Using the 3-30-300 Rule to Assess Urban Forest Access and Preferences in Florida (United States)

Introduction

A large and growing body of research has quantified the ecosystem services associated with urban trees as they relate to (among other things) storm water mitigation (Berland et al. 2017), urban heat reduction (Ko 2018; McDonald et al. 2020), carbon capture (Nowak and Crane 2002), and human health (Jennings and Gaither 2015; Wolf et al. 2020). Proximity to vegetation is an important driver for human health, with benefits including reduction of stress (Jiang et al. 2015; Turner-Skoff and Cavender 2019), improved school performance (Kuo et al. 2018; Turner-Skoff and Cavender 2019), and more normal childbirth weights (Donovan et al. 2011). Recognizing the importance of these benefits and the inequalities that exists across social-demographics (Gerrish and Watkins 2018; Watkins and Gerrish 2018), the 3-30-300 Rule has been proposed as a means of ensuring that individuals have sufficient tree cover and green space access at scales that are relevant, desirable, and/or beneficial to their well-being.

The 3-30-300 Rule draws on the large body of research documenting the benefits trees have on human health and well-being (Konijnendijk 2022). Each of the numbers in the 3-30-300 Rule is associated with specific performance criteria tied to individual access to urban trees and green spaces, and the need to bring trees and green space close to people to enhance their health, climate adaptation and other benefits. The “3” in 3-30-300 Rule captures urban forest access at a very local scale by asking the question, “Can you see 3 or more mature trees from your home (or workplace or school)?” (Konijnendijk 2022). Its inclusion is rooted in past research which has demonstrated (among other things) the benefits a green outside view provides to hospital patients (Jimenez et al. 2021), school children (Norwood et al. 2019), workers (Lottrup et al. 2015), and, more recently, people isolating as part of the COVID-19 pandemic (Zhang et al. 2022).

The “30” in the 3-30-300 Rule relates to neighborhood canopy cover. Individuals should have at least 30% canopy coverage in their neighborhood (Konijnendijk 2022). Often canopy goals are established city-wide as part of an urban forest management plan (Kenney et al. 2011; Hauer and Peterson 2016). However, scale is also important when considering environmental equity (Locke et al. 2016). Past studies at scales smaller than an entire city (e.g., neighborhoods or census blocks) have shown urban canopy can vary given local demographics—particularly race (Grove et al. 2018; Watkins and Gerrish 2018; Nesbitt et al. 2019; Locke et al. 2021) and income level (Gerrish and Watkins 2018; Nesbitt et al. 2019). As such, the 3-30-300 Rule specifically calls on urban forest managers to strive for 30% canopy cover in every neighborhood they manage, thus aiming for greater environmental equity.

The 30% canopy threshold is derived from multiple studies that have shown that a minimum tree cover of this magnitude is necessary for significant benefits to be realized (Konijnendijk 2022). For example, researchers in Europe found that 30% canopy coverage was associated with one-third less mortality during heatwaves (Barboza et al. 2021). Additionally, Astell-Burt and Feng found that 30% canopy cover was associated with more restful sleep (2020a) and reduced stress (2019). The authors also found that at least 30% canopy coverage served as a preventative for heart disease (Astell-Burt and Feng 2020b). While canopy coverage beyond 30% was associated with greater benefit in these studies, Konijnendijk (2022) adopted the threshold (30%) to account for urban greening challenges cities might face such as rapid development and changing climates.

The last criterion of the 3-30-300 rule is for individuals to be within 300 m of the nearest public park or green space (Konijnendijk 2022). This distance represents an approximate five-minute walk at a leisurely pace. People located 300 m from a green space visited these areas more frequently and were less likely to be obese than respondents located more than 1 km from a green space (Toftager et al. 2011). Beyond body weight, increased activity in green spaces can also help reduce the effects from health ailments such as heart disease and diabetes (Astell-Burt et al. 2014; De la Fuente et al. 2021). Although having easy access to larger green spaces (1 ha or more) is recommended by institutions such as the World Health Organization, smaller green spaces, such as pocket parks or community gardens, may be a necessary compromise in densely developed urban areas (Konijnendijk 2022).

While there is no shortage of research documenting the benefits of trees, including those directly associated with human health, management decisions regarding urban forests must reflect public values if they are to be successful (Sklar and Ames 1985; Carmichael and McDonough 2018a; Northrop et al. 2022; Landry et al. 2023). Given this, there is a large body of research that clarifies public perceptions as they relate to urban trees and forests (Ordonez Barona et al. 2022). In a recent review, Ordóñez Barona et al. (2022) identified 178 studies that investigated people’s perceptions of urban trees. The majority of these works were focused on respondents from a single community, often framed within the context of trees in gardens/yards, in urban woodlands, along streets, or in parks. Most works (47.2%) focused on trees and their functions in landscapes, but research also focused on public perception regarding the inherent value of trees themselves (40.4%) or the benefits or drawbacks of certain tree traits (12.4%)(Ordóñez Barona et al. 2022). One finding by Ordóñez Barona et al. (2022) is that the majority of studies did not allow for open ended responses, rather they asked questions which provided limited options for respondents to choose from when sharing their views. Moreover, respondents were typically only asked to offer their perceptions on tree benefits (Ordóñez Barona et al. 2022).

While much research has been conducted to assess the positive perceptions individuals hold regarding trees and urban forests, few studies have investigated how the public views the drawbacks oftrees (Ordóñez Barona et al. 2022). Failing to consider both the full range of views on trees including perceived ecosystem disservices can erode public trust and support for urban forest efforts. Furthermore, neglecting ecosystem disservices in decision-making processes can diminish the impact of management endeavors aimed at enhancing human well-being (Roman et al. 2021). The few studies that have examined negative perceptions of trees highlight ways for managers to address or account for these concerns (Su et al. 2022; Landry et al. 2023).

In working towards urban forest management goals, policy makers, managers, and practitioners must consider these competing values and determine which strategies are generally acceptable to their constituents. If management efforts do not align with the needs and wants of the public, their long-term success is questionable (Lockwood et al. 2010). Understanding how constituents value trees and the reasons for these attitudes is a critical guiding step when creating strategic plans, urban forestry programs, and educational efforts.

To address this research gap, this work represents a statewide assessment of values related to urban forest access and governance in Florida (United States). We ascertained how proximity to tree cover and green space access affected people’s perceptions using the 3-30-300 Rule as our main performance metric, as this rule makes an evidence-based connection between different types of access to trees and green space. In addition, we asked respondents if the tree cover and green space access they currently experienced was sufficient or whether it should be increased or decreased. Lastly, we asked our respondents to note their thoughts on trees regarding the services and disservices they provide and any negative experiences they had with trees in the past. This work is intended to assist urban forest managers and non-profits in their efforts, especially with regard to strategic planning, regulation/ordinance revision, and public engagement/education. Results can further inform research and practical applications beyond the study location.

Methods

Study Questions

Our questionnaire was designed to assess what level of green space residents currently have, what level of canopy is desired, benefits and drawbacks with trees, negative experiences, and desired tree protection (Appendix). In particular, the following topical areas were ascertained:

• What access to urban tree cover and green space do they currently have?

• What access to urban tree cover and green space do they want?

• What level of tree cover do they currently have along with how many trees can they see from a viewing point at their home (Figure 1)?

• How much time does it take to access green space?

• What benefits and also drawbacks are associated with trees?

• What types (if any) of negative experiences have you had with trees?

• Download figure
• Open in new tab
• Download powerpoint

Figure 1.

Street level rendering of a residential neighborhood with 30% canopy coverage. Respondents were shown similar images for 10%, 50%, 70%, and 90% canopy coverage and asked to select the scene that best represented their neighborhood.

In addition to the 3 themes above, we asked our respondents 2 open-ended questions. The first was “What are the top 3 benefits you associate with trees in your community or neighborhood?” The second was “What are the 3 biggest drawbacks associated with the trees in your community or neighborhood?”

Finally, to determine if past negative experiences with trees influenced their responses, we asked if they had had issues with trees damaging property, causing injury, requiring costly maintenance, preventing development, or causing issues with obtaining a new homeowners’ insurance policy.

Our last question was pertinent only to homeowners (Appendix). Respondents who selected “rent” when asked “Do you rent or own your home?” bypassed our last question (Appendix).

As our respondents had registered to participate as panelists through the panel service as described above, we had access to demographic (e.g., age, race, Hispanic status, gender) and location (i.e., postal code) information and did not need to ask these questions directly in our survey.

The study was approved by the University of Florida Internal Review Board (IRB) to collect data from human subjects. A soft launch (distributed to approximately 50 respondents) was conducted on 2022 October 5, to assess the performance of our questions prior to the full launch. We did not observe any issues and were able to release the survey as drafted. All responses were collected by 2022 October 17.

Results

What Benefits and Disservices Do Floridians Associate with Urban Trees?

In looking at the coded benefits, “gives shade” was by far the most common benefit listed. This was followed by “pleasing to the eye,” “brings nature closer,” and “filters pollutants from the air.” The remaining 11 coded benefits were less commonly listed by respondents (Figure 2).

• Download figure
• Open in new tab
• Download powerpoint

Figure 2.

Coded responses from our open-ended survey question, “What are the top 3 benefits associated with the trees in your community or neighborhood?” (n = 1,716). Responses were coded using the list of benefits offered to survey respondents in Schroeder and Ruffolo (1996).

In matching respondents’ stated drawbacks to Shroeder and Ruffulo’s (1996) original list of annoyances, we found that seasonal leaf drop was the most common complaint (Figure 3). This was followed by “falling limbs,” “attracts annoying insects,” and “fruit, nuts, or pods fall from the tree.” The remaining 13 annoyances from Shroeder and Ruffulo (1996) were not commonly listed by respondents (Figure 3). In general, respondents were more forthcoming with benefits than they were with drawbacks (Figures 2 and 3).

• Download figure
• Open in new tab
• Download powerpoint

Figure 3.

Coded responses from our open-ended survey question, “What are the 3 biggest drawbacks associated with the trees in your community or neighborhood?” (n = 1,716). Responses were coded using the list of drawbacks offered to survey respondents in Schroeder and Ruffolo (1996).

What Experiences Might Shape Floridian’s Preferences for Trees?

Observed changes in canopy cover did not influence who selected that they would prefer fewer trees in their neighborhood (P-value = 0.735)(Table 4). In contrast, those respondents who selected that they would prefer the current amount of trees in their neighborhood were less likely to have observed a decrease in tree cover in their neighborhood (P-value < 0.001)(Table 4). Those respondents who selected that they would prefer more trees in their neighborhood were more likely to have observed a decrease in tree cover in their neighborhood (P-value < 0.001) (Table 4).

View this table:

• View inline
• View popup

Table 4.

Comparison of past canopy changes in respondents’ neighborhoods to their current tree preferences. A test of equal proportions was used to assess if responses to the question, “I would prefer ______ trees in my neighborhood” differed given observed changes in neighborhood canopy (n = 1,716).

In assessing ecosystem disservices, 54.9% (n = 943) of our participants selected the response “I have never had a negative experience with a tree.” The most common negative experience expressed by respondents was a tree “causing property damage after losing a branch or tipping over.” This was reported by more than 1 in 5 respondents (23.3%; n = 399)(Figure 4). Other relatively common negative experiences included a tree “growing into and damaging your property” (18.6%; n = 319) and “requiring costly maintenance or removal” (19.0%; n = 326). The 2 least common of our predefined negative experiences were “causing issues when obtaining a new home insurance policy” (5.1%; n = 87) and “preventing you from developing your property given local protections” (3.7%; n = 64).

• Download figure
• Open in new tab
• Download powerpoint

Figure 4.

Responses (n = 1,715) to the question, “Have you ever had a negative experience with a tree?” The gray bars labeled “Fewer Trees Only” shows the results associated with respondents who noted they would like fewer trees in their neighborhood or community. This is contrasted with the results from the entire sample (“Overall Average”). Asterisks (*) indicate significant differences between paired bars, with * = P-value < 0.05, ** = P-value < 0.01, and *** = P-value < 0.001.

In addition to the negative experiences noted above, we included an “other” option. Of the 26 (1.5%) respondents that replied “other,” 7 described issues where tree parts grew into and damaged their property or neighboring infrastructure—specifically in an in-ground pool (n = 1), a nearby electrical transformer (n = 1), and septic or sewer systems (n = 5). Others noted damage to vehicles (n = 2) from limb drop and slipping issues given flower drop. Most of these examples could have been included in 2 of our pre-defined categories (i.e., “growing into or damaging your property” or “causing property damage after losing a branch or tipping over”) but were left as is for analysis. Four respondents noted losing trees after hurricanes or lightning strikes. One respondent was nearly hit when a tree fell near them in a park. Others noted negative experiences included trees attracting nuisance wildlife (n = 2), trees exacerbating allergies (n = 1), trees blocking sunlight (n = 1), and invasive trees taking over their property (n = 1).

Across the board, respondents who noted they would like fewer trees in their neighborhood or community were more likely to have had a negative experience with a tree in their past as compared to the total survey sample (minimum P-value = 0.015)(Figure 4). Respondents who indicated they would like fewer trees in their neighborhood or community were approximately twice as likely to have experiences with a local tree protection regulation preventing them from developing their property (2.5:1; P-value = 0.011) or have issues with getting a new homeowners’ insurance policy (2.2:1; P-value = 0.015)(Figure 4). This same subset of our sample were approximately 1.5 times more likely of have experienced a branch falling on their property (1.7:1; P-value < 0.001), a tree growing into their property (1.7:1; P-value = 0.002), or a costly maintenance or removal bill (1.6:1; P-value = 0.003) in the past (Figure 4).

Discussion

Our results offer early insights into what proportion of urban inhabitants live in a home and neighborhood which meets the criteria outlined by the 3-30-300 rule (Konijnendijk 2022). Our survey results indicate that more than a third (37.3%) of Floridians met or exceeded all 3 of the thresholds outlined in the 3-30-300 rule, with 71.9% able to view 3 trees from their home, 72.9% living in a neighborhood with 30% (or greater) canopy coverage, and 57.7% living within 300 m of a park or green space. By comparison, one of the first published studies to assess how a city fares with regard to the 3-30-300 rule was conducted in Barcelona, Spain (Nieuwenhuijsen et al. 2022). In this work, the authors found that 4.7% percent of respondents met all 3 criteria. In looking at the individual metrics, 62.1% of respondents were located near a major green space, 43% of respondents were able to view 3 trees from their home, and 8.7% lived in neighborhoods with 30% or more canopy coverage (Nieuwenhuijsen et al. 2022).

Looking beyond research in academic journals, a master’s thesis from the University of Toronto looked at entry-level home real estate listings in Toronto and Mississauga (Canada) to determine if their associated asking price was influenced by the criteria assessed in the 3-30-300 rule (Ling 2021). They found that 12% of the listings met all 3 criteria and that these tended to be the more expensive properties. Of these, 62% of properties had a view of 3 trees, 29% had 30% canopy coverage, and 32% were located within 300 m of a green space (Ling 2021).

Additionally, a geospatial analysis of 9 Swedish cities estimated that the percent of buildings with views of 3 trees ranged from (approximately) 31% (Kristianstad) to 61% (Lund)(Skåne Région 2023). In this same assessment, the research team found that, on average, 3% of the homes found within these 9 cities had 30% canopy coverage. In 3 of the cities assessed, Malmo, Lund, and Trelleborg, none of the homes met the 30% canopy coverage criterion (Skåne Region 2023). The best performing city, Ystad, by this criterion had 13% of homes located in 30% canopy coverage (Skåne Region 2023). Finally, the research found that 87% of homes were within 300 m of a 0.5-hectare green space. This ranged from 77% in Malmo to 95% in Lund (Skåne Region 2023).

Unlike Florida (where green space/park access was the most limiting factor), canopy coverage was the key limiting factor determining what percentage of Skåne Region households met the 3 criteria of the 3-30-300 rule. A testable reason outside the scope of this paper is addressing how history, landform, and urban design standards may influence access and barriers to greenspaces (Hauer et al. 2017). As United States park designs historically range from 2 ha (playgrounds) to 20 ha (community parks)(American Planning Association 1965), it may be that respondents did not consider these smaller green spaces when responding to the question, “Are you able to walk from your home to the nearest park, green space, or natural area in less than 5 minutes?” The within a 5-minute walking distance trip to places like a park is a normative standard, with up to 10 minutes also presented as a maximum threshold (Atash 1994). However, only 35% of respondents to a United States study took walking trips of up to 5 minutes (Yang and Diez-Roux 2012). Regardless of a places’ history, landform and urban design size, and a personal perception of what is a green space, our results are consistent with Yang and Diez-Roux (2012) that a 5 minute walking distance is an important reason for daily or weekly visits to a greenspace. As a walk approaches and exceeds 5 minutes the likelihood of visiting the location on foot greatly diminishes.

In addition to assessing current access to urban greening, our survey indicates that the majority of Floridians (51.5%) would prefer to have more trees in their neighborhood. This question was pulled from a similar survey administered by Landry et al. (2023) to Tampa, Florida residents. In the Tampa survey, 83% of respondents noted they would like more trees within the city and 72.4% of respondents noted they would like more trees in their neighborhood. As with our findings, only a small fraction (5.9%) of the Tampa respondents desired fewer trees in their neighborhood (Landry et al. 2023).

While the proportion of Florida residents looking for fewer trees in their neighborhood was low (6.4%), this group included a disproportionate number of Black/African American respondents (10.4%). In looking at other factors that might relate to someone’s desire to have fewer trees, things like high existing canopy coverage or recent changes in canopy coverage were not statistically significant (Tables 3 and 4). Respondents who desired fewer trees were more likely to have had a negative past experience with a tree (e.g., causing property damage or requiring costly maintenance) compared to the overall population (Figure 4). Negative past experiences were also a key factor in residents’ lack of support of urban greening efforts in the city of Detroit, United States (Carmichael and McDonough 2018b). However, in our study, Black/African American respondents were less likely to report experiences with trees growing into and damaging their property (13.3%), causing injury after losing a branch or tipping over (22.3%), or requiring costly maintenance or removal (9.4%) compared to our overall average. In contrast, Black/African American respondents were more likely to report trees preventing them from developing their property given local protections (5.4%) and causing issues when obtaining a new home insurance policy (8.9%).

As noted, relatively few studies have looked at both the benefits and drawbacks of urban trees. When asked in an open-ended question to name 3 drawbacks associated with urban trees, respondents focused primarily on safety (e.g., damage, falling, storm(s) such as hurricanes) and debris (e.g., leaves, branches, limbs, acorns, etc.).

In a 2004 study by Lohr et al., residents from across the United States were asked if they agreed with eight statements regarding problems associated with trees. None of the prompts used by Lohr et al. (2004) directly captured the two concerns raised by our respondents. Moreover, none of the statements provided by Lohr et al. (2004) were supported by their respondents (ranging from 1.30 to 1.64 on a 4-point scale where 1 = strongly disagree and 4 = strongly agree). This may highlight a limitation of surveys where specific scenarios are given when trying to assess values (e.g., trees should not be planted along streets because they drip sap or sticky residue on parked cars)(Lohr et al. 2004). Respondents may agree with statements they have never experienced in real life as they may sound like plausible nuisances. Moreover, the more universal and pressing issues to a given population of interest may be missed by the research team. That said, open-ended questions do require more labor-intensive qualitative analysis techniques like inductive coding in order to draw conclusions.

A more recent assessment of positive and negative beliefs surrounding urban trees was conducted by Su et al. (2022). In this study, the authors surveyed residents of the Toronto, Canada metro area and found that the highest rated positive beliefs were “produces oxygen,” “cleans the air,” and “provides shade” (4.53, 4.52, and 4.46, respectively—as rated on a 5-point scale). Interestingly, despite listing shade as a top positive belief, the most supported negative belief was “block the sun” (3.35). Similar to our findings, Su et al. (2022) found that dropped branches were a concern among their respondents (the second most supported in their list). Damage to property and infrastructure was more of a mid-level concern (rated 2.52 on a 5-point scale). This was rated lower than “cause allergies” (2.90)—a disservice that was barely mentioned by our respondents.

Tree safety is a top concern among our respondents (Figure 3). Tree safety concerns are noteworthy because hurricanes and tropical storms shape Florida’s urban forests and are a significant part of living in the state (Salisbury et al. 2022). These storms can topple even strong and healthy trees once they reach Category 3 and above (Saffir-Simpson Hurricane Wind Scale [date unknown]). Other researchers have found similar safety concerns among their urban respondents. In a 2015 study, Shackleton et al. found over 72% of residents in 2 South African towns expressed concern that trees may influence crime rates by making it difficult to detect criminal behavior. This was by far the most important concern in both communities they assessed (Shackleton et al. 2015).

Urban trees can have various benefits and drawbacks. Our respondents highlighted various benefits, key of which are “gives shade” or “pleasing to the eye”. This result is aligned with research in the suburbs of Chicago (United States) which also found that the aesthetics of trees was the most significant benefit identified by respondents, along with providing shade (Shroeder and Ruffalo 1996). That said, the difference between our less reported benefits and our most common benefits was much more pronounced than was noted in the data by Shroeder and Ruffolo (1996). This may reflect the differences in the method used to assess their values (open-ended questions versus questions with close-ended options), though it is difficult to gauge if this is truly the case from the older paper’s methods.

In looking at our coded drawbacks (Figure 3), “fallen leaves in autumn” was the most common complaint. This mirrors the results from Shroeder and Ruffolo (1996). That said, respondents were more likely to point to “falling limbs” as a key drawback. The respondents from Shroeder and Ruffolo appeared more concerned with “roots too close to the surface,” “sap drips from the tree,” and “sidewalk damaged by roots” than our respondents (Figure 3). This may reflect species (surface rooting, sap), climate (spring sap rise), and urban form (sidewalk damage) differences between the 2 regions assessed.

CONCLUSIONS

This paper provides one of the first public assessments of urban forest access through the lens of the 3-30-300 Rule. Our respondents, who come from a range of subtropical and tropical urban communities in Florida, United States had greater access to urban greening than those surveyed from other cities and countries. Of the 3 criteria, access to urban green spaces within 300 m was the most limiting. Overall, respondents valued their urban trees and would like to maintain or enhance the tree cover in their neighborhood despite complaints about debris and fears regarding storm-related failures. When making the case for trees to the general public, Florida urban forest managers will likely make the strongest connections when highlighting potential gains in shade, benefits to wildlife, and impacts to the overall beauty of their communities. Urban forest managers can use our results when developing management plans or replicate our survey efforts in their own communities in an effort to justify expenditures on maintenance and planting projects.

Conflicts of Interest

The authors reported no conflicts of interest.