Optimizing urban tree species composition to maximize nature-based solutions

Greentree reservoir management was initiated during a period when riparian forests of the Mississippi Alluvial Valley were disappearing rapidly. Greentree reservoirs (GTRs) were intended to provide a refuge for overwintering migratory waterfowl within a landscape of decreasing habitat availability. However, GTRs frequently are flooded as much as 2.5 months longer than unimpounded bottomland forests (UBF), and previous work has shown that such unnatural hydroperiods can have substantial negative effects on such ecosystem attributes as tree assemblage composition and invertebrate production. We conducted the present study to quantify (1) frequency of canopy gaps and (2) tree species composition in GTRs, as compared with UBFs. In general, GTRs were quite similar to UBF stands, in terms of canopy density, proportion of trees in the canopy versus mid-story, degree of stress exhibited by individual trees, gap frequency, and species diversity. However, multivariate comparisons of GTRs versus unimpounded areas indicated differences in species composition. Indicator Species Analyses and examination of the dominant species showed clear differences between GTRs and UBFs, with GTR tree species being, on average, better adapted to flooded conditions, based on wetland indicator status. Greentree reservoir canopies generally were dominated by a Taxodium distichum – Acer rubrum – Quercus lyrata mix, whereas unimpounded forest canopies were characterized as Liquidambar styraciflua – mixed Quercus stands. The midstories of the groups were more similar to one another, with dominance by Acer– Carpinus caroliniana – Planera aquatica in GTRs and Liquidambar – Carpinus – Acer in unimpounded stands. The GTRs included in this study had been managed for 40 to 48 years, providing a long history of flooding which served to select for highly adapted species assemblages.

Long-term recovery of forest structure and composition after harvesting in the coastal temperate rainforests of northern British Columbia

Forest management has been shown to affect biodiversity, but the effects vary among taxa and studies. Due to their host-tree preferences, many saproxylic, i.e. deadwood-dependent, beetle species are likely affected by forest management via changes in tree species composition. However, further structural differences caused by forest management, such as microclimatic conditions, may interfere with effects of tree species. We lack a more detailed understanding of how forest management intensity influences saproxylic beetles through tree species composition and structural properties.We analyzed the effect of forest management on saproxylic beetles using an eight-year dataset collected from 379 experimental logs of 13 different tree species, which were exposed in forests of different management intensity in three regions of Germany. To quantify forest management intensity, we first used a composite index (ForMI) which considers the share of locally non-native tree species, the origin of deadwood and the harvesting rate and then replaced it by five forest structural and compositional properties. This two-step approach allowed to assess the overall effects of management summarizing different aspects and to identify the main forest attributes driving these overall effects. We further investigated whether the effects differ between beetle assemblages emerging from conifer and broadleaf logs (host level), and between generalists, conifer-specialists, and broadleaf-specialists (beetle specialization level).Abundance and species richness increased with increasing ForMI for all beetles, generalists, and conifer-specialists, but not for broadleaf-specialists.Effects of ForMI were stronger for assemblages emerging from conifer than broadleaf logs. Among the evaluated structural and compositional variables, strongest effects were observed for conifer share at stand level and canopy cover. Conifer share positively affected the species richness of all beetles, generalists and conifer specialists, but not of broadleaf specialists. Canopy cover negatively affected all beetles, generalists and conifer specialists, but did not affect broadleaf specialists.Our results show that major drivers behind effects of forest management on saproxylic beetles are differences in tree species composition and canopy cover. Effects differ between beetle groups depending on their host specialization. Forest management decisions regarding tree species composition should therefore more strongly consider their effects on saproxylic beetle diversity to meet conservation goals also in the future.

This study presents an Eco-floristic analysis of tree species in Satlasana taluka in Mehsana district of Gujarat. The investigation aimed to document the diversity, distribution, and ecological characteristics of tree species in the region. A comprehensive survey was conducted across different habitats, and data on tree species composition, density, frequency, and abundance were collected. A total of 107 tree species belonging to 36 families were recorded. The study revealed a significant variation in tree species diversity and composition across different habitats. The findings of this study provide valuable insights into the ecological characteristics of tree species in the region and have implications for conservation and sustainable management of forest resources in Satlasana taluka.

Human exposure to green space and vegetation is widely recognized to result in physical and mental health benefits; however, to date, the specific effects of tree cover, diversity, and species composition on student academic performance have not been investigated. We compiled standardized performance scores in Grades 3 and 6 for the collective student body in 387 schools across the Toronto District School Board (TDSB), and examined variation in relation to tree cover, tree diversity, and tree species composition based on comprehensive inventories of trees on school properties combined with aerial-photo-based assessments of tree cover. Analyses accounted for variation due to socioeconomic factors using the learning opportunity index (LOI), a regional composite index of external challenges to learning that incorporates income and other factors, such as students with English as a second language. As expected, LOI had the greatest influence on student academic performance; however, the proportion of tree cover, as distinct from other types of “green space” such as grass, was found to be a significant positive predictor of student performance, accounting for 13% of the variance explained in a statistical model predicting mean student performance assessments. The effects of tree cover and species composition were most pronounced in schools that showed the highest level of external challenges, suggesting the importance of urban forestry investments in these schools.

Using stomatal conductance capacity during water stress as a tool for tree species selection for urban stormwater control systems

Sub-Saharan Africa (SSA) is the region most vulnerable to climate change and related hydro-meteorological risks. These risks are exacerbated in rapidly expanding urban areas due to the loss and degradation of green and blue spaces with their regulating ecosystem services. The potential of nature-based solutions (NBS) to mitigate hydro-meteorological risks such as floods is increasingly recognized in Europe. However, its application in urban areas of SSA still needs to be systematically explored to inform and promote its uptake in this region. We conducted a multidisciplinary systematic review following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) protocol to establish the general patterns in the literature on NBS and hydro-meteorological risk mitigation in SSA. We searched scientific journal databases, websites of 12 key institutions and 11 NBS databases and identified 45 papers for analysis. We found at least one reported NBS in 71 % of urban areas of SSA across 83 locations. 62 % of the papers were clustered in South Africa, Kenya, Tanzania and Nigeria only, while the most studied cities were Dar es Salaam and Kampala. Moreover, 66 NBS practices were identified, most of which (n=44) were for flood mitigation. With only Mozambique (n=2) reporting NBS among the most at-risk countries, we found that NBS are implemented where risks occur but not where they are most severe. Mangrove restoration and wetland restoration, reforestation and urban forests, and agroforestry and conservation agriculture were the most common NBS practices identified for floods, extreme heat and drought mitigation, respectively. Traditional practices that fit the definition of NBS, such as grass strips and stone bunds, and practices more popular in the Global North, such as green roofs and green façades, were also identified. These NBS also provided ecosystem services, including 15 regulatory, 5 provisioning and 4 cultural ecosystem services, while 4 out of every 5 NBS created livelihood opportunities. We conclude that reported uptake of NBS for hydro-meteorological risks in SSA is low. However, there could be more NBS, especially at the local level, that are unreported. Furthermore, NBS can help SSA address major development challenges such as water and food insecurity and unemployment and help the sub-region develop climate-resiliently. We, therefore, recommend that NBS be mainstreamed into urban planning and for knowledge exchange opportunities between SSA and Europe and other regions to be explored to promote uptake.

Higher tree species richness often increases the diversity of other taxonomic groups and is promoted in many managed forest systems. The reason for the higher diversity is due to, for example, inter‐specific differences in resource filtering of the trees. Resource filtering also depends on the total density of the tree layer, but the interaction between tree species composition and density is, so far, unexplored. Likewise, few studies have addressed whether mixtures of tree species host higher diversity, or support higher productivity, of other taxa than monocultures of the same tree species. We use a gradient in overstory tree species composition, ranging from pure Norway spruce (Picea abies) to pure Birch (Betula sp.), combined with a gradient from open to closed forest, to assess the joint effects of tree species mixture and forest density on the understory vegetation. The cover and species richness of understory vascular plants increased with an increasing proportion of birch and decreased with increasing forest density, while the cover of bryophytes decreased with an increasing proportion of birch and increasing forest density. There were clear interactions between tree species composition and forest density; the decrease in vascular plants with forest density was stronger in forest dominated by spruce than in forests dominated by birch, and the positive effect of an increasing proportion of birch was smaller in dense than in open forests. There were no indications of mixed forests supporting a higher species richness or plant cover than any of the two monocultures. Additionally, few species (10%) showed tendencies toward a higher probability of occurrence in mixed forests, and most of these also occurred in open pure stands. Our results indicate a potential conflict between goals for diversified forests and increased biomass production, as the positive effects for understory vegetation from mixtures may be lost to concomitant increases in forest density. Furthermore, the limited number of species benefiting from mixtures per se indicates that similar biodiversity benefits for understory vegetation may be obtained at landscape levels from the increased use of broadleaf and lower‐density production stands, as from mixtures.

The optimal foraging theory, the nutrient balance hypothesis, and the plant association theories predict that foraging decisions and resulting tree damage by large mammalian browsers may be influenced by the species richness and species composition of forest stands. This may lead to either associational susceptibility (increased damage on a focal plant in a mixed stand) or associational resistance (reduced damage in a mixed stand). Better understanding of the mechanisms and the relative importance of tree species richness and composition effects on foraging by mammalian browsers is needed to support sustainable management of forests and mammal populations. However, existing knowledge of forest diversity effects on foraging by large mammalian browsers comes largely from observational studies while experimental evidence is limited. We analysed winter browsing by moose (Alces alces L.) in a long-term, large-scale experiment in Finland, which represents a tree species richness gradient from monocultures to 2-, 3- and 5-species mixtures composed of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.), Siberian larch (Larix sibirica Ledeb.), silver birch (Betula pendula Roth.) and black alder (Alnus glutinosa L.). The intensity of browsing per plot increased with tree species richness while browsing selectivity decreased with tree species being targeted more equally in species-rich mixtures. Tree species composition of a plot was also an important determinant of intensity of browsing. The greatest browsing occurred in plots containing preferred species (pine and birch) while intermediate preference species (larch and alder) experienced associational susceptibility when growing with pine and birch compared with their monocultures or mixtures without pine and birch. In contrast, we found no evidence of associational resistance; the presence of a least preferred species (spruce) in a mixture had no significant effect on moose browsing on other tree species. We demonstrate that the presence of alternative forage species allows moose to spend longer opportunistically foraging in a plot, resulting in increased level of damage in species-rich stands and stands containing preferred tree species. Our results highlight the limitations of the optimal foraging theory in predicting browsing patterns and demonstrate the importance of associational effects within mixed stands.

The provisioning of critical ecosystem services to cities of the eastern USA depends on the health and physiological function of trees in urban areas. Although we know that the urban environment may be stressful for trees planted in highly developed areas, it is not clear that trees in urban forest patches experience the same stressful environmental impacts. In this study, we examine chlorophyll fluorescence parameters, leaf traits, foliar nutrients and stable isotope signatures of urban forest patch trees compared with trees growing at reference forest sites, in order to characterize physiological response of these native tree species to the urban environment of three major cities arranged along a latitudinal gradient (New York, NY; Philadelphia, PA; Baltimore, MD). Overall, white oaks (Quercus alba L.) show more differences in chlorophyll fluorescence parameters and leaf traits by city and site type (urban vs reference) than red maples (Acer rubrum L.). The exceptions were δ13C and δ15N, which did not vary in white oak foliage but were significantly depleted (δ13C) and enriched (δ15N) in urban red maple foliage. Across all sites, red maples had higher thermal tolerance of photosynthesis (Tcrit) than white oaks, suggesting a greater ability to withstand temperature stress from the urban heat island effect and climate change. However, the highest average values of Tcrit were found in the Baltimore urban white oaks, suggesting that species suitability and response to the urban environment varies across a latitudinal gradient. Stomatal pore index (SPI) showed inter-specific differences, with red maple SPI being higher in urban trees, whereas white oak SPI was lower in urban trees. These results demonstrate that differences in native tree physiology occur between urban and reference forest patches, but they are site- and species-specific. Data on local site characteristics and tree species performance over time remain necessary to gain insight about urban woodland ecosystem function.

AimWe examined species composition of urban forests from local to global scales using occurrence and abundance information to determine how compositional similarity is defined across spatial scales. We predicted that urban forests have become more homogeneous world‐wide, which should result in minimal scale dependence that is more pronounced for non‐native species, especially when considering abundance information.LocationThirty‐eight cities world‐wide.MethodsWe estimated compositional dissimilarities of urban forests, including both spontaneous and cultivated trees, from local to global spatial scales using six dissimilarity metrics. We used redundancy analysis to determine how climate, geographic distance and anthropogenic factors are related to compositional dissimilarity among cities. These analyses were implemented for all species combined and for native and non‐native species separately.ResultsThe 38 cities contained a median of 77 tree species, with a greater percentage of these classified as native (median = 58%). The similarity of urban forests was scale dependent, declining as the spatial scale increased – an outcome that did not differ when considering native and non‐native species separately. Climate, geographic distance and city age were the main factors describing variation in tree species composition among cities. The addition of abundance information resulted in lower dissimilarity across spatial scales.Main conclusionsCompositional similarity of urban forests is a scale‐dependent phenomenon that is not affected by the presence or absence of non‐native species, suggesting a limited role for biotic interchange in promoting homogenization. However, compositional similarity across spatial scales increased uniformly with the addition of abundance information, suggesting that patterns of abundance may have greater biological relevance when homogenization trends among urban forests are considered.

Urban areas increasingly face climate-related challenges such as extreme heat, flooding, and biodiversity loss, that demand innovative, resilient solutions. Nature-Based Solutions (NBS) have emerged as a transformative approach for adapting urban areas, by integrating natural processes into urban planning process to enhance resilience and sustainability. In this paper, the role of NBS in promoting urban resilience is examined, aligning closely with the United Nations Sustainable Development Goals (SDGs), particularly SDG 11, which is intended to alter cities to become inclusive, safe, resilient, and sustainable. Key NBS strategies—such as green roofs, urban forests, bioswales, permeable pavements, sustainable building materials having high solar reflectivity— offer climate adaptation benefits such as temperature regulation and stormwater management, improved air quality, carbon sequestering, encouragement of biodiversity, and the promotion of social well-being. The implementation of NBS faces however, multiple challenges, including policy, financial, technical, and social barriers. In this paper each of these obstacles are addresses and the need for a paradigm shift is emphasized to overcome such barriers that would involve policy incentives, hybrid solutions, and community-driven strategies. Through a review of case studies, taken from Toronto, Detroit, Singapore, Malmö, and Rotterdam, are used to illustrates how hybrid NBS approaches, in which ecological processes have been combined with traditional engineering, have successfully used to address specific urban challenges. These cases demonstrate the potential of NBS to deliver multifunctional benefits, especially when implemented through cross-sector collaboration and supported by adaptive management frameworks. By providing useful outcomes that can be turned directly into actionable insights for policymakers, urban planners, and stakeholders, the results described in this permit advocating for the integration of NBS as a pathway to sustainable, resilient urban landscapes. Indeed, it is shown that the implementation of NBS enhance urban adaptability and contribute significantly to global sustainability goals, offering scalable models for cities worldwide.

Tree species composition and soil properties in pure and mixed beech-conifer stands drive soil fungal communities

Objective: Stand structure, composition, abundance and diversity of tree species of the northern forest-savanna ecotone were characterized to determine their spatial variability for land management.Methodology and result: An inventory of the in-situ tree community of the northern forest-savanna ecotone of Ghana was undertaken using the stratified random sampling technique. In all, 1453 individuals, representing 88 species, 78 genera and 30 families were identified in the study. Antiaris toxicaria, Adansonia digitata, Acacia albida, Afzelia africana and Vitellaria paradoxum were found most dominant in the vegetation. A gradation of tree distribution was evident as the ‘near-savanna’ portion of the ecotone was more species-rich than the ‘nearforest’ portion. Significant differences were observed of the species richness, densities and diversity of trees across sites (P < 0.05) and savanna trees were preponderant over forest species.Conclusion and application: This work has provided evidence of variability in tree species composition, richness, density and diversity across the northern forest-savanna ecotone of Ghana. The information could be crucial for monitoring and managing agro-ecosystems sustainability. A future study would be required to isolate proximate factors of tree species distribution in the ecotone.Key Words: composition, density, diversity, forest-savanna ecotone, Ghana, richness, tree species,

The role of sacred forest/sacred groves in the conservation of biodiversity is well recognised and documented. Despite the importance of sacred forests in conservation, data of flora species composition and diversity in many sacred forests still remain scanty. The study was conducted to provide baseline data on tree species composition and diversity of Ipinu-Igede sacred forest with a view to promote the role of sacred forest in flora conservation in the area. Systematic sampling technique was adopted for the study. A base line transect of 2 km long was established and five (5) other transects 2 km long were laid at regular interval of 500 km apart. On each transect, 4 sampling plots of 50 mx50 m were established at a regular interval of 500m apart. Within the 50 m x50 m plots, trees with diameter at breast height (DBH)≥10 cm were identified and enumerated. Species Important Value Index (IVI), species richness, species evenness and species diversity were estimated. A total number of 50 tree species in 19 families were recorded. Cola gigantea was the most important tree species with IVI of 14.56, this was followed by Harungana madagascariensis with 13.14. Caesalpinioideae was the dominant family with 6 species, 48.15% of the families were represented by only one species. The species richness was D=9.436, Species Evenness was E´=0.7668 and species diversity was H=3.646. Thirty percent (30%) of the tree species were in the DBH class of 1-40cm indicating good regeneration status of the sacred forest. Acknowledgement of the traditional practices by scientists and other actors in natural resources conservation will help in promoting forest conservation.