Road Edge Effects Research Articles

Testing direct and indirect road edge effects on reproductive components of anemochoric plants

Road edge effects consist of changes in abiotic and biotic conditions resulting from the new artificial boundaries on the vegetation that are created by a road. It is known that edge effects can have variable direct and indirect influences on the biota, can be species-specific and also site-specific. However, edge effects for most plant species and most of their respective reproductive components have not been assessed yet, especially for anemochoric plants, which can directly influence the ecosystem structure. Here we evaluated directly and indirectly road edge effects on plant reproductive components (floral visiting bees, fruiting, diaspore herbivory, and diaspore dispersal) of three abundant and sympatric Malpighiaceae anemochoric species in a Brazilian savanna (Cerrado) reserve. We showed that (i) there are direct and indirect road edge effects on the reproductive components of the three anemochoric species; (ii) the road edge effects were not species-specific for all reproductive components, except for floral visiting bees; and (iii) edge influences in plants reproductive components in the cerrado sensu stricto area are restricted to 30 m from the road, except for fruit production. Our results suggest that anthropogenic changes in the landscape should be assessed in detail, as changes that are often considered to be negligible and that are believed to not cause negative damage to the structure of ecosystem, may have impacts on it. A mitigating measure is to avoid fragmentation of forest areas, such as the construction of dirt roads that cross preserved areas.

Bird community structure and species responses to edges in laurel forest fragmented by narrow roads (Tenerife, Canary Islands)

We examined interacting effects of habitat structure, topographic landscape, road edge and vehicle traffic (density and noise), on bird species composition, abundance and diversity in the laurel forest of Tenerife (Canaries). We examined multivariate habitat and landscape factors determining bird community composition and structure, and modality of specific responses by comparing road edge vs interior zones. Abundance of breeding birds in laurel forest showed slight to no increases in response to roads. Two specialized taxa, the palaeoendemic pigeon Columba bollii and Regulus regulus, revealed neatest negative reductions in abundance near roads. Higher noise levels, vegetation density, lower canopy closure and wood selective extraction characterized roadsides. Most passerines showed moderate affinity for forest edges and did not evidence decreases due to road proximity. The topographic landscape in these mountainous areas strongly interacted with road edge effects to determine bird community structure. Narrow road disturbances on the laurel forest was related to moderate increase in bird abundance and diversity near edges, but at the cost of losing presence of forest-demanding species playing important ecological roles.

Small logging roads do not restrict movements of forest rats in Bornean logged forests

AbstractSelective logging is driving the proliferation of roads throughout tropical rain forests, particularly narrow, unpaved logging roads. However, little is known about the extent of road edge effects or their influence on the movements of tropical understory animal species. Here, we used forest rats to address the following questions: (a) Does the occupancy of rats differ from road edges to forest interior within logged forests? (b) Do roads inhibit the movements of rats within these forests? We established trapping grids along a road edge‐to‐forest interior gradient at four roads and in three control sites within a logged forest in Sabah, Malaysia. To quantify the probability of road crossing, rats were captured, translocated across a road, and then recaptured on subsequent nights. We caught 216 individuals of eight species on 3,024 trap nights. Rat occupancy did not differ across the gradient from road edge to interior, and 48 percent of the 105 translocated individuals crossed the roads and were recaptured. This proportion was not significantly different from that of rats returning in control sites (38% of 60 individuals), suggesting that small roads were not barriers to rat movements within logged forests. Subadults were significantly more likely to return from translocation than adults in both road and control sites. Our results are encouraging for the ecology of small mammal communities in heavily logged forests, because small logging roads do not restrict the movements of rats and therefore are unlikely to create an edge effect or influence habitat selection.

Effects of roads and adjacent areas on diversity of terrestrial isopods of Hungarian highway verges

AbstractTransportation infrastructure may be the most important driver of social and economic development, but it is a major cause of environmental change in landscapes. The main objective of this paper is to report road edge effects on isopods of Hungarian highway verges. We examined the isopod diversity along five highways (M0, M1, M3, M5, M7) while accounting for road edge proximity and the adjacent areas. Double-glass pitfall traps were set in a total of 15 sites and at three distances from the edge of the roads next to different types of adjacent areas. We found differences between ecological parameters of isopod communities in relation to adjacent areas as well as to road edge proximity. The highest diversity was observed near urban areas, while the lowest was near the arable fields. Isopod diversity increased with decreasing distance from a road. Species diversity of different types of verges based on adjacent areas varied strongly in relation to road edge proximity. A medium distance (40 m) from roads had a positive effect on species richness, while verges next to arable fields were the most species-rich habitats. The general conclusion of this study is that highway verges provided suitable environment conditions for generalist isopod species but may be a limiting factor for specialist isopods. Moreover, highway verges function as corridors for isopods. The proximity of roads and urban areas positively affected isopods, and verges close to roads and urban areas are considered as an attractive environment for isopods in heterogeneous roadside verges.

The impact of forest roads on understory plant diversity in temperate hornbeam-beech forests of Northern Iran

Forest roads alter the biotic and abiotic components of ecosystems, modifying temperature, humidity, wind speed, and light availability that, in turn, cause changes in plant community composition and diversity. We aim at investigating and comparing the diversity of herbaceous species along main and secondary forest roads in a temperate-managed hornbeam-beech forest, north of Iran. Sixteen transects along main and secondary forest roads were established (eight transects along main roads and eight along secondary roads). To eliminate the effect of forest type, all transects were located in Carpinetum-Fagetum forests, the dominant forest type in the study area. The total length of each transect was 200m (100m toward up slope and 100m toward down slope), and plots were established along it at different distances from road edge. The diversity of herbaceous plant species was calculated in each plot using Shannon-Wiener index, species richness, and Pielou's index. The results showed that diversity index decreased when distance from road edge increases. This decreasing trend continued up to 60m from forest road margin, and after this threshold, the index slightly increased. Depending on the type of road (main or secondary) as well as cut or fill slopes, the area showing a statistical different plant composition and diversity measured through Shannon-Wiener, species richness, and Pielou's index is up to 10m. The length depth of the road edge effect found in main and secondary forest roads was small, but it could have cumulative effects on forest microclimate and forest-associated biota at the island scale. Forest managers should account for the effect of road buildings on plant communities.

Vertebrate Ticks Distribution and Their Role as Vectors in Relation to Road Edges and Underpasses.

Roads fragment vertebrate populations and affect the dynamics and dispersal patterns of vertebrate parasites. We evaluated how vertebrate ticks distribute near roads and road underpasses in human-caused road-fragmented landscapes in Seville, SW Spain. We sampled 49 stations with 93 individualized sampling points and assessed tick abundance. We explored the relationship between tick presence and abundance and distance to the nearest road and underpass (drainage culverts and other passages used by vertebrates), and landscape features through categorical regression and nonparametric statistics. The presence of the tick-borne pathogens Borrelia sp. and Bartonella sp. was also analyzed by PCR. We found preliminary evidence of high relative tick abundance next to roads and in the vicinity of road underpasses. Plant cover type was related to tick presence in this road context. Implications of road permeability and edge effect in patterns of vertebrate-tick relationships in road fragmentation contexts are discussed. Both Borrelia sp. and Bartonella sp. were detected in the ticks analyzed. This is the first report of these bacteria in ticks from Seville. The results confirm the potential risk of acquiring Lyme disease and bartonellosis in this area.

Edge effect of busy high traffic roads on the nest site selection of birds inside the city area: Guild response

The rapid development of road infrastructure is inevitable with increasing world human population and rise in the number of vehicles on the roads is going to be an increasing threat to native habitat of many wildlife populations around the world. The present work examines the edge effect of high traffic roads on nest site selection of birds in Udaipur city, Rajasthan (India). A total of 112 nesting site of 14 bird species (among six guilds), was recorded during the study. All six guilds (i.e., carnivore, omnivore, granivore, nectivore, frugivore and insectivore) were sharing similar kind of habitat with fine scale differences (P<0.0001). The PCA revealed that trees with suitable GBH, canopy and height were supporting birds’ nesting diversity, but the buildings were supporting the highest number of nesting. Different guilds showed different preference to different variables. Spatial heterogeneity, less predation, optimal feeding ground and higher number of advertising and display boards of shops at roadside buildings might be crucial factors for birds’ nesting in this highly disturbed area.

The floral characteristics of the road edge effect on the example of a road with low traffic volume in the &amp;#8220;Puszcza Notecka&amp;#8221; Forest

This paper concerns the edge effect of a provincial road on the broadly understood inventory characteristics of the neighbouring inland dune pine stands in the “Puszcza Notecka” Forest in Poland. The observations were conducted in the pine stands in the fresh coniferous forest and fresh mixed coniferous forest sites. Twelve rectangular experimental sites, called belt transects, were established perpendicular to the road axis. Each of them consisted of 3–4 plots located at different distances from the pavement edge. In the course of the survey of the flora, a total of 108 plant taxa, out of which 70% are found solely in the immediate vicinity of the road, 25% were found both along the road and in the stand interior and 5% were found only inside the stand. The shrub layer and the forest floor vegetation layer showed a higher coverage and species richness with the opposite trend observed for mosses and lichens. Despite the significant participation of synanthropic plants, there was no invasion of alien species. Due to the low volume of traffic and the lack of maintenance treatments of road surface, the reasons of changes in the species composition are attributed to the modifications of light and humidity conditions.

Road-Edge Effects on Herpetofauna in a Lowland Amazonian Rainforest

The impact of roads on the flora and fauna of Neotropical rainforest is perhaps the single biggest driver of habitat modification and population declines in these ecosystems. We investigated the road-edge effect of a low-use dirt road on amphibian and reptile abundance, diversity, and composition within adjacent lowland Amazonian rainforest at San Jose de Payamino, Ecuador. The road has been closed to vehicle traffic since its construction in 2010. Thus, effects from vehicle mortality, vehicle-related pollution, and road noise were not confounding factors. Herpetofauna were surveyed using both visual encounter surveys and drift fences with pitfall and funnel traps at varying distances from the road. Structural and microclimate features of the forest were measured at each sampling distance. Several habitat variables were found to differ at intermediate and interior sampling distances from the road compared to forest edge conditions, suggesting the road-edge effect began to attenuate by the intermediate sam...

Road Edge Effect and Elevation Patterns of Native and Alien Plants on an Oceanic Island (Tenerife, Canary Islands)

We studied road edge effects on floristic composition and richness of alien and native plants on five zonal ecosystems, following a steep altitudinal gradient from arid coastal and mid-elevation scrublands, through laurel and pine forests, to summit scrub, on Tenerife (Canary Islands). We analyzed vegetation within transects running from the road edge to the core of natural habitats. Alien richness significantly decreased with distance to road edge for most ecosystems. Native richness also decreased with increasing road distance for the coastal scrub and pine forest, but increased for the thermophilous scrub. We found a decrease in both native and alien species richness with elevation. Our results suggest that road edge effects in alien plant invasion are stronger in native shrub communities at low elevations than in forests (laurel and Canary Island pine forest), where aliens were limited to a narrow road edge band. Detrended correspondence analyses showed that road edge plots were floristically very different from interior plots and that each ecosystem harboured a specific alien assemblage with few species present in more than one ecosystem, suggesting a marked species turnover of roadside alien species across altitudinal belts up to the pine forest. However, at high elevations, very few aliens invaded roadsides, probably due to harsh environmental conditions and still relatively low propagule pressure.

The responses of leaf litter invertebrates to environmental gradients along road edges in subtropical island forests

Abstract Knowledge of how roads affect forest biodiversity can be improved by measuring the responses of indicator species to complex environmental gradients caused by these infrastructures. We studied litter invertebrate species responses to road edges in laurel and pine forests in Tenerife, Canary Islands. We sampled invertebrates from litter and assessed the environmental variation related to road proximity. We also assessed the effect of relevant environmental predictors on a diverse array of potential indicator species. We applied canonical ordination and non-parametric regression (Lowess) to classify invertebrate species responses to roads and their associated gradients. Three types of responses to road edge proximity were defined for the most common invertebrate taxa: edge-preferring or edge specialists, interior-preferring or edge-avoiders, and edge-indifferent or neutral species. Those species appearing most frequently and with higher population density between 1 and 20 m from the edge (commonly peaking at 10 m from the road) were categorized as edge-preferring. We classified taxa attaining peak population densities at or beyond 60 m from the edge (and most commonly 100 m) as interior species. Edge-neutral species were those without an evident pattern of stabilization in abundance along the gradient and with peaks in abundance at varying distance intervals. These edge litter communities contain a high native and endemic diversity but also a significant density of alien fauna. The specific patterns of penetration of road edge effects on invertebrate species should be seen as having a pervasive and cumulative impact considering the exceptionally large number of roads in these forests and the high population densities of alien invertebrates. Future management plans for forest conservation on the Canary Islands should include the highly altered but valuable litter communities along road edges.

Spatial road disturbance index (SPROADI) for conservation planning: a novel landscape index, demonstrated for the State of Brandenburg, Germany

The expansion of roads, and the subsequent changes to the surrounding landscape not only lead to landscape fragmentation but also have been shown to be a key driver of biodiversity loss and ecosystem degradation. Local declines of species abundance as well as changes in animal behaviour have drawn attention to wider ecosystem effects including altered species composition and a degradation of ecosystem functioning. However, methods for measuring and quantifying the distribution and environmental impacts of roads are not yet fully developed. We present a new technique for assessing the potential impacts of roads on biodiversity using a spatial road disturbance index (SPROADI). The index is calculated from three sub-indices: traffic intensity as a measure of traffic volume per time and space; vicinity impact, which is the assessment of edge effect of roads on adjacent habitats (the road-effect zone); and fragmentation grade, which provides an indication of the degree to which the landscape is intersected by roads. SPROADI was then tested using data from the Federal State of Brandenburg in north-eastern Germany. A sensitivity analysis was carried out on the results to assess the robustness of the index. The findings revealed expected patterns of high road disturbance in urban and peri-urban landscapes surrounding Berlin. Less obvious were the high levels of road density and impacts in forest plantations across the southern region of Brandenburg, and low levels of road disturbance in agricultural crop lands of the north-western region. Results were variable for areas under some form of protection. The only national park displayed substantially lower SPROADI values in contrast to the surrounding non-protected areas whilst other protected area categories, which were landscape conservation areas and nature parks, revealed SPROADI values that were equally high as those for non-protected areas. The results of this study demonstrate the strengths and potential applications of SPROADI as a quantitative means for identifying low-traffic areas in the context of conservation and sustainable transport planning.

Roadside habitats: effects on diversity and composition of plant, arthropod, and small mammal communities

Road edge effects cover extensive areas and exert a wide range of ecological influences on nearby plants and animals. Most studies have focused on individual and population level effects of the road edge; less is known about how communities and their functionality are altered in proximity to roads. Here, we studied the effect of road edges on species richness, rarity, endemism, composition, and functional (trophic) classification of communities of plants, ground-dwelling arthropods (beetles, spiders, scorpions, diplopods), and small mammals. The study, conducted in a Mediterranean ecosystem in central Israel, included sampling of these taxa in 10 plots adjacent to a regional road, and in 12 nearby control plots located in a typical shrubland habitat. We found a variety of community level road edge effects on the structure, composition, and function of the studied communities. The extent of effects varied among taxa, but they were generally positive or neutral. For the species-rich taxa (plants, beetles, and spiders), distinct road edge communities characterized by higher richness and altered species composition were found. Rarity and endemism were lower, and the proportion of disturbance-associated plant species was higher at the road edge. Among the species-poor taxa, scorpions and small mammals were more abundant along road edges than in control plots, while diplopods, the only negatively affected taxon, showed decreased abundance along the road. No ecologically meaningful changes in richness or composition were detected for the species-poor taxa along the road edge. Road edges profoundly affect floral and faunal communities, with possible implications for biodiversity conservation.

Influences of forest roads and their edge effects on the spatial pattern of burn severity

Previous research has shown that forest roads are an important feature in many landscapes and have significant effects on wildfire ignition and cessation. However, forest road effects on burn severity have not been studied at the landscape level. Therefore, the overarching goal of our study is to identify the influences of road edge effects on the spatial patterns of burn severity. We analyzed six fires within the Okanogan–Wenatchee National Forest on the eastern slope of the Cascades mountain range of central Washington.We generated two categories for assessing road variables: (1) Primary Road Effect Zone (area within 150m of the nearest road) and (2) Secondary Road Effect Zone (area from 150m to 300m to the nearest road). A regular sampling grid including one out of every 9cells was created for each fire.These grids were intersected with burn severity data in the form of the Relative Differenced Normalized Burn Ratio (RdNBR), road distance category, stream distance, elevation, slope, terrain shape index, heat load index, canopy cover, and fuel type. We fit spatial regression models with RdNBR as the dependent variable.We found that high burn severity is less likely to occur in the Primary Road Effect Zone for most fires, although one fire exhibited the opposite relationship. Forest road edge effects were hypothesized to be an important determinant of burn severity because fragmentation created by roads alters the roadside fuel profile and environment and because road corridors create barriers to fire spread. Recognizing roadside effects on burn severity patterns highlights the need for further study of the range of effects that roads have on fuels and the fire environment and the potential for incorporating road effects into landscape-level assessments of fire risk.

Road edge effects on litter invertebrate communities of subtropical forests

We assessed road edge effects on leaf-litter macroinvertebrates in laurel and pine forests in Tenerife (Canary Islands), studying composition, abundance, richness and diversity, and the role of environmental gradients. We sorted species to the finest taxonomic resolution possible and used a morphospecies approach when necessary. In all, 15,824 invertebrates were identified from 388 litter samples (from >500 species, five major phyla and 31 orders). Alien invasive species of Oligochaeta, Pulmonata, Isopoda, Diplopoda and Hymenoptera were frequent in both forests. Richness, diversity and rarefaction pointed to a disturbance threshold within the first 10 m off the road, and edge effects were steeper in laurel forest than in pine forest. Overabundant aliens were partially responsible for highly disturbed litter assemblages on this edge zone in both forests. Proximity to road edge caused gradients of disturbance of forest structure. Litter moisture, rock and litter cover in laurel forest, and grass and canopy cover in pine forest were the best predictors of community variation. Results seemed to give some empirical support to the intermediate disturbance hypothesis. This altered road edge zone may accumulate regionally causing net reductions of ecosystem area and quality, impacting on its integrity and biodiversity.

Estimating the road edge effect on adjacent Eucalyptus grandis forests in KwaZulu-Natal, South Africa, using texture measures and an artificial neural network

SPOT-5 multispectral and panchromatic image data were used to compute texture measures to estimate the road edge effect on adjacent Eucalyptus grandis forests. Employing a stepwise selection algorithm enabled the selection of optimal texture measures that were input into a backpropagation artificial neural network. The R2 of best models ranged from 0.67 to 0.89 for DBH, TH, BA, Volume and LAI on an independent test data set, with a root mean square error (RMSE) range of 0.01–5.36% for the respective variables. The result is critical for understanding and spatially predicting the road edge effect on adjacent vegetation.

Edge effect of low-traffic forest roads on bird communities in secondary production forests in central Europe

Worldwide forests fragmentation has lead to a massive increase of habitat edges, creating both negative and positive impacts on birds. While busy highways dissecting forested areas create edges which are known to reduce bird densities due to the disturbing effect of noise, the impacts of logging forest roads with low traffic volumes have rarely been studied. In this study, we compared species richness and similarity of canopy, cavity and shrub guilds of birds along low-traffic forest roads, in forest interior, and at forest edges in secondary forests in central Europe, where the forests have passed through extensive changes toward uniformly compact growths dominated by production conifers. Although we found tree diversity as positively affecting bird richness across all habitats, the bird richness along forest roads was higher than in forest interior but lower than along forest edges. The shrub guild of birds along forest roads resembled this guild along forest edges while canopy and cavity guilds at the roads were more similar to these guilds in forest interior. Forest interior had the highest probability for some guild to be absent. We conclude that low-traffic roads lead to increase of habitat heterogeneity in structurally poor forests and attract birds due to additional habitat attributes—including better light conditions—that are scarce in forest interior. Therefore, broader support for higher structural diversification of uniform plantations in central European production forests would benefit bird communities inhabiting these areas.

Changes in plant species composition and litter production in response to roads and trails in the laurel forest of Tenerife (Canary Islands)

Road density has increased in the Canary Islands' forests during the last century, affecting an unknown amount of forested area. We studied road effects on vegetation in the relict laurel forest of Tenerife. We assessed edge effects on plant species richness, plant composition and litter production. Effects of anthropogenic corridors on vegetation differed between paved roads and unpaved trails. Opportunistic species (shade intolerant) dominated road edges, but composition differed among all sites. Multivariate analysis revealed convergence in species composition along the corridor-interior gradient. For trails, both species richness and litter production did not differ significantly between edge and interior. Road edge effects on vegetation were detectable only within the first 10 m towards the interior. This suggests that the main effects of roads and trails on species richness are limited to the immediate edge of the laurel forest. Litter fall along road edges was half that of the interior. However, no significant differences were detected due to the high variability of the data. A buffer of approximately 10 m would result in the reduction of the total area of the remaining undisturbed laurel forest. Based on these results, the building of new paved roads should not be considered. Low human population inflow into the Anaga Rural Park needs to be maintained on a sustainable basis. Forest managers should take these road/trail effects into account when planning new road openings in this ecosystem.

Road edge effect on the abundance of the lizard Gallotia galloti (Sauria: Lacertidae) in two Canary Islands forests

Transportation infrastructure is a main cause of environmental change in forest landscapes worldwide. In the Canary Islands, a dense road system fragment the native Canarian pine and laurel forests causing potential changes in population densities of endemic lacertid lizards (genus Gallotia). Our aim was to assess road edge effects on relative abundance patterns of the endemic Gallotia galloti in both forests. We also explored the species–habitat relationships in this road-fragmentation context. We found that lizard relative density in relation to road edges differed between forests. Lizards were more abundant along edges and leeward interior, but virtually absent from the interior of the windward laurel forest. In the pine forest, lizards were present at three distances from edge, with a net decrease in abundance from edge to interior. These patterns may be explained partly by differences in vegetation structure regarding road proximity in each forest that potentially affect the helio- and thigmothermic character of G. galloti, and thus its habitat use. A general suggestion of this study is that road margins create corridors that may be used by native lizards for dispersal through inhospitable forest matrix. The high road density in Tenerife may have negative implications for the conservation of the genetic variability of G. galloti. At the island scale, increased communication between lizard populations through road corridors might increase homogenization of the gene pool. Ecological processes in which this lizard plays important roles may also experience changes along road edges.

Edge effects of roads on temperature, light, canopy cover, and canopy height in laurel and pine forests (Tenerife, Canary Islands)

The estimation of the road edge effect is useful to understand changes induced by the road network on ecosystems. Road networks on islands may break ecosystem integrity through microclimate edge effects, which are known to be associated with disturbances to animal and plant communities. Road edge effects have been scarcely studied on oceanic islands. In this paper we studied road edge effects on microclimate and canopy structure in laurel and pine forests in Tenerife (Canary Islands). We assessed depth of road edge effect for temperature at four vertical layers (soil, litter and air at 5 cm and 1.3 m above ground), light intensity, canopy cover and height, in transects running from narrow (6–7 m width) asphalt roads and dust trails to 100 m to the interior of both forests. We used an ANOVA procedure with Helmert difference contrasts to identify the distances along transects over which edge effects were significant. We detected significant gradients for most parameters but they were consistently narrow both within and between forests. In the laurel forest, we detected highly significant gradients for soil temperature, light, and canopy cover and height in both asphalt and unpaved roads. In the pine forest, we detected a highly significant gradient for soil temperature at asphalt roads, and a significant light gradient for both asphalt and unpaved roads. From the road edge to the forest interior, significant temperature changes persisted for only 3 m, light variation persisted for 6 m, and canopy cover and height changed significantly within the first 10 m. Asphalt roads and dust trails revealed different patterns of variation for temperature between edge and interior. No differences were found between the two types of roads in edge-interior trends for light or canopy structure. The abruptness of microclimate and canopy gradients was slightly higher in the laurel forest than in the pine forest, caused by a higher edge contrast in the former. The depth of the road edge effect found in laurel and pine forests was small, but it could have cumulative effects on forest microclimate and forest associated biota at the island scale. Such changes deserve attention by local road managers for planning and design purposes.