High temperatures and time to budbreak in low chill apricot ‘Palsteyn’. Towards a better understanding of chill and heat requirements fulfilment

The efficiency of different temperature cycles in inducing budburst of one-year-old shoots of the apricot cultivar ‘Palsteyn’ from dormancy was evaluated. Three replications of shoots were collected during two consecutive years from adult trees, following the accumulation of different amounts of chilling in the field. Thereafter, shoots were exposed to different temperature cycles in growth chambers, for 60 days. The temperature treatments included a continuous temperature of 5 °C; daily temperature cycles of 19/5 h at 5/15 °C, at 5/20 °C, and at 5/25 °C; and the same temperature cycles for the remainder of the 60-day period, after pretreatment at 5 °C for 30 or 45 days. After the temperature treatments, shoots were forced at 25 °C until budburst. The mean time to budburst (MTB) (in days) of lateral vegetative, terminal vegetative and reproductive buds was evaluated. The efficiency of the different treatments was greatly influenced by the date on which shoots were cut. High temperatures had a more positive effect on the reduction of MTB when chilling accumulation had occurred in the field instead of the growth chamber. After partial chilling accumulation in the field, high temperatures (25 °C) combined with low temperatures are more efficient than cycles of moderate temperatures (15 or 20 °C) to induce an earlier budburst. In view of these results, a parallel accumulation of both chilling and heat requirements after partial chilling accumulation is suggested. The application of these results could assist in the development of more accurate models for the prediction of the overcoming of dormancy and blooming.     

Towards a measure of functional connectivity: local synchrony matches small scale movements in a woodland edge butterfly

This study investigates the sensitivity of local synchrony to movement patterns of the Ringlet butterfly (Aphantopus hyperantus). We examine whether population synchrony, describing the correlated fluctuations of conspecific populations, may prove an effective surrogate measure for monitoring functional connectivity in this species without the requirement of exhaustive sampling. We compared the effect on population synchrony of two different distance measures, direct (Euclidean) distance and distance via woodland rides and edges, and also of habitat matrix composition. Population synchrony of A. hyperantus was calculated as the pairwise correlation between population time-series using 20?years of data from UK butterfly monitoring scheme transects. Local population synchrony was better explained by distance via woodland edges than direct distance, especially for woodland-dominated transects. These results are consistent with mark-recapture data previously collected on the Ringlet butterfly. The results indicate a sensitivity of population synchrony to butterfly local dispersal behaviour, particularly, to the use of habitat corridors and other functional dispersal routes. Population synchrony is considered to have potential as a surrogate measure of functional connectivity. With development, this method could become a valuable conservation tool for identifying important landscape features which promote species?? connectivity.     

Integrating meteorological factors for better understanding of the urban form-air quality relationship

Landscape Ecology - Understanding the urban form-air quality relationship is essential to mitigate intra-urban air pollution and to improve urban ecology. However, few studies considered urban form...     

Towards an integrated understanding of green space in the European built environment

In recent years social, economic and environmental considerations have led to a reevaluation of the factors that contribute to sustainable urban environments. Increasingly, urban green space is seen as an integral part of cities providing a range of services to both the people and the wildlife living in urban areas. With this recognition and resulting from the simultaneous provision of different services, there is a real need to identify a research framework in which to develop multidisciplinary and interdisciplinary research on urban green space. In order to address these needs, an iterative process based on the delphi technique was developed, which comprised email-mediated discussions and a two-day symposium involving experts from various disciplines. The two outputs of this iterative process were (i) an integrated framework for multidisciplinary and interdisciplinary research and (ii) a catalogue of key research questions in urban green space research. The integrated framework presented here includes relevant research areas (i.e. ecosystem services, drivers of change, pressures on urban green space, human processes and goals of provision of urban green space) and emergent research themes in urban green space studies (i.e. physicality, experience, valuation, management and governance). Collectively these two outputs have the potential to establish an international research agenda for urban green space, which can contribute to the better understanding of people's relationship with cities.     

Habitat edge effects alter ant-guard protection against herbivory

Edge effects are among the most important drivers of species interactions in fragmented habitats, but the impacts of edge effects on multitrophic interactions are largely unknown. In this study we assess edge effects on species interactions within an ant–plant mutualistic system—where ants protect plants against herbivory—to determine whether habitat edges alter the amount of protection ants provide. We focus on a single species of myrmecophytic plant, Solanum americanum, and experimentally manipulate ant access to study plants in large-scale fragmented habitat patches at the Savannah River Site National Environmental Research Park, USA. In this system, S. americanum commonly hosts honeydew-producing aphids that are tended by ants, and grasshoppers are the primary herbivores. We measured edge effects on the per-plant abundance of aphids and protective ants as well as the abundance of grasshoppers in each habitat patch, and we evaluated levels of ant protection against herbivory near and far from habitat edges. We found that ants provided significant protection to plants far from edges, where herbivory pressure was highest, despite the fact that aphids and ants were least abundant on these plants. Conversely, ants did not provide significant protection near edges, where herbivory pressure was lowest and aphids and ants were most abundant. We conclude that a strong edge effect on grasshopper abundance was a key factor determining the amount of protection ants provided against herbivory. Future studies of the impacts of habitat fragmentation on ant–plant mutualisms will benefit from studies of ant behavior in response to herbivory threats, and studies of edge effects on other species interactions may also need to consider how species’ behavioral patterns influence the interactions in question.     

Measuring edge contrast using biotic criteria helps define edge effects on the density of an invasive plant

Habitat edges can alter population dynamics, influence community structure, determine the success of conservation efforts, and facilitate the spread of invasive species. Despite recognition that edges influence the nature and strength of ecological interactions, edges are generally characterized using abiotic measures that likely capture habitat quality for only the focal taxa, and ignore the potential for biotic interactions to explain edge effects. Here we describe the association between edges and the density of an invasive shrub, Lonicera maackii, and infer the functional role of edges by using multiple criteria to weight edge contrast. We define edge contrast using both an abiotic criterion in which contrast is weighted by differences in light availability, and a biotic criterion in which edge contrast is weighted by the association between edges and the abundance of the American Robin (Turdus migratorius), an important avian seed disperser. Biotically defining edge contrast significantly improved model fit in all cases, demonstrating that the large-scale distribution of an invasive shrub is best predicted using both abiotic and biotic edge characterization. More generally, our work suggests that weighting edge contrast using key biological interactions in addition to abiotic criteria may be a promising way to understand the multiple pathways by which edges influence the distribution and abundance of organisms.     

Conservation management of complex natural forest and plantation edge effects

Timber plantation forestry is a major threat to indigenous grassland biodiversity, with ecological networks (ENs) currently being used to mitigate this threat. Being composed mostly of linear corridors, ENs create more edge than would occur naturally. To determine the minimum width of corridors for maximising biodiversity conservation, we need first to establish the extent of edge effects from plantation blocks into corridors. We compared arthropod diversity along transects that ran from within plantation blocks into grassland corridors. We also studied the edge effects of natural forest adjacent to natural grasslands within ENs. Sites in grasslands of neighbouring protected areas acted as natural reference sites against which the biodiversity of the EN transects were compared. Two types of exotic plantation trees and various tree age classes were studied. We found a 32 m edge zone from plantation blocks into grassland corridors. Few significant edge effects from plantation blocks occurred at greater distances than this, which suggested that grassland corridors with a width <64 m are essentially all edge. However, and importantly, this situation was complex, as different arthropod taxonomic groups responded differently to edges of plantation blocks and natural forest patches. Natural forest supported many additional species, not just within the forest, but also in associated grassland corridors. This means that maintaining natural forest imbedded within the ENs will protect both indigenous grassland and indigenous forest species as well as help maintain biodiversity across this timber production landscape.     

Interactive effects of drought and edge exposure on old-growth forest understory species

Landscape Ecology - Both climatic extremes and land-use change constitute severe threats to biodiversity, but their interactive effects remain poorly understood. In forest ecosystems, the effects...     

Habitat edge effects decrease litter accumulation and increase litter decomposition in coastal salt marshes

Context

Habitat fragmentation is known to be one of the leading causes of species extinctions, however few studies have explored how habitat fragmentation impacts ecosystem functioning and carbon cycling, especially in wetland ecosystems.

Objectives

We aimed to determine how habitat fragmentation, defined by habitat area and distance from habitat edge, impacts the above-ground carbon cycling and nutrient stoichiometry of a foundation species in a coastal salt marsh.

Methods

We conducted our research in a salt marsh in the Mid-Atlantic United States, where the foundation grass species Spartina patens is being replaced by a more flood-tolerant grass, leading to highly fragmented habitat patches. We quantified decomposition rates, live biomass, and litter accumulation of S. patens at patch edges and interiors. Additionally, we measured relevant characteristics (e.g., habitat area, elevation, microclimate) of S. patens patches.

Results

Habitat edge effects, and not habitat area effects, had distinct impacts on ecosystem functioning. Habitat edges had less litter accumulation, faster decomposition rates, a warmer and drier microclimate, and lower elevations than patch interiors. Patches with low elevation edges had the fastest decomposition rates, while interiors of patches at any elevation had the slowest decomposition rates. Notably, these impacts were not driven by changes in primary production.

Conclusion

Habitat fragmentation impacts the above-ground carbon cycling of S. patens in coastal wetlands by altering litter decomposition, but not primary production, through habitat edge effects. Future research should investigate whether this pattern scales across broader landscapes and if it is observable in other wetland ecosystems.

     

Landscape forest cover and edge effects on songbird nest predation vary by nest predator

Rates of nest predation for birds vary between and within species across multiple spatial scales, but we have a poor understanding of which predators drive such patterns. We video-monitored nests and identified predators at 120 nests of the Acadian Flycatcher (Empidonax virescens) and the Indigo Bunting (Passerina cyanea) at eight study sites in Missouri and Illinois, USA, during 2007–2010. We used an information-theoretic approach to evaluate hypotheses concerning factors affecting predator-specific and overall rates of predation at landscape, edge, and nest-site scales. We found support for effects of landscape forest cover and distance to habitat edge. Predation by Brown-headed Cowbirds (Molothrus ater) increased, and predation by rodents decreased as landscape forest cover decreased. Predation by raptors, rodents, and snakes increased as the distance to forest edges decreased, but the effect was modest and conditional upon the top-ranked model. Despite the predator-specific patterns we detected, there was no support for these effects on overall rates of predation. The interactions between breeding birds, nest predators, and the landscapes in which they reside are scale-dependent and context-specific, and may be resistant to broad conceptual management recommendations.     

The use of traits to interpret responses to large scale - edge effects: a study of epigaeic beetle assemblages across a <Emphasis Type="Italic">Eucalyptus</Emphasis> forest and pine plantation edge

Context

Edge effects due to habitat loss and fragmentation have pervasive impacts on many natural ecosystems worldwide.

Objective

We aimed to explore whether, in tandem with the resource-based model of edge effects, species feeding-guild and flight-capacity can help explain species responses to an edge.

Methods

We used a two-sided edge gradient that extended from 1000 m into native Eucalyptus forest to 316 m into an exotic pine plantation. We used generalised additive models to examine the continuous responses of beetle species, feeding-guild species richness and flight-capable group species richness to the edge gradient and environmental covariates.

Results

Phytophagous species richness was directly related to variation in vegetation along the edge gradient. There were more flight-capable species in Eucalyptus forest and more flightless species in exotic pine plantation. Many individual species exhibited multiple-peaked edge-profiles.

Conclusions

The resource based model for edge effects can be used in tandem with traits such as feeding-guild and flight-capacity to understand drivers of large scale edge responses. Some trait-groups can show generalisable responses that can be linked with drivers such as vegetation richness and habitat structure. Many trait-group responses, however, are less generalisable and not explained by easily measured habitat variables. Difficulties in linking traits with resources along the edge could be due to unmeasured variation and indirect effects. Some species’ responses reached the limits of the edge gradient demonstrating the need to examine edge effects at large scales, such as kilometres.

     

Contrasting edge and pasture matrix effects on ant diversity from fragmented landscapes across multiple spatial scales

Landscape Ecology - Harmful effects of habitat loss and fragmentation can be detected across multiple spatial scales, yet most studies that aim to characterize these effects take place at a single...     

Towards a comprehensive framework for modeling urban spatial dynamics

The increasing availability of spatial micro data offers new potential for understanding the micro foundations of urban spatial dynamics. However, because urban systems are complex, induction alone is insufficient. Nonlinearities and path dependence imply that qualitatively new dynamics can emerge due to stochastic shocks or threshold effects. Given the policy needs for managing urban growth and decline and the growing desire for sustainable urban forms, models must be able not only to explain empirical regularities, but also characterize system-level dynamics and assess the plausible range of outcomes under alternative scenarios. Towards this end, we discuss a comprehensive modeling approach that is comprised of bottom-up and top-down models in which both inductive and deductive approaches are used to describe and explain urban spatial dynamics. We propose that this comprehensive modeling approach consists of three iterative tasks: (1) identify empirical regularities in the spatial pattern dynamics of key meso and macro variables; (2) explain these regularities with process-based micro models that link individual behavior to the emergence of meso and macro dynamics; and (3) determine the systems dynamical equations that characterize the relationships between micro processes and meso and macro pattern dynamics. Along the way, we also clarify types of complexity (input and output) and discuss dimensions of complexity (spatial, temporal, and behavioral). While no one to date has achieved this kind of comprehensive modeling, meaningful progress has been made in characterizing and explaining urban spatial dynamics. We highlight examples of this work from the recent literature and conclude with a discussion of key challenges.     

Effects of varying forest edge permeability on seed dispersal in a neotropical montane forest

Hard (high-contrast with pastures) and soft (low-contrast with old-fields) forest edges created by slash-and-burn agriculture have become common landscape features in regions dominated by neotropical montane forest. However, little is know about the impacts of such edge types on forest regeneration dynamics. The consequences of varying forest edge permeability for oak acorn dispersal were investigated in a forest mosaic in the Highlands of Chiapas, Mexico. Rates of acorn production and removal, as well as the abundance and composition of small mammal seed consumers, were monitored along these different edge types (hard vs. soft) at specific distances from forest edges into forest patches and adjacent grasslands during two consecutive years. Results show that acorn removal declined significantly only in grasslands of sites characterised by hard edges (Logistic regression, P < 0.05). Movements of metal-tagged acorns support the hypothesis that soft edges are more permeable to small mammals, with rodents moving acorns up to 15 m into grasslands of sites with soft edges. In sites with hard edges, higher rates of acorn dispersal were recorded from the forest edge towards the forest interior. Peromyscus spp. were the main acorn predators and/or dispersers of acorns present in our study sites. Rates of acorn removal during a non-masting year were greater than the subsequent mast-seeding year (85% removal within 138 days vs. 75% within 213 days), demonstrating that mast seeding may allow some seeds to escape predation. The implications of these results for oak dispersal and regeneration along edges in fragmented tropical forest landscapes are discussed.     

Observed and modeled directional change in riparian forest composition at a cutbank edge

Lateral migrations of river meanders create transient, spatially transgressive edges where the advancing cutbank edge encroaches upon interior floodplain forest communities. This spatial movement of edge toward the forest interior should initiate directional changes in species composition within a forest plot as it is affected by a changing microclimate and hydrological regime. We found that cutbank edge and forest interior sites in an Iowa floodplain contained markedly different plant assemblages. Species commonly associated with later stages of succession dominated interior sites while cutbank edge sites favored secondary, successional species. Assuming that the cutbank edge sites once contained vegetation similar to that surveyed in the floodplain interior, the observed changes in community structure accompanying channel migration are suggestive of retrograde succession, or retrogression. To link cutbank erosional processes with retrogressional processes, we modified a computer simulation model already in use for floodplain environments. We incorporated the changing edge effects and compared model projections with the data collected from the field sites using detrended correspondence analysis. Without changes, the simulation projected a site compositionally similar to the sampled interior forest. When the changes were initiated, the simulated site progressively took on compositional characteristics similar to the riparian edge sites. Because we included only those forcing functions that would be initiated by cutbank erosion, the model supports the hypothesis that the spatially progressive edge effect results in a directional change in forest community composition analogous to retrogression. Our results demonstrate an interesting linkage between successional and fluvial-geomorphic processes and indicate that site dynamics may be controlled differently in landscapes where sites are progressively created and destroyed than where recurrent disturbances affect the same site.     

Living on the edge: quantifying the structure of a fragmented forest landscape in England

Forest ecosystems have been widely fragmented by human land use, inducing significant microclimatic and biological changes at the forest edge. If we are to rigorously assess the ecological impacts of habitat fragmentation, there is a need to effectively quantify the amount of edge habitat within a landscape, and to allow this to be modelled for individual species and processes. Edge effect may extend only a few metres or as far as several kilometres, depending on the species or process in question. Therefore, rather than attempting to quantify the amount of edge habitat by using a fixed, case-specific distance to distinguish between edge and core, the area of habitat within continuously-varying distances from the forest edge is of greater utility. We quantified the degree of fragmentation of forests in England, where forests cover 10 % of the land area. We calculated the distance from within the forest patches to the nearest edge (forest vs. non-forest) and other landscape indices, such as mean patch size, edge density and distance to the nearest neighbour. Of the total forest area, 37 % was within 30 m and 74 % within 100 m of the nearest edge. This highlights that, in fragmented landscapes, the habitats close to the edge form a considerable proportion of the total habitat area. We then show how these edge estimates can be combined with ecological response functions, to allow us to generate biologically meaningful estimates of the impacts of fragmentation at a landscape scale.