long-lived trees (reduces emissions from planting and removal)
6. Plant trees in energy conserving locations
7. Plant large trees as part of transportation corridors and parking lots

Notes on the report:

·        Size distribution (Appendix9 , p 58)

o       1.9 million trees (95% range 1.5 -2.3 million) (OUF p.57)

o       1.0 million trees have trunks below 7.7cm dbh or 3 inches. 

o       1.4 million trees have trunks below 15.3cm dbh or 6 inches.

o       91.4 % have trunks below 30cm or 12 inches. Only 164,000 trees have trunks above 12inches

o       8.2 % are trees with trunks between 30cm and 76cm (12  to 30 inches) 156,000 trees

o       3% have trunks above 46cm (18inches) compared to Chicago with 28.7% (Nowak. 1994 The State of Chicago's Urban Forest)

o       1% of trees have trunks above 61cm dbh or 24 inches – 24,000 trees

o       0.4% large stature trees (8,500) with trunks above 76cm or 30inches. The target for large stature trees is 10% (p.18)

[A guideline for tree distribution by diameter classes has been recommended (Richards, 1983), and it has been suggested that no more than 40% of the trees should be under 20 cm in diameter at breast height (DBH), 30% from 20-40 cm DBH, 20 from 40-60 cm DBH, and 10% in the >60 cm DBH class. (Podol, 2004, Species Diversity and Age Class Structure: University of Toronto’s Urban Forest http://www.forestry.utoronto.ca/pdfs/podol.pdf )

·        Canopy coverage

o       Current canopy coverage – average 29.1%

§         Ranges from 5% in industrial areas to 46% in woodlots

§         Urban areas in the U.S. have an average tree cover of 27.1% (Nowak, D.J., M.H. Noble, S.M. Sisinni, and J.F. Dwyer. 2001a. Assessing the U.S. urban forest resource. Journal of Forestry. 99(3): 37-42.) Toronto 20.5 % (Kenney, W.A., C. Idziak, and C. Anderson. 2001. The role of urban forests in greenhouse gas reduction. Report submitted to the Ontario Ministry of Environment. Contract ON ENV (99)

§         This canopy coverage figure includes shrub cover and is not necessarily consistent with canopy coverage determinations obtained through Landsat spectoanalysis,  (According to Cheryl Kollin, Vice President, Urban Ecosystem Center, American Forests)

§         We do not know what percentage of the canopy coverage is at a height of 3m or 20ft (the approx height for instance where shading benefits become significant)

o       Highest coverage Res Low density: 48.7% forest cover Eastlake (Winston Churchill to First and QEW to Lake) 39.9% forest cover Old Oakville 38.5% forest cover Bronte

o       Lowest coverage: 6.6% Midtown Core Industrial, 9.3% QEW West Industrial, 9.9% Burloak Industrial

o       Leaf carrying capacity or leaf area density

§         In conversation with Dr. Kenney, he suggests that Leaf Area Density or leaf carrying capacity is an alternative measurement parameter that is particularly helpful when considering pollution mitigation and stormwater runoff reduction. Note equation for leaf area density is given as

LAD = Se^{-4.3+0.29H + 0.73D+5.72Sh} *CF / A   where LAD reflects the three dimensional nature of the canopy (H height and D diameter), species variation (Sh) and tree condition (CF). 

·        Canopy growth projections

o       40% canopy coverage is a minimum target goal (with a potential for 60-80%) set by American Forests and Environment Canada and is attainable by 2050 assuming current trees are maintained and a 2% mortality rate (the report stresses the need to determine actual mortality rate).

§         2% mortality is low given size class of population and in comparison to other urban communities (e.g. Baltimore, MD averaged 6.6%, Boston, MA averaged 9%, Oakland CA averaged 19% for newly planted trees; etc.) “Morus alba, Ailanthus altissima, and trees in small diameter classes, poor condition, or in transportation or commercial - industrial land uses exhibited relatively high mortality rates.” Nowak, David et. Al., 2004,  “Tree mortality rates and tree population projections in Baltimore, Maryland" Urban Forestry Urban Greening. 2: 139-147

§         2% mortality does not take into account removal of healthy trees for development, home expansion, infill etc. (Consider recent Dec. 2006, clear cutting of 3 hectares Grand Oak Woods)

§         Health assessment indicated 11.7% trees are in poor condition (11.5% were dead).

·        Top ten tree species (OUF p.16)

o       10.6% Northern white cedar (Thuja occidentalis), 200,100 trees, mostly in hedgerows. They contribute proportionally small leaf surface area (LSA) - about 2.4% LSA. Native, small tree to 15m, dbh 30cm, lifespan 300 + (oldest recorded 1890)

o       9.2% Sugar maple (Acer saccharum) contributing 11.7% LSA. Native tree to 35m dbh 90cm, lifespan 200+ (oldest living 500)

o       7.2% White ash (Fraxinus americana) which contributes 4.6% LSA – (136,000 trees susceptible to Emerald Ash Borer issue below). Native tree to 35 m, dbh 150cm, lifespan 200 (oldest recorded 260)

o       5.5% Hawthorn (Crataegus spp?) contributing 1.2% LSA native shrubs or small trees to 12m, dbh 30cm, lifespan ? (oldest recorded 700).

o       6.1% Staghorn sumach (Rhus typhina) ) 0.6% LSA. Native shrubs or small tree to 6m, dbh 10cm, lifespan 50.

o       3% American Beech (Fagus grandifolia 20-35 m tall) 2.8% LSA. Native tree to 25m, dbh 100cm, lifespan 200 (oldest living 204)

o       2.3% Silver maples (Acer saccharinum) 7.1% LSA. Native tree to 35m dbh 100cm, lifespan 130 + (oldest living 380)

o       2.2% Norway maples (Acer platanoides) 9.2% LSA. Invasive alien tree species to 20 m, dbh 100cm, lifespan 80?

o       2% (40,000) European buckthorn (Rhamnus cathartica and Rhamnus frangula) 1% LSA. Invasive alien species of shrub to 8m, dbh 10cm, lifespan unknown (should be removed – see below)

o       1.9% White spruce (Picea  glauca) 3.5% LSA. Native tree to 35m, dbh 60cm, lifespan 200.

“It has been suggested that an urban street tree population should be made up of no more than 30% of one genus and 10% of one species (Richards, 1983) in order to provide maximum protection against pest outbreaks and diseases, and prevent over-dependence on a single species. It has also been suggested that no more than 10% of the trees in a community be of the same genus, and no more than 5% of the same species (Moll, 1989). The International Society of Arboriculture (ISA) has also adopted this guideline to maximize protection of the urban forest against potential hostspecific pest and disease outbreaks (McKay, 2000).” (Podol, 2004, Species Diversity and Age Class Structure: University of Toronto’s Urban Forest http://www.forestry.utoronto.ca/pdfs/podol.pdf )

·        Distribution of trees by location (OUF p. 17)

o       46% in woodlots (909Ha) 972 trees/ha (most trees under 8cm, only 0.3% of trees on woodlots are large stature or 2652LST/883,900T) (49% of woodlots are Town owned)

o       20% in Res Medium& High Density (3389ha) 113 trees/ha ( 0.8% of trees are large stature 3053LST/381,600T)

o       16% in Open space and pkwy (1690ha) 179 trees/ha

o       11% in Residential Low density   (1122ha) 193 trees/ha (about 1% of trees are large stature trees) (2163LST/216300T = 1%LST)

o       5% in Employment/Industrial (1670ha) 59trees/ha

·        Potential threats to our trees

§         Cutting of healthy trees

·        Clear cutting

o       For example: Dec clear cutting of 3.3ha Grand Oak Woods – (approx 3000 trees and 9 or 10 large stature trees, assuming density 972trees/ha and 2.9 LST per ha)

·        Homeowner discretion

·        Infill

§         Insects and disease

·        Emerald Ash Borer could severely impact the 140,000 Northern white ash (Fraxinus Americana), 7.2% population (176,000 host trees in total)

·        Oak Decline do to drought and repeated insect defoliation (e.g. 95% oak mortality in Iroquois Shoreline Woods Park in 2000  - Bayshore woods and Winston Park woods area 20% Oak population) (Jalil Hashemi, 2004, Mitigation of Oak Decline in Oakville. MFC report )

·        Other potential threats:   Asian longhorned beetle (760,000 host trees), Gypsy moth (419,000 host trees), Dutch elm disease (39,000 host trees), Pine shoot beetle, Sirex woodwasp, Brown spruce longhorn beetle, Spruce longhorn beetle, Hickory bark beetle, Jack pine budworm, etc.

·        Invasive alien species IAS of concern

o       European buckthorn (Rhamnus cathartica and Rhamnus frangula)  – serious problem in South and Central Ontario – should be removed an replaced with American elder (Sambucus canadensis), Black chokeberry (Aronia melanocarpa), and Juneberry (Amelanchier alnifolia) for examples. In the top 10 tree species.

o       Norway maple (Acer platanoides )– second most common tree species. (Serves as an excellent air filter making it a difficult protection issue – don’t plant more)

o       It is unknown how significant other IAS are: Horse chestnut (Aesculus hippocastanum), Tree-of-heaven, (Ailanthus altissima), European alder (Alnus glutinosa), European white birch (Betula pendula), Russian olive (Elaeagnus angustifolia), Autumn olive (Elaeagnus umbellata), White mulberry (Morus alba), Norway spruce (Picea abies), Scots pine (Pinus sylvestris), White poplar (Populus alba), Lombardy poplar (Populus nigra var. italica), Black locust (Robinia pseudoacacia), European mountain ash (Sorbus aucuparia),  Siberian elm (Ulmus pumila).

·        Pollution Mitigation

o       Air pollution – particle entrapment, carbon sequestration, ozone mitigation, temperature management etc.

§         Carbon sequestration: “Forests store two-thirds of terrestrial carbon in soil and biomass by absorbing carbon dioxide from the atmosphere and converting it into organic material, an equivalent of nearly 1 trillion tons. Of all the plant kingdom, forests provide the most long-lived storage sink in the carbon cycle tying carbon up in wood and soil accumulation for years before returning it to the atmosphere by respiration, decomposition, erosion, or burning.” (Nicodemus & Willams 2004 QUANTIFYING ABOVEGROUND CARBON STORAGE IN MANAGED FOREST ECOSYSTEMS IN OHIO, Proceedings of the 14th Central Hardwoods Forest Conference)

§         Annual per tree gross sequestration of carbon of small-stature tree (12-25 cm dbh) negligible compared to large stature tree (88-101cm dbh) [To calculate approx. carbon sequestered, c: c=a(dbh²*ht)^b where a and b are species specific constants] “Annual carbon sequestration rates are up to 90 times greater for healthy large trees as compared to healthy small trees, such as those commonly planted in urban areas.” Y (kg carbon) = a (dbh²* ht)^b (Johnston, Andra and Gerhold, Henry. Carbon Storage by Utility-Compatible Trees,  Journal of Arboriculture 27(2): March 2001) View PDF

§         29% air pollution filtration is from Town trees. Although they represent 43% of the total tree population by stem count, they are generally small stature trees.

§         Woodlots are the most efficient carbon sink, sequestering 2.7 tonnes followed by RL at .9 tonnes and RM +RH at 0.4 tonnes.

§         Sugar maple, white ash and Norway maple contribute almost one quarter of all carbon sequestration because they are large-stature trees, widely planted 50 - 80 years ago.

§         Oakville’s urban forest filtered 172 tonnes criteria pollutants.

The report briefly reviews other benefits (p6):

• Benefits of Trees http://www.treelink.org/linx/?navSubCatRef=56  
• Coder The identified benefits of community trees and forests, http://www.marshalltrees.com/upload/articles_files/art_31attached_file.pdf
• See http://oakvillegreen.org/content/view/74/88/ for additional links

o       Stormwater runoff reduction,

§         Zipperer, W. C., J. Wu, R. V. Pouyat, and S. T. A. Pickett. 2000. The application of ecological principles to urban and urbanizing landscapes. Ecological Applications 10(3): 685-688.)

§         Stormwater: (1) channel the water so it doesn't flood homes, property, or city streets and (2) make sure the water is reasonably clean before it flows into natural streams, rivers, and lakes… Depending on the species and the soil conditions (both the type of soil and its rain-saturation level), trees can absorb a considerable amount of water. Also, water-polluting nitrates, phosphorus, and potassium, which in many areas are spurring the development of total maximum daily loads (TMDLs) for receiving waters, are readily absorbed by trees, which consider these substances food. American Forests analyzed 10 sites in Garland, Texas… For example, a medium-size, 3.86-ac. residential site, with its 8% canopy cover, provided a 3% runoff reduction. If the site's tree canopy were increased to 35%, runoff reduction would quadruple, to 12.8%; a canopy cover of 45% would bring that number to 16.1%. (TREES: The oldest New Thing in Stormwater Treatment by Stormwater Journal)

·         Calculation BENEFITS of trees:

To capture the total value of annual benefits B, each benefit was summed:

B = E + AQ + CO[sub2] + H + O

where

E = price of net annual energy savings (cooling and heating)

AQ = price of annual air-quality improvement (pollutant uptake and avoided power plant

emissions)

CO[sub2] = price of annual carbon dioxide reductions

H = price of annual stormwater runoff reductions

O = price of aesthetics and other benefits

E. Gregory McPherson, James R. Simpson, Paula J. Peper, and Qingfu Xia. BENEFIT-COST ANALYSIS OF MODESTO'S MUNICIPAL URBAN FOREST,Journal of Arboriculture 25 no5 235-48 S 1999

http://www.sfrc.ufl.edu/urbanforestry/Resources/PDF%20downloads/mcpherson_modesto_1999.pdf

The Bigger Picture

• Forests cover about 45% of Canada and 65% of Ontario. Canada has about 10 per cent of the world's forests. Forests play an important role in the global carbon cycle, exchanging carbon with the atmosphere through photosynthesis and respiration, and storing a large amount of carbon in vegetation and soil.

Changhui Peng, et. al. 2000, Quantifying Ontario's Forest Carbon Budget. Ministry of Natural Resources

• Oakville is within the Carolinian Zone called ecological site region (ecoregion) 7E. This ecoregion covers approximately 22,000 km² in extreme southern Ontario, extending northeast from the United States border to Toronto, and northwest to Grand Bend on Lake Huron. It is bounded by four major lakes (Huron, St. Clair, Erie and Ontario), and the St. Clair, Detroit and Niagara rivers.
• According to LANDSAT ^TM satellite imagery (vintage 1987-1993), less than 15% of Ontario’s Carolinian landscape is classified as having “natural” cover. The Canadian portion of the Carolinian Life Zone has been described as the most ecologically-degraded part of the Great Lakes basin. Forest cover has been reduced from 80% to 11% (Table 1), and wetlands from 28% to 5% of the area. Only 0.07% of southern Ontario is now in old growth condition (over 120 years in age). Nearly all of the remaining “natural” cover in the Carolinian Zone has been logged, irrigated, cleared, polluted or otherwise disturbed by human activities at one time or another over the past few centuries. Because the most intact natural areas have persisted where feasibility of agricultural and urban development is poor, the remnant vegetation proportions differ significantly from pre-European settlement conditions.

Jarmo V. Jalava, Peter J. Sorrill, Jason Henson and Kara Brodri , 2002. The Big Picture Project: developing a natural heritage vision for Canada's southernmost ecological region. Ministry of Natural Resources.

http://www.spectranalysis.com/HTM/landcov.htm

1. Halton Region

• Current woodland extent in Halton Region is 16.9% based on Ontario Ministry of Natural Resources (OMNR) data and  24.2% based on Ontario Hydro data (these figures include plantations). This data includes plantations. This represents a 70% loss since pre-European settlement. (Jarmo V. et. al. , 2002.)

·         Halton Population and Projections of Population  (,000)

 2. The Town of Oakville