In 2010 the U.S. Forest Service, in cooperation with municipal arborists, conducted a research project to determine general costs and benefits of urban trees in Central Florida. The project used Orlando, Florida field data and other information drawn from municipal arborists across the west central Florida region including St. Petersburg, City of Tampa and Dunedin (Peper et. al. 2010).
Their work identifies a process for the quantification of costs and benefits for representative small, medium and large broadleaf trees and a conifers in the Central Florida region. This process can be used as a starting point for more specific cost – benefit analysis for the cities in this rapidly growing and diverse region.
Portions of the following are taken directly from the final report.
Calculating Benefits
Note* Benefits are realized at four geographic scales: parcel, neighborhood, community and global. Annual benefits are calculated as:
B = E + AQ + CO2 + H + A
Where:
E = value of net annual energy savings (cooling and heating)
AQ = value of annual air-quality improvement (pollutant uptake, avoided powerplant emissions, and BVOC emissions)
CO2 = value of annual CO2 reductions (sequestration, avoided emissions, release from tree care and decomposition)
H = value of annual stormwater-runoff reductions
A = value of annual aesthetics and other benefits
Annual costs (C) are the sum of costs for residential yard trees (CY) and public trees (CP) where:
CY = P + T + R + D + I + S + Cl + L
CP = P + T + R + D + I + S + Cl + L + A
Where:
P = cost of tree and planting
T = average annual tree pruning cost
R = annualized tree and stump removal and disposal cost
D = average annual pest and disease control cost
I = annual irrigation cost
S = average annual cost to repair/mitigate infrastructure damage
Cl = annual litter and storm cleanup cost
L = average annual cost for litigation and settlements from tree=related claims
A = annual program administration, inspection and other costs
Net benefits are calculated as the difference between total benefits and costs: Net benefits = B – C
Small broadleaf – crape myrtle
Medium broadleaf – southern magnolia
Large broadleaf – live oak
Conifer – slash pine
The Analysis
The analysis distinguished between “yard trees” (those planted in residential sites) and “public trees” (those planted on streets or in parks). Benefits were calculated based on tree growth curves and numerical models that consider regional climate, building characteristics, air pollutant concentrations, and prices. Tree care costs and mortality rates were based on results from a survey of municipal and commercial arborists. A 60-percent survival rate was assumed over a 40-year timeframe.
General outcomes from the U.S. Forest Service research project: Large trees provide the most benefits.
Average annual benefits over 40 years increase with mature tree size and differ based on tree location.
Except for conifers, the lowest values were for public trees and the highest values were for yard trees on the western side of houses.
Benefits range as follows (40 years after planting):
$23 to $30 for a small tree (24 ft tall)
$59 to $74 for a medium tree (46 ft tall)
$127 to $149 for a large tree (56 ft tall)
$32 to $34 for a conifer (67 ft tall)
*Benefits associated with reduced levels of stormwater runoff and increased property values accounted for the largest proportion of total benefits in this region. Energy savings, reduced levels of air pollutants and CO2 in the air were the next most important benefits.
*Energy conservation benefits differ with tree location as well as size. Trees located opposite west-facing walls provided the greatest net cooling energy savings.
The benefits of trees were offset by the costs of caring for them. Based surveys of municipal and commercial arborists from throughout the region, the average annual cost for tree care over 40 years ranges from $20 to $31 per tree.
Annual costs for yard and public trees, respectively:
$20 and $22 for a small tree
$23 and $27 for a medium tree
$25 and $31 for a large tree
$23 and $27 for a conifer
*Planting costs, annualized over 40 years, were the greatest expense for yard trees ($11 per tree per year); planting costs for public trees were significantly lower ($6 per tree per year).
*For public trees, pruning ($7 to $11 per tree per year) and removal and disposal expenses ($4 to $6 per tree per year) were the greatest costs.
*Public trees also incur administrative costs, including inspections ($2 to $4 per tree per year).
Average annual net benefits
Average annual net benefits (benefits minus costs) per tree for a 40-year period were calculated:
$1 for a small public tree to $10 for a small yard tree on the west side of a house
$32 for a medium public tree to $51 for a medium yard tree on the west side of a house
$96 for a large public tree to $123 for a large yard tree on the west side of a house
$7 for a public conifer to $9 for a yard conifer in a windbreak
*Environmental benefits alone, including energy savings, stormwater runoff reduction, improved air quality, and reduced atmospheric CO2, were greater than tree care costs for medium and large trees.
*Net benefits for a yard tree opposite a west wall and a public tree were substantial when summed over the entire 40-year period:
$403 (yard) and $23 (public) for a small tree
$2,039 (yard) and $1,266 (public) for a medium tree
$4,939 (yard) and $3,859 (public) for a large tree
$344 (yard) and $296 (public) for a conifer
*Private trees produce higher net benefits than public trees. Survey results indicated that this was primarily due to higher maintenance costs for street and park trees. The standard of care is often higher for public trees because municipalities need to manage risk, maintain required clearances for pedestrians and vehicles, remove tree debris after hurricanes, and repair damage to sidewalks and curbing caused by tree roots.
Here is the link to the full report:
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