Multi-Criteria Analysis of Three Walkable Surface Configurations for Healthy Urban Trees: Suspended Grating Systems, Modular Boxes, and Structural Soils

Abstract

The conflicting demands of urban trees and walkable surfaces result in significant financial burdens for municipal administrators who understand that urban residents want tree-lined walkable surfaces. This study investigates three methodologies for mitigating this tension: suspended grating systems, modular box systems, and structural soils. A Multi-Criteria Analysis (MCA) was conducted to evaluate their suitability in dense urban areas, employing criteria categorized into Environmental, Economical, and Other considerations. The comparison focused on critical aspects such as the impact on tree health (root growth, water availability), installation complexity, initial costs, and overall suitability for diverse urban contexts. The MCA indicates that, under the given weighting of criteria, suspended grating systems (especially those suited for existing trees) rank the highest, primarily due to their superior root protection and minimal disturbance to established root systems. In contrast, modular box systems and structural soils emerge as particularly strong contenders for new tree plantings. Structural soils may have application at sites with existing trees, but the costs of removing native soil are a consideration. Sensitivity analysis suggests that modular box systems may become the preferred option when greater emphasis is placed on stormwater management and new plantings, rather than on challenges for existing trees or underground infrastructure. Structural soils score well in cost-effectiveness and installation speed but require careful implementation to address their lower root protection performance and long-term maintenance concerns. Ultimately, the optimal solution depends on unique site-specific conditions and budgetary constraints, emphasizing the necessity of tailored approaches to balance urban infrastructure with tree health.

1. Introduction

1.1. Defining and Contextualizing Tree-Friendly Walkable Surfaces

The concept of tree-friendly walkable surfaces has emerged as a critical consideration within urban planning and environmental sustainability, moving beyond the traditional approach where pedestrian infrastructure and urban trees often exist in tension [1]. At its core, a tree-friendly walkable surface can be understood as a pedestrian walkway designed and constructed to foster the health and longevity of adjacent or integrated trees while maintaining or enhancing pedestrian safety and accessibility [2,3]. This represents a shift from traditional surface designs, which often contribute to root damage, structural cracking, and, in turn, the premature removal of mature urban trees [1,4]. Strategies for achieving this coexistence encompass providing adequate space for root growth, selecting appropriate tree species with less aggressive root systems, integrating tree placement with other street furniture, and considering the use of curb extensions to create more favorable growing environments [5,6]. Furthermore, the design of such pedestrian surfaces aligns with the broader principles of complete streets, aiming to create pedestrian-friendly urban environments that offer sufficient width, protective buffers from traffic, and various amenities [7]. This indicates a fundamental shift in urban infrastructure planning, where the needs of both pedestrians and the urban ecosystem are proactively considered and integrated from the outset [3].

Tree-friendly walkable surface approaches are essential for balancing ecological benefits with pedestrian accessibility [8]. These strategies encompass a range of methods, including nature-based solutions (NBSs), the use of innovative materials and structures, and careful soil management. The World Bank defines NBSs as “actions to protect, conserve, restore, sustainably use and manage natural or modified terrestrial, freshwater, coastal and marine ecosystems, which address social, economic and environmental challenges effectively and adaptively, while simultaneously providing human well-being, ecosystem services and resilience and biodiversity benefits” [9]. By integrating such measures, urban environments can foster healthy tree growth, contribute to biodiversity, and enhance ecosystem services without compromising the functionality and safety of pedestrian infrastructure. Walkable surface options that are compatible with tree growth, such as enlarged tree cut-outs, structural soils, permeable paving, and bioretention tree pits, mitigate infrastructure conflicts and enhance growing conditions, representing a nature-based solution. Similarly, innovative materials such as flexible pavement panels that preserve tree roots while reducing surface damage also fall into this category [8]. The selection of the most suitable NBSs for urban implementation addresses various challenges. The framework, tested in Lublin, Poland, considers ecological, social, and management aspects, leading to a final set of 20 best-suited NBS’s types for the city [10].

1.2. The Multifaceted Role of Urban Trees

The necessity of integrating trees into urban infrastructure stems from a wide array of environmental, social, and economic advantages. Environmentally, trees play a crucial role in stormwater management by intercepting rainfall, increasing soil permeability, and reducing the volume and velocity of runoff. This helps to mitigate urban flooding and improve water quality by filtering pollutants. Furthermore, urban areas often experience the “heat island effect,” where temperatures are significantly higher than those in surrounding rural areas. Trees combat this by providing shade and cooling the air through the process of evapotranspiration. Strategically planted trees provide shade, mitigating the urban heat island effect, which can increase average annual temperatures in urban agglomerations [8]. They also act as natural air purifiers, absorbing harmful pollutants, such as volatile organic compounds, carbon monoxide, particulate matter, and nitrogen oxides, while releasing essential oxygen. Each mature tree absorbs approximately 330 pounds of carbon dioxide annually. In the United States, trees and forests removed an estimated 17.4 million tons of air pollutants in 2010, resulting in substantial health benefits valued at USD 6.8 billion [11]. This underscores their crucial role in safeguarding public health. Additionally, urban trees enhance water quality by filtering pollutants from soil infiltration and reducing erosion and runoff, with urban forests reducing annual runoff by 2–7% [8]. Beyond these benefits, urban trees contribute to biodiversity by providing habitats for birds, insects, and other wildlife, and they play a vital role in carbon sequestration, absorbing and storing carbon dioxide from the atmosphere.

Beyond environmental contributions, urban trees yield substantial social benefits, including improved physiological and psychological health, stress reduction, and enhanced community cohesion [12,13,14]. The integration of biodiversity in urban green spaces further amplifies these benefits, enhancing ecosystem services and yielding social benefits like stress reduction and community interaction [13,15,16,17,18,19,20]. Conversely, biodiversity loss negatively impacts human health [6]. Moreover, urban trees augment property values, contributing to economic benefits [21].

1.3. The Conflicting Demands Between Urban Trees and Sidewalks/Plazas: Challenges and Costs

On the other hand, the conflicting demands between urban trees and walkable surfaces represent a recurrent and costly challenge for public space managers, leading to significant annual expenditures on sidewalk repairs [22,23]. Traditional pavement installation poses a threat to tree root systems, while urban residents prefer sidewalks planted with mature trees [24]. The tension between urban trees and pedestrian pathways is extensively documented, representing a recurrent and financially burdensome challenge for public space managers [25,26]. The absence of precise pavement repair cost data from Polish Municipal Road Administrations necessitates estimations, suggesting annual expenditures in the tens of millions of zlotys. These costs are frequently amalgamated within comprehensive street renovation projects. According to the Warsaw City Hall’s 2022 report, 87.3 thousand square meters of sidewalks underwent renovation that year [22]. Similarly, the Krakow City Road Administration reported that PLN 50.8 million was spent on road and sidewalk repairs in 2022 [23]. Market analysis indicates an average repair cost of PLN 100–150 per square meter of concrete sidewalk, with variations contingent upon damage type and surface material. International sources corroborate these figures, citing sidewalk unevenness repairs ranging from 50 to 200 USD per square meter. In cases involving root intrusion, arboricultural consultation is often required, with root excavation costs varying from USD 150 to 500. Annual replacement rates of 4–6% for sidewalk infrastructure are observed in countries like the UK and Australia, attributed to factors such as vehicular load, substandard concrete quality, inadequate substructure, impact damage, root migration, and deficient substructure drainage [27,28]. Traditional pavement installation, involving excavation for substructures and foundations, poses a significant threat to tree root systems [27]. At the same time, urban residents prefer sidewalks planted with trees. The more mature the tree, the more positive the perception of the pathway and the greater the willingness to walk that way [24].

1.4. The Challenge of Protecting Existing Urban Trees

Protecting existing trees within urban environments presents a unique set of challenges, particularly when integrating them with essential infrastructure like sidewalks and roads. The methodologies of suspended structures (grating), modular box systems, and structural soils offer varying degrees of protection [29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44], each with distinct advantages and limitations [45,46,47,48,49,50,51,52,53,54,55,56]. One of the primary challenges is root zone disturbance. Existing trees possess extensive root systems that are highly susceptible to damage from traditional construction methods, leading to stress and potential mortality [56,57]. Compounding this issue is the prevalence of compacted soils in urban settings, which restrict root growth and increase vulnerability. Furthermore, urban planners must balance infrastructure needs with the space requirements of tree roots, often in limited space environments where providing adequate soil volume and root protection is difficult.

To effectively protect existing trees, arborist consultation is essential. Certified arborists can assess tree health and recommend optimal protection methods. Early planning, integrating tree protection into the initial stages of urban development, is crucial. Finally, ongoing maintenance is necessary to ensure the long-term health of protected trees. By understanding the strengths and weaknesses of these methodologies and adhering to key considerations like arborist consultation and early planning, urban planners can make informed decisions. This approach allows for the creation of sustainable urban environments where existing trees thrive alongside necessary infrastructure, enhancing well-centered ecological and human urban development [55,58,59,60,61].

1.5. Benefits of Tree-Friendly Walkable Surfaces: Multi-Dimensional Perspective

Socially and economically, tree-friendly walkable surfaces enhance the livability of urban areas in numerous ways (

Table 1. Benefits of tree-friendly walkable surfaces (source: own elaboration based on [13,18,19]).

Benefit Category	Specific Benefits
Environmental	Stormwater management (runoff reduction, water quality improvement, groundwater recharge), heat island reduction, air quality improvement (pollutant absorption, oxygen release), biodiversity and habitat support, carbon sequestration
Social	Enhanced walkability and pedestrian comfort, improved esthetics and quality of life, creation of a sense of place and community identity, opportunities for recreation and outdoor activity, reduced noise pollution
Economic	increased property values, potential for increased local business activity, energy savings (reduced cooling needs), extended pavement lifespan (due to shade), reduced costs for stormwater infrastructure in the long term, potential for green job creation in maintenance and urban forestry sectors

). The presence of trees creates more pleasant and comfortable environments for pedestrians, encouraging walking and other forms of active transportation. Esthetically, trees improve the visual appeal of neighborhoods, contributing to a stronger sense of place and community identity [13]. Properties with mature trees often have higher real estate values, and tree-lined streets can attract more business activity [18]. Furthermore, street trees can contribute to traffic calming, making streets safer for both pedestrians and drivers. The combined effect of these advantages underscores that the importance of tree-friendly walkable surfaces extends beyond immediate localized benefits, contributing to the long-term resilience and sustainability of urban areas in the face of increasing environmental challenges. For example, the ability of trees to manage stormwater, reduce urban heat, and improve air quality directly addresses critical aspects of climate change adaptation in urban environments (Table 1) [18,19]. Moreover, the concept of “tree equity” highlights the social justice dimension, as lower-income neighborhoods often have less green infrastructure compared to wealthier areas. Initiatives focused on tree-friendly walkable surfaces can play a crucial role in addressing this disparity by prioritizing tree planting and ensuring equitable access to the benefits of urban green spaces.

1.6. Research Gap and Aim of This Article

The primary research gap identified is the lack of comparative studies directly evaluating the performance of structural soil, modular box systems, and suspended grating systems against each other in terms of tree health, growth, and overall environmental benefits. While individual studies exist for structural soil, often comparing it to traditional pavement methods, and some research explores modular box and suspended pavement systems, there is a distinct absence of the scientific literature that directly contrasts all three systems to provide a comprehensive understanding of their relative efficacy and suitability for various urban tree planting applications. This absence makes it difficult for urban planners and landscape architects to make informed, evidence-based decisions when selecting the most appropriate system for specific projects. The existing literature lacks a comprehensive Multi-Criteria Analysis (MCA) that specifically evaluates and compares the diverse ways in which tree-friendly walkable surface solutions can be configured or implemented, beyond assessing individual technologies in isolation.

The objective of this article is to evaluate and compare commercially available urban walkable surface systems that promote hydrological permeability and public space functionality while accommodating tree growth. The three tree planting systems under investigation are suspended grating systems, modular box systems, and structural soils. This study employs a Multi-Criteria Analysis (MCA) framework to systematically evaluate the performance of the three distinct tree planting systems within urban sidewalk environments [62]. The objective is to provide a comprehensive assessment of each system against a defined set of criteria, thereby supporting evidence-based decision-making in the context of sustainable urban tree infrastructure.

2. Materials and Methods

2.1. Methodologies for Construction of Tree-Friendly Walkable Surfaces

Three distinct tree-friendly walkable surface construction methodologies are investigated in this paper:

• Suspended grating systems.
• Modular box systems.
• Structural soils.

2.1.1. Suspended Grating Systems

Suspended grating systems (SGSs) offer a sophisticated engineering solution for protecting the root zones of urban trees (Figure 1). This method involves constructing a platform above the existing soil level, supported by strategically placed point foundations. This design minimizes disturbance to the tree’s root system, a crucial factor in maintaining tree health. Point foundations (1) significantly reduce the area of direct pressure on the soil, safeguarding delicate root structures. Wema grating systems (2), typically made of steel, facilitate excellent gas exchange and water infiltration into the root zone, essential for healthy tree growth. The system’s design allows for flexibility in adapting to complex root systems and uneven terrain, making it versatile for various urban environments, and enables surface laying within the root ball area, without the need for a substructure. Compatibility with aeration systems further enhances conditions for tree growth. The system is developed under the guidance of arborists, ensuring adherence to best practices in tree protection. Specialized materials and engineering requirements can increase construction expenses. The industrial appearance of the grating may not align with all urban design esthetics. Precise installation requires skilled labor, which can increase project time and costs. The installation requires holes to be drilled into the ground, which will cause some root disruption. These systems are ideally suited for protecting the root zones of existing trees in areas requiring paved surfaces for pedestrian and vehicle traffic. Construction elements are typically made of galvanized steel, with a standard construction height of 7.5 cm. Installation necessitates drilling holes for anchor bolts. In summary, suspended structures with Wema gratings provide an effective, albeit relatively costly, solution for urban tree protection. Their advantages in root protection and aeration make them a valuable tool in sustainable urban development [29,30,31,32,36]. These systems are primarily designed to help mature trees by providing root protection and optimal conditions in urban environments.

2.1.2. Modular Box Systems

Modular box systems (MBSs) represent another approach to integrating urban infrastructure with trees (Figure 2). This method utilizes prefabricated modular units to construct an elevated sidewalk surface, effectively bridging over the tree’s root system and minimizing direct soil compaction. These systems involve the construction of a structural framework beneath the pavement that supports the weight of the sidewalk and any traffic loads, creating a subsurface void space that can be filled with uncompacted, high-quality soil (1). Common examples of suspended pavement systems include modular units (2) constructed from recycled plastic or other durable materials. These systems offer significant advantages for tree health by providing large volumes of uncompacted soil, allowing for extensive root growth, improved aeration, and better water infiltration. Many suspended pavement systems can also be designed to incorporate stormwater management features, capturing and treating runoff before it enters the surrounding soil or drainage systems. By essentially decoupling the pavement structure from the soil, suspended pavement systems aim to create an optimal environment for urban trees to reach their full maturity, even in heavily paved areas [33,34,35,36,37]. This is an optimal solution tailored for integrating young trees into new sidewalk constructions.

2.1.3. Structural Soils

Another key technology in the realm of tree-friendly sidewalks is structural soil (SS) (Figure 3). This engineered soil mixture (1) is specifically designed to provide the load-bearing capacity required for pavements while still allowing tree roots to grow through it. Structural soil typically consists of approximately 80% crushed gravel or stone and 20% soil, often with the addition of a small amount of hydrogel to prevent the separation of the stone and soil components. The crushed stone forms a rigid lattice structure that can be compacted to meet engineering specifications for load-bearing, while the voids within this lattice are partially filled with soil, providing the necessary water and nutrients for root growth. This design allows tree roots to penetrate and expand beneath the pavement surface, potentially reducing the upward pressure that can lead to sidewalk heaving. A well-known example of structural soil is CU-Structural Soil™, a patented blend developed by Cornell University. Structural soil aims to reconcile the conflicting demands of pavement stability and tree root growth by creating a medium that is both structurally sound and horticulturally beneficial. Structural soils provide a unified surface that supports both pedestrian and vehicular traffic while simultaneously fostering tree growth [38,39,40,41,42]. This system is specifically intended for new sidewalks and the establishment of young trees. It can also be implemented in environments with existing mature trees, provided that a special air spade technology is first used to eliminate compacted soil.

2.2. Research Approach and MCA Criteria

To evaluate the suitability of tree-friendly walkable surface solutions in dense urban areas, a Multi-Criteria Analysis (MCA) was conducted using a set of criteria categorized into Environmental (

Table 2. Environmental criteria for material evaluation (source: own elaboration based on literature review [29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50]).

Criterion	Score of 1 (Least Favorable)	Score of 2	Score of 3	Score of 4	Score of 5 (Most Favorable)
Root Protection	Constrained—Severely limits root expansion	Limited—Restricts root growth to a small area	Adequate—Supports moderate root extension	Good—Allows for substantial root development	Optimal—Ensures the maximum root expansion and growth
Aeration Drainage	Very Poor—Almost no water infiltration possible	Poor—Restricts water movement significantly	Fair—Provides limited water flow	Good—Supports adequate water passage	Excellent—Allows for the maximum water infiltration
Impact on Ecosystems/Resources	Environmentally Damaging—Causes harm to ecosystems	Resource-intensive—Requires a significant use of resources	Neutral—Has no significant positive or negative impact	Resource-efficient—Minimizes resource use and waste	Eco-friendly—Uses recycled or low-impact materials
Impact on Existing Trees	Severe Impact—Construction severely compromises tree health	Major Impact—Significant stress or damage to trees	Moderate Impact—Noticeable effects on trees but manageable	Minor Impact—Trees experience slight disruption during construction	No Impact—Construction has no adverse effect on trees
Stormwater Management	Inadequate—Fails to manage stormwater effectively	Poor—Struggles with stormwater, needs frequent attention	Moderate—Requires regular maintenance to function well	Good—Effectively manages stormwater with some maintenance	Excellent—Efficiently handles stormwater with minimal upkeep

), Economical (

Table 3. Economical criteria for sidewalk/plaza system evaluation (source: own elaboration based on literature review [29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50]).

Criterion	Score of 1 (Least Favorable)	Score of 2	Score of 3	Score of 4	Score of 5 (Most Favorable)
Installation Cost	Very High—Premium cost, substantial financial outlay	High—Above average cost, significant investment	Moderate—Average cost, reasonable expense	Low—Low cost, affordable for most budgets	Very Low—Below average cost, highly affordable
Installation Speed	Very Slow—Installation takes over a month	Slow—Installation takes two to four weeks	Average—Installation takes one or two weeks	Quick—Installation takes less than a week	Rapid—Can be completed in days
Long-term Maintenance	Minimal—Requires constant attention and repair	Limited—Lasts 3–7 years with frequent repairs	Moderate—Survives for 7–15 years with regular upkeep	High—Lasts 15–25 years with occasional maintenance	Exceptional—Lasts for over 25 years with minimal upkeep
Installation Complexity	Highly Complex—Requires expert skills and extensive planning	Complex—Requires advanced skills and coordination	Challenging—Requires specialized skills and equipment	Moderate—Requires some specialized tools or skills	Simple—Requires basic tools and skills
Adaptability	Incompatible—Not possible to implement with underground technical infrastructure				Compatible—Fits well with underground technical installations/infrastructure and complements the surroundings

), and Other considerations (

Table 4. Other considerations for criteria for sidewalk/plaza system Evaluation (source: own elaboration based on literature review [29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50]).

Criterion	Score of 1 (Low)	Score of 3 (Medium)	Score of 5 (High/Heavy Loads)
Load-Bearing Capacity	Low—Supports light loads, suitable for pedestrian-only areas	Medium—Supports moderate loads, suitable for mixed-use areas	High—Supports heavy loads, suitable for high-traffic areas
Typical Applications	Industrial zones—Prioritizing function over form. Parking lots—Applicable for car spaces.	Sidewalks—Designed for pedestrian pathways, focusing on practicality. Residential development—Appropriate for urban neighborhoods. Urban parks—Suitable for urban parks.	Sidewalks—Designed for pedestrian pathways. Commercial areas—Ideal for commercial areas, balancing durability and appearance. Urban parks—Suitable for urban parks, enhancing esthetics and functionality. Sidewalks. Residential development.

To ensure comparability across all criteria, scores originally rated on a 1–3 scale (within the “Other considerations” category) were rescaled to a 1–5 scale using linear normalization. This adjustment preserved the proportional relationships of the original ratings while allowing for consistent aggregation across all criteria.

) [58]. The three tree planting systems under investigation were suspended grating systems, modular box systems, and structural soils. Research on academic databases, industry reports, and the gray literature was conducted to gather information on the design principles, implementation, and performance of each solution. The comparison focused on several key aspects including the impact on tree health (root growth, water and nutrient availability), installation complexity, initial and long-term costs, maintenance requirements, and suitability for various urban contexts. Data from experimental studies, case studies, and comparative analyses reported in the literature were synthesized to provide a balanced evaluation of the strengths and weaknesses of each tree-friendly walkable surface approach. Each criterion was scored on a scale, typically from 1 (least favorable) to 5 (most favorable), with specific definitions for each score. The criteria applied in our MCA are presented in the following table.

Weight of Criteria

The criteria weights for the Multi-Criteria Analysis were determined using a subjective method, deeply rooted in the authors’ collective professional experience in urban forestry, landscape architecture, and environmental planning. This approach, which draws upon the nuances of expert judgment and preference, is consistent with established methodologies for weight determination, particularly the Multiplicative Analytical Hierarchy Process (AHP) and the Simple Multi-Attribute Rating Technique (SMART) [58,59].

This judgment was cultivated over involvement in diverse urban greening projects, ranging from public space developments to targeted tree health interventions. As described by Chen et al. (2022) [59], subjective methods for weight determination calculate the weight of experts by integrating their mutual evaluations, considering factors such as their experience.

Environmental factors were given the highest cumulative weight (0.60), reflecting their primary importance in promoting tree health and ecological performance. Economic considerations were weighted moderately (0.35), recognizing their role in feasibility and lifecycle cost. Other technical factors, such as load-bearing capacity, were considered less critical in most design contexts and assigned lower weights (0.05). This weighting approach allows for a balanced comparison aligned with urban forestry priorities.

• Environmental Factors (Most Important)
  Existing Tree-Friendly: High weight (0.15).
  Root Protection: High weight (0.15).
  Impact on Tree Health: High weight (0.10).
  Stormwater Management: High weight (0.10).
  Aeration Drainage: High weight (0.10).
• Economic Factors (Second in Order)
  Installation Cost: Medium weight (0.1).
  Installation Speed: Medium weight (0.05).
  Long-Term Maintenance: Medium weight (0.1).
  Installation Complexity: Medium weight (0.05).
  Adaptability: Medium weight (0.05).
• Other Considerations (Important but Least Significant)
  Load-Bearing Capacity: Low weight (0.03).
  Typical Applications: Low weight (0.02).

3. Results

Dense urban areas present unique challenges for integrating trees with walkable surfaces, primarily due to limited space, high pedestrian traffic, extensive underground infrastructure, and a strong need for esthetics and functionality. We analyze the suitability of suspended grating systems, modular box systems, and structural soils based on the provided criteria. A growing body of research has investigated the impact of different tree-friendly sidewalk designs on both tree health and sidewalk performance. The main distinction between these systems lies in their primary application and their compatibility with existing mature trees and underground infrastructure. Suspended pavement systems are primarily engineered to protect mature trees by creating a platform above their root zones. Conversely, while modular box systems and structural soils are specifically designed for new sidewalk installations and the healthy establishment of young trees, they can also be implemented around existing mature trees, provided that a special air spade technology is first used to eliminate compacted soil (refer to accompanying

Table 5. Criteria, scores, and assigned weights (source: own elaboration based on [29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50]).

Category	Criterion	Weights	Suspended Grating System (SGS)	SGPS Weighted Score	Modular Box System (MBS)	MBS Weighted Score	Structural Soils (SSs)	SS Weighted Score
			Primarily for Existing Trees (can include integrated boardwalks)		Primarily for New Trees		Primarily for New Trees, Adaptable for Existing Trees
Environmental	Root Protection	0.15	Optimal (5)	0.75	Good (4)	0.6	Limited (2)	0.3
	Aeration Drainage	0.1	Excellent (5)	0.5	Good (4)	0.4	Fair (3)	0.3
	Impact on Tree Health	0.1	Eco-friendly (5)	0.5	Eco-friendly (5)	0.5	Neutral (3)	0.3
	Existing Tree-Friendly	0.15	No impact (5)	0.75	Severe impact (1)	0.15	Minor impact (2)	0.3
	Stormwater Management	0.1	Good (4)	0.4	Excellent (5)	0.5	Poor (2)	0.2
		0.6		2.9		2.15		1.4
Economical	Installation Cost	0.1	Very High (1)	0.1	Moderate (3)	0.3	Very Low (5)	0.5
	Installation Speed	0.05	Slow (2)	0.1	Quick (4)	0.2	Rapid (5)	0.25
	Long-term Maintenance	0.1	Exceptional (5)	0.5	High (4)	0.4	Limited (2)	0.2
	Installation Complexity	0.05	Complex (2)	0.1	Moderate (3)	0.15	Simple (5)	0.25
	Adaptability	0.05	Compatible (5)	0.25	Incompatible (1)	0.05	Compatible (5)	0.25
		0.35		1.05		1.1		1.45
Other Considerations	Load-Bearing Capacity	0.03	High (5)	0.15	Medium (3)	0.09	High (5)	0.15
	Typical Applications	0.02	Sidewalks—Designed for pedestrian pathways, focusing on practicality. Residential development—Appropriate for urban neighborhoods. Urban parks—Suitable for urban parks (3).	0.06	Commercial areas—Ideal for commercial areas, balancing durability and appearance. Urban parks—Suitable for urban parks, enhancing esthetics and functionality. Sidewalks. Residential development (5).	0.1	Commercial areas—Ideal for commercial areas, balancing durability and appearance. Urban parks—Suitable for urban parks, enhancing esthetics and functionality. Sidewalks. Residential development (5).	0.1
		0.05		0.21		0.19		0.25

for detailed criterion scores).

3.1. Suspended Grating System

The suspended grating system (SGS) demonstrates significant advantages, particularly concerning its environmental benefits crucial for the health and preservation of mature urban trees (Table 5). This system provides optimal root protection (scoring 5), which is a critical advantage in dense areas where underground utilities are abundant and root damage to infrastructure is a major concern, effectively preventing sidewalk heave and protecting subterranean pipes. It also offers excellent aeration and drainage (5), essential for promoting better water infiltration and oxygen supply to tree roots in typically compacted urban soils. Furthermore, the SGPS is rated as eco-friendly (5) with no impact on existing trees (5), suggesting minimal disruption during installation and a long-term positive environmental impact, aligning with sustainable urban development goals. Its good stormwater management (4) also contributes to urban resilience by helping manage runoff. Economically, the SGPS offers exceptional long-term maintenance (5), translating to lower recurring costs and reduced disruption for pedestrians and businesses. Its high compatibility with underground infrastructure (5) is a substantial advantage in complex urban environments. The system’s high load-bearing capacity (3) makes it suitable for most pedestrian sidewalks and potentially areas with occasional heavy vehicle access (Table 5).

However, the SGPS presents notable economic and logistical challenges. Its installation cost is very high (1), representing a substantial financial outlay that can impede widespread implementation in budget-constrained urban projects. Installation is also slow (2) and complex (2), leading to prolonged disruption to pedestrian flow, local commerce, and traffic in dense urban settings (Table 5). Despite these economic drawbacks, research generally recognizes suspended grating walkable surfaces as one of the most effective approaches for fostering healthy urban tree growth [51]. Overall, the suspended grating system is environmentally superior and offers excellent long-term benefits, especially regarding tree health, root protection, and low maintenance [55]. Its high initial cost and complex installation make it best suited for premium urban green spaces, main thoroughfares, or specific projects where tree preservation and long-term sustainability are paramount and budget constraints are less severe.

3.2. Modular Box System

The modular box system (MBS) presents a strong balance of environmental benefits, practical installation, and esthetic appeal, making it highly suitable for a wide range of dense urban pavement applications, especially for new tree plantings. A key strength is quick installation (4) with moderate complexity (3), resulting in less disruption to pedestrian traffic and businesses, which is vital in busy urban centers (Table 5).

Environmentally, the MBS offers good root protection (4) and aeration drainage (4), supporting substantial root development and adequate water/air flow compared to traditional methods. It provides excellent stormwater management (5), significantly benefiting urban resilience. The MBS is also rated as eco-friendly (5). However, it has a severe impact on existing trees (1), indicating significant stress or damage during construction. Long-term maintenance is rated as “high” (4), suggesting good durability and reasonable lifecycle costs. While its load-bearing capacity is medium (3), suitable for typical pedestrian sidewalks, it may not be ideal for areas requiring frequent heavy vehicle access. The installation cost is moderate (3), positioning it between the high cost of the SGPS and the very low cost of structural soils. Its adaptability is incompatible (1), making it less practical for integration with existing underground infrastructure (Table 5).

Recent research has highlighted the benefits of modular boxes (often referred to as soil cells) for newly planted trees [32,33,34]. These systems streamline the construction process, leading to quicker installation times. The design provides ample space and structural support for root growth, promoting healthy tree development, and can encourage vertical root growth [37]. Studies comparing structural soil and soil cells have generally concluded that soil cells offer a greater volume of usable soil, which often translates to better tree growth [56]. Their ability to minimize root disturbance and promote healthy root development makes MBSs a strong contender for sustainable urban design. While MBSs can be difficult to install around existing well-developed root systems, the use of air spade technology can facilitate their implementation around mature trees.

3.3. Structural Soil System

The structural soil (SS) system offers significant economic advantages, making it a highly budget-friendly option for extensive urban projects, primarily for new plantings but also adaptable for use with existing trees. Its installation cost is very low (5), and installation is rapid (5) with simple complexity (5), minimizing the disruption critical in busy urban areas. It also possesses a high load-bearing capacity (5), similar to the SGPS, making it versatile for various urban sidewalk types, including parking lots and industrial zones (Table 5).

However, SS demonstrates notable environmental and practical limitations for tree health in a dense urban context. It provides limited root protection (2), which is a major concern as it can lead to sidewalk damage (heave) and compromise tree health over time due to compaction and a lack of space for root expansion. Aeration and drainage are only fair (3), leading to sub-optimal water and air infiltration. Its impact on tree health is rated as neutral (3), indicating that it does not actively promote robust tree growth as effectively as other systems. Stormwater management is poor (2), suggesting that it is less effective at mitigating urban runoff issues. Its long-term maintenance is limited (2), implying more frequent repairs and a shorter lifespan (3–7 years), leading to higher recurring costs and disruptions. Its adaptability is compatible (5), making it practical for integration with existing underground infrastructure (Table 5).

Compared to suspended structures, structural soils offer a practical and cost-effective approach to reconciling urban infrastructure with tree preservation. When properly formulated, structural soils can provide adequate drainage and aeration for healthy root development. The stone matrix provides the necessary strength to support pavement loads [38,39,40,41,42]. However, research highlights that despite being engineered to minimize compaction, improper installation or exposure to heavy loads can still lead to soil compression, hindering root growth [38]. The soil matrix, if not precisely formulated, may also restrict air and water movement compared to suspended systems. While structural soil has been shown to result in larger root diameters in some studies, the contact area with the pavement can be less than expected due to intervening gravel layers, suggesting complex interactions with pavement damage [52,53]. Although structural soil is sometimes considered a more affordable and readily available alternative to soil cells [57], its limited root protection and sub-optimal drainage make it generally unsuitable for dense urban sidewalk applications where long-term tree health and infrastructure integrity are paramount.

3.4. Results of Data Aggregation and Sensitivity Analysis

The aggregated scores for each walkable surface system indicate that the suspended grating system (4.16) is the most preferred in the context of existing tree protection, followed by the modular box system (3.44) and structural soil system (3.10).

Four distinct test scenarios were developed to explore different plausible shifts in weighting. The first one covered Baseline Weights (Reference Point). This scenario utilized the initial set of weights derived from expert input, serving as the primary reference for comparison. The category weights were as follows: 0.60 for Environmental, 0.35 for Economical, and 0.05 for Other considerations.

The second scenario covered Increased Economical Factor Significance and investigated the impact of elevating the importance of economic considerations. The weight of the “Economical” category was increased by 0.10, concomitantly reducing the “Environmental” category’s weight by 0.10, while that of “Other considerations” remained unchanged. Specifically, the category weights were adjusted to the following: 0.50 for Environmental, 0.45 for Economical, and 0.05 for Other considerations. Individual criterion weights within each category were proportionally rescaled to maintain consistency with the new category totals.

The test scenario related to the Increased Significance of “Other Considerations” explored the effects of assigning greater importance to the “Other considerations” category. Its weight was increased by 0.10, with corresponding decrements of 0.05 from those of both the “Environmental” and “Economical” categories. The resulting category weights were as follows: 0.55 for Environmental, 0.30 for Econonmical, and 0.15 for Other considerations. As in Scenario 2, individual criterion weights were proportionally rescaled within their respective categories.

The test scenario regarding Heightened “Root Protection” Priority specifically assessed the sensitivity of the ranking to an amplified emphasis on a single critical environmental criterion: “Root Protection.” The weight for “Root Protection” was fixed at a new, higher value of 0.25 (up from its baseline of 0.15). To maintain a total sum of 1.0 for all weights, the remaining eleven criterion weights were proportionally reduced based on their original relative contributions, ensuring that their collective sum equaled the remaining available weight (1.00 − 0.25 = 0.75)

The sensitivity analysis revealed remarkable stability in the ranking of the evaluated walkable surface systems (

Table 6. Sensitivity analysis results (source: own elaboration).

Scenario	SGS	MBS	SS	Ranking	Comments
1. Baseline (from previous calculations)	4.16	3.44	3.10	1. SGPS. 2. MBS. 3. SS.	Baseline/reference point
2. Weight of “Economic” Criterion Increased	3.98	3.40	3.28	1. SGPS. 2. MBS. 3. SS.	SGPS maintains its position; MBS gets closer to SGPS
3. Weight of “Other Considerations” Criterion Increased	4.58	3.82	3.60	1. SGPS. 2. MBS. 3. SS.	SGPS strengthens its position
4. Weight of “Root Protection” Increased	4.14	3.42	3.07	1. SGPS. 2. MBS. 3. SS.	SP, MBS, and SS slightly drop

). Across all simulated scenarios, the suspended grating system (SGS) consistently maintained its superior performance, securing the first-place rank. This consistent dominance underscores its inherent robustness and suggests that its desirability is largely independent of moderate fluctuations in stakeholder priorities. Similarly, the modular box system (MBS) consistently occupied the second position, with structural soils (SSs) invariably ranking third. While the absolute aggregate scores for each system varied across the different weighting scenarios, their ordinal relationship remained invariant (Table 6). Specifically, an increase in the weight assigned to economic factors (Scenario 2) did not alter the primary ranking but demonstrably narrowed the performance gap between the SGPS and MBS. This observation is consistent with the MBS’s comparatively stronger performance in certain economic criteria. Conversely, enhancing the influence of “Other considerations” (Scenario 3) yielded only marginal alterations in both the absolute and relative scores. Furthermore, a targeted increase in the weight of “Root Protection” (Scenario 4) served to further accentuate the leading position of the SGPS, a system highly rated in this specific environmental criterion, without negatively impacting its overall superiority. In conclusion, the robust nature of the SGPS’s top ranking, demonstrated through this comprehensive sensitivity analysis, confirms its resilience to variations in criterion weighting and strongly supports its recommendation as the preferred walkable surface system based on the initial evaluative framework.

4. Discussion

4.1. Comparative Synthesis

The analysis reveals distinct trade-offs among the three systems when considering their application in tree-friendly walkable surfaces in dense urban areas. The modular box system emerges as a strong contender due to its excellent stormwater management abilities. However, its severe impact on existing trees and incompatibility with underground infrastructure present significant drawbacks that must be carefully weighed (Table 5). In contrast, the suspended grating system stands out for its superior environmental performance, particularly in providing optimal root protection and its minimal impact on existing trees. Its exceptional long-term maintenance benefits also offer significant lifecycle cost savings. However, the very high initial installation cost, along with slower and more complex construction, limits its widespread adoption, positioning it as a premium solution for high-value urban greening projects (Table 5). Structural soils, while offering considerable advantages in terms of very low installation cost and rapid, simple deployment, face substantial limitations due to their limited root protection, poor stormwater management, and potential for soil compression. Despite their high adaptability to underground infrastructure, their overall impact on tree health and long-term maintenance suggest that they are less viable in contexts where robust tree growth and integrated urban systems are priorities (Table 5).

The findings from this Multi-Criteria Analysis provide valuable insights into the comparative performance of the three walkable surface systems under consideration. The aggregation of weighted scores, as detailed in Section 3.4, clearly identified the suspended grating system (SGS) as the leading alternative based on the established criteria and their initial weights. This outcome reflects the SGPS’s strong performance across several highly weighted environmental factors, which were prioritized in the current evaluation framework. However, the inherent subjectivity in assigning criterion weights necessitates a thorough examination of the robustness of these results.

The scientific literature encompasses studies on urban ecosystem services, tree physiological responses to urban stressors, stormwater management best practices, and the economic valuation of green infrastructure [60]. These bodies of work consistently underscore that environmental conditions—such as adequate root protection [55], effective stormwater management [61], and proper aeration—are paramount for ensuring the health, longevity, and ecological functionality of urban trees. Our expert judgment, therefore, is not only derived from professional experience but is also empirically supported by observing the outcomes of numerous case studies where the neglect of these environmental factors led to significant tree decline or failure, while their prioritization resulted in flourishing urban canopy. This combined foundation of extensive practical experience, the direct observation of empirical contexts, and a thorough review of the established scientific literature provided a robust and transparent basis for assigning the highest cumulative weight to environmental factors, reflecting their undeniable primary importance in sustainable urban forestry.

To address this, a comprehensive sensitivity analysis was conducted (Section 3.4), exploring various scenarios by systematically adjusting the weights of both criterion categories and specific key criteria (Table 6). A critical observation from this analysis is the remarkable stability of the ranking. Despite variations in the relative importance assigned to Environmental, Economical, and Other considerations, the SGPS consistently maintained its top position, followed by the modular box system (MBS) and structural soils (SSs). While the absolute aggregate scores fluctuated across scenarios—for instance, the MBS’s relative standing improved when economic factors were given greater emphasis, aligning with its stronger performance in certain cost-related criteria—the ordinal ranking remained invariant. This consistent outcome across diverse weighting schemes significantly enhances the confidence in the recommendation of the SGPS (Table 6). This suggests that the superior performance of the SGPS is not merely an artifact of a specific weighting set but is robustly supported across a range of plausible decision-maker priorities. Such resilience is a crucial characteristic for informing reliable decision-making in complex engineering and urban planning contexts.

As evidenced by the provided scientific articles, there is a substantial body of research on structural soil, largely due to its development at a university [45]. Studies frequently compare tree health in structural soil versus traditional pavement [45], and some even compare it to that in modular box systems [49]. This indicates a visible data pool for understanding its performance and benefits. In contrast, there appears to be a scarcity of scientific material directly comparing or thoroughly evaluating suspended grating systems or modular box systems. While Tirpak et al. (2019) [50] discuss modular box systems as opportunities for subsurface bioretention, and mention observations about biomass and rooting depth in structural cells compared to structural soil, there is a clear indication that these are often commercial products. This commercial nature may contribute to a lack of independent, peer-reviewed comparative research on their direct performance against each other or against structural soil in a consistent manner. The provided text, while offering some insights into the performance of trees within structural cells (a type of modular box system), does not present a direct scientific comparison with structural soil or suspended grating systems across multiple parameters in a controlled study.

4.2. Successful Implementation: Case Studies of Cities and Projects

Several cities and projects have successfully implemented tree-friendly walkable surfaces, providing valuable examples and lessons learned for future endeavors. These case studies highlight the diverse approaches taken and the observed outcomes.

Boston, Massachusetts, is home to one of the earliest known installations of suspended pavement in the United States at the Christian Science Center, dating back to 1968 [63,64]. This long-standing example showcases the long-term viability of suspended pavement systems in supporting mature urban trees in a heavily paved environment. Downtown Charlotte, North Carolina, implemented a custom suspended pavement system using precast concrete to provide approximately 1000 cubic feet of soil per tree for nearly 170 street trees [65]. Despite a contractor error that resulted in a slightly lower soil volume, the trees in this project have flourished, demonstrating the potential for robust tree growth when sufficient soil is provided beneath paved surfaces. One example of WEMA grating implementation surrounding existing mature trees is its installation as a designated private parking space and gate entrance for the private plot in Komorów-garden city, Poland (Figure 4).

At the High Line, New York, a suspended grating walkable surface application allows for a walkable surface above the existing railway infrastructure (Figure 5). These examples illustrate the application of suspended pavement technology in different urban contexts, highlighting its ability to provide ample soil volume for tree growth beneath plazas and sidewalks and parking places.

Lincoln Center in New York City has also incorporated Silva Cells, a modular suspended pavement system, in its Barclay Capital Grove, installed in 2009 [64,65]. Another Silva Cell system was installed in front of Brightside’s office in St. Louis, Missouri, incorporating a porous paver walkway to enhance water and oxygen reaching the tree roots while also serving as a stormwater storage space [66].

Structural soil has been implemented in various projects, with mixed results depending on the specific application and maintenance practices. Navy Pier in Chicago and the World Trade Center in Manhattan are often cited as successful examples of structural soil use, although the latter involved very large root balls and irrigation [67,68,69].

The rationale behind selecting a particular design often involves balancing factors like cost, available space, the need for stormwater management, and the desire for long-term tree health and minimal sidewalk disruption. Observed outcomes vary depending on the technology and the quality of implementation and maintenance. While suspended pavements often show the most promising results for tree growth, other methods like the use of structural soil can also be effective when applied appropriately and maintained diligently. The lessons learned from these case studies emphasize the importance of meticulous planning, proper installation by experienced contractors, and the establishment of long-term maintenance strategies to ensure the success of tree-friendly sidewalk initiatives.

4.3. Legal Imperatives for Tree-Friendly Sidewalk Solutions

The evolving legal landscape mandates integrating tree protection into urban development, making tree-friendly walkable surface systems compulsory for sustainable planning. The recent EU Directive 2024/1203 strengthens environmental safeguards, broadening criminal offenses to include harm to ecosystems and plants (Art. 3), detailing criminal liability (Art. 13, 15, 21), and specifying penalties (Art. 30–37) [70]. This EU framework establishes a critical baseline.

Many countries, like Poland, reinforce these principles with national legislation. The Polish Nature Conservation Act (Journal of Laws 2004 No. 92, item 880) meticulously regulates earthworks near vegetation (Art. 87a, 87b), imposing penalties for damage or removal (Art. 88, para. 1) and protecting the tree’s surroundings [71]. The Environmental Protection Law (Journal of Laws 2001 No. 62, item 627) mandates environmental protection in construction (Art. 75, 101), with violations subject to fines (Art. 330) [72]. The Construction Law (Journal of Laws 1994 No. 89, item 414) holds construction managers directly responsible for protecting natural elements [73].

In the United States, tree protection is primarily enacted at the state and local levels through municipal ordinances governing tree removal, planting, and protection on public and private property. Many cities have specific guidelines for infrastructure design around trees, and federal acts like NEPA may also influence protection through environmental impact assessments [74].

In China, urban tree protection combines national laws, local regulations, and ambitious greening plans. The Forest Law of the People’s Republic of China provides a general framework, while local urban greening regulations in major cities mandate planting, protect existing trees, and outline removal procedures, enforced by urban management bureaus. China’s “ecological civilization” push further integrates tree protection into urban planning [75].

Collectively, these legislative instruments at the EU and national levels, exemplified by Poland, the United States, and China, underscore a clear legal imperative for urban development practices to prioritize the preservation and health of urban trees through innovative and non-invasive sidewalk solutions.

5. Future Directions in Tree-Friendly Walkable Surface Research and Development

The field of tree-friendly walkable surface systems is continually evolving, with ongoing research and development aimed at improving existing technologies and exploring new approaches. Several key areas warrant further investigation to advance the state of the art. Long-term studies are needed to comprehensively evaluate the performance of different designs of tree-supportive walkable surface configurations over extended periods. While initial research has provided valuable insights, understanding the long-term impacts on both tree health and walkable surface integrity over several decades is crucial. Such studies should track root growth patterns, tree survival rates, the occurrence and extent of pavement deformation and cracking, and the frequency and types of maintenance required for various designs under different urban conditions. Long-term maintenance is crucial for the sustained functionality and benefits of tree-friendly walkable surface systems (Table 1), encompassing essential tree care like watering, mulching, and preventing compaction, alongside specific system needs such as irrigation for structural soil or monitoring stormwater components in modular boxes. Strategies to mitigate winter salt damage are also vital. Developing comprehensive maintenance plans is paramount for maximizing system lifespan and ensuring the long-term health of urban trees and pedestrian well-being [76,77,78,79,80,81].

A significant area for future development is the creation of more cost-effective tree-friendly walkable surface solutions focusing on new materials that may be used. The higher initial costs associated with some advancements can be a barrier to their widespread adoption. Research efforts should focus on optimizing material blends, simplifying installation techniques, and exploring innovative construction methods to reduce the overall cost, making these solutions more accessible to a wider range of urban areas, particularly those with budget constraints. Beyond the systems we analyzed, boardwalks offer an often-overlooked alternative for urban walkable surfaces, particularly for preserving and fostering nature restoration or conservation [82]. As demonstrated by sections of NYC’s High Line, where trees thrive in soil beneath the boardwalk, this approach provides ample, uncompacted root volume [83]. Importantly, when constructed from timber or composite materials, a boardwalk can be less expensive than grating systems, making it a potentially more affordable option that could be placed over both new and existing trees.

Historically, boardwalks served as effective pathways, especially in harsh peat conditions. Unlike concrete, an unsustainable material prone to root-induced heaving, boardwalks offer a more responsive and repairable solution [84,85]. They allow for easy access to and the repair of underlying utilities, minimizing disruption and cost compared to solid pavements. While not originally designed for trees, Steward Brand’s concept of “tilt-up sidewalks” with liftable panels highlights the benefit of easy access [86,87]. This integrated approach warrants further exploration as a sustainable and cost-effective strategy for enhancing urban canopy.

Long-term studies are also required to quantify the cumulative impact of widespread implementation on urban microclimates and air quality. While the benefits of individual trees are well-documented, understanding the broader effects of increased urban tree canopy facilitated by these pavement designs on reducing the urban heat island effect and improving air quality on a city-wide scale requires further investigation over extended timeframes. The development of standardized guidelines and best practices for the design, installation, and maintenance of such systems would be valuable for practitioners. These guidelines, based on research findings and lessons learned from case studies, could help to ensure more consistent and successful implementation across different urban contexts.

Exploring the integration of tree-friendly walkable surfaces with emerging smart city technologies could also offer new avenues for research and development. For example, incorporating sensors to monitor soil moisture levels, temperature, and tree vitality within these systems could enable more proactive and efficient management and maintenance. Finally, future research should consider species-specific design considerations. Different urban tree species have varying root growth patterns and requirements. Understanding these differences in relation to various pavement designs could allow for more tailored and effective solutions that optimize the health and longevity of specific tree species in urban environments.

6. Conclusions

Tree-friendly walkable surfaces represent a crucial evolution in urban infrastructure, acknowledging the vital role of trees in creating sustainable and livable cities. By prioritizing the coexistence of pedestrian infrastructure and urban trees, these innovative designs offer a multitude of environmental, social, and economic benefits, ranging from improved stormwater management and air quality to enhanced walkability and property values. A range of technologies, including permeable pavements, structural soil, and suspended pavement systems, have been developed to achieve this goal, each with its own set of characteristics, advantages, and limitations. Research has consistently highlighted the positive impacts of these designs on tree health and pavement performance, with suspended pavement systems often demonstrating the most favorable outcomes for tree growth. However, the successful implementation of tree-friendly walkable surfaces requires a careful consideration of factors such as initial costs, installation complexity, and long-term maintenance needs. Case studies from cities around the world provide valuable real-world examples of both successes and challenges in this field, emphasizing the importance of meticulous planning, proper execution, and ongoing care. The selection of appropriate materials, including sustainable and recycled options, is also a critical aspect of creating environmentally responsible and high-performing tree-friendly walkable surfaces.

Moving beyond a general call for further research, the critical next step in urban forestry demands a paradigm shift towards proactive, experimental, and publicly engaged methodologies. Future studies should move beyond observation to implement innovative, adaptive tree planting systems directly within urban sidewalks, treating streets as living laboratories. Imagine designated “incubator sidewalks” across cities, each employing a distinct planting technique, complete with clear signage explaining the ongoing experiment to pedestrians, fostering public awareness and participation. Such pioneering initiatives could be funded through a combination of targeted municipal and national green infrastructure grants, partnerships with horticultural and engineering firms, and even public crowdfunding platforms, leveraging the community’s investment in their local environment.

To further advance this field, future research should focus on comprehensive, long-term performance evaluations, the integration of these designs with other green infrastructure elements, and the development of more cost-effective solutions. The optimization of material performance, a deeper understanding of social and economic impacts, the establishment of standardized guidelines, and the exploration of integration with smart city technologies also hold immense promise. Moreover, the integration of biodiversity initiatives into urban planning is paramount for enhancing ecosystem services and promoting human well-being, necessitating policies that prioritize the creation and maintenance of biodiverse green spaces.

Ultimately, urban planners, policymakers, and infrastructure developers are encouraged to embrace the principles of tree-friendly walkable surface design and to invest in research and pilot projects that can further refine these technologies. By prioritizing the integration of nature into the built environment, we can create greener, more sustainable, and more livable urban environments for generations to come. The long-term environmental, social, and economic returns on investing in tree-friendly infrastructure far outweigh the initial challenges, contributing to urban resilience and a higher quality of life for all residents. Fostering strong collaboration between diverse disciplines, including urban planning, landscape architecture, engineering, and arboriculture, will be essential for ensuring the successful and widespread adoption of these vital infrastructure solutions. In essence, the successful integration of urban trees into cityscapes requires a multidisciplinary approach that balances ecological, economic, and social considerations, ensuring that cities can create vibrant, sustainable environments that benefit both present and future generations. The ongoing investment in the research, development, and implementation of tree-friendly urban design practices is essential for realizing the full potential of urban trees as a vital component of urban ecosystems.