TREE INVENTORY SUMMARY
Having a healthy, diverse urban forest can provide many benefits to residents as well as the ecosystem. In addition to being aesthetically pleasing, trees also provide a number of ecosystem services for the city. For example, they scrub the air of pollutants, slow the release of stormwater runoff into the watershed, filter stormwater, provide oxygen, reduce energy costs, provide shade, and offer habitat and food for wildlife.
Trees in urban environments not only contribute services to the city, but also provide residents with invaluable green space and health benefits. Proximity to green space has been linked to better mental health (Barton, et al. Environmental Science & Technology, 2010) as well as increases in social connections (Holtan, et al. Environment and Behavior, 2014) and physical well-being (Takano, Journal of Epidemiology & Community Health, 2002).
The inventory data were analyzed in Microsoft Excel and Fremont’s own TreePlotter app (https://pg-cloud.com/FremontCA/) to determine the state, characteristics, and trends of the city’s urban forest. Analyses and summaries were completed for the inventoried trees to determine the health and diversity of the trees in the city.
The data include 77,387 trees and 23,781 planting sites that were inventoried in 2020 by Certified Arborists accredited by the International Society of Arboriculture and analyzed for site quality, health observations, and structural defects among other data points.
It should be noted that while the city does not maintain all the trees included in this inventory, the data analysis contained in this report typically looked at the city’s urban forest as a whole. In cases where the analysis was separated by city-maintained or privately-maintained trees, it is noted in this report.
Lastly, it is important to remember that the key to maintaining a sustainable and healthy urban forest is species and age diversity, proper tree maintenance, risk management, and community support, which can be accomplished with an urban forest management plan. The information in this report is provided to guide future maintenance and management and to better plan for the health and longevity of Fremont’s urban forest.
TREE INVENTORY STRUCTURE
Urban forest structure describes the tree population in the city in terms of its species composition, number of trees, age classes, and tree distribution. These summaries assist city tree managers in proper tree management and planting to ensure long-lasting canopy and benefits are distributed equally throughout the city. It’s important to note again that the city does not maintain street trees and this inventory includes a mix of both publicly and privately maintained trees.
TREE DIVERSITY AND COMPOSITION
Species composition data are essential since the types of trees present throughout the city dictate the amount and type of benefits produced, tree maintenance activities required, and budget considerations. The 77,387 trees inventoried consist of 510 different species and cultivar classifications. The highest percentage consists of Chinese pistache with 7% (5,699 trees) of the total tree population, followed by common crapemyrtle at 6% (4,578 trees) and sweetgum with 6% (4,281 trees). Figure 1 below shows the remaining top species and their percentages compared to the other 501 species that were inventoried.
SIZE AND AGE DISTRIBUTION
The distribution of tree ages influences the structure of the urban forest as well as the present and future costs. An unevenly aged urban forest offers continued flow of ecological benefits and a more uniform work flow allowing managers to more accurately allocate annual maintenance schedules and budgets.
To optimize the value and benefits of Fremont’s trees, the urban forest should have a high percentage of large canopy trees which provide greater ecosystem benefits. On the other hand, there must be a suitable number of younger, smaller trees in the urban forest to account for and eventually replace large and mature trees in decline. Having a healthy percentage of young trees in the urban forest will ensure a sustainable tree population as well as age distribution in future years. To compare Fremont’s urban forest structure to industry-recommended standards, the “ideal distribution” is used (McPherson et. al, 2011).
Overall, the age distribution of Fremont’s urban forest (blue bars) is similar to the ideal age distribution (green bars). As the figure above shows, 58% of the urban forest (44,811 trees) is composed of trees with a DBH (or “diameter at breast height,” measured at 4.5 feet above grade) ranging from 1 to 11 inches. This indicates that the majority of trees are young or small statured. Trees in this size class are crucial for a healthy urban forest, however the inventory found that there are 18% more trees in this category than the ideal distribution of 40%. This could be due to increasing devlopment in the city over the last 2-3 decades and the prioritization of planting smaller trees that are more popular with property owners, such as the Chinese pistache and crape myrtle. Development often shapes the tree diversity in a city and the city should work with developers to ensure that the species they are planting allow for larger species where possible.
Trees with a DBH of 27 inches or greater make up just 5% (3,981) of Fremont’s trees. City trees in this DBH range can offer larger ecological benefits if the trees are properly maintained and remain healthy, but trees of this size should be monitored frequently to determine maintenance needs, potential risks, and signs of decline. The DBH range of 20 to 26 inches, which makes up 10% of the tree population (or 7,352 trees) is 11% below the ideal distribution and extra care should be taken to ensure the health of these trees to maintain an ideal distribution in the future. The average DBH for the entire population is 11 inches, and the largest recorded DBH is 125 inches.
An ideal age distribution in the tree population allows managers to allocate and project annual maintenance costs uniformly. This ensures continuity in overall tree canopy coverage and associated benefits which are often dependent on the growing space of individual trees (e.g. open grown versus restricted growing areas). It is recommended to monitor and strategically manage large trees throughout the city and weigh the risks and benefits that are associated with large, mature trees.
TREE INVENTORY MANAGEMENT
Tree characteristics and environmental factors affect the management needs for urban trees. An analysis of the condition and maintenance requirements assists managers in planning Fremont’s urban forest. Tree condition indicates how well trees are managed and how well they perform, given site-specific conditions. Tree maintenance needs are assigned for public safety reasons and for the health and longevity of the trees themselves. Understanding the maintenance needs assists tree managers in establishing daily work plans and maintaining public safety.
URBAN FOREST CONDITION
The inventory data were analyzed to identify potential trends in tree condition and management needs. Information on the condition of trees plays an important role in planning, budgeting, and use of resources. Each inventoried tree’s health was evaluated by ISA Certified Arborists based on the condition of the wood and the foliage as well as the structure.
The figure above summarizes the 77,387 trees that were assigned a condition rating and shows the detailed information for each condition class.
The data show that a majority of the trees inventoried are classified as being in “Fair” condition, comprising 48% or 36,857 trees, followed by those in “Good” condition comprising 44% (33,800 trees).
4,820 trees are noted as being in “Poor” condition and 1,722 trees are classified as dead / removal required. The dead trees or trees noted for removal should be adressed and planned for immediately.
Tree observations were recorded during the 2020 inventory to further describe a tree’s health, structure, or location when more detail was needed. A total of 21 unique observations were included in the inventory. The complete list of observations, including their definitions, can be found in Appendix A.
The table to the right provides a summary of the observations for Fremont’s trees. A total of 81,189 observations were recorded during the tree inventory, with 44,288 sites (57%) noted as having at least one observation while 33,099 sites (43%) have no observation recorded. Poor structure was the most frequent observation recorded (26% or 19,741 trees) during the 2020 tree inventory. 1 out of every 4 trees (25% or 19,138) were noted as having crown dieback, and nearly 1 in 5 (18%) were observed to have been pruned improperly.
Poor Root System
All Other Observations
All Other Maintenance Needs
PRIMARY MAINTENANCE NEED
The inventory required an assessment of the maintenance needs, if any, for each tree. This information along with location and the TreePlotter application were used to guide the maintenance recommendations. A total of 18 unique maintenance needs were included in the inventory. This table provides a summary of the maintenance and pruning recommendations for all of the inventoried trees. Of the 77,387 trees that were inventoried, 53,571 (69%) trees were assigned a maintenance task. 31% of inventoried trees did not have any maintenance recommendation, however these trees should be routinely monitored to assess for any new maintenance issues that may arise in the future.
Crown cleaning, the selective removal of dead, dying, diseased, and broken branches from the tree’s crown, was recommended for 47% of the city’s trees and clearance pruning, or pruning to provide clearance for pedestrians, vehicles, utilities, and buildings, accounted for 13% of maintenance needs. Sidewalk damage was noted at 5,541 trees (7%).
Properly maintained and healthy trees are key to the success of Fremont’s urban forest. Since the city does not maintain street trees, it is recommended that the city implement an education campaign to address the maintenance needs with property owners. Working with property owners to prioritize high risk tree removals and to educate them about the proper maintenance of their trees will ensure a successful urban forest for future generations. If possible, it is recommended that the city identify funding sources to assist homeowners in properly caring for their trees where needed.
TREE INVENTORY DISTRIBUTION & GROWING SPACE
Tree distribution across land uses can affect maintenance costs, schedules, potential risks such as pests or diseases, and the effects of climate change. Adequate distribution of trees also contributes to Fremont’s pursuit for equitable distribution of tree canopy and associated benefits and equal access to the resource by all residents.
Trees located near a Single or Multi-Family residence made up a majority of the inventory with a combined 65% or 50,677 trees. 22% (17,055) of trees in the inventory dataset are in a Park/Vacant/Other land use type. The reamainder (9,655 trees) are in the Industrial and Commercial parts of the city. The figure below shows the complete breakdown of the land use type for the entire tree inventory.
PLANTING SITE WIDTH
The planting site width for tree roots can impact tree growth, health and maintenance costs over time. Adequate space and soil volume should be considered for each site based on tree species requirements and root biology. Frequency of maintenance is also a consideration for tree selection when a tree needs to be replaced. An analysis of growing space can assist tree managers in making future tree species selections for sites with similar characteristics.
The smallest planting site width measurements were collected for each inventoried tree. Table 3 to the right shows the number of trees and percentage of each planting site width classification. 37,749 (49%) of the inventoried trees are growing in a Class I (Small) site with 1-5 feet of space. 19%, or 14, 919 trees, are growing in a Class II (Medium) site with 6-10 feet of growing space. The remaining 32%, or 24,719 trees, are growing in a Class III (Large) site with widths greater than 11 feet.
Planting Site Width
CLASS I (SMALL): 1-5 ft
CLASS II (MEDIUM): 6-10 ft
CLASS III (LARGE): >11 ft
Tree growing space was identified for each inventoried tree. The area of land between the curb and a sidewalk, or the curbside strip, accounted for nearly half of the city’s trees (44% or 34,020). 15,926 or 21% of trees are growing in a Tree Lawn in the Righ of-Way (ROW), or the open and maintained area opposite of a curb. The Open/Parks growing space was identified for 10,408 trees, or 13% of the inventory. The remaining growing spaces, along with their respective quantities and percentages, are listed below.
TREE INVENTORY ECONOMIC & ECOSYSTEM BENEFITS
To identify the dollar value provided and returned to the community, the city’s TreePlotter software application provided by PlanIT Geo was used which incorporates i-Tree research to quantify the benefits of individual trees and the tree inventory population. This tool in TreePlotter creates an annual benefit report that demonstrates the value public trees provide. These quantified benefits and the reports generated are described below:
Shows the tangible and intangible benefits of trees reflected by increases in property values (in dollars).
Presents annual reductions in atmospheric CO2 due to sequestration by trees and reduced emissions from power plants due to reductions in energy use. This is measured pounds and has been translated to tons for this report. The model accounts for CO2 released as trees die and decompose and CO2 released during the care and maintenance of trees.
Monetary increase due to the contribution of the urban forest toward conserving energy in terms of reduced natural gas use in winter.
Presents monetary savings due to reductions in annual stormwater runoff due to rainfall interception by tree canopy, as well as the reduction in annual stormwater runoff due to rainfall interception by tree canopy.
Tallies all of the carbon dioxide (CO2) stored in the urban forest over the life of its trees as a result of sequestration. Carbon stored is measured in pounds.
Contribution of the urban forest toward conserving energy in terms of reduced natural gas use in winter (measured in therms).
CARBON MONETARY BENEFIT
CARBON MONETARY BENEFIT
Calculates the dollar value associated with the amount of carbon stored or sequestered by trees based on calculations of the social cost of carbon.
Presents the contribution of the urban forest towards conserving energy in terms of reduced electricity use for air conditioning in the summer (measured in Megawatt-hours [MWh]).
Quantifies the air pollutants (ozone [O3], nitrogen dioxide [NO2], sulfur dioxide [SO2], particulate matter less than 10 micrometers in diameter [PM10]) deposited on tree surfaces, and reduced emissions from power plants (NO2, PM10, volatile organic compounds [VOCs], SO2) due to reduced electricity use in pounds. The potential negative effects of trees on air quality due to biogenic volatile organic compounds (BVOC) emissions is also reported.
ECONOMIC & ECOSYSTEM BENEFIT SUMMARY
The data collected from the inventory of trees completed in October 2020 were analyzed in TreePlotter for an understanding of the value and benefits of Fremont’s urban forest. The following provides a summary of the results:
8,746,990 lbs C sequestered 14,235,700 lbs C stored
*Distribution of benefits per tree and per capita based on 77,387 trees and a population of 241,110 people (based on 2019 US Census Estimate).
The trees in Fremont provide value in terms of increased property values, air quality improvements, reduction in stormwater volumes and an improvement in water quality, energy savings from the shade of their canopy and protection from cool winds, and their ability to sequester and store carbon. These values, originating from research conducted by the U.S. Forest Service, and implemented in i-Tree software, equate to nearly: