Urban Green Infrastructure and Urban Landscape Ecology: Advances in Structure, Function, and Adaptive Management

Urbanization, as one of the most profound anthropogenic drivers of global environmental change, poses unprecedented challenges to ecosystem stability, human health, and social equity. Urban Green Infrastructure (UGI), including street trees, urban forests, parks, and wetlands, has emerged as a cost-effective and nature-based solution to mitigate these challenges, including urban heat islands, air pollution, carbon accumulation, and biodiversity loss. However, the functionality and sustainability of UGI are shaped by complex interactions between ecological processes, human activities, and urban planning policies, requiring interdisciplinary insights to optimize its design, management, and long-term resilience.

The Special Issue, Urban Green Infrastructure and Urban Landscape Ecology, collates eight cutting-edge studies from diverse geographical contexts and methodological perspectives to address critical gaps in UGI research. These studies focus on four interrelated themes: (1) urban tree biomass quantification and carbon sequestration; (2) UGI structural parameter inversion and pollutant capture; (3) spatial accessibility and equity of urban green spaces; and (4) ecological network dynamics under urban expansion. Collectively, they provide novel empirical evidence and theoretical frameworks to advance our understanding of UGI’s role in sustainable urban development.

1. Urban Tree Biomass and Carbon Cycling

Accurate quantification of urban tree biomass and carbon storage is foundational to evaluating UGI’s climate mitigation potential. However, traditional allometric equations developed for natural forests often fail to capture the unique growth patterns of urban trees. Two studies in this Special Issue address this challenge through innovative modeling and empirical validation. Dapsopoulou and Zianis developed allometric equations for stem, branch, and total dry aboveground biomass of 10 urban tree species in Athens, Greece, using 52 destructively sampled specimens [1]. They employed nonlinear seemingly unrelated regression to circumvent the caveat of the additivity property for estimating the biomass of different tree components. A key finding was that the widely used i-Tree model underestimated or overestimated biomass by a mean of 134% (range: 3–520%), highlighting the urgency of urban-specific allometries, particularly for Mediterranean climates. Drolen et al. modified the Perfect Plasticity Approximation—a rural forest dynamics model—to simulate carbon storage and sequestration of urban street trees [2]. Through 100-year simulations across a density gradient, they found that carbon storage and sequestration increase with density until saturation, with optimal conditions achieved by high productivity, maximized crown allometry, and low mortality. This study provides a quantitative tool for urban planners to balance tree density, maintenance costs, and climate benefits.

2. UGI Structural Inversion and Pollutant Capture

Remote sensing and field-based studies of UGI’s functional traits—such as leaf area index and pollutant capture capacity—are essential for assessing its role in improving urban air quality. Zhai et al. integrated Airborne Laser Scanning and Terrestrial Laser Scanning data to invert the effective leaf area index of three coniferous forests in Changchun, China [3]. They systematically evaluated the impact of point cloud diameter on the extraction of 10 forest structure parameters (e.g., canopy openness, gap fraction) and found that a 0.1 cm point diameter optimized extraction accuracy. This work demonstrates the potential of multi-source LiDAR data for high-precision UGI structural monitoring. Elkaee et al. investigated the capacity of five common urban tree species (Morus alba, Ailanthus altissima, Platanus orientalis, Robinia pseudoacacia, and Ulmus minor) in Tehran, Iran, to capture particulate matter (PM), heavy metals (Ni, Fe, Cd, Pb), and carbon (OC, EC, TC) [4]. Species-specific differences were pronounced: U. minor and M. alba exhibited high PM retention, A. altissima effectively adsorbed fine PM (0.1–2.5 μm), and R. pseudoacacia and A. altissima captured higher levels of heavy metals. These findings offer evidence-based guidance for selecting pollution-reduction species in heavily urbanized, arid regions.

3. Spatial Pattern and Equity of Urban Green Spaces

The ecological and social benefits of UGI are only realized if green spaces are accessible and equitably distributed. Xiao et al. assessed the availability and spatial fairness of street greenery in 49 subdistricts of Changchun, China [5]. Using boosted regression trees, they identified landscape patterns—particularly the percentage of green landscape (PLAND) and edge density—as the dominant drivers (explaining 88.3% of Green View Index variation and 71.2% of Gini variation), with a threshold effect. Shu et al. quantified the distance decay of urban park visitation in Changsha, China, using 2535 visitor surveys [6]. They found a median visitation distance of 1.3 km and frequency of 24 times per season. Personal characteristics and visitation patterns significantly modified decay rates. This work highlights the importance of considering human behavior in park planning to enhance accessibility for vulnerable groups.

4. Urban Expansion and Ecological Network Dynamics

Urban expansion (or shrinkage) reshapes UGI patterns, with profound impacts on ecological connectivity. Two studies in this Special Issue explore UGI dynamics under contrasting urban trajectories—shrinkage and expansion—using long-term spatial data and scenario modeling. Zhou et al. analyzed the spatiotemporal patterns of urban forest fragmentation in 195 shrinking cities across China, focusing on the moderating effects of moisture and altitude [7]. From 2000 to 2022, forest coverage increased slightly (40.05% to 40.47%), but fragmentation varied by region. The study highlights that population shrinkage does not uniformly mitigate fragmentation, requiring region-specific conservation strategies. Luo et al. constructed future green space ecological networks for Chengdu, China, under four urban expansion scenarios (cultivated land protection, economic development, ecological priority, natural development) using the CLUE-S model [8]. The ecological priority scenario demonstrated the highest ecological connectivity, with a complete and stable network structure that promoted species migration and energy flow, which is crucial for biodiversity conservation and ecosystem resilience, demonstrating that proactive ecological planning can maintain UGI connectivity amid urban growth.

5. Conclusions and Future Directions

The studies in this Special Issue collectively demonstrate that UGI is a dynamic, multifunctional system whose value depends on context-specific design, evidence-based management, and equitable distribution. By integrating ecological principles with urban planning, these works provide a foundation for building resilient, healthy, and inclusive cities. We hope this Special Issue inspires further interdisciplinary research to unlock UGI’s full potential in addressing the global urban sustainability challenge.

This Special Issue advances UGI research by linking empirical observation, methodological innovation, and practical management. However, several critical directions remain to be addressed:

Cross-Scale Integration: Most studies focus on single scales (e.g., tree-level biomass or subdistrict-level fairness). Future work should integrate microscale (e.g., leaf traits) and macroscale (e.g., regional UGI networks) processes to understand cascading effects of UGI change.

Long-Term Dynamic Monitoring: Short-term datasets (1–5 years) dominate current research. Long-term (decadal) monitoring of UGI structure and function—coupled with climate and land-use data—will improve predictions of resilience to extreme events (e.g., heatwaves, droughts).

Climate-Adaptive Design: With climate change intensifying urban environmental stress, future UGI research should prioritize “climate-smart” design (e.g., selecting drought-tolerant species, optimizing green corridor orientation for heat mitigation).

Social–Ecological Coupling: Integrating socioeconomic data (e.g., household income, community preferences) with ecological metrics will enhance UGI’s ability to deliver equitable benefits, particularly for marginalized communities.