Using suitability analysis to select and prioritize naturalization efforts in legacy cities: An example from Flint,Michigan

Given the lack of market demand and the abundance of vacant lots in legacy cities, not all vacant lands can be redeveloped or even maintained in a highly manicured state. While many vacant lots are being creatively reused as community gardens and side lots, in areas where residents are few and vacancy is high, the best use for vacant lands may be in a naturalized state such as meadows or forests. The author argues that in legacy cities, the critical question is not whether to naturalize (i.e. to stop mowing lots and allow for succession), but rather how to determine which properties to naturalize, in what order, and how. Using the example of Flint, Michigan, the author proposes suitability analysis as a method for selecting and prioritizing naturalization. Every property in the city of Flint was assigned a naturalization score derived by calculating subscores on nine variables, weighing the subscores by their importance, and summing. The nine variables included were contiguous vacant land, prospective vacancy, public ownership, land use designation, parks adjacency, proximity to industry, waterway buffers, property values, and population change. The naturalization scores can be combined with the results of a prior study to create a vacant land use decision tree pre- and post-demolition. Ultimately, the purpose of the paper is to facilitate property selection for naturalization while encouraging public discourse around what should happen with vacant lots in legacy cities.     

Using traffic flow theory to model traffic mortality in mammals

Traffic has a considerable effect on population and community dynamics through the disruption and fragmentation of habitat and traffic mortality. This paper deals with a systematic way to acquire knowledge about the probabilities of successful road crossing by mammals and what characteristics affect this traversability. We derive a model from traffic flow theory to estimate traffic mortality in mammals related to relevant road, traffic and species characteristics. The probability of successful road crossing is determined by the pavement width of the road, traffic volume, traversing speed of the mammals and their body length. We include the traversability model in a simple two-patch population model to explore the effects of these road, traffic and species characteristics on population dynamics. Analysis of the models show that, for our parameter ranges, traffic volume and traversing speed have the largest effect on traffic mortality. The population size is especially negatively affected when roads have to be crossed during the daily movements. These predictions could be useful to determine the expected effectiveness of mitigating measures relative to the current situation. Mitigating measures might alter the road and traffic characteristics. The effects of these changes on traffic mortality and population dynamics could be analysed by calculating the number of traffic victims before and after the mitigating measures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Using traffic flow theory to model traffic mortality in mammals

Traffic has a considerable effect on population and community dynamics through the disruption and fragmentation of habitat and traffic mortality. This paper deals with a systematic way to acquire knowledge about the probabilities of successful road crossing by mammals and what characteristics affect this traversability. We derive a model from traffic flow theory to estimate traffic mortality in mammals related to relevant road, traffic and species characteristics. The probability of successful road crossing is determined by the pavement width of the road, traffic volume, traversing speed of the mammals and their body length. We include the traversability model in a simple two-patch population model to explore the effects of these road, traffic and species characteristics on population dynamics. Analysis of the models show that, for our parameter ranges, traffic volume and traversing speed have the largest effect on traffic mortality. The population size is especially negatively affected when roads have to be crossed during the daily movements. These predictions could be useful to determine the expected effectiveness of mitigating measures relative to the current situation. Mitigating measures might alter the road and traffic characteristics. The effects of these changes on traffic mortality and population dynamics could be analysed by calculating the number of traffic victims before and after the mitigating measures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Using graph theory to analyse and assess changes in Mediterranean woodland connectivity

Landscape Ecology - The Portuguese montado is an agro-silvopastoral system, similar to the Spanish dehesa, known for its cultural, economic and ecological value. Despite its importance, contrasting...     

Integrating a generic focal species,metapopulation capacity,and connectivity to identify opportunities to link fragmented habitat

Context

A challenge devising revegetation strategies in fragmented landscapes is conserving for the widest spectrum of biodiversity. Habitat network reconstruction should improve landscape capacity to maintain species populations. However, the location of revegetation often fails to account for species occurrence and dispersal processes operating across spatial scales.

Objectives

Our objective was to integrate metapopulation theory with estimates of landscape capacity and dispersal pathways to highlight connectivity gaps. Maintenance of populations could thereby be facilitated through reconnecting habitat networks across regional and broader scales, with assumed benefit for the dispersal needs of less sensitive species.

Methods

Predicted occupancy and metapopulation capacity were calculated for a generic focal species derived from fragmentation-sensitive woodland birds, mammals and reptiles. A metapopulation connectivity analysis predicted regional dispersal links to identify likely routes through which individuals may move to contribute to the viability of the population. We used the revegetation programmes of the Brigalow–Nandewar Biolinks project, eastern New South Wales, Australia, to demonstrate our approach.

Results

Landscape capacity of the current landscape varied across the region. Low-value links between populations provided greatest opportunities for revegetation and improved landscape capacity. Where regional connectivity did not indicate a pathway between populations, broader scale connectivity provided guidance for revegetation.

Conclusions

The metapopulation-based model, coupled with a habitat dispersal network analysis, provided a platform to inform revegetation locations and better support biodiversity. Our approach has application for directing on-ground action to support viable populations, assess the impact of revegetation schemes or monitor the progress of staged implementations.

     

Microclimates in a desert city were related to land use and vegetation index

A heterogeneous patchwork mosaic of soil, vegetation, and built surfaces that result from a variety of urban land uses cause urban microclimates within cities. We studied the seasonal relationships of land use, urban plant cover and microclimate in Phoenix, Arizona, USA, metropolitan. Early morning (0500 HR) and afternoon (1500 HR) near-surface temperatures and humidities were measured along multiple transects in this desert city and outlying areas during June and December 1999. A Landsat thematic mapper normalized differential vegetation index (NDVI) image was used to quantify spatial patterns of plant density. Land use had the most pronounced effect on microclimate during the early morning hours of summer. Agricultural and residential land uses had the highest relative humidities, dew point temperatures, and NDVI, and the lowest air temperatures. Commercial and industrial land uses had highest temperatures and lowest NDVI. Temperatures were generally negatively correlated to NDVI, while humidity and dew point temperatures were generally positively correlated to NDVI. Distance from the urban core did not affect NDVI but had a significant negative effect on adjusted air temperature. In addition, a historical comparison of land use, NDVI and microclimate data collected during 1976 and again during 1999 along two transects revealed overall decreases in NDVI and relative increases in air temperature indicative of urban expansion. These findings show that microclimates in this desert city are caused by more than just variations in plant cover, and are likely an interactive effect of vegetation density and other non-vegetative urban surfaces.     

A combined grazing and fire management may reverse woody shrub encroachment in desert grasslands

Context

Fire and controlled grazing have been widely adopted as management interventions to counteract woody shrub proliferation in many arid and semiarid grassland systems. The actual intensity of grazing and fire, along with the timing of the interventions, however, are difficult to determine in practice.

Objectives

This study aims to establish model simulations to access the long-term landscape changes under different land management scenarios.

Methods

We developed a cellular automata model to evaluate landscape dynamics in response to scenarios of grazing, fire, time of intervention, and initial coverage of grasses and shrubs.

Results

With current grazing intensity and fire suppression, the landscape may shift to a shrub-dominated landscape in 100–150 years. An appropriate combination of grazing and fire management could help maintain over 50% of grass cover and reduce the shrub cover to less than 2%, keeping the landscape highly reversible. Even using 1% grazing intensity and periodic fire once a year, the management tools should be implemented in 60 years, otherwise, they may lose effectiveness and the vegetation transition to grasslands would become impossible.

Conclusions

This study highlighted that the reintroduction of fire not only directly removes shrubs but also reallocates soil water and resources among different microsites, which may accelerate grass recovery and suppress shrub regrowth, potentially reversing the shrub invasion process. The combined grazing and fire management plans should be carried out before a threshold time depending on the chosen management tools.

     

Effects of exurban development on trophic interactions in a desert landscape

Context

Mechanisms of ecosystem change in urbanizing landscapes are poorly understood, especially in exurban areas featuring residential or commercial development set in a matrix of modified and natural vegetation. We asked how development altered trophic interactions and ecosystem processes in the matrix.

Objectives

We examined the effect of varying degrees of exurban development (housing density) on a trophic system that included an apex mammalian predator (coyote, Canis latrans), mammalian herbivores (lagomorphs and rodents), and herbaceous plants. We tested the hypothesis that plant recruitment would be negatively affected by exurban development due either to increases in herbivores associated with increased resource availability (a bottom–up effect) or to a reduction in predators that avoid humans (a top–down effect).

Methods

In Las Cruces, New Mexico, USA, four replicate sites were located in each of three urbanization levels: high density exurban, low density exurban, and wildland dominated by Chihuahuan Desert vegetation. Seedling trays measured herbivory rates, live trapping estimated abundance of pocket mice and kangaroo rats, and remotely-triggered wildlife cameras estimated the activity of lagomorphs and coyotes.

Results

Increased herbivory on seedlings and decreased herbaceous plant recruitment were observed in high density exurban areas. Overall rodent abundance, seed consumption rates, and activity of the lagomorph Lepus californicus did not vary with urbanization level. Activity by another lagomorph, Sylvilagus audubonii, and coyotes was highest in dense exurban areas, consistent with a bottom–up effect.

Conclusions

Exurban development can have important indirect effects on trophic interactions occurring in adjacent, untransformed ecosystems. Similar to earlier studies, such effects in the Chihuahuan Desert may be mediated by bottom–up processes associated with anthropogenic inputs.

     

Using binary and probabilistic habitat availability indices derived from graph theory to model bird occurrence in fragmented forests

Loss of connectivity is one of the main causes of decreases in habitat availability and, thus, in species abundance and occurrence in fragmented landscapes. It is therefore important to measure habitat connectivity for conservation purposes, but there are several difficulties in quantifying connectivity, including the need for species movement behavioral data and the existence of few consistent indices to describe such data. In the present study, we used a graph theoretical framework to measure habitat availability, and we evaluate whether this variable is adequate to explain the occurrence pattern of an Atlantic rainforest bird (Pyriglena leucoptera, Thamnophilidae). The playback technique was used to parameterize the connectivity component of habitat availability indices and to determine the presence or absence of the study species in forest patches. Patch- and landscape-level habitat availability indices were considered as explanatory variables. Two of these were landscape-level indices, which varied in terms of how inter-patch connections are defined, using either a binary or probabilistic approach. This study produced four striking results. First, even short open gaps may disrupt habitat continuity for P. leucoptera. Second, the occurrence of P. leucoptera was positively affected by habitat availability. Third, proper measures of this explanatory variable should account for the landscape context around the focal patch, emphasizing the importance of habitat connectivity. Finally, habitat availability indices should consider probabilistic and not binary inter-patch connections when intending to explain the occurrence of bird species in fragmented landscapes. We discuss some conservation implications of our results, stressing the advantages of an ecologically scaled graph theoretical framework.     

Dry-washes determine gene flow and genetic diversity in a common desert shrub

Context

In deserts, many plant species exhibit a patchy spatial distribution within a harsh habitat matrix, where the likelihood of propagule dispersal among patches is uncertain, but may be promoted by landscape corridors or dispersal vectors.

Objectives

We examine the connectivity of a representative desert plant species (Acacia (Senegalia) greggii), and the ability of three major factors (animal dispersal agents, water flow along dry-washes, and climate) to facilitate dispersal within four watersheds in the Mojave National Preserve.

Methods

We genotyped 323 individuals sampled across 22 one-hectare sites using ten nuclear microsatellite markers.

Results

A hierarchical AMOVA revealed no significant differentiation among watersheds (F _RT = 0.00, P > 0.10), and very little genetic structure among all sites (F _ST = 0.03, P < 0.001), indicating regional connectivity. Mantel tests indicated distance along dry-washes best explained genetic distance between sites (r = 0.47, P < 0.05) when compared to Euclidean distance (P > 0.05), a distance measure based on rodent dispersal (P > 0.05), and a distance measure avoiding inhospitable climate (P > 0.05). An AIC comparison of generalized linear models found that within site genetic diversity (H _E and allelic richness) and average relatedness were best explained by slope (which increases seed dispersal potential via water flow) and area of the upstream watershed (which determines the number of potential seed donors), rather than plant density or habitat suitability.

Conclusions

Together, these findings indicate that dry-washes are key landscape features that enhance dispersal and regional connectivity in this patchy desert plant.

     

Interactions between plant life span, seed dispersal capacity and fecundity determine metapopulation viability in a dynamic landscape

Classical metapopulation models do not account for temporal changes in the suitability of habitat patches. In reality, however, the carrying capacity of most habitat types is not constant in time due to natural succession processes. In this study, we modeled plant metapopulation persistence in a successional landscape with disappearing and emerging habitat patches, based on a realistic dune slack landscape at the Belgian–French coast. We focused on the effects of the variation of different plant traits on metapopulation persistence in this changing landscape. Therefore, we used a stage based stochastic metapopulation model implemented in RAMAS/Metapop, simulating a large variation in plant traits but keeping landscape characteristics such as patch turnover rate and patch lifespan constant. The results confirm the conclusions of earlier modeling work that seed dispersal distance and seed emigration rate both have an important effect on metapopulation persistence. We also found that high population growth rate or high recruitment considerably decreased the extinction risk of the metapopulation. Additionally, a long plant life span had a strong positive effect on metapopulation persistence, irrespective of the plant's dispersal capacity and population growth rate. Plant species that invest in life span require less investment in offspring and dispersal capacity to avoid extinction, even in dynamic landscapes with deterministic changes in habitat quality. Moreover, metapopulations of long-lived plant species were found to be much less sensitive to high levels of environmental stochasticity than short-lived species.     

The use of metapopulation and optimal foraging theories to predict movement and foraging decisions of mobile animals in heterogeneous landscapes

Metapopulation and optimal foraging theories predict the presence of animals and their duration, respectively, in foraging patches. This paper examines use of these two theories to describe the movements and patterns of foraging in patches used by Caspian gulls (Larus cachinnans) at inland reservoirs during the chick-rearing period. We assumed that birds would move differently across diverse habitats, with some types of land cover less permeable than others, and some landscape features acting as corridors. We also expected larger and less isolated patches, and patches that were close to corridors, to have a higher probability of the presence of foraging birds, and that they would be more abundant, forage for a shorter time, and hunt smaller prey than in small, more isolated patches surrounded by barriers. Forests seem to be a much less permeable type of land cover, whereas rivers became corridors for Caspian gulls during foraging trips. Probability of bird presence was positively related to the size of foraging patches and negatively linked with distance to the nearest river, distance to the nearest foraging patch, and the presence of forests in the vicinity. The same factors significantly affected bird abundance. Contrary to expectations, the duration and success of foraging were not influenced by any variable we measured, suggesting that although larger patches contain a higher abundance of fish, their density and the probability of capturing prey were relatively stable among the various patches. However, gulls that foraged in more isolated ponds that were located further from the river and the colony, and also surrounded by forest, captured larger fish more often than birds that foraged near the colony in less-isolated patches. Pooling metapopulation and optimal foraging concepts seems to be valuable in describing patch use by foraging animals. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Using a gestalt to measure the quality of in vitro responses

Overall “quality” of in vitro responses can sometimes be difficult to assess using measured response variables (e.g., shoot number and height, and callus fresh weight). Gestalt Theory is the idea that the whole is perceived to be greater than the sum of the individual parts. To determine if a gestalt assessment could be used to assess quality of in vitro responses two plant tissue culture systems were examined—Brugmansia x candida shoot multiplication and sweet orange nonembryogenic callus growth. The gestalt assessment of each system was compared to measured responses—shoot number, leaf length and width for Brugmansia x candida, and fresh weight accumulation for citrus. The gestalt analysis modeled as precisely as the measured response variables for both in vitro systems while satisfying the statistical assumptions necessary for a valid analysis. We concluded that the gestalt response is a valid response as it was indistinguishable, in terms of statistical quality, from the measured responses.     

Using a species-centered approach to predict bird community responses to habitat fragmentation

Landscape Ecology - The relative importance of habitat fragmentation versus loss on species richness has been much debated. However, recent findings that fragmentation effects are relatively weak...     

Characterizing the importance of habitat patches and corridors in maintaining the landscape connectivity of a Pholidoptera transsylvanica (Orthoptera) metapopulation

Since the fragmentation of natural habitats is one of the most serious problems for many endangered species, it is highly interesting to study the properties of fragmented landscapes. As a basic property, landscape connectivity and its effects on various ecological processes are frequently in focus. First, we discuss the relevance of some graph properties in quantifying connectivity. Then, we propose a method how to quantify the relative importance of habitat patches and corridors in maintaining landscape connectivity. Our combined index explicitly considers pure topological properties and topographical measures, like the quality of both patches (local population size) and corridors (permeability). Finally, for illustration, we analyze the landscape graph of the endangered, brachypterous bush-cricket Pholidoptera transsylvanica. The landscape contains 11 patches and 13 corridors and is situated on the Aggtelek Karst, NE-Hungary. We characterize the importance of each node and link of the graph by local and global network indices. We show how different measures of connectivity may suggest different conservation preferences. We conclude, accordingly to our present index, by identifying one specific habitat patch and one specific corridor being in the most critical positions in maintaining connectivity.This revised version was published online in May 2005 with corrections to the Cover Date.     

Using stochastic simulation to evaluate competing risks of wildfires and fuels management on an isolated forest carnivore

Natural resource managers are often challenged with balancing requirements to maintain wildlife populations and to reduce risks of catastrophic or dangerous wildfires. This challenge is exemplified in the Sierra Nevada of California, where proposals to thin vegetation to reduce wildfire risks have been highly controversial, in part because vegetation treatments could adversely affect an imperiled population of the fisher (Martes pennanti) located in the southern Sierra Nevada. The fisher is an uncommon forest carnivore associated with the types of dense, structurally complex forests often targeted for fuel reduction treatments. Vegetation thinning and removal of dead-wood structures would reduce fisher habitat value and remove essential habitat elements used by fishers for resting and denning. However, crown-replacing wildfires also threaten the population’s habitat, potentially over much broader areas than the treatments intended to reduce wildfire risks. To investigate the potential relative risks of wildfires and fuels treatments on this isolated fisher population, we coupled three spatial models to simulate the stochastic and interacting effects of wildfires and fuels management on fisher habitat and population size: a spatially dynamic forest succession and disturbance model, a fisher habitat model, and a fisher metapopulation model, which assumed that fisher fecundity and survivorship correlate with habitat quality. We systematically varied fuel treatment rate, treatment intensity, and fire regime, and assessed their relative effects on the modeled fisher population over 60 years. After estimating the number of adult female fishers remaining at the end of each simulation scenario, we compared the immediate negative effects of fuel treatments to the longer-term positive effect of fuel treatment (via reduction of fire hazard) using structural equation modeling. Our simulations suggest that the direct, negative effects of fuel treatments on fisher population size are generally smaller than the indirect, positive effects of fuel treatments, because fuels treatments reduced the probability of large wildfires that can damage and fragment habitat over larger areas. The benefits of fuel treatments varied by elevation and treatment location with the highest net benefits to fisher found at higher elevations and within higher quality fisher habitat. Simulated fire regime also had a large effect with the largest net benefit of fuel treatments occurring when a more severe fire regime was simulated. However, there was large uncertainty in our projections due to stochastic spatial and temporal wildfires dynamic and fisher population dynamics. Our results demonstrate the difficulty of projecting future populations in systems characterized by large, infrequent, stochastic disturbances. Nevertheless, these coupled models offer a useful decision-support system for evaluating the relative effects of alternative management scenarios; and uncertainties can be reduced as additional data accumulate to refine and validate the models.     

栽培技术对沙漠边缘地区苹果幼树越冬的影响

甘肃省白银市地处我国西北沙漠边缘地区,光照充足,生长期积温高、温差大、空气干燥、降雨少,有一定的灌溉条件,适宜大部分温带果树生长,生产的瓜果品质好,综合品质均居同类果品之首.     

Graph theory as an invasive species management tool: case study in the Sonoran Desert

Context

Biodiversity in arid regions is usually concentrated around limited water resources, so natural resource managers have constructed artificial water catchments in many areas to supplement natural waters. Because invasive species may also use these waters, dispersing into previously inaccessible areas, the costs and benefits of artificial waters must be gauged and potential invasion- and climate change-management strategies assayed.

Objectives

We present a network analysis framework to identify waters that likely contribute to the spread of invasive species.

Methods

Using the Sonoran Desert waters network and the American bullfrog (Lithobates catesbeianus)—a known predator, competitor, and carrier of pathogens deadly to other amphibians—as an example, we quantified the structural connectivity of the network to predict regional invasion potential under current and two future scenarios (climate change and management reduction) to identify waters to manage and monitor for invasive species.

Results

We identified important and vulnerable waters based on connectivity metrics under scenarios representing current conditions, projected climate-limited conditions, and conditions based on removal of artificial waters. We identified 122,607 km² of land that could be used as a buffer against invasion and 67,745 km² of land that could be augmented by artificial water placement without facilitating invasive species spread.

Conclusions

Structural connectivity metrics can be used to evaluate alternative management strategies for invasive species and climate mitigation.

     

Post-fire resource redistribution and fertility island dynamics in shrub encroached desert grasslands: a modeling approach

A common form of land degradation in desert grasslands is associated with the relatively rapid encroachment of woody plants, a process that has important implications on ecosystem structure and function, as well as on the soil hydrological and biogeochemical properties. Until recently this grassland to shrubland transition was thought to be highly irreversible. However recent studies have shown that at the early stages of shrub encroachment in desert grasslands, there exists a very dynamic shrub–grass transition state with enough grass connectivity between the shrub islands to allow for fire spread. In this state fire could play a major role in determining the dominance of grasses and their recovery from the effects of overgrazing. Using a spatially explicit cellular automata model, we show how the patch-scale feedbacks between fires and soil erosion affects resource redistribution and vegetation dynamics in a mixed grass–shrub plant community at landscape to regional scales. The results of this study indicate that at its early stages, the grassland-to-shrubland transition can be reversible and that the feedbacks between fire and soil erosion processes may play a major role in determining the reversibility of the system.