Hoverflies (Diptera: Syrphidae) as biodiversity indicators for assessing urban forest habitats

Urban forested natural areas are valuable ecological and social resources, but long-term sustainability of these habitats is challenged by environmental and social factors associated with urban ecosystems. Advances in city-scale assessments of urban forests have increased the resolution of forest community types and conditions, allowing for improved understanding of ecological function, such as natural regeneration, in these urban habitats. By applying metrics of tree regeneration that are commonly used for the management of rural forests, urban ecologists can test the potential for traditional forest management strategies within our cities. In this study, we compare urban and rural oak-hickory forest composition and structure and the capacity for natural regeneration in the New York metropolitan area. Specifically, we use two metrics of advance regeneration that describe the abundance of seedlings and saplings at different size classes to test whether this management for natural regeneration is a viable option. We found differences in recruitment dynamics between urban and rural forests that have implications for the sustainability of these forests and new management strategies. First, after controlling for forest community type, species composition in urban and rural sites was significantly different across multiple strata and within the seed bank. Species-specific capacity for natural regeneration was different in urban and rural sites, signaling the possibility of divergent successional trajectories. Second, while differences in species composition exist, both urban and rural sites were dominated by native species across all forest strata except for urban seed banks. Third, despite finding significantly lower average annual seedling abundance in urban (1.9 seedlings/m2 ) compared to rural (7.1 seedlings/m2 ) sites, we observed greater density of saplings in urban forests, and no significant difference in stocking index between sites. These findings suggest that early-establishment barriers to recruitment are greater in urban forest sites. However, once established, seedling transition into advance regeneration stages may not be different between site types, and advance regeneration may, in some cases, be more viable in urban forested natural areas. These results highlight functional differences between urban and rural forest recruitment dynamics that may impact on the future community composition of oak-hickory forests in the two landscape settings.

Comparing the carbon sequestration capacity of temperate deciduous forests between urban and rural landscapes in central Japan

Urban and peri-urban forests are green infrastructures (GI) that play a substantial role in delivering ecosystem services such as the amelioration of air quality by the removal of air pollutants, among which is ozone (O3), which is the most harmful pollutant in Mediterranean metropolitan areas. Models may provide a reliable estimate of gas exchanges between vegetation and atmosphere and are thus a powerful tool to quantify and compare O3 removal in different contexts. The present study modeled the O3 stomatal uptake at canopy level of an urban and a peri-urban forest in the Metropolitan City of Rome in two different years. Results show different rates of O3 fluxes between the two forests, due to different exposure to the pollutant, management practice effects on forest structure and functionality, and environmental conditions, namely, different stressors affecting the gas exchange rates of the two GIs. The periodic components of the time series calculated by means of the spectral analysis show that seasonal variation of modeled canopy transpiration is driven by precipitation in peri-urban forests, whereas in the urban forest seasonal variations are driven by vapor pressure deficit of ambient air. Moreover, in the urban forest high water availability during summer months, owing to irrigation practice, leads to an increase in O3 uptake, thus suggesting that irrigation may enhance air phytoremediation in urban areas.

The process of rapid urbanization is a global phenomenon that exposes the natural landscape to high levels of nitrogen (N) deposition, leading to serious ecological consequences. How does soil biological nitrogen fixation (BNF), a crucial process for replenishing nitrogen in terrestrial ecosystems, respond to urban expansion and consequent N deposition? To address this, we established a transect from the city center to the countryside to capture the urban–rural gradient. Permanent sites were set up along the gradient to encompass urban, suburban, and remote rural forests. A 5-year large-scale field experiment of N addition was conducted to simulate N deposition, aiming to investigate the impact of N deposition on soil BNF along this urban-rural gradient. We found that soil BNF activity was drastically reduced (dropped by 94.2% to 96.5%) in both urban and suburban forests compared with the rural forest without additional N application. Nitrogen addition treatments had no effect on BNF activity in the urban forest, but significantly decreased BNF activity in the rural forest by over 50% with low N addition. Further analysis revealed that reductions in BNF activity were associated with changes in the composition of diazotrophic communities, favoring facultative diazotrophs that are detrimental to soil BNF. Soil acidification was primarily responsible for limiting soil BNF and associated microbes in the urban forest. Overall, our findings indicate that external N inputs primarily pose a threat to soil diazotrophic communities and their N fixation capacity in rural forests, whereas this adverse effect is not persisted in urban forests, thereby improving our understanding of soil behavior and biogeochemical cycles in forest landscapes.

BackgroundLand-use change has led to a dramatic decrease in total forest cover, contributing to biodiversity loss and changes of ecosystems’ functions. Insect communities of medical importance can be favored by anthropogenic alterations, increasing the risk of novel zoonotic diseases. The response of mosquito (Diptera: Culicidae) abundance and richness to five land-use types (shade coffee plantation, cattle field, urban forest, peri-urban forest, well-preserved montane cloud forest) and three seasons (“dry”, “rainy” and “cold”) embedded in a neotropical montane cloud forest landscape was evaluated.MethodsStandardized collections were performed using 8 CDC miniature black-light traps, baited with CO2 throughout the year. Generalized additive mixed models were used to describe the seasonal and spatial trends of both species richness and abundance. Rank abundance curves and ANCOVAs were used to detect changes in the spatial and temporal structure of the mosquito assemblage. Two cluster analyses were conducted, using 1-βsim and the Morisita-Horn index to evaluate species composition shifts based on incidences and abundances.ResultsA total of 2536 adult mosquitoes were collected, belonging to 9 genera and 10 species; the dominant species in the study were: Aedes quadrivittatus, Wyeomyia adelpha, Wy. arthrostigma, and Culex restuans. Highest richness was recorded in the dry season, whereas higher abundance was detected during the rainy season. The urban forest had the highest species richness (n = 7) when compared to all other sites. Species composition cluster analyses show that there is a high degree of similarity in species numbers across sites and seasons throughout the year. However, when considering the abundance of such species, the well-preserved montane cloud forest showed significantly higher abundance. Moreover, the urban forest is only 30 % similar to other sites in terms of species abundances, indicating a possible isolating role of the urban environment.ConclusionMosquito assemblage was differentially influenced by land-use change and seasonality, but at the same time the assemblage is rather homogeneous across the studied landscape, suggesting a high degree of spatial connectivity. Information generated in this study is potentially useful in the development of urban planning and surveillance programs focused mainly on mosquito species of medical and veterinary importance.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-1086-9) contains supplementary material, which is available to authorized users.

In urbanized areas, wind disturbances can be intensified by anthropogenic stresses under which trees may become hazardous, creating serious threats and damages to nearby targets. Therefore, species with notably lower both wood mechanical properties and compartmentalization, such as pioneers, are considered to have higher wind damage risk if subjected to unfavorable growing conditions. Eurasian aspen (Populus tremula L.) and silver birch (Betula pendula Roth.), are frequently found in both urban and peri-urban forests in Northeastern and Central parts of Europe, which strengthen the necessity for the evaluation of mechanical stability of such species. Therefore, static pulling tests were performed to compare the mechanical stability of the studied species in both urban and peri-urban forests. The loading resistance of the studied species differed, with birch being more stable than aspen, indicating aspen to be more prone to wind damage. Additionally, the mechanical stability of birch did not differ between trees growing in urban and peri-urban forests, suggesting static pulling tests are a suitable method for comparing trees from completely different growing conditions.

Urban, peri-urban forests and other natural areas provide a wide range of material and non-material benefits to people known as ecosystem services. Access to these areas has been linked to benefits for physical and mental health of local populations. In the spring of 2020, the COVID-19 global pandemic forced many governments to impose a set of restrictions including the closure of businesses, cancelation of public events and schooling, social distancing, limitations on the size of social gatherings, and travel restrictions. During this period of restrictions, we conducted a study assessing the importance of urban and peri-urban forests and other natural areas to people living in and around the city of Burlington, Vermont, USA. We evaluated the self-reported use and changes in personal importance related to these natural areas before and during the period of restrictions. We received over 400 responses to our field survey. The results show that 69.0% of the respondents had increased or greatly increased their visitation rate to our natural areas and urban forests, and 80.6% of respondents considered that the importance of these areas, and access to them, either increased or greatly increased. Moreover 25.8% of the sample had either never, or very rarely accessed their local natural areas before the pandemic, but 69.2% of the first time or infrequent visitors reported that having access to these areas during COVID-19 as ‘very important’. People reported that these areas were important for a wide range of activities from exercise to birding, but also reported values related to reducing stress in a time of global chaos. Our results indicate the increasing demand and value of such areas in times of crisis such as COVID-19. Experts in zoonotic disease predict the potential for more frequent pandemic events, thus predicating the importance for continued funding for, maintenance of, and improved access to, natural areas to our largely urban civilization.

The perception of ecosystem goods and services by local residents is studied in Brazzaville, around the periurban forest of Djoumouna. This study, which documents the ecosystem services provided to communities by this ecosystem facing anthropogenic degradation, evaluates the understanding and consideration of these functions, according to socioprofessional categories. Socioeconomic and ethnobotanical surveys conducted among the group of informants are supported by direct field observations and literature review. The data collected within a 2 km radius around the forest were subjected to descriptive and statistical analysis. The group of informants, including all socioprofessional strata, was organised into 4 age groups and involved 143 heads of household aged from 15 to over 45. The survey reveals 14 ecosystem services that fall into three categories. The provisioning services included food, wood energy, pharmacopoeia, and wood services. The regulatory functions cited are maintaining air quality, shade, erosion control, and windbreak. Recognized sociocultural services are the source of income, recreation, and ecotourism, source of inspiration, fishing, initiation sanctuary, and hunting. According to gender, men are more dependent on the forest than women, and those aged 15–25 and over 45 are the most active. The socioprofessional scale shows an unequal exploitation of the forest. The informants, at least for the majority, integrate the notions of the value of ecosystem services, provided by the Djoumouna periurban forest, into their daily lives. Finally, the study highlights the social and ecological value of periurban and urban forests in the daily lives of people and urban resilience.

The disappearance of forests and biodiversity in Côte d'Ivoire is also due to the expansion of urban areas. This expansion was carried out without any concern for the preservation or restoration of the natural resources. The Daloa area, in addition to the forest relics, contains shallows, important for agriculture. These shallows were mostly landing sites for drainage water from various horizons. To assess the conservation status of these environments, amphibians, due to their high sensitivity to changes in environmental conditions, were used to assess the biotic integrity of the ecosystems. Thus, daytime and night-time sampling were carried out in urban, peri-urban shallows and peri-urban forests. These acoustic, visual and capture samplings lasted 12 months and revealed the presence of 20 amphibian species. Nineteen species were found in urban shallows, peri-urban forests and 17 species in peri-urban shallows respectively. There was no significant difference between the species richness of the different habitats (Kruskal-Wallis test, p > 0.05). Furthermore, in the rainy season, amphibian diversity was higher in peri-urban forests than in shallows. In addition, over the whole study area, Amphibian abundance was higher in the rainy season than in the dry season. Also, the most frequent species in this area was Ptychadena mascareniensis. Finally, in the rainy season, the distribution of Amphibians in peri-urban forests was more equitable than that of dry season and in other sites.

Recreation use of urban forests: An inter-area comparison

Human activity has changed land surfaces by converting native ecosystems to urban and agricultural land uses. This conversion has caused increases in air and soil temperatures that influence soil C and N cycling. Efforts to model changes in soil temperature resulting from urban land use change have not accounted for changes in both plant cover and land use and thus fail to produce accurate predictions at high‐resolution spatial and temporal scales. We measured average daily soil temperature at a 10‐cm depth at urban and rural forest and grassland sites for 8 yr in the Baltimore, MD, metropolitan area and developed a model of the average daily soil temperature that accounts for two vegetation and two land use types. Average annual soil temperature was higher in urban than rural sites under both turfgrass (15.0°C vs. 13.5°C) and forest (12.6°C vs. 12.2°C). The application of climate‐change scenarios predicted by general circulation models to our soil temperature model suggested that the highest increases in mean soil temperatures will occur in August, September, February, and March, and will range from 1.2 to 2.0°C, while air temperature is predicted to change from 3.4 to 5.6°C between 2070 and 2099. The model can be used to predict the average daily soil temperature in the Baltimore area for sites with similar hydrologic and soil conditions, i.e., remote from the shoreline and characterized by loamy soils.

Urban parks are likely the last green areas to preserve fauna diversity in urban ecosystems. We predicted that 1) species richness and ant diversity would increase with increasing park size, and species richness and ant diversity would be inversely related to distance from a peri-urban forest. 2) Larger ants would be predictably prevalent in less-complex habitats but the reverse should be true for small ants. The study was conducted in 47 parks of varying size located in Taichung City, Taiwan. In total, 14,324 ant individuals from 50 morphospecies and 22 genera were collected. No relationship between ant diversity and distance from a peri-urban forest. No significant clustering in functional composition with increasing park size and distance from a peri-urban forest. However, urban ant diversity marginally increased with increasing park size. Larger parks, characterize by heterogeneous fine-scale habitats, had the highest ant species and abundance of ants. The prevalences of opportunist, generalised myrmicinae (GM), and cryptic ant species were linked to increased soil moisture, number of tree species, and leaf litter depth. The positive association between GM and the number of trash bins. Our finding disproved the size-grain hypothesis, but hotter ground surface favored the presence of long-legged ants. The significant association between head width, inter-eye distance, eye width, and environmental variables such as understory vegetation cover, leaf litter depth, and soil temperature suggest that predaceous ants might be prevalent in heterogeneous fine-scale local microhabitats. In conclusion, our study evidenced the importance of heterogeneous fine-scale habitats in urban park to biodiversity.

Landscape fragmentation has created large areas of forest edge. Understanding how soil organic carbon (SOC) stocks within forest edges respond to fragmentation is essential to assess carbon budgets; however, the causes and magnitude of edge effects on SOC stocks have been poorly characterized. Here, we quantify the edge effects on SOC stocks within and across urban to rural forest patches from three fragmented urban forests to a large patch of rural forest. The SOC stocks within 20 m of the rural forest edge (1.86kgCm−2) is on average 80% lower than the interiors of rural forest (10.47kgCm−2). We found that biotic factors, including annual litterfall mass (R2 > 0.94), peak leaf area index (R2 > 0.92), and fine-root mass density (R2 > 0.77), explained the spatial variation in SOC stocks within the rural forest. In urban forests, human activities at forest edges led to contrasting edge effects on SOC stocks, for instance, the SOC stocks at the east edges (4.74 kgC m−2) were 56% greater than at the west edges (3.03 kgC m−2) explained by the adjacent land uses (e.g., paved roads vs. non-paved soils) and in-situ litterfall management. We also found significant differences in summer soil temperature (ΔTS > 2.8 °C) and soil moisture (ΔVWC > 0.05 m3 m−3) between the east and west forest edges. Our results reveal that the factors responsible for the edge effects on SOC stocks in rural forests are biotic factors, while heterogeneous human activities at the local scale lead to complex edge effects on urban forest SOC stocks.

By 2050, nearly 70% of the global population will live in cities (UN, 2018), increasing the demand for urban green spaces. Urban areas are facing increasing risks from climate change, including heatwaves, flooding, wildfires, and growing social inequality, which challenges urban planning and design. Urban forests form the backbone of green infrastructure supporting resilient, equitable, and sustainable cities. Importantly, their cost-effective benefits advance sustainable development, climate action, and biodiversity conservation. Urban forests include all woody and understorey vegetation within and around dense settlements, from cultivated trees in streets, parks, and gardens to self-sustaining stands in remnant and peri-urban woodlands (FAO, 2016). As essential nature-based solutions (Cohen-Shacham et al., 2016), urban forests provide multiple ecosystem services. They help cool urban temperatures, reduce air pollution, enhance soil infiltration, slow stormwater runoff, buffer extreme weather, and support human health (Livesley et al., 2016). They contribute significantly to climate adaptation and moderately to mitigation by reducing the energy demand for cooling (McPhearson et al., 2023). Urban forests also enhance biodiversity by providing habitats and climate refugia at multiple scales (Alvey, 2006). Trade-offs in urban forest benefits, costs, and the impacts of policy interventions, such as those related to measurement, outcomes, or implementation, remain complex (Vogt et al., 2015), but the loss of canopy reduces air quality, biodiversity, and resilience to floods, droughts, pests, and extreme heat (Nowak, 2018). Canopy loss impairs recreation and impacts physical and mental health (Carrus et al., 2015). Because urban forests are inherently dynamic systems, the death or removal of large and mature trees should be anticipated through proactive planning for their replacement, including careful consideration of which species are selected and why. Unequal access drives social-environmental injustice and health inequities, which can be addressed through greenspace expansion, equitable distribution, and better management (Esperon-Rodriguez et al., 2025). Urban forests are increasingly at risk due to significant stewardship gaps. Despite the existence of international management standards, ongoing tree losses result from pests introduced through trade, climate and pollution stress, inadequate legal protections, rapid urban densification, and insufficient maintenance (Esperon-Rodriguez et al., 2022; Paap et al., 2017; Vogt et al., 2015). Planting alone cannot offset accelerated mature tree losses or replace the vital functions these trees provide over their shortened lifespans in urban environments. Closing the stewardship gap demands urgent investment, robust funding, and stronger policy to sustain diverse and resilient urban forests. Urban forests are among the most effective, equitable nature-based solutions available. When protected and resourced, they cool neighborhoods, manage stormwater, store carbon, support biodiversity, and improve health, especially in underserved communities. Yet mature tree loss outpaces replacement amid increasing climate and biological stresses. We urge COP30 policymakers to treat urban forests as essential and critical city infrastructure: safeguard mature trees, set and finance SMART canopy, diversity and access targets, mainstream urban forests in climate and biodiversity plans, and fund long-term operations, monitoring, nursery capacity, and biosecurity. Implementing this visionary action delivers cooler, healthier, more biodiverse, and more equitable cities now and for future generations. MER and MGT led the initiative and drafted the letter. All authors provided feedback, edited, and agreed with the content of the letter. All authors, except MER and MGT, are listed alphabetically. MER received funding from Western Sydney University's Research Theme Program. KDP was supported by the Research Foundation Flanders (FWO, grant 12A0L25N). RMM was supported by a Discovery Early Career Researcher Award (project DE200100649), funded by the Australian Research Council of the Australian Government. JCS received funding from the Danish National Research Foundation (grant DNRF173) and EARTHKEEPER (Global South Biodiversity Leadership Initiative). CS's contribution was funded by the National Research Foundation of South Africa (grant no 84379). We declare no conflict of interest. There are no data associated with the article.

The largest natural biological sink for the radiatively active trace gas methane (CH4) is bacteria in soils that consume CH4 as an energy and carbon source. This sink has been shown to be sensitive to nitrogen (N) inputs and alterations of soil physical conditions. Given this sensitivity, conversion of native ecosystems to urban, suburban, and exurban managed lawns thus has potential to affect regional CH4 budgets. We measured CH4 fluxes monthly from four urban forest, four rural forest and four urban lawn plots in the Baltimore, MD, metropolitan area from 2001 to 2005. Our objectives were to evaluate the effects of urban atmospheric and land use change on CH4 uptake and the importance of these changes relative to other greenhouse forcings in the urban landscape. Rural forests had a high capacity for CH4 uptake (1.68 mg m(-2) day(-1)). This capacity was reduced in urban forests (0.23 mg m(-2) day(-1)) and almost completely eliminated in lawns. Possible mechanisms for these reductions include increases in atmospheric N deposition and CO2 levels, fertilization of lawns, and alteration of soil physical conditions that influence diffusion. Although conversion of native forests to lawns had dramatic effects on CH4 uptake, these effects do not appear to be significant to statewide greenhouse gas forcing.