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Article

Tree Species as Metabolic Indicators: A Comparative Simulation in Amman, Jordan

Doctoral School of Landscape Architecture and Landscape Ecology, Hungarian University of Agriculture and Life Sciences, Villányi Str. 29-43, 1118 Budapest, Hungary
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Author to whom correspondence should be addressed.
Land 2025, 14(8), 1566; https://doi.org/10.3390/land14081566
Submission received: 30 June 2025 / Revised: 23 July 2025 / Accepted: 26 July 2025 / Published: 31 July 2025

Abstract

Urban metabolism frameworks offer insight into flows of energy, materials, and services in cities, yet tree species selection is seldom treated as a metabolic indicator. In Amman, Jordan, we integrate spatial metabolic metrics to critique monocultural greening policies and demonstrate how species choices forecast long-term urban metabolic performance. Using ENVI-met 5.61 simulations, we compare Melia azedarach, Olea europaea, and Ceratonia siliqua, mainly assessing urban flow related elements like air temperature reduction, CO2 sequestration, and evapotranspiration alongside rooting depth, isoprene emissions, and biodiversity support. Melia delivers rapid cooling but shows other negatives like a low biodiversity value; Olea offers average cooling and sequestration but has allergenic pollen issues in people as a flow; Ceratonia provides scalable cooling, increased carbon uptake, and has a high ecological value. We propose a metabolic reframing of green infrastructure planning to choose urban species, guided by system feedback rather than aesthetics, to ensure long-term resilience in arid urban climates.

1. Introduction

1.1. Framing Urban Metabolism as a Diagnostic Lens for Green Infrastructure

Urban metabolism (UM) has long been established as a framework for understanding the complex flows of materials, energy, water, and nutrients in cities [1,2]. Traditionally, it has been used to assess resource efficiency, identify bottlenecks in urban performance, and evaluate sustainability strategies. However, this paper proposes a conceptual shift: rather than merely using urban metabolism to evaluate green infrastructure, we argue that urban metabolism flows can be used as a diagnostic tool that actively informs and critiques green infrastructure planning— particularly through biological elements such as tree species.
In cities like Amman, Jordan—where greening initiatives are rapidly expanding in response to climatic stress and public pressure—decisions around which tree species to plant have rarely been evaluated through a metabolic framework.
This can be encouraged by how trees function as metabolic agents: they absorb, store, and release water, carbon, and nutrients; they affect thermal comfort, biodiversity, and pollution dynamics [3,4]. In this sense, tree species are not just passive landscape elements—they are embedded in and indicative of the city’s metabolic health.

1.2. Green Infrastructure in Amman

Amman’s green infrastructure has long been constrained by its topography, water scarcity, and rapid urbanization. With steep terrain, a semi-arid climate, and frequent drought conditions, green space allocation has historically been low compared to regional and global benchmarks. Estimates based on satellite-derived NDVI analysis place the city’s average vegetative cover between 2.5% and 4.8%, depending on the neighborhood and season, with significant disparities across socioeconomic zones [5,6]. High-income districts like Abdoun and Dabouq show higher canopy and private garden coverage, while eastern and southern districts exhibit far lower green surface ratios.
The Greater Amman Municipality (GAM) has acknowledged these inequalities and launched several greening programs over the past decade. Among them, the “Green Amman 2030” initiative seeks to raise the per capita green space from under 1 m2 to 15 m2, aligning with World Health Organization (WHO) recommendations [7]. However, implementation has been sporadic, and tree planting campaigns—such as along Airport Road, Queen Rania Street, and various school and university campuses—have often lacked ecological assessment, favoring fast-growing species like Melia azedarach over native or adaptive alternatives [8].
In terms of planning frameworks, the Jordanian Ministry of Environment has published urban forestry guidelines in collaboration with the Royal Scientific Society and Arab Group for the Protection of Nature, encouraging tree planting with drought-resilient and low-allergen species [7,9]. Yet these recommendations are not binding and are inconsistently enforced across districts.

1.3. Amman’s Shifting Urban Tree Landscape

Over the last two decades, Amman has seen an aggressive expansion of Melia azedarach, also known as the Chinaberry or umbrella tree, in newly planned neighborhoods [7,10]. Fast growth and visual appeal have made it popular even in private landscaping. However, its spread has come at the cost of native species such as Ceratonia siliqua (carob), Pistacia atlantica (wild pistachio), and Quercus calliprinos (native oak). This paper raises questions about the choices of tree species within the city, and it explores Melia azedarach, a non-native tree species with its sudden proliferation, which signals a policy-driven effort to create quick canopy coverage. However, the limited biodiversity support and potential allelopathic behavior of Melia azedarach [11] reinforce concerns about the ecological suitability of non-native species in Amman’s urban planning. Olea europaea on the other hand, was historically one of the most widely planted species, promoted by both municipal policies and embraced by residents for its cultural and agricultural value. However, despite its drought resistance, it produces high levels of allergenic pollen [9,12] affecting the urban metabolic flow of people. These chosen species, which are the most common ones within Amman neighborhoods, further underscore the need for employing diagnostic tools prior to urban planting. By applying urban metabolism as a diagnostic framework, this study positions the species not only as a sustainability feature, but also as a metabolic signal—highlighting mismatches between environmental policy, ecological function, and urban system health.

1.4. Research Gap and Objectives

Despite advances in urban metabolism frameworks, critical gaps persist in applying UM principles to green infrastructure. Within the UM literature, species-level metabolic accounting is absent in neighborhood-scale UM models and trade-offs between short-term cooling and long-term resource efficiency remain unquantified in arid cities. This study addresses these gaps by developing a simulation-based framework to evaluate tree species as metabolic agents across three spatial scales in Amman, Jordan. Using microclimatic modeling, we quantify species-specific performance with respect to temperature regulation and carbon sequestration to inform climate-resilient urban forestry.

1.5. Aim and Contribution

This paper aims to demonstrate that urban metabolism, originally conceptualized in the 1970s to understand resource flows in large cities, has since evolved into a flexible framework that can be applied to small-scale urban design interventions—including species selection within green infrastructure [13], This article examines urban systems through the analytical framework of street-level urban metabolism, expanding upon Kennedy’s multi-layered studies of urban metabolic processes [14]. While traditional urban metabolism analyzes cities as macro-scale systems, this study focuses on neighborhood street networks as critical units of resource flow, applying Kennedy’s indicator framework to a finer-grained assessment of streets as metabolic conduits. Focusing on Amman, Jordan, the study dissects seven key metabolic flows (e.g., water, energy, and waste) at the street level, adapting methodologies from Rotterdam’s neighborhood-scale metabolic analysis. This approach reveals how hyper-localized flows interact with environmental stressors such as water scarcity, extreme heat, and limited green infrastructure. By comparing four distinct typical neighborhoods in the city, the study identifies disparities in flow efficiencies tied to urban design, offering targeted strategies to enhance resilience. The research’s goal is to generate actionable strategies for enhancing urban infrastructure by mapping resource flows and proposing interventions. Ultimately, the study aims to develop a scoring system that quantifies the impact of each flow within the cities studied, and is complemented by a survey to understand the local perspective and analytically identify the flows and elements that enhance the city’s metabolism and environmental stresses [5,13]. Projects like Schoonship [15], have already shown how metabolic models can operate at the level of residential blocks or even individual buildings. Building on the shift from macro-scale to neighborhood-level applications of urban metabolism, we argue that urban metabolism can serve not just as a descriptive or evaluative tool, but as a diagnostic lens for guiding tree species choices in climate-stressed cities.
Although species selection may seem like a reductionist lens for understanding urban metabolism, it is in fact a pragmatic and actionable entry point. Trees are metabolic agents—modulating thermal balance, carbon uptake, water cycles, and biodiversity—yet their performance is rarely evaluated through systemic flows. By focusing on tree species, we can detect broader mismatches between ecological function, planning policies, and long-term urban resilience.
The novelty of this study lies in the introduction of the concept of “metabolic misselection”—a condition where the short-term visual or cooling benefits of a species mask long-term inefficiencies or ecological drawbacks. We test this concept through scale-responsive simulation metrics, combining ecological literature, spatial profiling, and ENVI-met modeling across three nested spatial scenarios.
Our key contributions focus on the ability to introduce metabolic misselection in urban forestry, demonstrate how tree species distribution can serve as an indicator of urban metabolic health, and show how urban metabolic health influences tree species distribution, since both can be evaluated through a metabolic lens. Finally, we apply this evaluation method integrating field observation, simulation, and ecosystem assessment to inform green infrastructure decisions.

2. Literature Review

2.1. Urban Metabolism Scales and Urban Vegetation

The relationship between urban vegetation and urban metabolism has been acknowledged but under-theorized. The earliest metabolism models by Wolman [13] were focused on 1 million residents, which clearly grew in scale with time in different case studies like IABR’s Rotterdam [16] and Barles’ Paris [2] study. The models improved gradually, with Kennedy et al. [14] describing cities as “complex systems of metabolic processes,” yet focusing largely on energy, material throughput, and introduces anthropogenic activities. In the latest studies, smaller scale projects, which could be zoomed in to small structures like Schoonship [17], introduced architectural metabolic models within residences and offices.
More recent perspectives have begun including ecosystem services and biological flows and understanding urban metabolism on a neighborhood scale [5], but few studies explore trees as active components of urban metabolism. Species selection plays a pivotal role in the ecological performance of green infrastructure. For instance, trees differ widely in their water use [18], CO2 sequestration potential [19] pollutant removal, and impact on biodiversity.

2.2. Tree Species as Metabolic Infrastructure

In arid and semi-arid climates, tree species selection becomes a critical factor in the performance of GI. Native or adaptive species are generally favored due to their lower water demands, ecological compatibility, and resilience to extreme weather events. In contrast, the introduction of fast-growing, non-native monocultures has often led to reduced biodiversity, poor long-term performance, and even ecological dysfunction [20].
Melia azedarach is widely recognized for its fast growth and drought tolerance, which makes it attractive for urban planting. In Riyadh, this species is present in areas such as the Diplomatic Quarter’s Tuwaiq Palace garden, indicating its role in local green infrastructure [21]. Similarly, in Cairo, Melia azedarach is featured in El-Azhar Park [22], a significant urban green space, where it contributes to the park’s biodiversity and offers respite from the city’s heat, but studies cite allelopathic effects and weak ecological integration [11]. Its wood density is moderate [23] (~440–610 kg/m3) and it suffers from weak branch integrity. It also showed a relatively low habitat value for native pollinators or bird species [24]. High isoprene emissions make it less desirable from an air quality perspective [25], especially in hot, stagnant environments.
Other arid cities—such as Tehran, where Platanus orientalis has triggered health concerns due to allergenic pollen [26,27], or Muscat, where introduced species led to excessive water use—demonstrate the risks of poorly evaluated greening strategies [28]. In contrast, cities like Tunis and Marrakech have begun prioritizing species with high ecological integration and a low environmental cost. The lack of alignment between the ecological characteristics of M. azedarach and the metabolic needs of Amman’s urban ecosystem exemplifies what we term metabolic misselection (a condition where species choices lead to long term inefficiencies or failures in urban ecological functions). A recent article published in Land [29], calls for integrating species-specific ecological indicators into urban planning to avoid the pitfalls of short-term greening and climate tokenism. Our study builds on this direction by testing simulation-based species profiling as a metabolic diagnostic tool for green infrastructure.

3. Methodology

This study employs a multi-layered methodological approach that integrates the previous literature-based ecological assessment and spatial analysis-based ENVI-met microclimatic simulation to evaluate the metabolic implications of using the three tree species. The research aims to test the hypothesis that different metabolic flows can be used as a diagnostic tool, not merely a descriptive framework, to evaluate the performance and appropriateness of urban green infrastructure, particularly tree species selection. The methodology is designed to both reveal systemic misalignments in urban decisions and explore alternative solutions that support long-term metabolic health.

3.1. Literature-Based Ecological Profiling and Comparative Assessment

The first methodological layer involves selecting and profiling tree species through a comparative ecological review. We focused on three species presented in Figure 1:
  • Melia azedarach (chinaberry)—currently promoted and widely planted in Amman.
  • Olea europaea (olive tree)—a native species commonly found in Jordan’s arid and semi-arid zones. It was extremely popular and found throughout neighborhoods in the early 1990–2000s.
  • Ceratonia siliqua (carob)—another native, drought-resistant species suitable for urban conditions and suggested as a comparative tool for widely planted trees like chinaberry and olive trees.
  • No-tree scenario—used as a baseline to compare the performance of areas without any planted tree species against those with vegetation.
These species were chosen based on their suitability for urban pavements, tolerance to aridity, root stability, maintenance needs, and ecosystem service delivery (e.g., biodiversity support, shade provision, and air quality regulation).

3.2. ENVI-Met Microclimatic Simulation Framework

ENVI-met is a validated 3D non-hydrostatic microclimate model designed for simulating urban environmental interactions, including vegetation impacts on air temperature, humidity, radiation balance, and pollutant dispersion [30]. To capture peak summer heat conditions, the metabolic performance of the selected species were simulated using data from 1 July 2024. The model was spun up at 12:00 midday and run throughout the day. Boundary conditions were derived from EnergyPlus Weather (EPW) files for Amman (2024), which included hourly data for global radiation, wind speed, humidity, and temperature. Wind direction was set to the prevailing northwest (315°), with relative humidity initialized at 30% to reflect typical arid midday conditions. Soil type was defined as loamy, and the initial albedo for pavements was set to gray colored pavements that are typical in each neighborhood of Amman. Details regarding the buffer zones, values, and parameters are available in Appendix A.
The simulation will assess the metabolic performance of Melia azedarach vs. native species on multiple urban scales and simulate species impacts on temperature reduction, CO2 flux, evapotranspiration, and shading, which will be helpful results to infer urban metabolic flows (energy, carbon, and water) and detect metabolic inefficiencies. Finally, each model was simulated in 3 different scenarios showcased in Figure 2, to ensure precision and to understand performance in different scales and conditions as follows:
  • Scenario A. Single residential plot
    A 20 × 20 m courtyard in a typical apartment within Amman. This scale helps measure microclimatic cooling and solar blockage. Two trees of each species were planted on each side of the sidewalk.
  • Scenario B. Urban Street Segment
    A 60 × 20 m layout of sidewalk with typical apartments, helping to understand the shading of facades and pedestrian comfort. Tree-lined street simulation.
  • Scenario C. Neighborhood Cluster
    A 150 × 150 m urban block, showcasing a typical mini neighborhood within Amman, with its ability to evaluate cumulative effects on urban heat island mitigation [31], CO2 sequestration, and shading potential. This reflects the typical building heights and apartment styles within the city, with each comprising 50–55 residential buildings (10–15 m per side) that form mini-districts.

4. Results and Discussion

4.1. Results of Ecological Profiling and Species Comparative Assessment

Comparative analysis revealed distinct metabolic profiles among the three species (Table 1). Melia azedarach exhibited high isoprene emissions and shallow roots, contrasting with Ceratonia siliqua’s deep rooting and low emissions (0.23 nmol m−2 s−1). Olea europaea showed moderate traits but significant allergenic pollen production. These trait differences directly influence their performance as metabolic agents in urban systems. The datasets showcasing ecological profiling along with the parameters described in the methodology chapter which can also be aided by the Supplementary Files attached were later used in the ENVI-met microclimatic simulation in the results [Appendix A].
The literature-based profiling of the three species reveals divergent metabolic functions that extend beyond simple aesthetics or growth rate. Melia azedarach, although fast-growing and initially effective in thermal mitigation, shows high isoprene emissions (44 nmol m−2 s−1), shallow roots, and a low biodiversity value. These traits compromise long-term metabolic contributions and raise air quality concerns. Olea europaea, while culturally and climatically adapted, contributes limited canopy cover and produces allergenic pollen, posing challenges for human-centered urban flows. In contrast, Ceratonia siliqua exhibits deep rooting (up to 18 m), low emissions (0.23 nmol m−2 s−1), and high biodiversity support, rendering it a robust metabolic contributor with scalability potential. These findings validate the idea that species differ not only in their visual or ecological appeal but in how they perform metabolically over time and across spatial scales.

4.2. ENVI-Met Simulation Results for Metabolic Performance

Microclimatic simulations quantified species performance across different scales, as demonstrated in Table 2. Melia azedarach consistently delivered the strongest cooling effect but maintained rigid vapor flux and moderate CO2 flux. Olea europaea showed stable but unresponsive metabolic fluxes with limited cooling benefits. Ceratonia siliqua demonstrated remarkable scaling effects, with CO2 sequestration increasing widely and vapor flux tripling, suggesting adaptive resource utilization. These simulation results can also be viewed visually to understand thermal distribution in Figure 3 and Figure 4.

4.3. Interpretation of Results in the Context of Amman’s Urban Metabolism

Across Amman—from the densely built neighborhoods of downtown to the rapidly expanding corridors such as Airport Road—urban tree planting has become a widespread visual response to environmental pressures. However, this study reveals that not all commonly planted tree species contribute equally to the city’s long-term metabolic health. Using both ecological profiling and spatial simulations, we found marked differences in performance between the three dominant species in use today: Melia azedarach, Olea europaea, and Ceratonia siliqua. When benchmarked against a baseline condition of no vegetation (State 0), the findings reveal compelling implications for tree selection as a metabolic decision—not just an aesthetic one.
The no-tree condition, which reflects many of Amman’s underserved public spaces, recorded the highest daytime temperatures, reaching 35.10 °C in neighborhood-scale simulations (Scenario C). This condition also lacked any measurable CO2 sequestration or evapotranspiration, emphasizing the urgent need for vegetation in the city’s semi-arid urban fabric, where water scarcity, urban heat stress, and declining air quality takes place. Even the mere presence of any tree species yields measurable benefits; however, the degree and quality of those benefits vary sharply by species.
Among the three species, Melia azedarach, which has been planted in large numbers along Queen Rania Street, Airport Road, and many institutional landscapes, demonstrated the highest cooling capacity, lowering neighborhood-scale temperatures to 34.22 °C, a reduction of 0.88 °C compared to State 0. This can be attributed to its broad canopy, high leaf area index, and fast transpiration rate. These properties offer immediate thermal relief, especially at the pedestrian level. However, this short-term gain masks longer-term trade-offs. Melia’s metabolic profile remains rigid across scenarios: its CO2 flux showed little variation (−0.60 to −0.66 mg/m2·s), and its vapor flux was consistently high (0.05 g/kg·m·s), suggesting inefficient water use—an issue of serious concern in a country where the annual per capita water availability is among the lowest in the world (x). Moreover, its shallow root systems threaten pavements, and its high isoprene emissions raise air quality risks under stagnant summer conditions. Thus, despite its popularity, Melia exemplifies what we define as metabolic misselection: a species that visually and thermally performs in the short term but fails to integrate functionally with the city’s environmental needs over time.
In contrast, Olea europaea, the iconic olive tree of Jordan, presented a different profile. It achieved moderate cooling (34.85 °C in Scenario C, a reduction of 0.25 °C from State 0), with stable but unremarkable CO2 flux values around −0.66 mg/m2·s. Its evapotranspiration rate was identical to Melia (0.05 g/kg·m·s), but unlike Melia, its evergreen foliage and water-conservative physiology make it more metabolically sustainable under arid conditions. However, its small canopy limits shading potential, and its allergenic pollen negatively impacts the human component of the city’s metabolic flow—especially in spring months when concentrations spike (x). Olea’s role, therefore, lies more in cultural continuity and drought endurance than in transformative ecosystem service delivery. While not a misselection, it is metabolically static—providing predictable but plateaued benefits that do not scale with planting density.
Ceratonia siliqua, or carob, emerges as a strong metabolic candidate for Amman’s long-term ecological planning. Although its early-stage cooling was modest (34.82 °C in Scenario C; only 0.28 °C lower than State 0), its metabolic performance scaled significantly with spatial context. Carbon uptake increased thirtyfold from −0.01 mg/m2·s in small residential scenarios to −0.29 mg/m2·s in the neighborhood simulation. Likewise, vapor flux rose from 0.01 to 0.03 g/kg·m·s, suggesting a responsive evapotranspiration mechanism rather than a static one. This is likely due to its deep pivot root system (up to 18 m), enabling the species to access stable groundwater layers and sustain physiological activity without excessive surface irrigation. Ceratonia also showed the highest biodiversity value, supporting pollinators, soil microbes, and urban birds. These attributes position it not only as a biological agent within the city’s water–carbon–energy cycles but also as a systemic buffer against environmental shocks.
Overall, the simulations affirm that vegetation always improves urban metabolic flows compared to a bare scenario, but not all species do so equally or sustainably. In the context of Amman, where both water and biodiversity are in extreme shortage [5], Ceratonia siliqua proves to be the most scalable and adaptive species, aligning with long-term ecological resilience goals. Melia, though visually appealing and fast-acting, presents metabolic drawbacks that intensify over time. Olea remains viable but limited.
The implication is clear: species selection is not a neutral act—it shapes urban metabolic performance for decades. Municipal greening programs should resist the temptation to plant hundreds of the same fast-growing species. Instead, they should adopt hybrid strategies, combining short-term coolers like Melia with slow, deep-rooted anchors like Ceratonia. This metabolic diversity mirrors ecological resilience and maximizes urban sustainability under the constraints of arid urbanization.

5. Conclusions and Discussions

5.1. Interpretation of Results

This study reframes urban tree species selection through the diagnostic lens of urban metabolism, revealing that species choices in arid cities like Amman are not merely aesthetic decisions but metabolic interventions with long-term systemic consequences.
Ceratonia siliqua emerges as a highly integrative species, demonstrating improved CO2 and vapor flux performance with increasing spatial scale, supporting urban biodiversity, and maintaining low emissions. Its dynamic behavior embodies a “slow metabolism, strong resilience” model that aligns well with long-term sustainability goals in arid cities.
This metabolic evaluation framework holds broader implications beyond Amman. As cities across the Middle East, North Africa, and other arid zones expand their greening initiatives, the risk of metabolic misselection looms large.
From the previous analysis, it would also be recommended to combine species like Melia for immediate microclimatic benefits with resilient anchors like Ceratonia for long-term system health instead of growing hundreds of the same species without hybrid solutions.
As a final remark, these findings suggest that municipal greening policies should shift from rapid canopy provision to metabolically informed species palettes. By integrating indicators such as CO2 flux, vapor efficiency, and biodiversity contribution, planners can better align green infrastructure with long-term ecological resilience. Regulatory frameworks should mandate ecological impact assessments not only for invasive risk but also for long-term metabolic contribution.
This study establishes that urban tree species function as metabolic agents, actively modulating energy, carbon, water, and biodiversity flows by integrating spatial simulations with ecological trait analysis. The concept of metabolic misselection thus serves as a diagnostic tool to detect policy–ecology mismatches: Melia’s proliferation signals a focus on expedient canopy coverage, while the underutilization of Ceratonia reflects the undervaluation of deep systemic integration.

5.2. Methodological and Operational Limitations

While this study employs validated microclimatic modeling and ecological profiling, several limitations persist. First, the ENVI-met simulations are based on simplified input models that do not fully capture interspecies competition, unique pollutants that exist in Amman, or weather events like sandstorms. Lastly, long-term biodiversity impacts remain speculative and should be validated through longitudinal field studies. Future research should integrate in situ sensor data, resident perception studies, and real-time phenological monitoring to enhance metabolic assessments

5.3. Future Research Directions

The study emphasizes a wide array of directions within the spectrum of arid cities and Amman in particular. Socio-metabolic surveys must be developed to capture residents’ perceptions of tree species tradeoffs—such as allergen exposure versus shading benefits—in order to better align species selection with community health and preferences. On the other hand, longitudinal ecological assessments are needed to quantify biodiversity outcomes—including pollinator visitation rates, avian species richness, and soil microbiome health. Finally researching opportunities to incorporate urban tree species to function as metabolic agents in the work field would give the opportunity for wide developments. Advancing these interdisciplinary pathways will enable more empirically grounded, context-sensitive diagnostics of urban green infrastructure, while harmonizing ecological functionality with socio-cultural relevance.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/land14081566/s1.

Author Contributions

Conceptualization, A.T.; methodology, A.T.; software, A.T.; validation, A.T.; formal analysis, A.T.; investigation, A.T.; resources, A.T.; data curation, A.T.; writing—original draft preparation, A.T.; writing—review and editing, A.T.; visualization, A.T.; supervision, Á.S.; project administration, A.T. and Á.S. All authors have read and agreed to the published version of the manuscript.

Funding

The authors report financial support was provided by the Hungarian University of Agriculture and Life Sciences. The authors declare that they have no known competing financial interests that could have appeared to influence the work reported in this paper.

Data Availability Statement

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

Appendix A

The following table summarizes the species-specific morphological and physiological parameters input into the ENVI-met “Plant Editor”, which can be replicated:
Table A1. Species specific parameters and values used in the ENVI-met simulation.
Table A1. Species specific parameters and values used in the ENVI-met simulation.
ParameterMelia azedarachOlea europaeaCeratonia siliqua
LAI3.52.12.8
Albedo0.180.180.18
Transmittance0.400.250.30
Emissivity0.950.950.95
Canopy Height7 m5 m9 m
Leaf TypeDeciduousEvergreenEvergreen
Leaf Size (avg)0.15 m20.1 m20.12 m2
Stomatal Conductance280160140
To evaluate peak summer metabolic performance, all simulations were conducted for 1 July 2024, using EnergyPlus Weather (EPW) Amman. The model was initialized at 12:00 PM and run for a full 24 h cycle to capture diurnal microclimatic patterns. The soil type is loamy, with pavements albedo being 0.18 (typical gray concrete surfaces in Amman), relative humidity initialized at 30%, and wind direction prevailing northwest 315°.
The table below outlines the spatial configuration of the simulation scenarios.
Table A2. Spatial configuration, grid resolution, and buffer allocation for each ENVI-met simulation scenario.
Table A2. Spatial configuration, grid resolution, and buffer allocation for each ENVI-met simulation scenario.
ScenarioENVI-Met
Dimensions X × Y × Z
ENVI-Met Grid Size (Cells)
dx, dy, dz
Domain SizeBuffer % Domain Width
Scenario A30 × 30 × 301 M, 1 M, 1 M20 × 20 m7–10 m35–50%
Scenario B 50 × 20 × 502 M, 2 M, 2 M60 × 20 m10 m12–17%
Scenario C 50 × 50 × 503 M, 2 M, 2 M150 × 150 m3 m~2%

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Figure 1. Visual representation of the three selected tree species in order from left to right (Ceratonia siliqua, Olea europaea, and Melia azedarach) in Amman’s urban greening schemes.
Figure 1. Visual representation of the three selected tree species in order from left to right (Ceratonia siliqua, Olea europaea, and Melia azedarach) in Amman’s urban greening schemes.
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Figure 2. Simulation design framework showing three nested scenarios: (A) Single Residential Plot (20 × 20 m), (B) Urban Street Segment (60 × 20 m), and (C) Neighborhood Cluster (150 × 150 m).
Figure 2. Simulation design framework showing three nested scenarios: (A) Single Residential Plot (20 × 20 m), (B) Urban Street Segment (60 × 20 m), and (C) Neighborhood Cluster (150 × 150 m).
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Figure 3. ENVI-met simulation results of Melia azedarach, Olea europaea, and Ceratonia siliqua in terms of median air temperature, CO2 flux (mg/m2s), and vapor flux (g/kg·m·s) across Scenarios A–C.
Figure 3. ENVI-met simulation results of Melia azedarach, Olea europaea, and Ceratonia siliqua in terms of median air temperature, CO2 flux (mg/m2s), and vapor flux (g/kg·m·s) across Scenarios A–C.
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Figure 4. ENVI-met simulation results of an empty option in terms of median air temperature, CO2 flux (mg/m2s), and vapor flux (g/kg·m·s) across Scenarios A–C.
Figure 4. ENVI-met simulation results of an empty option in terms of median air temperature, CO2 flux (mg/m2s), and vapor flux (g/kg·m·s) across Scenarios A–C.
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Table 1. Comparative traits of Melia azedarach, Olea europaea, and Ceratonia siliqua with respect to urban metabolic performance in arid climates. This table consolidates key morphological, physiological, and ecological attributes.
Table 1. Comparative traits of Melia azedarach, Olea europaea, and Ceratonia siliqua with respect to urban metabolic performance in arid climates. This table consolidates key morphological, physiological, and ecological attributes.
TraitMelia azedarachOlea europaeaCeratonia siliqua
Known nameChinaberryOlive Carob
OriginNon-native (Asia)Native (Mediterranean)Native (Mediterranean)
Height6–10 m [32,33]5–7 m [34]8–15 m [35]
Root DepthShallow within top 0.70–1 m [36]4–6 m [37]Up to 18 m [38]
Canopy Width4.6–7.6 m [39]3–4 m [37]5–8 m [35]
Isoprene Emissions44 nmol m−2 s−1 [25]~2 nmol m−2 s−1 [40]~0.23 nmol m−2 s−1 [41]
Leaf TypeDeciduousEvergreenEvergreen
Root InvasivenessHigh (surface-level and infrastructure-damaging) [36]Moderate [37]Low (deep pivot system) [38]
Heat/Drought ToleranceHigh [39]Very High [37]Extremely High [38]
Shade ProvisionModerate to High [33]Low [37]Moderate [35]
Air Quality ContributionMixed (ozone-forming potential) [25]Low (allergenic pollen) [9]Positive (low emission, high filtration) [41,42]
Life Span30–50 years [33]Over 100 years [34]Over 100 years [38]
Biodiversity ValueLow [8,36]Moderate (but allergenic to humans) [9,43]High (supports pollinators, birds, and soil ecology) [42,44]
Table 2. ENVI-met simulation outputs for median air temperature, CO2 flux, and vapor flux across Scenarios (A–C) for Olea europaea, Melia, Ceratonia siliqua, and no trees.
Table 2. ENVI-met simulation outputs for median air temperature, CO2 flux, and vapor flux across Scenarios (A–C) for Olea europaea, Melia, Ceratonia siliqua, and no trees.
SpeciesScenarioMedian Temp (°C)CO2 Flux (mg/m2s)Vapor Flux (g/kg·m·s)
OliveA34.50−0.640.05
B34.77−0.660.05
C34.85−0.660.05
ChinaberryA34.38−0.600.05
B34.37−0.640.05
C34.22−0.660.05
CarobA34.50−0.010.01
B34.73−0.250.03
C34.82−0.290.03
No trees A 34.55N/AN/A
B34.86N/AN/A
C35.10N/AN/A
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Tuffaha, A.; Sallay, Á. Tree Species as Metabolic Indicators: A Comparative Simulation in Amman, Jordan. Land 2025, 14, 1566. https://doi.org/10.3390/land14081566

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Tuffaha A, Sallay Á. Tree Species as Metabolic Indicators: A Comparative Simulation in Amman, Jordan. Land. 2025; 14(8):1566. https://doi.org/10.3390/land14081566

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Tuffaha, Anas, and Ágnes Sallay. 2025. "Tree Species as Metabolic Indicators: A Comparative Simulation in Amman, Jordan" Land 14, no. 8: 1566. https://doi.org/10.3390/land14081566

APA Style

Tuffaha, A., & Sallay, Á. (2025). Tree Species as Metabolic Indicators: A Comparative Simulation in Amman, Jordan. Land, 14(8), 1566. https://doi.org/10.3390/land14081566

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