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Urban forest fragments buffer trees from warming and pests
Abstract
Trees are important components of urban landscapes because of the ecosystem services they provide. However, the effects of urbanization, particularly high temperatures, can benefit chronic insect pests and threaten ecosystem services offered by urban trees. Urban forest fragments are an often-overlooked component of the greater urban forest which may help to mitigate the damaging effects of urbanization. Melanaspis tenebricosa (gloomy scale) is a common pest of Acer rubrum (red maple) that becomes more abundant because of the urban heat island effect. We conducted observational and manipulative field experiments to test the hypothesis that trees in urban forest fragments would be cooler than those in surrounding ornamental landscapes and would thus have fewer M. tenebricosa, particularly in a hot mid-latitude city. Trees in forest fragments were 1.3° cooler and had three orders of magnitude fewer M. tenebricosa than trees in ornamental landscapes in Raleigh, NC USA. However, there was no difference in M. tenebricosa density between forest and landscape trees in Newark, DE and Philadelphia, PA USA which are 3.95 degrees of latitude higher, and nearer to the northern range extent. Trees in landscapes and forest fragments did not differ in predawn water potential, a measure of water stress, but likely differed in soil composition and moisture. We used potted trees to control for these differences and found that M. tenebricosa density still increased three times more in landscapes than forests suggesting temperature and not tree stress is the dominant factor. Taken together our results indicate two things. First, that trees growing in urban forest fragments are buffered from a chronic urban tree pest due to lower temperatures. Second, that temperature-driven differences in M. tenebricosa density which we saw in Raleigh could predict future density of the pest in higher latitude cities as the climate warms.
... Direct effects of temperature on scale insect survival and fitness have natural consequences for their geographic distributions at local and landscape extents (Table 1). Locally, the distribution of many scale insect species differs between urban street trees and nearby forest trees (Hanks and Denno 1993a, Speight et al. 1998, Tooker and Hanks 2000, Long et al. 2018). This has been attributed to the urban heat island effect for gloomy scale and Parthenolecanium spp., which form dense populations on street trees in the hottest urban locations and sparse populations on street trees in cooler locations or trees in forests (Meineke et al. 2013, Dale and Frank 2014a, b, Youngsteadt et al. 2015, Long et al. 2018, Meineke and Frank 2018. ...
... Locally, the distribution of many scale insect species differs between urban street trees and nearby forest trees (Hanks and Denno 1993a, Speight et al. 1998, Tooker and Hanks 2000, Long et al. 2018). This has been attributed to the urban heat island effect for gloomy scale and Parthenolecanium spp., which form dense populations on street trees in the hottest urban locations and sparse populations on street trees in cooler locations or trees in forests (Meineke et al. 2013, Dale and Frank 2014a, b, Youngsteadt et al. 2015, Long et al. 2018, Meineke and Frank 2018. Climate also affects scale distribution at landscape and continental scales (Preisser et al. 2008a, Wei et al. 2018. ...
... Climate also affects scale distribution at landscape and continental scales (Preisser et al. 2008a, Wei et al. 2018. For example, gloomy scale was historically restricted to low latitudes in the southern US but is now found in urban areas outside this range (Metcalf 1922, Just et al. 2018, Long et al. 2018. Cold temperatures restrict the range of gloomy scale. ...
Higher temperatures and drought are key aspects of global change with the potential to alter the distribution and severity of many arthropod pests in forest systems. Scale insects (Hemiptera: Coccoidea) infest many tree species and are among the most important pests of trees in urban and rural forests, plantations and other forest systems. Infestations of native or exotic scale insects can kill or sicken trees with economic and ecosystem-wide consequences. Warming can have direct effects on the life history, fitness and population dynamics of many scale insect species by increasing development rate, survival or fecundity. These direct benefits can increase the geographic distribution of scale insects and their consequences for tree health. Warming and drought can affect scale insects indirectly by altering the quality of their host trees. Additive or interactive effects of warming and drought can change tree quality in such a way that it increases scale insect fitness and population growth. However, the effects are species- and context-dependent with some scale insect species negatively affected by drought-induced changes in tree quality. Warming and drought are often coincident in urban forests and predicted to co-occur in many parts of the world under climate change scenarios. The individual and interactive effects of these factors require further research to inform predictions and management of scale insect pests. Warming also indirectly affects scale insects by altering interactions with natural enemies. This includes changes in natural enemy phenology, community composition and abundance. In addition, warming can alter scale insect phenology or voltinism causing asynchrony with natural enemies or population growth too rapid for natural enemies to suppress. Direct and indirect effects of warming and drought on scale insects can increase the potential for some exotic species to become established and for some native species to become invasive. Unfortunately, much research on scale insects is confined to a few particularly important native or exotic pests which limits our ability to predict the effects of warming on many current or potential pests. More research is required to understand how warming and drought affect scale insects, scale insect management and the forest systems they inhabit.
... Herbivorous insects are often more abundant on trees and shrubs in cities compared to rural areas (Raupp et al. 2010). Scale insects in particular, tend to be more abundant on urban trees than forest trees (Hanks and Denno 1993a, Tooker and Hanks 2000, Long et al. 2019. Urban features, such as impervious surface cover, cause warm temperatures and dry soil that increase water stress for trees and improve their quality as hosts to scale insects Frank 2017, Meineke and. ...
... We found that scale-infested oaks hosted more natural enemies than scale-uninfested oaks and this may be due to scales serving as hosts for parasitoids and prey for predators. Dense scale populations on urban vegetation are often associated with abundant parasitoid communities (Hanks and Denno 1993a, Tooker and Hanks 2000, Dale and Frank 2014, Long et al. 2019, Nighswander et al. 2021). Although we found more parasitoids in scale-infested than scaleuninfested trees in 2019, we did not find a similar effect in 2020. ...
Scale insects are frequently abundant on urban trees. Although scales can worsen tree condition, some tree species tolerate moderate scale densities. Scales are prey for many natural enemies. Therefore, scale-infested trees may conserve natural enemies in their canopies and in nearby plants. We examined if scale-infested oaks—Quercus phellos L.—hosted more natural enemies than scale-uninfested oaks—Q. acutissima Carruth. and Q. lyrata Walter in Raleigh, NC. USA. We also tested if natural enemies were more abundant in holly shrubs (Ilex spp.) planted below scale-infested compared to scale-uninfested oaks. We collected natural enemies from the canopies of both tree types and from holly shrubs planted below these trees. To determine if tree type affected the abundance of natural enemies that passively dispersed to shrubs, we created hanging cup traps to collect arthropods as they fell from trees. To determine if natural enemies became more abundant on shrubs below scale-infested compared to scale-uninfested trees over short time scales, we collected natural enemies from holly shrubs below each tree type at three to six-day intervals. Scale-infested trees hosted more natural enemies than scale-uninfested trees and shrubs below scale-infested trees hosted more natural enemies than shrubs under scale-uninfested trees. Natural enemy abundance in hanging cup traps did not differ by tree type; however, shrubs underneath scale-infested trees accumulated more natural enemies than shrubs under scale-uninfested trees in six to nine days. Tolerating moderate pest densities in urban trees may support natural enemy communities, and thus biological control services, in shrubs below them.
... Analyses of insect herbivory patterns on woody and herbaceous plants along urban-rural gradients have received increasing attention in recent decades (Dreistadt et al., 1990;Kozlov et al., 2017;Moreira et al., 2019;Raupp et al., 2010). Several studies measured the response of a single herbivore species (Dale & Frank, 2014a;Long et al., 2019;Meineke et al., 2013;Parsons & Frank, 2019;Shrewsbury & Raupp, 2000;Turrini et al., 2016), responses of different herbivore feeding guilds (Cuevas-Reyes et al., 2013;Kozlov et al., 2017;Moreira et al., 2019), or diversity and abundance of herbivores (Fenoglio et al., 2020;Rickman & Connor, 2003;Shrewsbury & Raupp, 2006;Youngsteadt et al., 2015) in urban compared to rural environments (but see Parsons & Frank, 2019). Although there seems to be a general tendency toward reduced insect abundance and diversity in urban settings compared to rural environments (Baldock, 2020;Blair & Launer, 1997;Fenoglio et al., 2020), there is no consensus on whether insect herbivory is higher (Christie & Hochuli, 2005;Moreira et al., 2019) or lower (Kozlov et al., 2017;Moreira et al., 2019;Nuckols & Connor, 1995) in urban compared to rural habitats. ...
... Cities are warmer than the surrounding rural areas as a result of the "heat island effect" (Kalnay & Cai, 2003;Parker, 2010;Roth et al., 1989;Ziter et al., 2019), which is locally buffered by the presence of trees (Loughner et al., 2012;Nuruzzaman, 2015;Ziter et al., 2019). Forest patches in urban environments serve as habitats for both herbivores and predators, which is likely to modify the strength of horizontal (herbivore-herbivore) and vertical (herbivore-predator) interactions in urban trees (Long et al., 2019;Long & Frank, 2020). Endophagous herbivores such as gall inducers and leaf miners are more sheltered from the environment than ectophagous herbivores. ...
Urbanization is an important driver of the diversity and abundance of tree‐associated insect herbivores, but its consequences for insect herbivory are poorly understood. A likely source of variability among studies is the insufficient consideration of intra‐urban variability in forest cover. With the help of citizen scientists, we investigated the independent and interactive effects of local canopy cover and percentage of impervious surface on insect herbivory in the pedunculate oak (Quercus robur L.) throughout most of its geographic range in Europe. We found that the damage caused by chewing insect herbivores as well as the incidence of leaf‐mining and gall‐inducing herbivores consistently decreased with increasing impervious surface around focal oaks. Herbivory by chewing herbivores increased with increasing forest cover, regardless of impervious surface. In contrast, an increase in local canopy cover buffered the negative effect of impervious surface on leaf miners and strengthened its effect on gall inducers. These results show that—just like in non‐urban areas—plant–herbivore interactions in cities are structured by a complex set of interacting factors. This highlights that local habitat characteristics within cities have the potential to attenuate or modify the effect of impervious surfaces on biotic interactions. We investigated the independent and interactive effect of impervious surface and local canopy cover on insect herbivory on the pedunculate oak throughout most of its distribution in Europe through a citizen science project. We found that local canopy cover within cities has the capacity to mitigate the effect of impervious surface on biotic interactions, as it influences the effect of impervious surface on herbivores differently. Therefore, this study supports the importance of maintaining trees in urban areas as it may consequently contribute to the preservation of biodiversity of insect herbivores in urban areas.
... Instead, temperature was positively associated with gloomy scale fecundity and density. Similarly, Long et al. (2019) found that temperature, rather than natural enemies or biological control, was a significant predictor of gloomy scale density on red maple street trees. Gloomy scale density was five times greater than on red maples in urban forest fragments that were 1.2°C cooler. ...
... However, natural enemies may be unable to control severe gloomy scale infestations in urban areas, where warmer temperatures lead to high gloomy scale densities and low vegetation complexity reduces natural enemy habitat availability (Frank 2020). Long et al. (2019) found that natural enemy abundances associated with landscape red maples were fourfold greater than forest trees. They also found that gloomy scale densities were five times greater between landscape and forest trees, suggesting that natural enemies do not suppress gloomy scale in urban locations where abiotic factors like heat and water stress drive scale population growth . ...
Gloomy scale, Melanaspis tenebricosa (Comstock), is native to the eastern United States and feeds on deciduous trees. In natural areas, it is a background herbivore that typically remains at low densities. Gloomy scale generally responds positively to warming with greater egg production, size, survival, and abundance. In urban areas, which are warmer than surrounding natural areas, gloomy scale is pestiferous on planted trees, particularly red maple (Acer rubrum L.; Sapindales: Sapindaceae) but other native maples as well. They live on the bark and damage host trees by feeding from plant cells and tissues, which deprives the trees of energy and nutrients, reducing the trees’ growth and overall health. Gloomy scales are likely to expand their range beyond the Southeast and become pestilent in new areas with continued climatic warming and urbanization. Here we present a review of the biology, ecology, response to environmental conditions, host range and damage, and management of gloomy scale.
... The extent of microclimatic buffering by urban forests and parks is largely determined by structural characteristics, such as canopy cover, tree species identity and richness, but also topography (Feyisa et al., 2014;Zellweger et al., 2019;Schwaab et al., 2021;Wang et al., 2021). The buffering capacity of urban forests is crucial for the health of citizens living in urban areas (Smoyer et al., 2000;Gillerot et al., 2022;Iungman et al., 2023), but can also substantially mitigate urban heat impacts on flora and fauna, such as temperatures that exceed species' thermal limits, as well as changes in phenology and pest infestations (Zipper et al., 2016;Long et al., 2019). For all these reasons, urban forests are increasingly proposed as a viable nature-based solution to moderate UHIs (van den Bosch and Ode Sang, 2017;Ziter et al., 2019;Wang et al., 2021;Iungman et al., 2023). ...
The urban heat island (UHI) causes strong warming of cities and their urban forests worldwide. Especially urban forest edges are strongly exposed to the UHI effect, which could impact urban forest biodiversity and functioning. However, it is not known to what extent the UHI effect alters edge-to-interior microclimatic gradients within urban forests and whether this depends on the forests' structure. Here we quantified gradients of air temperature, relative air humidity and vapour pressure deficits (VPD) along urban forest edge-to-interior transects with contrasting stand structures in six major cities across Europe. We performed continuous hourly microclimate measurements for two consecutive years and analysed the magnitude and depth of edge effects, as well as forest structural drivers of microclimatic variation. Compared to edge studies in rural temperate forests, we found that edge effects reached deeper into urban forests, at least up to 50 m. Throughout the year, urban forest edges were warmer and drier compared to forest interiors, with the largest differences occurring during summer and daytime. Not only maximum, but also mean and minimum temperatures were higher at the urban forest edge up to large edge distances (at least 85 m). Denser forests with a higher plant area index buffered high air temperatures and VPDs from spring to autumn. We conclude that urban forest edges are unique ecotones with specific microclimates shaped by the UHI effect. Both forest edges and interiors showed increased buffering capacities with higher forest canopy density. We advocate for the conservation and expansion of urban forests which can buffer increasingly frequent and intense climate extremes. To this end, urban forest managers are encouraged to aim for multi-layered dense forest canopies and consider edge buffer zones of at least 50 m wide.
... Compared to the small fragments in urban areas, urban forests (isolated by constructions) are generally less fragmented and play a pivotal role in maintaining arthropod populations (Chace and Walsh, 2006;Ferreira et al., 2018;Koricho et al., 2022). As stressed earlier (Kantsa et al., 2013;Xie et al., 2016;Liu et al., 2019), soil conditions, coupled with environmental changes in urban areas, are unfavorable for arthropod communities in urban forests, especially for the dominant animals (such as collembolans and mites) and invasive species (such as Solenopsis invicta) (Dale and Frank, 2014;Long et al., 2019), and this likely results in altered food web structure and function. For example, high density of Entomobrya sp. ...
... We studied this topic in two cities, to determine if relationships between plant and arthropod communities are consistent, or not, in different regions with different nonnative plant communities. Previous reports suggest plant and arthropod communities differ between cities at different latitudes (Long et al., 2019;Mitchell et al., 2023b;Youngsteadt et al., 2017). ...
Aim
Ecological theory and empirical evidence indicate that greater structural complexity and diversity in plant communities increases arthropod abundance and diversity. Nonnative plants are typically associated with low arthropod abundance and diversity due to lack of evolutionary history. However, nonnative plants increase the structural complexity of forests, as is common in urban forests. Therefore, urban forests are ideal ecosystems to determine whether structural complexity associated with nonnative plants will increase abundance and diversity of arthropods, as predicted by complexity literature, or whether structural complexity associated with nonnative plants will be depauperate of arthropods, as predicted by nonnative plant literature.
Location
We sampled 24 urban temperate deciduous and mixed forests in two cites, Raleigh, North Carolina and Newark, Delaware, in the eastern United States.
Methods
We quantified ground cover vegetation and shrub layer vegetation in each forest and created structural complexity metrics to represent total, nonnative and native understory vegetation structural complexity. We vacuum sampled arthropods from vegetation and quantified the abundance, biomass, richness and diversity of spiders and non‐spider arthropods.
Results
Nonnative plants increase understory vegetation complexity in urban forests. In Raleigh and Newark, we found support for the hypotheses that dense vegetation will increase arthropod abundance and biomass, and against the hypothesis that nonnative vegetation will decrease arthropods. Urban forest arthropod abundance and biomass, but not diversity, increased with greater nonnative and native structural complexity.
Main Conclusions
Invaded urban forests may provide adequate food in the form of arthropod biomass to transfer energy to the next trophic level, but likely fail to provide ecological services and functions offered by diverse species, like forest specialists. Urban land managers should survey urban forests for nonnative and native plant communities and prioritize replacing dense nonnative plants with native species when allocating vegetation maintenance resources.
... The benefits of urban trees and forests to city dwellers are increasingly recognized for their ecohydrological functions and costeffectiveness for storm runoff abatement (Nowak and Dwyer 2007;Boggs and Sun, 2011;Hao et al., 2015), water quality improvement, and shading and cooling (Hao et al., 2018;Huang et al., 2022), air pollution filtering (Nowak et al., 2018), and adaptation to climate change (Long et al. 2019). Urban forest distribution, canopy manipulation, and tree species choices can significantly alter urban watershed hydrological processes (Van Stan et al., 2018). ...
... Although several studies have sought to explain this observed variation (Speight et al. 1998;Sperry, Chaney, and Shao 2001;Shrewsbury and Raupp 2006;Meineke et al. 2013;Meineke, Dunn, and Frank 2014;Dale, Youngsteadt, and Frank 2016;Dale andFrank 2014a,b, 2017;Meineke and Frank 2018;Long, D'Amico, and Frank 2019;Parsons et al. 2020), the existing literature is dominated by studies that focus on a single herbivore species, with particular emphasis on hemipterans and other piercing/sucking feeders. As such, this topic remains largely unexplored. ...
Urban forests are critically important for providing ecosystem services to rapidly expanding urban populations, but their health is threatened by invasive insect herbivores. To protect urban forests against invasive insects and support future delivery of ecosystem services, we must first understand the factors that affect insect density across urban landscapes. This study explores how a variety of environmental factors that vary across urban habitats influence density of invasive insects. Specifically, we evaluate how vegetational complexity, distance to buildings, impervious surface, canopy temperature, host availability and density of co-occurring herbivores impact three invasive pests of elm trees: the elm leaf beetle (Xanthogaleruca luteola), the elm flea weevil (Orchestes steppensis) and the elm leafminer (Fenusa ulmi). Insect responses to these factors were species-specific, and all environmental factors were associated with density of at least one pest species except for distance to buildings. Elm leafminer density decreased with higher temperatures and was influenced by an interaction between vegetational complexity and impervious surface. Elm flea weevil density increased with greater host availability, and elm leaf beetle density increased with higher temperatures. Both elm leaf beetle and elm flea weevil density decreased with greater leafminer density, suggesting that insect density is mediated by species interactions. These findings can be used to inform urban pest management and tree care efforts, making urban forests more resilient in an era when globalization and climate change make them particularly vulnerable to attack.
... Cities are warmer than the surrounding rural areas as a result of the "heat island effect" (Kalnay and Cai, 2003;Parker, 2010;Roth et al., 1989), which is buffered by the presence of trees (Loughner et al., 2012;Nuruzzaman, 2015). Likewise, forest patches in urban environments serve as habitats for both herbivores and predators, which is likely to modify the strength of horizontal (herbivores-herbivores) and vertical (herbivorespredators) interactions in urban trees (Long et al., 2019;Long and Frank, 2020). Endophagous herbivores such as gall-inducers and leaf-miners are more sheltered from the environment than ectophagous herbivores. ...
Urbanization is recognized as an important driver of the diversity and abundance of tree associated insect herbivores, but its consequences for insect herbivory are controversial. A likely source of variability among studies is the insufficient consideration of intra-urban variability in forest cover. With the help of citizen scientists, we investigated the independent and interactive effect of urbanization and local canopy cover on insect herbivory in the pedunculate oak (Quercus robur) throughout most of its geographic range in Europe. The damage caused by chewing insect herbivores as well as the incidence of leaf-mining and gall-inducing herbivores consistently decreased with increasing urbanization around focal oaks. Herbivory by chewing herbivores increased with increasing forest cover, regardless of urbanization. In contrast, an increase in local canopy cover buffered the negative effect of urbanization on leaf-miners and strengthened its effect on gall-inducers. These results show the complexity of plant-herbivore interactions in urbanized areas, highlighting that the presence of local canopy cover within cities has the potential to attenuate or modify the effect of urbanization on biotic interactions.
... Urbanization can alter urban soil chemistry and microbial communities, reducing growth rates compared to trees planted in natural areas (Ward et al., 2021). The urban heat island effect combined with rising global temperatures can create conditions beneficial to insect pests, which may also be able to better take advantage of already-stressed urban trees (Tubby and Webber, 2010;Long et al., 2019). The increases in storm severity combined with growing space limitations has caused increased mortality of street trees (Johnson et al., 2019). ...
Urban trees play an important role in helping cities adapt to climate change, but also are vulnerable to changes in climate themselves. We developed an approach for assessing vulnerability of urban tree species and cultivars commonly planted in cities in the US Upper Midwest to current and projected climate change through the end of the 21st century. One hundred seventy-eight tree species were evaluated for their adaptive capacity to a suite of current and future-projected climate and urban stressors using a weighted scoring system based on an extensive literature review. These scores were then evaluated and adjusted by leading experts in arboriculture in the region. Each species or cultivar’s USDA hardiness zone and American Horticultural Society heat zone tolerance was compared to current and future heat and hardiness zones for 14 municipalities across Michigan, Wisconsin, and Minnesota using statistically downscaled climate data. Species adaptive capacity and zone tolerance was combined to assign each species one of five vulnerability categories for each location. We determined the number of species and trees in each category based on the most recent municipal street tree data for each location. Under a scenario of less climate change (RCP 4.5), fewer than 2% of trees in each municipality were considered highly vulnerable across all 14 municipalities. Under a scenario of greater change (RCP 8.5), upwards of 25% of trees were considered highly vulnerable in some locations. However, the number of vulnerable trees varied greatly by location, primarily because of differences in projected summer high temperatures rather than differences in species composition. Urban foresters can use this information as a complement to other more traditional considerations used when selecting trees for planting. https://www.frontiersin.org/articles/10.3389/fevo.2021.721831/abstract
... Street trees are common urban trees that grow along public streets, the greatest value of a street tree is its ecosystem services value, i.e., all economic benefits that a tree provides for a community [1]. However, urban street trees are prone to periodic outbreaks of diseases and insect pests [6,7] that reduce ecosystem services [8,9] and lead to the destruction of the urban street landscape. Pesticides are considered effective and can be used preferentially for the pest control of street trees, however, many street trees are too high (even higher than 30 m) to conduct drug delivery, and thus, a sufficient drug delivery machine is needed. ...
High-range sprayers (HRSs) are widely used in tree pest control. However, the design of the HRS is complex and time-consuming. This paper proposed a case study of developing a design platform for the HRS based on a virtual reality (VR) visualization. Firstly, the function of the HRS design platform was introduced. And then, an architecture of the HRS and the compositions of the HRS design platform, including calculation, optimization, assembly, and verification, were illustrated. Meanwhile, development methods and related theories of building the HRS design platform were presented in detail. The VR-based HRS design platform proposed in this paper has a significant advantage in reducing the design period and costs, which can also lower the experimental threshold and improve the training of new designers.
... Moderate climatic variations around build in established as a biodiversity spot in crowded and concrete dominated cities which ultimately contribute to enhancing the quality of human life (Botkin and Beveridge, 1997;Long and Nair, 1999;Aminzadeh and Khansefid, 2010;Chaudhry and Tewari, 2010;Nagendra and Gopal, 2010;Vogt et al., 2015;Fan et al., 2019). Urban forest justifies the role of trees as a critical part of the urban infrastructure (Singh et al., 2010;Long et al., 2019). In denuded urban environments, trees act as a critical habitat and the last refuge of biodiversity as small green islands to support urban wildlife (Krishen, 2006). ...
Urban scape constitutes the manifestation of various natural and anthropic elements entangled in a specific form. However, arbitrary land-use changes during the last few decades have witnessed a significant biodiversity loss in urban areas. Over 50% of the earth’s human population lives in the urban settlement, which accounts for less than 3% of the earth’s urbanized area. Urban green spaces act as biodiversity refuge in urban areas. In such crucial circumstances, an urban forest can play a critical role in biodiversity conservation and management through academic green spaces. To understand and evaluate the role of the urban forest, the present study carried out on the campus of [CSIR-National Environmental Engineering Research Institute (NEERI)], Nagpur. Furthermore, an innovative and multifaceted index named total importance value (TIV) index was developed, which used to analyze the importance of the trees present on the campus. Results revealed the presence of more than 200 plant species belonging to both native and exotic groups and their contributions to improve the urban environment in terms of the TIV index. The study also advocates the usages of TIV as a framework for the development and planning of climate-smart green cities, which is resilience to climate change.
... In particular, small urban forests are more subject to higher temperatures and lower humidity (Marzluff et al., 2008;Dale & Frank, 2014), which can negatively (Valladares et al., 2006) or positively impact herbivorous insects (Youngsteadt et al., 2015). A previous study conducted in the same forest sites could not detect any temperature increase in forests in highly urbanised areas (Melliger et al., 2017), probably because forests can buffer part of the elevated temperature in urban areas (Long et al., 2019). ...
Urbanisation is increasing globally and is considered to be a main driver of environmental change. Urbanisation-related factors include reduced habitat size and increased spatial isolation of the remaining habitats. As a consequence, the dynamics of plant and animal populations may change, which in turn might influence the quality and quantity of plant resources. Thus, urbanisation has the potential to disturb plant-animal interactions such as herbivory or galling. In the urban-rural setting of Basel (Switzerland), we aimed to assess whether the degree of urbanisation and forest size influence plant-galling infestation rates and leaf damage by mining and chewing arthropods on three tree species (sycamore, beech, and ash). We recorded species-specific responses to the degree of urbanisation and forest size. Gall infestation rate on sycamore leaves was affected by urbanisation but not by forest size. In contrast, gall infestation rates of beech gall midges responded sensitively to increasing urbanisation and decreasing forest size. The total leaf area damage caused by mining and chewing arthropods on sycamore was influenced by urbanisation and increased with increasing forest size. Leaf area damage by miners in beech tended to be affected by the degree of urbanisation, but not in ash. Urbanisation and forest size have the potential to alter herbivorous insect abundances. However, the effects depend on tree species and herbivore guild.
... Herbarium specimens have also revealed that historical M. tenebricosa abundances tracked periods of warmer and cooler climates, where warmer periods had greater densities ( Youngsteadt et al. 2015). Under increased warming, M. tenebricosa may retreat to cooler areas within the south like forests ( Long et al. 2019) and become a less-important pest of ornamental trees, but may become more important forest pests. However, some scales may adapt to the heat [e.g., heat adaptation has been suggested for oak lecanium scale; Parthenolecanium quercifex (Fitch); Hemiptera: Coccidae) ( Meineke et al. 2014)] and thrive in the additionally warmed cities. Future research should consider heat tolerance for all M. tenebricosa life stages with individuals collected during seasons associated with those stages. ...
An insect species' geographic distribution is probably delimited in part by physiological tolerances of environmental temperatures. Gloomy scale (Melanaspis tenebricosa (Comstock)) is a native insect herbivore in eastern U.S. forests. In eastern U.S. cities, where temperatures are warmer than nearby natural areas, M. tenebricosa is a primary pest of red maple (Acer rubrum L.; Sapindales: Sapindaceae) With warming, M. tenebricosa may spread to new cities or become pestilent in forests. To better understand current and future M. tenebricosa distribution boundaries, we examined M. tenebricosa thermal tolerance under laboratory conditions. We selected five hot and five cold experimental temperatures representative of locations in the known M. tenebricosa distribution. We built models to predict scale mortality based on duration of exposure to warm or cold experimental temperatures. We then used these models to estimate upper and lower lethal durations, i.e., temperature exposure durations that result in 50% mortality. We tested the thermal tolerance for M. tenebricosa populations from northern, mid, and southern locations of the species' known distribution. Scales were more heat and cold tolerant of temperatures representative of the midlatitudes of their distribution where their densities are the greatest. Moreover, the scale population from the northern distribution boundary could tolerate cold temperatures from the northern boundary for twice as long as the population collected near the southern boundary. Our results suggest that as the climate warms the M. tenebricosa distribution may expand poleward, but experience a contraction at its southern boundary.
... Urban trees provide shade, cool city streets and beautify our urban spaces (Nowak and Dwyer 2000). However, urban trees often have more pests than trees in natural areas (Hanks and Denno 1993;Raupp, Shrewsbury, and Herms 2010;Long, D'Amico, and Frank 2019). Pests can negatively affect trees and the services they provide for city residents (Dreistadt, Dahlsten, and Frankie 1990;Raupp, Shrewsbury, and Herms 2012). ...
Trees provide many ecosystem services in our urban environments. However, city trees are often stressed by pests that are typically higher than those in nearby natural areas. Our research highlights a potential mismatch in scale between the habitat elements that affect the densities of pests and their natural enemies on city trees. We tested a well-known ecological concept, the enemies hypothesis, in the city, where relationships of pests and their enemies have not been thoroughly studied. To test our hypothesis that natural enemies and aphid predation services on urban trees increase with more local structural complexity around trees, we collected data on crape myrtle trees on NC State University’s campus from 2016 to 2017. We measured local structural complexity of vegetation around study trees, quantified impervious cover among other urban habitat elements, collected crape myrtle aphids (Tinocallis kahawaluokalani) and their natural enemies on trees, and performed predation experiments. We found that aphid abundance was positively correlated with more impervious cover within 100 m of crape myrtle trees. Alternatively, greater local structural complexity within the 10 × 10 m area around crape myrtles correlated with a higher abundance of natural enemies. Aphid predation was mostly predicted by local structural complexity and impervious cover within 20 m of crape myrtle trees. Together, these findings suggest that although the impervious nature of our cities may mean higher densities of some pests, local landscapes around trees can play an important role in maintaining natural enemies and predation services that help regulate pest populations.
... Complex forest patches are a critical component of urban ecosystems. They provide a full spectrum of ecosystem services, referring to the benefits that human populations obtain directly or indirectly [7,12,13] from natural ecosystems [14,15], which serve as the basis of economic development and social wellbeing [16][17][18]. Some well-recognised and well-studied examples of urban forest ecosystem services include alleviating summer heat through evaporation and shading [19,20], reducing stormwater runoff by intercepting and absorbing water and improving infiltration [21,22], enhancing air quality by removing gaseous pollutants and particulate matter [23], reducing greenhouse gas emissions by storing and sequestering a considerable amount of carbon [24][25][26][27]; addressing food security by supplying food, medicine and materials [28], pollination [29][30][31], outdoor recreation opportunities [1,32], as well as serving as important places for aesthetics and spirituality [33,34]. ...
Increasing recognition of the importance of urban forest ecosystem services calls for the sustainable management of urban forests, which requires timely and accurate information on the status, trends and interactions between socioeconomic and ecological processes pertaining to urban forests. In this regard, remote sensing, especially with its recent advances in sensors and data processing methods, has emerged as a premier and useful observational and analytical tool. This study summarises recent remote sensing applications in urban forestry from the perspective of three distinctive themes: multi-source, multi-temporal and multi-scale inputs. It reviews how different sources of remotely sensed data offer a fast, replicable and scalable way to quantify urban forest dynamics at varying spatiotemporal scales on a case-by-case basis. Combined optical imagery and LiDAR data results as the most promising among multi-source inputs; in addition, future efforts should focus on enhancing data processing efficiency. For long-term multi-temporal inputs, in the event satellite imagery is the only available data source, future work should improve haze-/cloud-removal techniques for enhancing image quality. Current attention given to multi-scale inputs remains limited; hence, future studies should be more aware of scale effects and cautiously draw conclusions.
Urban trees often host greater insect pest abundance than trees in rural forests. This may be due, in part, to differences in tree diversity and canopy cover between these settings. Urban trees are often planted in isolation or monoculture, which favors pest accumulation. Gloomy scale, Melanaspis tenebricosa Comstock, is a pest of urban red maples (Acer rubrum L.) that is abundant where impervious surfaces dominate the local landscape. Increasing tree diversity and canopy cover around urban red maples may reduce gloomy scale abundance by supporting natural enemy communities. We investigated the effect that surrounding tree species richness and tree canopy cover had on gloomy scale abundance, natural enemy abundance, and biological control in red maple trees in Raleigh, NC, USA. We collected scales and natural enemies from red maples that spanned a gradient of tree species richness, canopy cover, and impervious surface values. We also measured gloomy scale parasitism and predation of sentinel prey in red maple canopies. Greater tree species richness and canopy cover were associated with lower gloomy scale density. Red maples in diverse settings also hosted fewer scales per natural enemy. Parasitoids were less common in maples in diverse settings, but generalist predator abundance was unaffected by tree diversity. Finally, tree species richness and canopy cover did not increase biological control of scales or sentinel prey. Our findings suggest that higher tree diversity and greater canopy cover may reduce gloomy scale density, but this is not entirely explained by the effects of natural enemies and biological control.
Urban forests globally face severe degradation due to human activities and natural disasters, making deforestation an urgent environmental challenge. Remote sensing technology and very-high-resolution (VHR) bitemporal satellite imagery enable change detection (CD) for monitoring forest changes. However, deep learning techniques for forest CD concatenate bitemporal images into a single input, limiting the extraction of informative deep features from individual raw images. Furthermore, they are developed for middle to low-resolution images focused on specific forests such as the Amazon or a single element in the urban environment. Therefore, in this study, we propose deep learning-based urban forest CD along with overall changes in the urban environment by using VHR bitemporal images. Two networks are used independently: DeepLabv3+ for generating binary forest cover masks, and a deeply supervised image fusion network (DSIFN) for the generation of a binary change mask. The results are concatenated for semantic CD focusing on forest cover changes. To carry out the experiments, full scene tests were performed using the VHR bitemporal imagery of three urban cities acquired via three different satellites. The findings reveal significant changes in forest covers alongside urban environmental changes. Based on the accuracy assessment, the networks used in the proposed study achieved the highest F1-score, kappa, IoU, and accuracy values compared with those using other techniques. This study contributes to monitoring the impacts of climate change, rapid urbanization, and natural disasters on urban environments especially urban forests, as well as relations between changes in urban environment and urban forests.
Urbanization filters arthropod communities and selects for species tolerant of urban conditions. Spiders are key generalist predators in urban ecosystems, but certain spider families are rare in cities compared to rural areas. The unique arthropod communities found in different tree species likely affects their ability to conserve spiders by providing different prey resources. If arthropods disperse from trees to plants growing below trees, the conservation benefits of the arthropod communities found in trees may also extend to plants growing beneath them. Certain urban tree species can host high densities of scale-insects and other arthropods that may provide important prey resources for spiders. To assess the conservation value of different arthropod communities in urban trees, we collected spiders from scale-infested and scale-uninfested trees and from shrubs under these trees. We also used hanging cup traps to collect spiders that fell from both tree types. Spider abundance was greater within, and in shrubs below, scale-infested compared to scale-uninfested trees. Scale-infested trees hosted more orb web weaving spiders than scale-uninfested trees. Shrubs under scale-infested trees hosted more hunting, orb web weaving, and space web weaving spiders than shrubs under uninfested trees. Our findings suggest that scale-infested urban trees, and the robust arthropod communities they support, conserve certain spider guilds, and these benefits extend to other plants in the landscape.
Implications for insect conservation: The ability of urban trees to conserve spider communities is in part attributable to the abundance of potential prey available within trees. Therefore, tolerating pests such as scale insects in urban trees can conserve spider communities both within trees and in shrubs planted below these trees.
Scale insects are common tree pests in
urban ecosystems. Although severe scale infestations
can worsen tree condition, trees can tolerate moderate
scale densities. Scale insects are prey for many arthro�pod natural enemies that also feed on plant pests
throughout urban landscapes. Because scale-infested
trees support natural enemy communities, they may
support biological control services on nearby plants
and function analogously to banker plants in greenhouse production systems. In this study we tested if sentinel insect prey were more likely to be removed on shrubs below scale-infested trees compared to scale-uninfested trees. We conducted several biological control experiments from 2019 to 2021 using fruit flies, aphids, and caterpillars in potted and planted holly shrubs below scale-infested and scale-uninfested oak trees. We found that caterpillars in potted. shrubs and fruit flies in planted landscape shrubs were more likely to be removed underneath scale-infested trees compared to scale-uninfested trees. Caterpillars were also more likely to be removed from landscape Ilex vomitoria shrubs compared to I. cornuta shrubs. In all other experiments we found no effect of scale infestation status or shrub species on prey removal. Our results suggest that scale-infested trees can support biological control services in shrubs below them but that this effect can vary depending on prey and shrub species. The natural enemy communities in urban trees and shrubs appear to be linked and tolerating tree pests can favor conservation biological control services in urban landscapes.
Purpose of Review
Our goal is to provide an overview of how urban heat islands affect forests and synthesize recent literature on that topic. We focused on direct effects of high temperatures from urban heat islands on forest trees and indirect effects via changes in soil moisture and pest density. We also focused on the effects of urban heat islands on arthropods with particular emphasis on tree pests.
Recent Findings
Urban heat islands can push trees and arthropods closer to their thermal limits with consequences for tree growth and arthropod fitness. Urban heat islands can alter the distribution of trees and arthropods allowing species to survive at higher altitudes or latitudes than they could otherwise. A primary risk for trees is that urban heat islands can increase pest density and damage.
Summary
Urban heat islands can increase forest air and soil temperature and reduce soil moisture especially when combined with greater climate change. Land managers should consider the surrounding urban density and forest size when trying to determine which plants and animals can persist in urban forests. As forests are fragmented or encroached upon by urbanization, the forest environment will change and become more hospitable for some species and less hospitable for others. Overall, there is insufficient research focused on urban-forest interfaces and the consequences of urbanization for plants and animals within forests. This research is not only important for urban forest conservation. Tree and arthropod responses to urban heat islands will help scientists and land managers predict responses to climate warming in rural areas as well.
Urban tree isolation affects the abundance of pests and their enemies. • Urban tree isolation affects the top-down regulation of pests by their enemies. • Monospecific Eucalyptus patches had more herbivore insects than isolated trees. • Pest parasitism rate was 30-fold greater in urban forest patches than isolated trees. • Pest-predator-parasitoid abundance interdependence differed by tree arrangement. A R T I C L E I N F O Keywords: Anthocoris nemoralis Glycaspis brimblecombei Psyllaephagus bliteus Urban forest Top-down regulation Resource concentration A B S T R A C T The proximity to transportation hubs and the large movement of goods and people in cities make trees especially prone to invasive insect pests. Urban tree arrangements, in isolated tree sites or in forest patches, may alter their susceptibility to insect herbivory. Surprisingly little is known about how urban tree spatial arrangements influence pest abundance and top-down regulation by natural enemies. We sampled the abundance of an invasive pest of Eucalyptus, the psyllid Glycaspis brimblecombei, and of two of its natural enemies, the specialist exotic parasitoid Psyllaephagus bliteus and the generalist native predator Anthocoris nemoralis over two years. We measured insect abundances in isolated trees versus monospecific planted forest patches in 17 pairs of sites, each within a Portuguese city. The abundance of the exotic pest was threefold higher in forest patches than in isolated trees. The parasitism rate was ~ 30 times higher in forest patches (11.5 %) than in isolated trees (0.4 %). The interdependence among insect species abundances also differed between spatial arrangements. In isolated trees, predator and parasitoid abundances depended markedly on prey abundance. In forest patches, we found a marked dependence of the predator on the composition of the surrounding landscape. Our study adds empirical data indicating that urban tree isolation matters for pest abundance and regulation by its enemies. In similar systems, avoiding dense monospecific patches of exotic trees and increasing the compositional heterogeneity of the landscape are promising paths to maintain the sustainability of urban trees and their environmental and societal benefits.
Urban forest fragments are highly multifunctional and provide many ecosystem services to people. However, the expansion and densification of cities is threatening this particular type of urban forest, resulting in further fragmentation, degradation and a change in forest function. Understanding how urbanization affects urban forests fragments and the multiple ecosystem services they provide is important for the creation of livable cities. We used an urban-to-rural gradient in Maple Ridge, Canada, to explore relationships between urban forest structure, urbanization, surrounding landscape structure, and the supply of eight different ecosystem services, including merchantable timber, carbon storage, flood control, food (berries), non-native shrub control, cultural use, and habitat provision. We found that the supply of multiple ecosystem services was higher at the rural end of our gradient and that forest fragments spaced closer together showed strong negative associations with most services. Crucially, forest fragment size had very weak effects on most services, emphasizing the importance of conserving small urban forest fragments with large trees. We also identified key tree genera, including Picea and Thuja, that could be retained or planted in urban forests to maximize individual services and multifunctionality. Our results highlight the potential for strategically managing urban landscapes to maintain forest fragments and enhance their ability to provide ecosystem services and multifunctionality. Our findings are relevant to inform urban conservation and greening strategies in cities around the world that are currently expanding into surrounding forests or losing greenspace through densification.
Teaching ecological concepts and field methods for introductory biology courses can be challenging, especially when class sizes are large and activities or topics depend on environmental conditions that can change dramatically from semester to semester. We provide a laboratory module that can be used throughout the year, where students can explore plant-insect interactions on campus trees in urban environments using nondestructive measures. Students are provided a transparent grid, a measuring tape, and a random selection protocol to estimate gloomy scale (Melanaspis tenebricosa) insect density on preselected Acer rubrum tree trunks. Students are also given a pace-to-plant protocol to evaluate how impervious surfaces around trees in urban environments may be associated with scale insect abundance. This module highlights ecological concepts, such as population dynamics, species interactions, competition, and food webs, among others. Through this module, students also learn skills in ecological field sampling techniques, particularly how to randomly sample, how to estimate insect abundance, and how to use observation skills to inform scientific inquiry.
Most ecosystems are increasingly being degraded and reduced by human activities at the local and global scales. In contrast, urban environments are expanding as increasing portions of humanity move into cities. Despite the common perception among biologists that urban areas are biological deserts, cities offer habitat for many non-human species, but their ecology and conservation remain poorly studied. In this review, we first provide an update on the current state of knowledge on urban wildlife, then briefly examine the indirect effects of the COVID-19 pandemic on urban wildlife and add four components not previously included in comprehensive reviews. (1) We show that by reducing human activity, COVID-19 has temporarily enhanced urban habitat quality for some species and diminished it for others. (2) Thoughtful horticulture can contribute to urban wildlife by providing complex habitat structures that benefit biodiversity while enhancing human wellbeing. (3) Recent literature on urban invertebrate biodiversity has grown, though is still focused on pollinators. (4) Finally, employing insights from the discipline of communication can enhance the success of urban biodiversity conservation among both biologists and the public.
Warmer temperatures and frequent drought directly affect urban tree health. Both abiotic conditions also affect tree health via increased density of some insect pests. Warming is predicted to benefit urban trees by increasing carbon sequestration and allocation to biomass. However, increased drought and pests are rarely considered despite often co-occurring with heat. To determine the combined effects of these abiotic and biotic factors, we manipulated water availability for established urban red maple trees across a gradient of warming and pest density and measured leaf-level processes and tree growth over two years. We find that water availability is a major determinant of tree growth, physiological processes, and resilience to urban stress factors. Maples performed better with more water, which also made them resistant to effects of temperature and pest density. However, when drought became too severe, leaf-level processes declined with warming. Tree basal area growth was unaffected after two years, but stem elongation increased with increasing water, temperature, and pest density. We discuss potential mechanisms driving these responses and the implications in the context of urban forest management. Urban forest designs that reduce drought and align species adaptations to local conditions are critical for designing more resilient and productive urban forests.
Urbanization can change interactions in insect communities, and the few studies of tritrophic interactions in urban settings focus on interactions between plants, herbivorous insects and their mutualists and natural enemies. Plant pathogen infection is also widespread and common, and infection may also alter such interactions, but we have no understanding of whether the ecological consequences of pathogen infection vary with urbanization. Using replicated aphid colonies on experimental plants, we investigated how infection by the plant pathogen Botrytis cinerea influences interactions between plants, aphids and the aphid natural enemies and ant mutualists in highly urbanized, suburban and rural study sites. Aphid and natural enemy abundance were highest in the suburban site, while mutualist ants were most abundant in the urban site, reversing the usual positive density-dependent relationship between natural enemies and aphids. The effect of pathogen infection varied with trait and site, mediated by natural enemy preference for hosts or prey on uninfected plants. The effect of infection on aphid abundance was only seen in the suburban site, where natural enemies were most abundant on uninfected plants and aphid numbers were greatest on infected plants. In the urban site, there was no effect of infection, while in the rural site, aphid numbers were lower on infected plants. Uninfected plants were smaller than infected plants and differed between locations. This study suggests that the effects of urbanization on ecological interactions may become more complex and difficult to predict as we study ecological assemblages and communities at greater levels of structural complexity.
In recent decades, unsustainable urban development stemming from uncontrolled changes in land cover and the accumulation of population and activities have given rise to adverse environmental consequences, such as the formation of urban heat islands (UHIs) and changes in urban microclimates. The formation and intensity of UHIs can be influenced not only by the type of land cover, but also by other factors, such as the spatial patterns of thermal clusters (e.g., dimensions, contiguity, and integration). By emphasising the differences between semi-arid and cold-and-humid climates in terms of the thermal−spatial behaviours of various types of land cover in these climates, this paper aims to assess the behavioural patterns of thermal clusters in Tehran, Iran. To this end, the relationship between the land surface temperature (LST) and the types of land cover is first demonstrated using combined multispectral satellite images taken by Operational Land Imager (OLI), Thermal Infrared Sensor (TIRS) of the Landsat8 and MODIS, and Sentinel satellites to determine LST and land cover. The effects of different behavioural patterns of thermal clusters on the formation of daytime urban heat islands are then analysed through spatial cross-correlation analysis. Lastly, the thermal behaviours of each cluster are separately examined to reveal how their spatial patterns, such as contiguity, affect the intensity and formation of UHI, with the assumption that each point in a contiguous surface may exhibit different thermal behaviours, depending on its distance from the edge or centre. The results of this study show that the daytime UHIs do not occur in the central parts of Tehran, and instead they are created in the surrounding layer, which mostly consists of barren cover. This finding contrasts with previous research conducted regarding cities located in cold-and-humid climates. Our research also finds that the more compact the hot and cool clusters are, the more contiguous they become, which leads to an increase in UHIs. The results suggest that for every 100 pix/km 2 increase, the cluster temperature increases by approximately 0.7−1 °C. Additionally, placing cool clusters near or in combination with hot clusters interrupts the effect of the hot clusters, leading to a significant temperature reduction. The paper concludes with recommendations for potential sustainable and context-based solutions to UHI problems in semi-arid climates that relate to the determination of the optimal contiguity distance and land use integration patterns for thermal clusters.
Urbanization can affect arthropod abundance in different ways. While species with narrow habitat range and low dispersal ability often respond negatively to urban environments, many habitat generalist species with good dispersal ability reach high densities in city centers. This filtering effect of urban habitats can strongly influence predator-prey-mutualist interactions and may therefore affect the abundance of predatory and phytophagous species both directly and indirectly. Here, we assessed the effect of urbanization on aphids, predatory arthropods, and ants on field maple (Acer campestre) trees in and around the city of Budapest, Hungary. We used the percentage of impervious surfaces within a 500 m radius of each site as an index of the degree of urbanization. We found that the abundance of aphids increased with increasing level of urbanization. However, abundance of predatory arthropods and occurrence of poorly dispersing species within the predator community were negatively related to urbanization, and we identified these two independent factors as significant predictors of aphid abundances. The abundance of ants decreased with urbanization, and contrary to our expectations, did not affect the abundance pattern of aphids. Our results suggest that urbanization, by altering the abundance and composition of predator communities, can disrupt biological control of aphid populations, and thus may contribute to the aphid outbreaks on urban trees.
Sleeper species are innocuous native or naturalized species that exhibit invasive characteristics and become pests in response to environmental change. Climate warming is expected to increase arthropod damage in forests, in part, by transforming innocuous herbivores into severe pests: awakening sleeper species. Urban areas are warmer than natural areas due to the urban heat island effect and so the trees and pests in cities already experience temperatures predicted to occur in 50-100 years. We posit that arthropod species that become pests of urban trees are those that benefit from warming and thus should be monitored as potential sleeper species in forests. We illustrate this with two case studies of scale insects that are important pests of urban trees in parts of the US. Melanaspis tenebricosa and Parthenolecanium quercifex are geographically native to the US but take on invasive characteristics such as higher survival and reproduction and become disconnected from natural enemies on urban trees due to the urban heat island effect. This allows them to reach high densities and damage their host trees. Parthenolecanium quercifex density increases up to 12 times on urban willow oaks with just 2 °C of warming due to higher survival and adaptation to warmer temperatures. The urban heat island effect also creates a phenological mismatch between P. quercifex and its parasitoid complex, and so egg production is higher. Melanaspis tenebricosa density can increase 300 times on urban red maples with 2.5 °C of warming. This too is due to direct effects of warmer temperatures on survival and fecundity but M. tenebricosa also benefits from the drought stress incurred by warmer urban trees. These effects combine to increase M. tenebricosa density in forests as well as on urban trees at latitudes higher than its native range. We illustrate how cities provide a unique opportunity to study the complex effects of warming on insect herbivores. Studying pestilent urban species could be a pragmatic approach for identifying and preparing for sleeper species.
Predation by natural enemies is important for regulating herbivore abundance and herbivory. Theory predicts that complex habitats support more natural enemies, which exert top-down control over arthropods and therefore can reduce herbivory. However, it is unclear if theory developed in other more natural systems similarly apply to predation by vertebrate and invertebrate natural enemies across urban habitats of varying complexity. We used plasticine caterpillar models to assess risk of predation by birds and insects, collected leaf-feeding arthropods, and measured herbivory in willow oak trees (Quercus phellos) in two seasons to determine how predation influenced herbivory across urban forest fragments, street trees planted near forest fragments, and downtown street trees. Predation attempts by birds and abundance of chewing folivores were greater on trees growing in urban forest fragments than downtown street trees. Bird predation attempts and herbivory levels were inconsistent for near-forest trees. Predation attempts by arthropods did not statistically vary among the three urban tree habitats. Contrary to expectations based on theory, chewing folivore abundance and herbivory were generally highest on trees growing in urban forests, the most complex habitat we studied, and the habitat where risk of bird predation was greatest. We suggest that urban forest fragments provide better habitat than other urban landscapes for both urban birds and chewing folivores by having greater habitat complexity. Therefore, basal resources, such as availability of suitable habitat, mediate top-down effects on herbivores in cities.
Trees provide many ecosystem services in our urban environments. However, city trees are often stressed by pests and hot urban temperatures. Our research highlights how temperature affects a common tree pest, crape myrtle aphid (Tinocallis kahawaluokalani), natural enemies, and egg predation services on crape myrtles in the city. This research addresses an area of study that has largely been unexplored, effects of temperature on urban natural enemies, and it sheds light on how hot urban temperatures affect one species of piercing-sucking herbivore, a guild that is generally thought to be benefitted in hot city environments. To test our hypothesis that temperature increases T. kahawaluokalani density, fecundity and population growth, yet decreases natural enemy density and egg predation services on street trees, we collected data on crape myrtle trees in Raleigh, NC and conducted lab experiments in 2018. We collected canopy temperature and arthropod data on study trees from May–August and measured local structural complexity around trees and plant water potential. Aphid density decreased with hotter urban temperatures. However, natural enemies and egg predation were not affected by temperature. Natural enemy density was most correlated with local structural complexity. Together these findings suggest that increasing local structural complexity around trees may be a way to support natural enemies on both cool and hot urban trees. Our findings also emphasize the need for similar studies that evaluate temperature effects on common tree pests to help landscape managers prioritize pest targets for pest control in a warmer and more urban world.
Pest abundance on urban trees often increases with surrounding impervious surface. Gloomy scale (Melanaspis tenebricosa Comstock; Hemiptera: Diaspididae), a pest of red maples (Acer rubrum L.; Sapindales: Sapindaceae) in the southeast United States, reaches injurious levels in cities and reduces tree condition. Here, we use a chronosequence field study in Raleigh, NC, to investigate patterns in gloomy scale densities over time from the nursery to 13 yr after tree planting, with a goal of informing more efficient management of gloomy scale on urban trees. We examine how impervious surfaces affect the progression of infestations and how infestations affect tree condition. We find that gloomy scale densities remain low on trees until at least seven seasons after tree planting, providing a key timepoint for starting scouting efforts. Scouting should focus on tree branches, not tree trunks. Scale density on tree branches increases with impervious surface across the entire studied tree age range and increases faster on individual trees that are planted in areas with high impervious surface cover. There is a lag between the onset of pest infestations and a decline in tree condition, indicating that gloomy scale management should begin prior to a visible decline in tree condition. Our results inform management of gloomy scale in cities.
Urban trees serve a critical conservation function by supporting arthropod and vertebrate communities but are often subject to arthropod pest infestations. Native trees are thought to support richer arthropod communities than exotic trees but may also be more susceptible to herbivorous pests. Exotic trees may be less susceptible to herbivores but provide less conservation value as a consequence. We tested the hypotheses that native species in Acer and Quercus would have more herbivorous pests than exotic congeners and different communities of arthropod natural enemies. The density of scale insects, common urban tree pests, was greatest on a native Acer and a native Quercus than exotic congeners in both years of our research (2012 and 2016) and sometimes reached damaging levels. However, differences in predator and parasitoid abundance, diversity, and communities were not consistent between native and exotic species in either genus and were generally similar. For example, in 2012 neither predator nor parasitoid abundance differed among native and exotic Acer congeners but in 2016 a native species, A. saccharum , had the least of both groups. A native, Q. phellos , had significantly more predators and parasitoids in 2012 than its native and exotic congeners but no differences in 2016. Parasitoid communities were significantly different among Acer species and Quercus species due in each case to greater abundance of a single family on one native tree species. These native and exotic tree species could help conserve arthropod natural enemies and achieve pest management goals.
Urbanization represents an unintentional global experiment that can provide insights into how species will respond and interact under future global change scenarios. Cities produce many conditions that are predicted to occur widely in the future, such as warmer temperatures, higher carbon dioxide (CO2) concentrations and exacerbated droughts. In using cities as surrogates for global change, it is challenging to disentangle climate variables-such as temperature-from co-occurring or confounding urban variables-such as impervious surface-and then to understand the interactive effects of multiple climate variables on both individual species and species interactions. However, such interactions are also difficult to replicate experimentally, and thus the challenges of cities are also their unique advantage. Here, we review insights gained from cities, with a focus on plants and arthropods, and how urban findings agree or disagree with experimental predictions and historical data. We discuss the types of hypotheses that can be best tested in cities, caveats to urban research and how to further validate cities as surrogates for global change. Lastly, we summarize how to achieve the goal of using urban species responses to predict broader regional- and ecosystem-level patterns in the future.
The increase of minimally managed vacant land resulting from population loss and the subsequent removal of infrastructure is a reoccurring feature in shrinking cities around the globe. Due to the low frequency and intensity of management, these spaces create a unique environment for plant colonization, establishment, and succession. Herein we refer to these plants and the habitats they form as urban spontaneous vegetation (USV). As a form of urban green space, USV has the potential to provide a number of ecological and sociological benefits to shrinking cities, such as supporting urban wildlife, enhancing the provision of regulating ecosystem functions and services, connecting residents with nature, and improving human health and well-being. Conversely, USV can also support undesirable animals such as vectors of disease, and due to its wild and disorderly appearance, can evoke negative emotions in residents while signaling community neglect. This review aims to explore the potential ecological and sociological tradeoffs of USV within the context of shrinking cities. Through this evaluation, we aim to inform future planning and management to exploit the benefits offered by this resource while minimizing negative outcomes, thereby leading to the enhanced sustainability of shrinking cities worldwide.
Plant post-drought recovery performance is essential to predict shifts in ecosystem dynamics and production during frequent climate change-driven drought events. Yet, it is not clear how post-drought recovery is related to evolutionary and geographic variations in plants. In this study, we generated a global data set of post-drought recovery performance in 140 plant species from published studies. We quantified the plant post-drought recovery performance by calculating a recovery index for multiple plant physiological and hydraulic parameters, including leaf water potential, net photosynthetic rate, leaf hydraulic conductance and shoot biomass. The magnitude of recovery among four plant functional types (deciduous angiosperms, evergreen angiosperms, gymnosperms, and crops), two plant growth forms (shrubs and trees), two water management strategies (isohydric and anisohydric), four xylem porosity types (diffuse, ring, semi-ring and tracheid), and four major biomes (dry sclerophyll forest, boreal forest, temperate forest and tropical/subtropical forest) were compared. We found the inability to completely recover immediately after severe water stress is ubiquitous across all plant functional types and growth forms, while the rate and magnitude of post-drought recovery varied greatly across different plant taxonomic categories and geographic ranges. In general, plant hydraulic architecture, leaf anatomy and physiology affect plants’ propensity towards recovery, and reflect evolutionary consequences of plant adaptation to their habitat. Due to the essential role of plant functional traits in regulating carbon storage in each biome, a better understanding plant post-drought recovery performance could improve our predictions on ecosystem productivity in a rapidly changing climate.
Urban habitats are characterized by impervious surfaces, which increase temperatures and reduce water availability to plants. The effects of these conditions on herbivorous insects are not well understood, but may provide insight into future conditions. Three primary hypotheses have been proposed to explain why multiple herbivorous arthropods are more abundant and damaging in cities, and support has been found for each. First, less complex vegetation may reduce biological control of pests. Second, plant stress can increase plant quality for pests. And third, urban warming can directly increase pest fitness and abundance. These hypotheses are not mutually exclusive, and the effects of temperature and plant stress are particularly related. Thus, we test the hypothesis that urban warming and drought stress combine to increase the fitness and abundance of the scale insect, Melanaspis tenebricosa, an urban tree pest that is more abundant in urban than rural areas of the southeastern U.S. We did this by manipulating drought stress across an existing mosaic of urban warming. We found support for the additive effect of temperature and drought stress such that female embryo production and body size increased with temperature and was greater on drought-stressed than watered trees. This study provides further evidence that drivers of pest insect outbreaks act in concert, rather than independently, and calls for more research that manipulates multiple abiotic factors related to urbanization and climate change to predict their effects on ecological interactions. As cities expand and the climate changes, warmer temperatures and drought conditions may become more widespread in the native range of this pest. These changes have direct physiological benefits for M. tenebricosa, and potentially other pests, that may increase their fitness and abundance in urban and natural forests.
A substantial amount of global carbon is stored in mature trees. However, no experiments to date test how warming affects mature tree carbon storage. Using a unique, citywide, factorial experiment, we investigated how warming and insect herbivory affected physiological function and carbon sequestration (carbon stored per year) of mature trees. Urban warming increased herbivorous arthropod abundance on trees, but these herbivores had negligible effects on tree carbon sequestration. Instead, urban warming was associated with an estimated 12% loss of carbon sequestration, in part because photosynthesis was reduced at hotter sites. Ecosystem service assessments that do not consider urban conditions may overestimate urban tree carbon storage. Because urban and global warming are becoming more intense, our results suggest that urban trees will sequester even less carbon in the future. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
In light of catastrophic tree losses caused by Dutch elm disease, foresters recommended that the urban forest be diversified. The intent was to create a more sustainable urban forest that would not be decimated by a single pathogen or insect pest. However, recent introductions of deadly borers such as Asian longhorned beetle and emerald ash borer reveal that new introductions can have disastrous consequences for urban forests. An analysis of tree inventories from 12 cities in eastern North America reveals an overabundance of certain genera of trees such as Acer and Fraxinus. Introduced pests with broad host ranges such as the Asian longhorned beetle may be capable of killing or forcing intervention on large numbers of trees. Even cities that have diversified at a low taxonomic level (cultivar or species) may suffer greatly from the depredations of insect pests such as the emerald ash borer that specialize on plants at the generic level. Generalists capable of feeding on plants in several families will create problems for urban forests even when attempts have been made to diversify at higher taxonomic levels. Urban foresters should avoid planting susceptible taxa of trees, especially in cities that are overstocked in these taxa, and consider diversifying greatly the types of trees in cities.
Understanding the value of an urban forest can give decision makers a better foundation for urban tree management. Based on tree-valuation methods of the Council of Tree and Landscape Appraisers and field data from eight cities, total compensatory value of tree populations in U.S. cities ranges from $101 million in Jersey City, New Jersey, to $5.2 billion in New York, New York. Compensatory values represent compensation to owners for the loss of an individual tree and can be viewed as the value of the tree as a structural asset. Based on national urban forest tree cover data, the total compensatory value for the urban forests of the 48 adjacent United States is estimated at $2.4 trillion.
We monitored crown air temperature, volumetric soil moisture, leaf water potential, rates of gas exchange, and insect pests of green ash (Fraxinus pennsylvanica 'Marshall's Seedless'), Austrian pine (Pinus nigra Arnold), and northern red oak (Quercus rubra L.) trees during a relatively hot summer in Lincoln, Nebraska, U.S. Air temperatures and vapor pressure deficits (VPD) were much higher in trees growing downtown than in nearby trees growing on the University of Nebraska campus. Increased VPDs and reduced soil moisture decreased pre-dawn water potential and gas exchange of ash and oak trees on the downtown site compared to trees on campus. Green ash trees downtown had more damage from lilac borers (Podosesia syringae (Harris) (Sesiidae)) than did trees on campus. Aphids (Aphidiae) and lace bugs (Tingidae Corythucha arcuata (Say)) appeared to be more numerous on oak trees growing downtown than on those growing on campus. Cultural treatments that improve soil moisture availability, such as irrigating, increasing planter size, and mulching, are especially critical on heat island sites and may reduce tree stress, pest damage, and mortality.
Cerambycid beetles are abundant and diverse in forests, but much about their host relationships and adult behavior remains unknown. Generic blends of synthetic pheromones were used as lures in traps, to assess the species richness, and phenology of cerambycids in forest fragments in northern Delaware. More than 15,000 cerambycid beetles of 69 species were trapped over 2 yr. Activity periods were similar to those found in previous studies, but many species were active 1-3 wk earlier in 2012 than in 2013, probably owing to warmer spring temperatures that year. In 2012, the blends were tested with and without ethanol, a host plant volatile produced by stressed trees. Of cerambycid species trapped in sufficient numbers for statistical analysis, ethanol synergized pheromone trap catches for seven species, but had no effect on attraction to pheromone for six species. One species was attracted only by ethanol. The generic pheromone blend, especially when combined with ethanol, was an effective tool for assessing the species richness and adult phenology of many cerambycid species, including nocturnal, crepuscular, and cryptic species that are otherwise difficult to find.
Climate warming is predicted to cause many changes in ectotherm communities, one of which is phenological mismatch, wherein one species' development advances relative to an associated species or community. Phenological mismatches already lead to loss of pollination services, and we predict that they also cause loss of biological control. Here, we provide evidence that a pest develops earlier due to urban warming but that phenology of its parasitoid community does not similarly advance. This mismatch is associated with greater egg production that likely leads to more pests on trees.
© 2014 The Author(s) Published by the Royal Society. All rights reserved.
Trees are essential to urban habitats because they provide services that benefit the environment and improve human health. Unfortunately, urban trees often have more herbivorous insect pests than rural trees but the mechanisms and consequences of these infestations are not well documented. Here, we examine how temperature affects the abundance of a scale insect, Melanaspis tenebricosa (Comstock) (Hemiptera: Diaspididae), on one of the most commonly planted street trees in the eastern U.S. Next, we examine how both pest abundance and temperature are associated with water stress, growth, and condition of 26 urban street trees. Although trees in the warmest urban sites grew the most, they were more water stressed and in worse condition than trees in cooler sites. Our analyses indicate that visible declines in tree condition were best explained by scale-insect infestation rather than temperature. To test the broader relevance of these results, we extend our analysis to a database of more than 2700 Raleigh, US street trees. Plotting these trees on a Landsat thermal image of Raleigh, we found that warmer sites had over 70% more trees in poor condition than those in cooler sites. Our results support previous studies linking warmer urban habitats to greater pest abundance and extend this association to show its effect on street tree condition. Our results suggest that street tree condition and ecosystem services may decline as urban expansion and global warming exacerbate the urban heat island effect. Although our non-probability sampling method limits our scope of inference, our results present a gloomy outlook for urban forests and emphasize the need for management tools. Existing urban tree inventories and thermal maps could be used to identify species that would be most suitable for urban conditions.
Honeylocust (Gleditsia twaanthos L. var. inemnis) trees in urban areas are attacked principally by three insect pests: honeylocust plant bug, nirmosa web-wormn, and honeylocust spider mite. One hundred honeylocust trees on the Purdue University campus were studied to better understand the influence of landscape characteristics on the populations of these insect pests. Specifically, the amount of hardscape, defined as impervi-ousness under and around trees, including roads, side-walks, parking lots, and buildings; density of honeylocust; and diversity of tree species around each tree were calcu-lated at nurnerous spatial scales and correlated with insect pest abundance on honeylocust. Each of these landscape factors influenced insect pest and their natural enemy populations on honeylocust trees at a wide range of scales. No single combination of these factors was associated with lower densities of honeylocust pests. Key Words. Honeylocust; Gleditsia triacanthos L. var. inenmis; hardscape; honeylocust plant bug; mimosa web-worm; honeylocust spider mite; urban tree planting; tree species diversity; geographic information systems (GIS). Increased insect and disease problems on honeylocust (Gleditsia triacanthos L. var. inermis) in urban areas are a product of the liberal planting of this species in the past decades (Wheeler and Henry 1976). The popularity of honeylocust is due to its adaptability to urban sites, attractive ap-pearance, rapid growth, and the aftermath of the Dutch elm disease epidemic that forced urban foresters to seek trees other than American elm for planting. Three insect and mite pests com-monly encountered on honeylocust are mimosa webworm (ffomaduala anisocentra), honeylocust plant bug (Diaphnocoris chlotionis), and honeylocust
The mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins), a major pine forest pest native to western North America, has extended its range north and eastward during an ongoing outbreak. Determining how the MPB has expanded its range to breach putative barriers, whether physical (nonforested prairie and high elevation of the Rocky Mountains) or climatic (extreme continental climate where temperatures can be below -40 °C), may contribute to our general understanding of range changes as well as management of the current epidemic. Here, we use a panel of 1,536 single nucleotide polymorphisms (SNPs) to assess population genetic structure, connectivity, and signals of selection within this MPB range expansion. Biallelic SNPs in MPB from southwestern Canada revealed higher genetic differentiation and lower genetic connectivity than in the northern part of its range. A total of 208 unique SNPs were identified using different outlier detection tests, of which 32 returned annotations for products with putative functions in cholesterol synthesis, actin filament contraction, and membrane transport. We suggest that MPB has been able to spread beyond its previous range by adjusting its cellular and metabolic functions, with genome scale differentiation enabling populations to better withstand cooler climates and facilitate longer dispersal distances. Our study is the first to assess landscape-wide selective adaptation in an insect. We have shown that interrogation of genomic resources can identify shifts in genetic diversity and putative adaptive signals in this forest pest species.
Global change has a large and growing influence on forests, particularly in urban and urbanizing areas. Compared to rural forests, urban forests may experience warmer temperatures, higher CO2 levels, and greater nitrogen deposition, with exacerbated differences at urban forest edges. Thus, comparing urban to rural forests may help predict future effects of global change on forests. We focused on the conifer western red-cedar (Thuja plicata) to test three hypotheses: at urban forest edges, relative to rural forests and urban forest centers, trees experience 1) higher temperatures and nitrogen levels, 2) lower seedling recruitment, and 3) greater growth. We additionally tested anecdotal reports that 4) tree seedling recruitment in urban and rural forests is much lower than in “pristine” old-growth forests. To test these hypotheses, we quantified air temperature, soil nitrate, adult T. plicata growth and seedling recruitment in five urban and three rural parks at both forest edges and centers. We also quantified T. plicata recruitment at five old-growth “pristine” sites. Temperatures were highest at urban forest edges, and soil nitrate was highest in urban forests. In urban relative to rural forests, we observed greater T. plicata growth, but no difference in seedling densities. However, seedling densities were lower in urban and rural forests than in old-growth forests. In all, our results suggest urban influences enhance adult T. plicata growth, but not seedling recruitment. Recruitment in urban and rural forests was reduced compared to old-growth forests, implying that fragmentation and logging reduce T. plicata seedling recruitment.
Favored for their rapid growth and brilliant fall color, maple (Acer spp.) trees are among the most commonly grown deciduous shade trees in urban landscapes and commercial production nurseries. Many maple species used as ornamental plants share a suite of important arthropod pests that have the potential to reduce the trees' economic and esthetic value. We review the biology, damage, and management for the most important pests of maples with emphasis on integrated pest management (IPM) tactics available for each pest. Unfortunately, the biology of some of these pests is not well studied. This knowledge gap, paired with the low esthetic threshold for damage on ornamental plants, has hindered development of IPM tactics for maple pests in nurseries and landscapes. Maples will likely remain a common landscape plant. Therefore, our challenge is to improve IPM of the diverse maple pest complex.
The paper demonstrates the relationship existing between the size of a village, town or city (as measured by its population), and the magnitude of the urban heat island it produces. This is accomplished by analyzing data gathered by automobile traverses in 10 settlements on the St. Lawrence Lowland, whose populations range from 1000 to 2 million inhabitants. The locations of these settlements effectively eliminate all non-urban climatic influences. The results are compared with previously published data.The analysis shows the heat island intensity under cloudless skies to be related to the inverse of the regional windspeed, and the logarithm of the population. A simple model is derived which incorporates these controls. In agreement with an extension of Summers' model the heat island appears to be approximately proportional to the fourth root of the population. With calm and clear conditions the relation is shown to hold remarkably well for North American settlements, and in a slightly modified form, for European towns and cities.
Urban trees occupy a wide variety of habitats, from a single specimen competing in the urban jungle to extensive remnant or planted forest stands. Each is shown to produce distinct micro- to local scale climates contributing to the larger urban climate mosaic. These effects are discussed in relation to the radiative, aerodynamic, thermal and moisture properties of trees that so clearly set them apart from other urban materials and surfaces in terms of their exchanges of heat, mass and momentum with the atmosphere. Their resulting ability to produce shade, coolness, shelter, moisture and air filtration makes them flexible tools for environmental design.
The statistical distributions of the counts of organisms are generally skewed, and hence not normally distributed, nor are variances constant across treatments. We present a likelihood-ratio testing framework based on the negative binomial distribution that tests for the goodness of fit of this distribution to the observed counts, and then tests for differences in the mean and/or aggregation of the counts among treatments. Inferences about differences in means among treatments as well as the dispersion of the counts are possible. Simulations demonstrated that the statistical power of ANOVA is about the same as the likelihood-ratio testing procedure for testing equality of means, but our proposed testing procedure also provides information on dispersion. Type I error rates of Poisson regression exceeded the expected 5%, even when corrected for overdispersion. Count data on Orange-crowned Warblers (Vermivora celata) are used to demonstrate the procedure.
Hydraulic failure is one of the main causes of tree mortality in conditions of severe drought. Resistance to cavitation is known to be strongly related to drought tolerance and species survival in conifers, but the threshold of water-stress-induced embolism leading to catastrophic xylem dysfunction in angiosperms has been little studied. We investigated the link between drought tolerance, survival and xylem cavitation resistance in five angiosperm tree species known to have contrasting desiccation resistance thresholds. We exposed seedlings in a greenhouse to severe drought to generate extreme water stress. We monitored leaf water potential, total plant water loss rate, leaf transpiration, stomatal conductance and CO2 assimilation rate during drought exposure and after rewatering (recovery phase). The time required for the recovery of 50% of the maximum value of a given ecophysiological variable after rewatering was used to determine the critical water potential corresponding to the threshold beyond which the plant failed to recover. We also investigated the relationship between this potential and stem xylem cavitation resistance, as assessed from vulnerability curves. This minimum recoverable water potential was consistent between ecophysiological variables and varied considerably between species, from -3.4 to -6.0 MPa. This minimum recoverable water potential was strongly correlated with P50 and P88, the pressures inducing 50 and 88% losses of stem hydraulic conductance, respectively. Moreover, the embolism threshold leading to irreversible drought damage was found to be close to 88%, rather than the 50% previously reported for conifers. Hydraulic failure leading to irreversible drought-induced global dysfunction in angiosperm tree species occurred at a very high level of xylem embolism, possibly reflecting the physiological characteristics of their stem water-transport system.
Cities profoundly alter biological communities, favoring some species over others, though the mechanisms that govern these changes are largely unknown. Herbivorous arthropod pests are often more abundant in urban than in rural areas, and urban outbreaks have been attributed to reduced control by predators and parasitoids and to increased susceptibility of stressed urban plants. These hypotheses, however, leave many outbreaks unexplained and fail to predict variation in pest abundance within cities. Here we show that the abundance of a common insect pest is positively related to temperature even when controlling for other habitat characteristics. The scale insect Parthenolecanium quercifex was 13 times more abundant on willow oak trees in the hottest parts of Raleigh, NC, in the southeastern United States, than in cooler areas, though parasitism rates were similar. We further separated the effects of heat from those of natural enemies and plant quality in a greenhouse reciprocal transplant experiment. P. quercifex collected from hot urban trees became more abundant in hot greenhouses than in cool greenhouses, whereas the abundance of P. quercifex collected from cooler urban trees remained low in hot and cool greenhouses. Parthenolecanium quercifex living in urban hot spots succeed with warming, and they do so because some demes have either acclimatized or adapted to high temperatures. Our results provide the first evidence that heat can be a key driver of insect pest outbreaks on urban trees. Since urban warming is similar in magnitude to global warming predicted in the next 50 years, pest abundance on city trees may foreshadow widespread outbreaks as natural forests also grow warmer.
Contrasts mixed species plantings (polycultures) with bare-ground sole-crop fields (monocultures), the former being characterised by the simultaneous occurrence of herbivory with both inter- and intraspecific plant competition, and where plants are interspersed at spatial scales similar to the shorter movement scales of the arthropod herbivores and their natural enemies. The review examines whether generalities can be drawn from the arthropod response to polyculture, or whether these responses are idiosyncratic, depending on the particular combination of plants and arthropods. The diversity-stability hypothesis (the greater the biological diversity of a community the greater its stability) is evaluated. Herbivore response to polycultures might be expected to be determined by natural enemies: generalist and specialist natural enemies are more abundant in polycultures and therefore suppress herbivore populations to a greater extent. The resource concentration hypothesis argues that many herbivores, especially those with a narrow host range, are more likely to find and remain on host plants that are concentrated. Plants experience associational resistance, and arthropods can respond to plant-stand characteristics (resource concentration) or plant life history characteristics (plant apparency). Mechanisms underlying resource concentration are discussed. -P.J.Jarvis
Urban areas in the conterminous United State doubled in size between 1969 and 1994, and currently cover 3.5 percent of the total land area and contain more than 75 percent of the US population. Urban areas contain approximately 3.8 billion trees with an average tree canopy cover of 27 percent. The extent and variation of urban forests across the 48 states are explored to help build a better understanding of this significant national resource. Urbanization and urban forests are likely to be a significant focus of forestry in the 21st century.
Pine needle scale, Chionaspis pinifoliae (Fitch), is a pest of many species of conifers in urban habitats and Christmas tree farms. We found that the scale was abundant in impoverished habitats, such as ornamental landscapes, and scarce in more natural, park-like habitats. Rates of parasitism were highest in impoverished habitats, suggesting that parasitoids were not effective in suppressing scale populations. Generalist predators, however, were more diverse and abundant in natural habitats and appear to be more effective in controlling scales in structurally complex plant communities. Total densities of arthropods and densities of plant-feeding species were greatest in impoverished habitats, suggesting that populations were poorly regulated. Outbreaks of pine needle scale in ornamental landscapes and Christmas tree farms may be discouraged by increasing plant structural and species diversity to favor natural enemies.
There is now a solid body of theoretical work(1-4) demonstrating that the spatial structure of the habitat combined with animal movement strongly influence host-parasitoid dynamics. The spatial pattern over which parasitoid search takes place can be affected by the distribution of the hosts(5), by the spatial arrangement of the host's habitat(6) and by the spatial scale at which the parasitoid perceives variation in host abundance(7,8). Empirical work, however, has been largely restricted to small-scale field studies of less than one hectare(6,9) with very few larger(10,11). Here we report initial results of a many-year, large-scale study that is among the first to examine the interaction between a population-level process (parasitism) and anthropogenic forest fragmentation at large and at multiple spatial scales. We demonstrate that parasitism by four species of parasitoids attacking the forest tent caterpillar, Malacosoma disstria, is significantly reduced or enhanced depending on the proportion of forested to unforested land. Each of the parasitoid species responds to this mosaic at four different spatial scales that correspond to their relative body sizes, Our data give empirical support to the argument that changes in landscape structure can alter the normal functioning of ecological processes such as parasitism, with large-scale population consequences(3'4).
Environmental stresses, particularly water deficit, predispose eucalypt trees to attack by the eucalyptus longhorned borer,
Phoracantha semipunctata F. (Coleoptera: Cerambycidae). Our experiments with potted eucalypts revealed that reduced tree water potential was associated
with lower resistance to colonization by neonate P. semipunctata, but the linear relationship between water potential and colonization success was reversed at higher larval densities. There
was no indication that the bark exudate “kino” served to defend trees from borer attack. Larvae were not able to colonize
the cambium of eucalypt logs with high bark moisture, and survival was low under high moisture conditions in artificial hosts
composed of pure cellulose. In trees and cut logs with moist bark, larvae failed to reach the cambium, feeding instead in
poorer-quality tissues just beneath the bark surface. Our findings suggest that variation in resistance of eucalypts to attack
by the borer is associated with moisture content of the bark.
Understanding the value of an urban forest can give decision makers a better foundation for urban tree management. Based on tree-valuation methods of the Council of Tree and Landscape Appraisers and field data from eight cities, total compensatory value of tree populations in U.S. cities ranges from $101 million in Jersey City, New Jersey, to $5.2 billion in New York, New York. Compensatory values represent compensation to owners for the loss of an individual tree and can be viewed as the value of the tree as a structural asset. Based on national urban forest tree cover data, the total compensatory value for the urban forests of the 48 adjacent United States is estimated at $2.4 trillion.
Impervious surfaces are a ubiquitous urban feature that increase temperature and tree drought stress and are a demonstrated indicator of Acer rubrum L. tree condition and insect pest abundance. We examined the relationship between A. rubrum condition, impervious surface cover, and Melanaspis tenebricosa (Comstock) abundance, a primary herbivore of urban A. rubrum, in eight cities across the southern distribution of A. rubrum. We predicted that the effects of warming, due to impervious surface, would be greater in warmer southern cities than in cooler northern cities. We found that impervious surface was a robust predictor of tree condition, but this effect was not significantly affected by background temperature. Melanaspis tenebricosa abundance was a function of impervious surface and background temperature, with greatest abundances occurring at mid latitudes. Based on these relationships, we developed impervious surface thresholds to inform site selection for A. rubrum throughout the southeastern USA. Planting criteria based on habitat characteristics should maximize urban tree longevity and services provided.
Biological effects of climate change are expected to vary geographically, with a strong signature of latitude. For ectothermic animals, there is systematic latitudinal variation in the relationship between climate and thermal performance curves, which describe the relationship between temperature and an organism's fitness. Here we ask whether these documented latitudinal patterns can be generalized to predict arthropod responses to warming across mid and high temperate latitudes, for taxa whose thermal physiology has not been measured. To address this question, we used a novel natural experiment consisting of a series of urban warming gradients at different latitudes. Specifically, we sampled arthropods from a single common street tree species across temperature gradients in 4 US cities, located from 35.8 to 42.4° latitude. We captured 6746 arthropods in 34 families from 111 sites that varied in summer average temperature by 1.7 to 3.4 °C within each city. Arthropod responses to warming within each city were characterized as Poisson regression coefficients describing change in abundance per °C for each family. Family responses in the two mid latitude cities were heterogeneous, including significantly negative and positive effects, while those in high latitude cities varied no more than expected by chance within each city. We expected high-latitude taxa to increase in abundance with warming, and they did so in 1 of the 2 high latitude cities; in the other, Queens (New York City), most taxa declined with warming, perhaps due to habitat loss that was correlated with warming in this city. With the exception of Queens, patterns of family responses to warming were consistent with predictions based on known latitudinal patterns in arthropod physiology relative to regional climate. Heterogeneous responses in mid latitudes may be ecologically disruptive if interacting taxa respond oppositely to warming. This article is protected by copyright. All rights reserved.
Accelerated urbanization continues to convert natural lands to impervious surfaces, resulting in serious impacts to the environment, and affecting the growth of urban plants. In this study, we evaluated eight environmental factors, and nine eco-physiological characteristics of Ginkgo biloba planted on two types of impervious surface (totally impervious surface and partly impervious surface), and one non-impervious surface (grass land). Results showed that the primary effect of the impervious surfaces on the environment were increasing air temperature (Ta) and soil temperature (Ts), and decreasing relative humidity of air (RH) and soil moisture content (SMC). G. biloba net photosynthetic rate (Pn) on totally impervious surfaces (TIS), and partly impervious surfaces (PIS) was 39% and 22% lower than trees on an urban grass land (GL). Tr and Gs also showed similar reductions. Compared to GL, FV/Fm on TIS and PIS decreased 7% and 6%, respectively, and ΦPSII decreased 32% and 41%, respectively. Water use efficiency (WUE), light use efficiency (LUE), and CO2 use efficiency (CUE) of G. biloba growing on impervious surfaces were 20–40% less than those on the grass land. Redundancy analysis (RDA) indicated the combination of environmental factors explained 66% of the variation of G. biloba eco-physiological responses. This study revealed the eco-physiological responses and variation of G. biloba to different substrates. Results indicated it is vital to improve plant environmental quality, and enhance urban green ecological services. Our study provides a scientific reference for urban greening, and ecological land construction.
Projected climate warming will potentially have profound effects on the earth's biota, including a large redistribution of tree species. We developed models to evaluate potential shifts for 80 individual tree species in the eastern United States. First, environmental factors associated with current ranges of tree species were assessed using geographic information systems (GIS) in conjunction with regression tree analysis (RTA). The method was then extended to better understand the potential of species to survive and/or migrate under a changed climate. We collected, summarized, and analyzed data for climate, soils, land use, elevation, and species assemblages for >2100 counties east of the 100th meridian. Forest Inventory Analysis (FIA) data for >100 000 forested plots in the East provided the tree species range and abundance information for the trees. RTA was used to devise prediction rules from current species-environment relationships, which were then used to replicate the current distribution as well as predict the future potential distributions under two scenarios of climate change with twofold increases in the level of atmospheric CO2. Validation measures prove the utility of the RTA modeling approach for mapping current tree importance values across large areas, leading to increased confidence in the predictions of potential future species distributions. With our analysis of potential effects, we show that roughly 30 species could expand their range and/or weighted importance at least 10%, while an additional 30 species could decrease by at least 10%, following equilibrium after a changed climate. Depending on the global change scenario used, 4-9 species would potentially move out of the United States to the north. Nearly half of the species assessed (36 out of 80) showed the potential for the ecological optima to shift at least 100 km to the north, including seven that could move >250 km. Given these potential future distributions, actual species redistributions will be controlled by migration rates possible through fragmented landscapes.
(1) Grass-sown raised earth banks were created as `islands' in the centres of two cereal fields to provide improved overwintering conditions for invertebrate predators. They recreated those aspects of existing field boundaries which had previously been shown to favour predator overwintering. (2) During the first year of establishment, the new habitats provided overwintering refuge sites for many species of Araneae, Carabidae and Staphylinidae. Ground-zone searches produced total polyphagous predator densities of up to 150 m-2. (3) During the second year, grass establishment increased still further and destructive sampling revealed predator numbers exceeding 1500 m-2 in some grass treatments. (4) Vacuum-net samples taken during the second spring after establishment, showed that the overwintering populations of two predator species in the new habitats influenced dispersal patterns into the crop. (5) Prospects for the long-term enhancement of predator populations via field scale manipulations of farmland habitats are discussed.
Trees in urban areas increase the liveability of towns and cities but street tree growth can be constrained by the limited soil volume available for root growth and by reduced water and nutrient availability under impervious urban surfaces. An approach to improve the growth and health of street trees is the installation of permeable pavements. This study assessed whether permeable pavements with varying depths (0, 100 or 300 mm) of an underlying base layer affected soil moisture, soil temperature, tree growth and leaf nutrient status when broad-leaf paperbark (Melaleuca quinquenervia) trees were planted in two soil types, sand and clay.
Street trees are an integral element of urban life. They provide a vast range of benefits in residential and commercial precincts, and they support healthy communities by providing environmental, economic and social benefits. However, increasing areas of impermeable surface can increase the stresses placed upon urban ecosystems and urban forests. These stresses often lead tree roots to proliferate in sites that provide more-favourable conditions for growth, but where they cause infrastructure damage and pavement uplift. This damage is costly and a variety of preventative measures has been tested to sustain tree health and reduce pavement damage. This review explores a wide range of literature spanning 30 years that demonstrates the benefits provided by street trees, the perceptions of street trees conveyed by urban residents, the costs of pavement damage by tree roots, and some tried and tested measures for preventing pavement damage and improving tree growth.
Urban trees help towns to cope with climate warming by cooling both air and surfaces. The challenges imposed by the urban environment, with special reference to low water availability due to the presence of extensive pavements, result in high rates of mortality of street trees, that can be increased by climatic extremes.
We investigated the water relations and xylem hydraulic safety/efficiency of Quercus ilex trees growing at urban sites with different percentages of surrounding impervious pavements. Seasonal changes of plant water potential and gas exchange, vulnerability to cavitation and embolism level, and morpho‐anatomical traits were measured.
We found patterns of increasing water stress and vulnerability to drought at increasing percentages of impervious pavement cover, with a consequent reduction in gas exchange rates, decreased safety margins toward embolism development, and increased vulnerability to cavitation, suggesting the occurrence of stress‐induced hydraulic deterioration.
The amount of impermeable surface and chronic exposure to water stress influence the site‐specific risk of drought‐induced dieback of urban trees under extreme drought. Besides providing directions for management of green spaces in towns, our data suggest that xylem hydraulics is key to a full understanding of the responses of urban trees to global change.
Trees provide ecosystem services that counter negative effects of urban habitats on human and environmental health. Unfortunately, herbivorous arthropod pests are often more abundant on urban than rural trees, reducing tree growth, survival, and ecosystem services. Previous research where vegetation complexity was reduced has attributed elevated urban pest abundance to decreased regulation by natural enemies. However, reducing vegetation complexity, particularly the density of overstory trees, also makes cities hotter than natural habitats. We ask how urban habitat characteristics influence an abiotic factor, temperature, and a biotic factor, natural enemy abundance, in regulating the abundance of an urban forest pest, the gloomy scale, (Melanaspis tenebricosa). We used a map of surface temperature to select red maple trees (Acer rubrum) at warmer and cooler sites in Raleigh, North Carolina, USA. We quantified habitat complexity by measuring impervious surface cover, local vegetation structural complexity, and landscape scale vegetation cover around each tree. Using path analysis, we determined that impervious surface (the most important habitat variable) increased scale insect abundance by increasing tree canopy temperature, rather than by reducing natural enemy abundance or percent parasitism. As a mechanism for this response, we found that increasing temperature significantly increases scale insect fecundity and contributes to greater population increase. Specifically, adult female M. tenebricosa egg sets increased by approximately 14 eggs for every 1°C increase in temperature. Climate change models predict that the global climate will increase by 2–3°C in the next 50–100 years, which we found would increase scale insect abundance by three orders of magnitude. This result supports predictions that urban and natural forests will face greater herbivory in the future, and suggests that a primary cause could be direct, positive effects of warming on herbivore fitness rather than altered trophic interactions.
Cities experience elevated temperature, CO 2 , and nitrogen deposition decades ahead of the global average, such that biological response to urbanization may predict response to future climate change. This hypothesis remains untested due to a lack of complementary urban and long-term observations. Here, we examine the response of an herbivore, the scale insect Melanaspis tenebricosa, to temperature in the context of an urban heat island, a series of historical temperature fluctuations, and recent climate warming. We survey M. tenebricosa on 55 urban street trees in Raleigh, NC, 342 herbarium specimens collected in the rural southeastern United States from 1895 to 2011, and at 20 rural forest sites represented by both modern (2013) and historical samples. We relate scale insect abundance to August temperatures and find that M. tenebricosa is most common in the hottest parts of the city, on historical specimens collected during warm time periods, and in present-day rural forests compared to the same sites when they were cooler. Scale insects reached their highest densities in the city, but abundance peaked at similar temper-atures in urban and historical datasets and tracked temperature on a decadal scale. Although urban habitats are highly modified, species response to a key abiotic factor, temperature, was consistent across urban and rural-forest ecosystems. Cities may be an appropriate but underused system for developing and testing hypotheses about biological effects of climate change. Future work should test the applicability of this model to other groups of organisms.
Greening is a useful mitigation strategy for planners mainly from a visual perspective. For high-density urban living environment such as Hong Kong, urban greening helps cooling the air and providing shade; it also helps lowering building energy consumption by providing a better outdoor boundary condition. Many researchers have also suggested that greening may be employed as a strategy for combating the ill effects of urban Heat Island (UHI). Working towards a set of better greening guidelines for urban planners, the current paper first provides a comprehensive review of planning with urban greening. It then describes parametric studies that have been conducted to investigate the preferred location, amount, and types of vegetation for urban planning. The parametric studies employed the numerical model ENVI-met, verified using field measurements, to simulate 33 cases with different combinations of factors. For benefiting urban activities, ambient air temperatures at the pedestrian level are compared among different greening strategies and building heights. For a city such as Hong Kong, which has a high building-height-to-street-width (H/W) ratio, the present study reveals that roof greening is ineffective for human thermal comfort near the ground. Trees are also suggested to be more effective than grass surfaces in cooling pedestrian areas. The amount of tree planting needed to lower pedestrians level air temperature by around 1 °C is approximately 33% of the urban area. The present study allows urban planners to identify more precisely the greening principles, amount and policies necessary for better urban living environment in high-density cities.
In urban settings, Pseudaulacaspis pentagona infests mulberry Morus spp. trees in disturbed landscape habitats (roadsides, parking lots) but not trees in forested habitats (woodlots). Populations of P. pentagona are contagiously distributed. The patchy distribution of P. pentagona in Maryland is best explained by the combined influences of natural enemies and plant water relations. P. pentagona infests a small subset of mulberry trees in the urban landscape that are without water deficits and free of generalist invertebrate predators. -from Authors
Mimosa webworm, Homadaula anisocentra Meyrick (Lepidoptera: Plutellidae) exhibits dramatic fluctuations in population levels on ornamental honeylocust, Gleditsia triacanthos L, in northern urban settings. Winter temperatures and tree location were evaluated for their effects on overwintering pupal survivorship and defoliation. Extremely cold winters caused high pupal mortality and were followed by low first-generation defoliation; an extremely mild winter caused low pupal mortality and was followed by very high first-generation defoliation. Pupal overwintering sites on heated structures were 5 to 9°C (3 to 5°C) above the ambient low temperatures, decreasing the probability of pupal exposure to lethal temperatures. Second-generation larvae moved 50 to 80 ft. (ca. 25 m) from infested trees to overwintering sites.
In urban communities, arboriculture clearly contributes to the health of the biological ecosystem; does it contribute to the health of the social ecosystem as well? Evidence from studies in inner-city Chicago suggests so. In a series of studies involving over 1,300 person-space obser- vations, 400 interviews, housing authority records, and 2 years of police crime reports, tree and grass cover were systematically linked to a wide range of social ecosystem indicators. These indicators included stronger ties among neighbors, greater sense of safety and adjustment, more supervision of children in outdoor spaces, healthier patterns of children's play, more use of neighborhood common spaces, fewer incivilities, fewer property crimes, and fewer violent crimes. The link between arboriculture and a healthier social ecosystem turns out to be surprisingly simple to explain. In residential areas, barren, treeless spaces often become "no man's lands," which discourage resident interaction and invite crime. The presence of trees and well-maintained grass can transform these no man's lands into pleasant, welcoming, well-used spaces. Vital, well- used neighborhood common spaces serve to both strengthen ties among residents and deter crime, thereby creating healthier, safer neighborhoods.
The urban forest of Sacramento County, California, contains approximately 6 million trees. Tree density and basal area decrease along an urban-rural gradient from city (73 trees/ha, 13.4 m2/ha), to suburban (64 trees/ha, 4.5 m2/ha), to rural (10 trees/ha, 0.9 m2/ha) sectors. Within the city and suburban sectors, where 90% of all residents live, approximately 75% of total tree numbers, basal area, and leaf area occurs on residential land. Sacramento's urban forest is relatively sustainable. Seventy percent of the trees are in excellent or good condition, the population is well distributed by age and species, and the most abundant species are reasonably well suited to local conditions. Factors likely to trigger change in Sacramento's urban forest during the next 50 years are described (e.g., water conservation, development patterns, landscape maintenance issues) and species with potential to thrive in these conditions are listed for future planting and evaluation. A comparison of canopy cover, density, and basal area of trees in the city sectors of Sacramento and Chicago, Illinois, reveal surprising similarities. However, in Sacramento these values decrease along the urban-rural gradient, while in Chicago they increase. As human influences wane along the gradient, such factors as climate, soils, competition, and natural regeneration become more important forces in causing urban forest structure to approach presettlement
The heat island effect and the high use of fossil fuels in large city centers are well documented, but by how much fossil fuel consumption is elevating atmospheric CO2 concentrations and whether elevations in both atmospheric CO2 and air temperature from rural to urban areas are consistently different from year to year are less well known. Our aim was to record atmospheric CO2 concentrations, air temperature and other environmental variables in an urban area and compare it to suburban and rural sites to see if urban sites are experiencing climates expected globally in the future with climate change. A transect was established from Baltimore city center (Urban site), to the outer suburbs of Baltimore (suburban site) and out to an organic farm (rural site). At each site a weather station was set-up to monitor environmental variables for 5 years. Atmospheric CO2 was consistently and significantly increased on average by 66ppm from the rural to the urban site over the 5 years of the study. Air temperature was also consistently and significantly higher at the urban site (14.8°C) compared to the suburban (13.6°C) and rural (12.7°C) sites. Relative humidity was not different between sites whereas the vapor pressure deficit (VPD) was significantly higher at the urban site compared to the suburban and rural sites. An increase in nitrogen deposition at the rural site of 0.6% and 1.0% compared to the suburban and urban sites was small enough not to affect soil nitrogen content. Dense urban areas with large populations and high vehicular traffic have significantly different microclimates compared to outlying suburban and rural areas. The increases in atmospheric CO2 and air temperature are similar to changes predicted in the short term with global climate change, therefore providing an environment suitable for studying future effects of climate change on terrestrial ecosystems.
Increasingly, city trees are viewed as a best management practice to control stormwater, an urban-heat–island mitigation measure for cleaner air, a CO2-reduction option to offset emissions, and an alternative to costly new electric power plants. Measuring benefits that accrue from the community forest is the first step to altering forest structure in ways that will enhance future benefits. This article describes the structure, function, and value of street and park tree populations in Fort Collins, Colorado; Cheyenne, Wyoming; Bismarck, North Dakota; Berkeley, California; and Glendale, Arizona. Although these cities spent $13–65 annually per tree, benefits ranged from $31 to $89 per tree. For every dollar invested in management, benefits returned annually ranged from $1.37 to $3.09. Strategies each city can take to increase net benefits are presented.
Urban land-cover change threatens biodiversity and affects ecosystem productivity through loss of habitat, biomass, and carbon storage. However, despite projections that world urban populations will increase to nearly 5 billion by 2030, little is known about future locations, magnitudes, and rates of urban expansion. Here we develop spatially explicit probabilistic forecasts of global urban land-cover change and explore the direct impacts on biodiversity hotspots and tropical carbon biomass. If current trends in population density continue and all areas with high probabilities of urban expansion undergo change, then by 2030, urban land cover will increase by 1.2 million km(2), nearly tripling the global urban land area circa 2000. This increase would result in considerable loss of habitats in key biodiversity hotspots, with the highest rates of forecasted urban growth to take place in regions that were relatively undisturbed by urban development in 2000: the Eastern Afromontane, the Guinean Forests of West Africa, and the Western Ghats and Sri Lanka hotspots. Within the pan-tropics, loss in vegetation biomass from areas with high probability of urban expansion is estimated to be 1.38 PgC (0.05 PgC yr(-1)), equal to ∼5% of emissions from tropical deforestation and land-use change. Although urbanization is often considered a local issue, the aggregate global impacts of projected urban expansion will require significant policy changes to affect future growth trajectories to minimize global biodiversity and vegetation carbon losses.
1. Overwintering survivorship of pupae of the mimosa webworm, Homadaula anisocentra Meyrick (Lepidoptera: Plutellidae), was examined in several urban habitats in central Iowa during the winters of 1981–82, 1982–83 and 1983–84.
2. Survivorship and supercooling point temperatures were determined throughout the winters. Corroborative laboratory studies were conducted during the winter of 1982–83.
3. Minimum ambient temperatures that equalled or were below the supercooling point of the insect, at any time, were lethal.
4. Prolonged cold exposure below 0°C and above the supercooling point resulted in high mortality levels. To quantify this relationship, a concept of minimum-temperature exposure was developed by tabulating the number of degrees that the daily minimum temperature was below 0°C for a given sampling period.
5. Some mimosa webworm pupae were found to overwinter in highly protected sites (2.5–5.0°C warmer than the ambient air temperatures) in the urban environment, resulting in less minimum-temperature exposure and reducing the probability of reaching the lethal supercooling point temperature.
Global warming is predicted to cause distributional changes in organisms whose geographic ranges are controlled by temperature. We report a recent latitudinal and altitudinal expansion of the pine processionary moth, Thaumetopoea pityocampa, whose larvae build silk nests and feed on pine foliage in the winter. In north-central France (Paris Basin), its range boundary has shifted by 87 km northwards between 1972 and 2004; in northern Italy (Alps), an altitudinal shift of 110–230 m upwards occurred between 1975 and 2004. By experimentally linking winter temperature, feeding activity, and survival of T. pityocampa larvae, we attribute the expansions to increased winter survival due to a warming trend over the past three decades. In the laboratory we determined the minimum nest and night air temperatures required for larval feeding and developed a mechanistic model based on these temperature thresholds. We tested the model in a translocation ex-periment that employed natural temperature gradients as spatial analogues for global warm-ing. In all transects we transferred colonies of T. pityocampa larvae to sites within zones of historical distribution, recent distribution, and outside the present range. We monitored air and nest temperature, incoming solar radiation, larval phenology, feeding activity, and survival. Early-season temperature effects on phenology were evident, with delayed de-velopment of colonies in the more extreme (colder) sites. In the coldest months, our model was consistent with the observed patterns of feeding activity: Feeding was progressively reduced with increasing latitude or elevation, as predicted by the lower number of hours when the feeding threshold was reached, which negatively affected final survival. Insolation raised nest temperature and increased feeding activity on the south but not the north aspect. Prolonged temperature drops below the feeding thresholds occurred at all sites, leading to starvation and partial mortality. Nonetheless, even the most extreme sites still allowed some feeding and, consequently, up to 20% colony survival and successful pupation. Given that the present distribution of the oligophagous T. pityocampa is not constrained by the dis-tribution of its actual or potential hosts, and that warmer winters will cause the number of hours of feeding to increase and the probability of the lower lethal temperature to decrease, we expect the trend of improved survival in previously prohibitive environments to continue, causing further latitudinal and altitudinal expansion. This work highlights the need to develop temperature-based predictive models for future range shifts of winter-limited spe-cies, with potential applications in management.