Urban Forest Outcomes (O). Second-, third-, and fourth-tier variables relating to (O), one of the five core first-tier factors in the UFSES framework. Abbreviations in the “Other UF frameworks” column correspond to shorthand citation keys for frameworks described in Table 2. Notes for Table 3 through Table 9 appear in Appendix D. UFSES (urban forest social-ecological system); UF (urban forest); DBH (diameter and breast height); RGR (relative growth rate).
| Number | Second-tier variable | Third-a and fourth-tierb variable(s) | Description and possible values | Other UF frameworks |
|---|---|---|---|---|
| O1 | Urban forest composition | At a system- (e.g., entire city) or sub-system (e.g., neighborhood, block face) level. | LEG, PAT | |
| O1-1 | Richness or diversitya | Number of taxa (genera, species, cultivars) represented in a particular area; number of native (noninvasive) species; biodiversity metrics (that take into account both the number of taxa present as well as the number of individual trees of each taxa)(Note 4). | VULN, LEG | |
| O1-1a | Species distributionb | Follows a desired rule (“10-20-30”, “5-10-15”); or that no single species (or genus) comprises more than X% of population in a particular boundary. | SUS | |
| O2 | Individual tree structure | These metrics can be aggregated to the level of the urban forest or evaluated on their own in statistical models that predict individual tree outcomes (Note 5). | ||
| O2-1 | Tree growtha | Increase in DBH or circumference; for smaller trees, perhaps caliper (diameter 6” from the base of the tree) or total tree height. Could also use RGR calculated as the difference in the natural logs of tree DBH taken at 2 points in time divided by the length of time in between measurements. | SES1 | |
| O2-2 | Tree conditiona | Qualitative (e.g., good, fair, poor, dead) or numeric-based (e.g., tree appraisalbased) overall condition rating. | SUS, VULN | |
| O2-3 | Tree survival/mortalitya | Alive, standing dead, removed/missing, stump. | SES1, MORT | |
| O2-X | Other individual tree outcomea | Any individual tree metric deemed meaningful by the relevant community and stakeholder groups and measurable either in qualitative or quantitative terms (e.g., pest presence, native species or not). | ||
| O3 | Urban forest structure | At a system- (e.g., entire city) or sub-system (e.g., site, neighborhood, block face) level. | VULN, PAT | |
| O3-1 | Tree size (age) distributiona | Distribution of tree sizes (or age, as calculated by either tree planting date or using a formula based on tree size and species) into bins (e.g., < 6” DBH, 6” to 12” DBH, etc.) to reflect the relative maturity of the trees. | SUS, VULN | |
| O3-2 | Total canopy cover (relative canopy cover)a | % of total land area covered by tree canopy (relative canopy cover indicates % of plantable land area covered by tree canopy and excludes buildings from denominator). | SUS, LEG | |
| O3-3 | Total number of treesa | Total # of stems or total # planted or removed; net # of trees planted or removed. | ||
| O3-4 | Basal areaa | Calculated using the diameter or circumference of trees to determine the total cross-sectional area occupied by tree stems (generally expressed as something like square feet per acre when used by foresters)(Note 6). | ||
| O3-5 | Stocking levela | For a particular part of the urban forest, generally used for street trees, where stocking indicates the % of plantable public right-of-way, street-adjacent spaces occupied by trees. | ||
| O3-6 | Natural areasa | Area or percentage of land in natural areas (e.g., remnant woodlots, “trees managed extensively”)(Kenney et al. 2011). | SUS | |
| O3-X | Other metric of overall urban forest structurea | Any urban forest structure metric deemed meaningful by the relevant community and stakeholder groups and measurable either in qualitative or quantitative terms (e.g., percent native species, leaf area index). | ||
| O4 | Urban forest function and benefits (& monetary value) | Also called “ecosystem services” (Note 7). | INST, VULN, BEY | |
| O4-1 | Individual function or benefita | A particular benefit of interest (e.g., reduction in asthma rates) or category of benefits (improvements in human health and well-being). | ||
| O4-2 | Monetary value of an individual benefita | This is most commonly calculated via the tree benefits tools in the i-Tree software suite (i-Tree Tools, www.itreetools.org). | ||
| O4-3 | Aggregated benefits (for a category of benefits expressed in comparable terms)a | Total value of measurable benefits (all benefits that can be calculated in terms of money value, all benefits included in the i-Tree software/tools, etc.; expressed in $ or local currency, # of lives saved or increased life expectancy years for health benefits, carbon dioxide equivalencies for climate benefits, or other means of standardizing different kinds of benefits). | ||
| O4-1a, O4-2a, O4-3a | Annual benefitsb | Annualized benefits provided by the urban forest of interest (e.g., carbon sequestered annually) or benefits accruing annually. For an individual function/benefit (O4-1a), monetary value (O4-2a), or aggregated benefits (O4-3a). | ||
| O4-1b, O4-2b, O4-3b | Total benefitsb | Total benefits provided by the urban forest at any given point in time (e.g., carbon stored). For an individual function/benefit (O4-1b), monetary value (O4-2b), or aggregated benefits (O4-3b). | ||
| O5 | Urban forest ecosystem disservices & costs | Some disservices and costs could be conceptualized of as “externalities” in an economic sense (Note 8). | INST, VULN, BEY | |
| O5-1 | Infrastructure interference costs (private cost)a | Repair of sewer/water infrastructure due to tree root interference with aging pipes; removal of tree limbs or debris blocking signage, power lines, storm drains, etc.; lost revenue/repair costs from tree-initiated power outages; etc. (Note 9). | ||
| O5-2 | Liability costsa | “Damages paid from a lawsuit or settlement awarded when trees or parts of trees cause injury to persons or property, such as an improperly cared for tree falling on a house, vehicle, or person” (Vogt 2020b)(Note 9). | ||
| O5-3 | Opportunity costsa | Costs resulting from the opportunities forgone when spaces in which trees are planted “cannot be allocated to other competing uses, such as parking, bike lanes, sidewalk cafés, etc.; shade from trees may preclude use of sunny areas for installation of solar panels or for gardening” (Vogt 2020b)(Note 9). | ||
| O5-4 | True ecosystem disservices (externality-related costs)a | Disservices are “ecosystem generated functions, processes and attributes that result in perceived or actual negative impacts on human wellbeing” (Shackleton et al. 2016; Roman et al. 2021b); examples include “emissions of biogenic volatile organic compounds (VOCs) by trees; allergies due to tree pollen; release of carbon dioxide during decomposition of trees or tree debris or by maintenance equipment (gas-powered chain saws, lift trucks used to access tree canopy during maintenance, etc.); leaf/debris clean-up,” etc. (Vogt 2020b)(Note 9). | ||
| O5-X | Other disservices or costsa | Any metric of disservices/costs deemed meaningful by the relevant community and stakeholder group and measurable either in qualitative or quantitative terms. | ||
| O6 | Urban forest sustainability & persistence | Overall metric of change over time; usually requires collecting data from at least 2 points in time, but sometimes it is possible to assess change retroactively such as through aerial photos, historical records, or other tools (Note 10). | VULN | |
| O6-1 | Change in canopy covera | % increase or decrease in canopy cover between time 0 and time x. | ||
| O6-2 | Survival (or mortality) ratea | A proportion or percentage of a tree population or sample surviving or dying, calculated annually or cumulatively over a particular time period. | ||
| O6-2a | Annual survival (mortality) rateb | “...proportion of individuals [trees] surviving [dying] over a year, from time x to time x + 1” (Roman et al. 2016)(Note 11). | MORT | |
| O6-2b | Survivorship (cumulative survival)b | “...proportion of a cohort surviving from planting to year x (in other words, cumulative survival)” (Roman et al. 2016)(Note 11). | MORT | |
| O6-3 | Net change in stocking levela | Number of trees planted during time 1 less number of trees removed during time 1; can be expressed as a percentage or proportion of total number of trees (if available) or as a ratio (# planted:# removed) where > 1 indicates more plantings than removals and < 1 indicates fewer plantings than removals. | ||
| O6-4 | Change in average tree sizea | Change in average tree size (as indicative of a decline in overall urban forest maturity and consequential loss of benefits). | ||
| O6-X | Other metric of urban forest sustainability/persistencea | Any sustainability/persistence metric deemed meaningful by the relevant community and stakeholder groups and measurable either in qualitative or quantitative terms (e.g., does the tree population meet a sustainable age distribution, achieve a desirable cost-benefit ratio, produce a certain level of net benefits; community-determined satisfaction with urban forest resources; is there an increase or decrease in the number of plantable spaces along street right-of-way, or of plantable area in the city). | ||
| O7 | Urban forest multifunctionality | Outcomes related to measuring and achieving multiple urban forest functions simultaneously | ||
| O7-1 | Multifunctionalitya | Ability of the urban forest to meet multiple desired functions simultaneously, including environmental, ecological, social, economic, human health, etc. | MOS | |
| O7-2 | Positive synergiesa | “‘A win-win situation that involves a mutual improvement of two ecosystem services,’ with an implied reduction in disservices; more broadly speaking, positive synergies are situations in which the holistic impact is greater, and more beneficial, than each individual component” (Felipe-Lucia et al. 2015; Roman et al. 2021b)(Note 12). | BEY | |
| O7-3 | Negative synergiesa | “A lose-lose situation that involves a mutual increase in ecosystem disservices, with an implied reduction in ecosystem services; also called ‘jointly negative’ outcomes; more broadly speaking, negative synergies are situations in which the holistic impact is worse than each individual component” (Roman et al. 2021b)(Note 12). | BEY | |
| O7-4 | Tradeoffsa | “A ‘[s]ituation in which land use or management actions increase the provision of one ecosystem service and decrease the provision of another’, but could also refer to a situation in which an ecosystem service increases while disservice(s) also increase (i.e., win-lose)” (Felipe-Lucia et al. 2015; Roman et al. 2021b) (Note 12). | BEY | |
| O7-X | Other multifunctionality metrica | Any multifunctionality metric deemed meaningful by the relevant community and stakeholder groups and measurable either in qualitative or quantitative terms (e.g., a ratio or other comparison of selected/relevant urban forest benefits and disservices). | ||
| O8 | Urban forest response to disturbance | Outcomes related to how the urban forest reacts when perturbed or disturbed by natural or human pressures | ||
| O8-1 | Social-ecological resiliencea | Demonstrated or predicted ability of the UFSES to withstand perturbation/disturbance from pests, fire, climate disturbances, etc., after the Folk (2006) definition of resilience as “capacity of a system to absorb disturbance and re-organize while undergoing change so as to still retain essentially the same function, structure, identity and feedbacks” (Note 13). | ||
| O8-2 | Institutional robustnessa | Demonstrated or predicted ability of urban forest social institutions, policies, etc. to “maintain some desired system characteristic despite changes in the behavior of its components parts, circumstances that contribute to long-enduring or sustainable systems overall” (Anderies et al. 2004; Mincey et al. 2013). Robust institutions are functional across a range of social-ecological characteristics (Note 14). | INST | |
| O8-3 | Urban forest adaptive capacitya | Demonstrated or predicted “capacity for a system to shift or alter its conditions to reduce its vulnerability or to improve its ability to function while stressed” (Adger 2006; Steenberg et al. 2017)(Notes 15, 16). | VULN | |
| O8-4 | Urban forest vulnerabilitya | How much the urban forest will be harmed or damaged after exposure to a stressor or hazard, for example pest infestations, storms, or climate change (Steenberg et al. 2017)(Note 17). | VULN, CC | |