Linear Landscape Features Research Articles

Living on the edge: roads and edge effects on small mammal populations

1. Roads may affect wildlife populations through habitat loss and disturbances, as they create an abrupt linear edge, increasing the proportion of edge exposed to a different habitat. Three types of edge effects have been recognized: abiotic, direct biotic, and indirect biotic. 2. We explored the direct biotic edge effects of 3- to 4-m wide roads, and also a previously unrecognized type of edge effect: social. We live-trapped two threatened endemic rodents from Cozumel Island (Oryzomys couesi cozumelae and Reithrodontomys spectabilis) in 16 plots delimited by roads on two sides, to compare edge effects between two adjacent edges (corners), single-edge and interior forest, on life history and social variables. 3. No significant edge effects were observed on the life-history variables, with the exception of differences in body condition between males and females of O. c. cozumelae near edges. Both species showed significant and contrasting effects on their social variables. 4. O. c. cozumelae was distributed according to its age and sex: the proportion of adults and males was higher in interior than near edges, while juveniles and females were more abundant near edges. More nonreproductive females were present in corners than in single-edge and interior, while the opposite distribution was observed for nonreproductive males. 5. The distribution of R. spectabilis was related to its age and reproductive condition, but not to its sex. The proportion of adults was significantly higher in corners, while juveniles were only caught in single-edge and interior quadrants. The proportion of reproductive individuals was higher in edge than interior quadrants, while reproductive females were only present in edge quadrants. 6. We found significant differences between the quadrants with the greatest edge exposure in comparison with other quadrants. The social edge effects we identified complement the typology of edge effects recognized in ecological literature. Our study provides insight into the effects that sharp road edges have on biological and social characteristics of small mammal populations, highlighting how such effects vary among species. Our findings have important conservation implications for these threatened species, but are also applicable in a broader context wherever there are abrupt edges caused by linear landscape features.

Environmental Consequences of the Demise in Swidden Cultivation in Montane Mainland Southeast Asia: Hydrology and Geomorphology

The hydrological and geomorphological impacts of traditional swidden cultivation in Montane Mainland Southeast Asia are virtually inconsequential, whereas the impacts associated with intensified replacement agricultural systems are often much more substantial. Negative perceptions toward swiddening in general by governments in the region beginning half a decade ago have largely been based on cases of forest conversion and land degradation associated with (a) intensified swidden systems, characterized by shortened fallow and extended cropping periods and/or (b) the widespread cultivation of opium for cash after the Second World War. Neither of these practices should be viewed as traditional, subsistence-based swiddening. Other types of intensive agriculture systems are now replacing swiddening throughout the region, including semi-permanent and permanent cash cropping, monoculture plantations, and greenhouse complexes. The negative impacts associated with these systems include changes in streamflow response, increased surface erosion, a higher probability of landslides, and the declination in stream water quality. Unlike the case for traditional swiddening, these impacts result because of several factors: (1) large portions of upland catchments are cultivated simultaneously; (2) accelerated hydraulic and tillage erosion occurs on plots that are cultivated repetitively with limited or no fallowing to allow recovery of key soil properties, including infiltration; (3) concentrated overland flow and erosion sources are often directly connected with the stream network; (4) root strength is reduced on permanently converted hillslopes; (5) surface and ground water extraction is frequently used for irrigation; and (6) and pesticides and herbicides are used. Furthermore, the commercial success of these systems relies on the existence of dense networks of roads, which are linear landscape features renowned for disrupting hydrological and geomorphological systems. A new conservation focus is needed to reduce the impacts of these intensified upland agricultural practices.

Distribution of badger latrines in a high‐density population: habitat selection and implications for the transmission of bovine tuberculosis to cattle

Eurasian badgers Meles meles habitually deposit droppings and other scent marks at latrines, which may be associated with territorial defence, and communicate information related to group and individual identity and status, and food resources. Understanding patterns of latrine distribution contributes to our understanding of badger social behaviour, and may be relevant to managing the risks of transmission of bovine tuberculosis from badgers to cattle. We investigated the distribution of badger latrines relative to habitat composition in a high-density badger population occupying a 7 km2 area of diverse landscape in south-west England. Results indicated that the frequency and density of badger latrines varied according to land use, with woodland and linear landscape features (particularly hedges and stone walls) being positively selected. The number of latrines decreased significantly with distance from linear features. Grassland was negatively selected given its availability, but contained the highest number of latrines. The tendency for latrines to be associated with particular habitat types covaried spatially across the study area. We present a habitat selection probability function, based on the output of our analyses, to allow comparison of observed versus expected latrine counts per habitat type at different sites. Habitat manipulation on farmland may offer opportunities to manage exposure of cattle to badger latrines. However, our analyses indicate that other factors (perhaps demographic or environmental) may also exert a substantial local influence on latrine location.

Spatial relationships between intensive land cover and residual plant species diversity in temperate farmed landscapes

Summary In temperate farmed landscapes conservation policies increasingly emphasize large‐scale reductions in land‐use intensity. Yet despite a managed reversion to more favourable abiotic conditions, depleted regional species pools may prevent the re‐assembly of target communities. Using national‐scale survey data recorded across Great Britain in 1998, we investigated the extent to which grassland indicator plant species persisted on potential refuge habitats across a spatial gradient of intensive land cover in lowland 1‐km squares. These habitats comprised road verges, field boundaries, watercourse banks and small biotope fragments. Intensive land cover comprised built land, arable and improved grassland. The rate of reduction in indicator species richness across the intensive land cover gradient was significantly lower in all potential refuge features than in surrounding fields and larger areas of habitat. The best refuge locations were watercourse banks and small biotopes. In both cases, indicator species richness was higher than adjacent fields at the lowest intensive land cover and stayed higher as intensive land cover increased. However, as intensive land cover increased, plant traits associated with higher nutrient availability were more prominently represented among indicator species. Although richer assemblages of indicator species persisted on refuge features, population sizes are likely to be small, because of species–area effects, and also vulnerable to nutrient surpluses and reduced or inappropriate disturbance. Synthesis and applications. Across the British lowlands, linear landscape features and small habitat fragments can provide limited safe havens for unimproved grassland plant species. However, the identity of refuge features and their species richness and composition are likely to vary with local conditions. Three activities are therefore paramount in assessing their role in larger scale extensification schemes: (i) development of rapid ways of assessing the plant diversity and distribution of refuge features in local areas; (ii) quantification of the risks posed to the viability of residual source populations through implementation of different options for incorporating them into extensification schemes; (iii) maximization of scheme performance by targeting landscapes with sufficient residual diversity to enable increases in population size of the target species in the medium term.

Interacting effects of landscape context and habitat quality on flower visiting insects in agricultural landscapes

Summary Landscape context and habitat quality may have pronounced effects on the diversity of flower visiting insects. We investigated whether the effects of landscape context and habitat quality on flower visiting insects interact in agricultural landscapes in the Netherlands. Landscape context was expressed as the area of semi-natural habitats or the density of linear landscape features, and was quantified at spatial scales ranging from 250 to 2000 m. Habitat quality was determined as flower abundance. Species richness and abundance of hoverflies and bees were determined along 16 stream banks experiencing similar environmental conditions but situated in areas with contrasting landscape context. Only flower abundance and the area of semi-natural habitats within 500–1000 m were significantly related to species richness of hoverflies and bees and these factors had interacting effects on both species groups. Our results suggest that the regional area of semi-natural habitats had a positive effect on hoverfly species richness when flower abundance was relatively high, but not when flower abundance was low. Moreover, flower abundance had positive effects on hoverfly species richness only in areas with relatively many semi-natural habitats. Contrastingly, flower abundance had a more positive effect on bee species richness in landscapes with few semi-natural habitats compared to landscapes with more semi-natural habitats. Our results suggest that the importance of landscape context for the species richness of flower visiting insects depends upon the quality of the habitat patches.

Tracking butterfly flight paths across the landscape with harmonic radar

For the first time, the flight paths of five butterfly species were successfully tracked using harmonic radar within an agricultural landscape. Until now, butterfly mobility has been predominantly studied using visual observations and mark-recapture experiments. Attachment of a light-weight radar transponder to the butterfly's thorax did not significantly affect behaviour or mobility. Tracks were analysed for straightness, duration, displacement, ground speed, foraging and the influence of linear landscape features on flight direction. Two main styles of track were identified: (A) fast linear flight and (B) slower nonlinear flights involving a period of foraging and/or looped sections of flight. These loops potentially perform an orientation function, and were often associated with areas of forage. In the absence of forage, linear features did not provide a guiding effect on flight direction, and only dense treelines were perceived as barriers. The results provide tentative support for non-random dispersal and a perceptual range of 100-200 m for these species. This study has demonstrated a methodology of significant value for future investigation of butterfly mobility and dispersal.

Forest bird diversity and ski-runs: a case of negative edge effect

Among tourist activities in the Alps, winter sports have a prominent role because of the large scale of changes they cause at the habitat and landscape level. We have analysed whether ski resorts lead to significant threats to the avian diversity in the coniferous forests of the western Italian Alps, by comparing the bird communities of plots located in (1) the forest interior, (2) forest at the edge of ski-runs and (3) forest at the edge of pastures (the latter two are anthropogenic elements of forest fragmentation). Ski-runs produce a negative edge effect in the study forests: plots at their edges present lower bird species richness and Shannon diversity than those located in the forest interior or at the edges of pastures. In particular, birds typical of ecotone habitats seem to favour forest plots set at the edge of pastures. Ski-run-edges are linear landscape features that create high contrast edges; conversely, vegetation structure is more complex at the edge of pastures, attracting a rich and diverse avifauna. In the study area, pastures tend to be abandoned whereas winter sport resorts are increasing in extent. Accordingly, there is a need for coordinated management and cooperation between sport- and land-management agencies, in order to preserve native biodiversity while simultaneously managing land for sport activities.

Do field boundaries act as refugia for grassland plant species diversity in intensively managed agricultural landscapes in Britain?

Initiatives to restore characteristic plant species diversity to degraded habitats require target plant species populations to be established and maintained. In landscapes managed intensively for agriculture, species that are foci for restoration efforts may be scarce, being confined to core reserves of less-modified habitat or persisting as fragmented populations on linear landscape features. Botanical data from small and large-scale surveys across Britain was used to investigate whether grassland plants favoured by less intensive management persisted on field boundaries despite increasing productivity in the adjacent field. At low field productivity, field species richness was, on average, higher than in field boundaries. As productivity increased, boundary plots reduced in richness at a slower rate than adjacent fields thus boundaries became relatively richer in grassland species than adjacent fields. Species compositional similarity between fields and their boundaries also declined with increasing field productivity. Grassland field boundaries can function as refugia. However, the lower relative species richness of boundaries next to the least productive fields indicated that some plant species will, on average, be increasingly uncommon or absent in boundaries as field productivity increases. High residual variation in these relationships was linked to local variation in conditions between fields and their boundaries. Field boundaries next to highly productive grasslands appear to function as partial refugia for grassland plants. While highly species rich boundaries can locally occur next to species poor fields, the species richness of most boundaries falls well short of values typical of the least productive fields.

Communicating clearly about conservation corridors

Conflicting definitions lead to confusion when people communicate about ‘corridors’, particularly when they come from different disciplinary backgrounds. Usage of ‘corridor’ in game management, island biogeography, and metapopulation literature focused on function, namely, the movement of flora and fauna from one area to another. A structural usage of the term arose in the field of landscape ecology as it developed in North America with the matrix–patch–corridor paradigm of landscape structure. ‘Corridor’ is now used to describe both the structural and functional aspects of linear landscape features, often implicitly, in a wide range of disciplinary literature. Lack of a clear and consistent terminology leads to confusion about the goals or implied functions of corridors. Consequently, the manner in which corridors should be designed, managed, and evaluated is also unclear. Proper design and management of a corridor depends critically on a clear and explicit statement of its intended functions. If corridors are not designed to perform well-defined functions, the outcome may be disappointing, or even deleterious. The roles corridors play derive from six ecological functions: habitat, conduit, filter, barrier, source, and sink. These ecological functions have been recognized widely and adopted by a number of disciplines, including conservation biology, wildlife management, landscape ecology, and landscape planning. We review briefly the history of the term ‘corridor’ in the context of conservation, catalog some of its definitions and uses, review the functions of corridors, and differentiate between the structural and functional aspects of corridors. We reject the notion of defining ‘corridor’ succinctly, because of the complex and multiple functions a corridor may serve. Instead, we suggest that conservationists and planners consider and document explicitly all of the possible functions of corridors when designing them. Addressing explicitly these functions when designing a corridor should eliminate much of the confusion surrounding their roles, and focus attention on establishing design criteria for corridors that function as intended.

Quantifying changes in abundance of food plants for butterfly larvae and farmland birds

Summary 1. Recent changes in population size of butterflies and farmland birds across north‐west European landscapes have been linked to the effects of agricultural intensification. Reduction in food supply has been postulated as one of the proximal causes of these trends but the generality of this explanation has not been tested at a large scale and across animal species. 2. Changes in abundance of food plants for butterfly larvae and lowland farmland birds in the British countryside were analysed for the period 1978–90 using data from fixed plots recorded as part of the countryside surveys of Britain. 3. Associations were sought between these changes and trends in population size of selected butterflies and birds recorded from long‐term monitoring schemes. 4. No associations were found between change in abundance of food plants and either increasing, stable or decreasing animal groups. At the level of individual animal species, significantly more decreases than increases in food plant frequency were found for herbivorous bird species irrespective of population trend. The size of the reduction in food plant frequency was also significantly greater for the declining bird group than for stable or increasing groups. 5. Few significant associations were detected between population trend and food plant trend for butterfly species. However, the results suggested a positive relationship between increasing butterflies and increased abundance of Elytrigia repens and Urtica dioica. 6. Food plants that increased in abundance comprised species favoured by lack of management and increased nutrient availability. Increases in abundance were also associated with linear landscape features such as hedges and streamsides. Decreasing plant species included arable weeds and stress‐tolerant species typical of unimproved grasslands. 7. Based on evidence of local associations between animal and food plant change and the need for viable populations of food plants to exist within the range of each animal species, we support measures designed to enhance and maintain populations of declining food plants. Much evidence now exists to identify practical measures that husband food resources for many bird and butterfly species. The challenge for conservation policy is to manage their implementation at scales necessary to influence national trends.

The role of corridors in conservation: Solution or bandwagon?

Corridors are currently a major buzzword in conservation biology and landscape ecology. These linear landscape features may perform numerous functions, but it is their role in facilitating movement of fauna that has attracted much recent debate. The database supporting the idea of corridors acting as faunal conduits is remarkably small, and few studies have actually demonstrated that movement along corridors is important for any given species. Such data are very difficult to obtain, and conservation biologists are thus faced with the problem of whether to recommend the allocation of resources to corridors on the assumption that they may be important.