Linear infrastructure intrusions into natural ecosystems are man-made linear infrastructure such as roads and highways, electric power lines, railway lines, canals, pipelines, firebreaks, and fences. These intrusions cause linear opening through the habitat or breakage in landscape connectivity due to infrastructure creation and maintenance, which is known to have multiple ecological effects in terrestrial and aquatic ecosystems. [1] [2] These effects include habitat loss and fragmentation, spread of invasive alien species, desiccation, windthrow, fires, animal injury and mortality (e.g., roadkill), changes in animal behaviour, pollution, microclimate and vegetation changes, [3] loss of ecosystem services, [4] increased pressures from development, tourism, hunting, garbage disposal, and associated human disturbances. [5] These intrusions, considered crucial infrastructure for economic sectors such as transportation, power, and irrigation, may also have negative social impacts on indigenous and rural people through exposure to novel social and market pressures, loss of land and displacement, [6] and iniquitous distribution of costs and benefits from infrastructure projects. The study of the ecological effects of linear infrastructure intrusions has spawning sub-fields of research such as road ecology and railroad ecology.
Establishment and maintenance of roads and highways causes direct loss of habitat because it involves clearing of trees and other vegetation, cutting and dumping of soil and excavated materials, movement of heavy vehicles and earth-movers, and establishment of worker settlements. Besides immediate effects of these disturbances, roads and other linear infrastructure intrusions may cause changes that may persist in the landscape for years to decades. In tropical rainforests in Amazonia and other parts of the world, satellite imagery reveals roads to have contributed to a 'fish-bone' pattern of ramifying habitat loss. [7] [8] In the Garo Hills in Meghalaya, an area of 456 ha of biodiversity-rich forest was lost to roads between 1971 and 1991. [9]
Loss of tree cover and its effects may be significant in wildlife reserves. In four tiger reserves in Karnataka, a geographic information system analysis revealed a high road density of around 1 km of forest road per square kilometre of forest, increasing in the tourism zone in Bandipur Tiger Reserve to 2.25 km of road per square kilometre of forest. [10] Taking just the 800 km of road in Bandipur Tiger Reserve (Gubbi 2010), and assuming an average width of 10 m of the road itself, this translates into 800 hectares (8 km2) of direct habitat loss. [5]
Vegetation clearing along and on either side of the linear infrastructure intrusion for maintenance, visibility, or as 'viewlines' within wildlife reserves, contributed to further habitat loss, disturbance, and associated effects. One study from southern India, found that tree death is 250% higher along roads than forest interior. [11] Physical and biotic effects such as weed invasion and tree death are added edge effects spreading on either side of the cleared area. Tropical forests experience greater diurnal fluctuations in light, temperature, and humidity within 50 – 100 m of edges that are typically drier and hotter than forest interiors. As a result, elevated tree mortality, numerous canopy gaps and a proliferation of disturbance-adapted vines, weeds, and pioneer species may occur along edges. [2] Thus, an area about 100 m wide may be affected along intrusions such as roads, with each kilometre of road affecting about 10 ha of habitat (comparable figures for federal highways in the US are 13.5 ha per km of road). [1] [5] [12]
Mortality of wildlife in natural ecosystems is one of the direct impacts of linear infrastructure intrusions. This occurs in a variety of ways: roadkill (or wildlife – vehicle collisions, WVC) in the case of roads and highways, [13] electrocution along power lines, [14] [15] drowning in irrigation canals, [16] [17] and impalement or snagging on fences. Animals may also be killed during construction of the infrastructure, earthwork and annual maintenance operations, which may particularly affect slow-moving and burrowing species such as turtles, snakes, and soil fauna. Plant and animal mortality may also be caused by road construction equipment. [18] Wildlife mortality may have several consequences on animal populations in the vicinity of linear infrastructures. Disruptions caused by linear infrastructure may increase negative human – wildlife interactions (conflicts) involving species such as wild elephants and large carnivores thereby leading to additional mortality. [19] The effects may result in reduced wildlife population densities or avoidance of areas close to linear infrastructure. A review of studies found mammal and bird population densities declined with their proximity to infrastructure, with the influence of infrastructure on bird populations extending up to about 1 km, and effects on mammal populations up to about 5 km. [20]
Roadkill surveys reveal that a wide variety of species are killed ranging from invertebrates and herpetofauna to many birds and mammals, including large mammals such as elephants, deer, and carnivores such as tiger and leopard. Studies from southern India have found road mortality of dozens of animal species, including invertebrates, amphibians, reptiles, birds, and mammals. [21] [22] Along roads in Brazil, a range of mammal species are known to be killed along roads including crab-eating fox, capybara, maned wolf, and jaguar, with a 3-year study recording roadkills of 40 bird species, 24 mammal species and 8 reptile species along the BR-040 highway. [23]
Studies from tropical forest regions suggest that reptiles and amphibians are numerically amongst the most frequently road-killed taxa. [24] [25] In Sharavathi river basin in India, a study estimated an amphibian kill rate on roads averaging about 10 kills/km per day on a National Highway during the monsoon. [26] In contrast, birds and mammals may be killed more frequently than herpetofauna along roads through grassland and scrubland habitats [27] [28] or in landscape dominated by open pastures as in New South Wales. [29]
Mortality of wildlife species due to collisions with power lines and electrocution is reported for a large diversity of bird species [14] and also large mammals such as Asian elephants. [15] A study from the Karoo, South Africa, found high-voltage transmission lines and low-voltage distribution lines killed thirty bird species, with Ludwig's bustards comprising 69% and other bustards (including Kori bustards) a further 18% of 679 carcasses found. [30] This study reported higher collision rates on transmission lines (1.12 bustards/km/yr) than on distribution lines (0.86 bustards/km/yr), but the latter probably kill more birds as the smaller distribution lines are four times as extensive in South Africa.
Linear intrusions like roads and highways by disrupting dispersal and movement of animals may affect gene flow and genetic structure of populations. A review noted that several studies have reported negative effects of roads on genetic diversity and genetic differentiation, especially for some large mammals and amphibian species. [31] This was despite the fact that most roads and highways were relatively recently been built or been in existence only for a few generations.
Linear infrastructure intrusions may cause landslides and soil erosion, particularly on steep and mountainous terrain. In southeast Asian tropical forests, roads on steep terrain contribute the largest surface erosion and landslide losses (per unit area disturbed) compared to other land uses. Landslide and surface erosion fluxes are typically ten to more than 100 times higher compared to undisturbed forests. [32] In the Indian Himalaya, roads, road-building, and dumping of debris lead to loss of forest cover, increasing erosion, and creating a need for further maintenance. [33] [34] Roadside natural vegetation in forests play a role in slope stabilization, thereby accounting for a negative correlation between forest cover and landslide activity in the region. [34] In humid tropical forests of Puerto Rico, landslide frequency within 85 m on either side of a road was 30 landslides per square kilometre, which was five times higher than the study area background frequency of about six landslides per square kilometre. [35]
The forest raven, also commonly known as the Tasmanian raven, is a passerine bird in the family Corvidae native to Tasmania and parts of southern Victoria, such as Wilsons Promontory and Portland. Populations are also found in parts of New South Wales, including Dorrigo and Armidale. Measuring 50–53 cm (20–21 in) in length, it has all-black plumage, beak and legs. As with the other two species of raven in Australia, its black feathers have grey bases. Adults have white irises; younger birds have dark brown and then hazel irises with an inner blue rim. New South Wales populations are recognised as a separate subspecies C. tasmanicus boreus, but appear to be nested within the Tasmanian subspecies genetically.
Roadkill is a wild animal that has been killed by collision with motor vehicles. Wildlife-vehicle collisions (WVC) have increasingly been the topic of academic research to understand the causes, and how they can be mitigated.
Urban ecology is the scientific study of the relation of living organisms with each other and their surroundings in an urban environment. An urban environment refers to environments dominated by high-density residential and commercial buildings, paved surfaces, and other urban-related factors that create a unique landscape. The goal of urban ecology is to achieve a balance between human culture and the natural environment.
The Atlantic Forest is a South American forest that extends along the Atlantic coast of Brazil from Rio Grande do Norte state in the northeast to Rio Grande do Sul state in the south and inland as far as Paraguay and the Misiones Province of Argentina, where the region is known as Selva Misionera.
Wildlife crossings are structures that allow animals to cross human-made barriers safely. Wildlife crossings may include underpass tunnels or wildlife tunnels, viaducts, and overpasses or green bridges ; amphibian tunnels; fish ladders; canopy bridges ; tunnels and culverts ; and green roofs.
Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes that slowly alter the layout of the physical environment, and human activity such as land conversion, which can alter the environment much faster and causes the extinction of many species. More specifically, habitat fragmentation is a process by which large and contiguous habitats get divided into smaller, isolated patches of habitats.
Habitat destruction occurs when a natural habitat is no longer able to support its native species. The organisms once living there have either moved to elsewhere or are dead, leading to a decrease in biodiversity and species numbers. Habitat destruction is in fact the leading cause of biodiversity loss and species extinction worldwide.
The Biological Dynamics of Forest Fragments Project is a large-scale ecological experiment looking at the effects of habitat fragmentation on tropical rainforest. The experiment which was established in 1979 is located near Manaus in the Brazilian Amazon rainforest. The project is jointly managed by the Amazon Biodiversity Center and the Brazilian Institute for Research in the Amazon (INPA).
Mudumalai National Park is a national park in the Nilgiri Mountains in Tamil Nadu in southern India. It covers 321 km2 (124 sq mi) at an elevation range of 850–1,250 m (2,790–4,100 ft) in the Nilgiri District and shares boundaries with the states of Karnataka and Kerala. A part of this area has been protected since 1940. The national park has been part of Nilgiri Biosphere Reserve since 1986 and was declared a tiger reserve together with a buffer zone of 367.59 km2 (141.93 sq mi) in 2007. It receives an annual rainfall of about 1,420 mm (56 in) and harbours tropical and subtropical moist broadleaf forests with 498 plant species, at least 266 bird species, 18 carnivore and 10 herbivore species. It is drained by the Moyar River and several tributaries, which harbour 38 fish species.
The Lower Guinean forests also known as the Lower Guinean-Congolian forests, are a region of coastal tropical moist broadleaf forest in West Africa, extending along the eastern coast of the Gulf of Guinea from eastern Benin through Nigeria and Cameroon.
The Guinean forest-savanna, also known as the Guinean forest-savanna transition, is a distinctive ecological region located in West Africa. It stretches across several countries including Guinea, Sierra Leone, Liberia, Ivory Coast, Ghana, Togo, Benin, Nigeria, and Cameroon. This region is characterized by a unique blend of forested areas and savannas, creating a diverse and dynamic landscape.
Railroad ecology or railway ecology is a term used to refer to the study of the ecological community growing along railroad or railway tracks and the effects of railroads on natural ecosystems. Such ecosystems have been studied primarily in Europe. Similar conditions and effects appear also by roads used by vehicles. Railroads along with roads, canals, and power lines are examples of linear infrastructure intrusions.
A wildlife corridor, also known as a habitat corridor, or green corridor, is an designated area that connects wildlife populations that have been separated by human activities or structures, such as development, roads, or land clearings. These corridors enable movement of individuals between populations, which helps to prevent negative effects of inbreeding and reduced genetic diversity, often caused by genetic drift, that can occur in isolated populations. Additionally, corridors support the re-establishment of populations that may have been reduced or wiped out due to random events like fires or disease. They can also mitigate some of the severe impacts of habitat fragmentation, a result of urbanization that divides habitat areas and restricts animal movement. Habitat fragmentation from human development poses an increasing threat to biodiversity, and habitat corridors help to reduce its harmful effects. Corridors aside from their benefit to vulnerable wildlife populations can conflict with communities surrounding them when human-wildlife conflicts are involved. In other communities the benefits of wildlife corridors to wildlife conservation are used and managed by indigenous communities.
Defaunation is the global, local, or functional extinction of animal populations or species from ecological communities. The growth of the human population, combined with advances in harvesting technologies, has led to more intense and efficient exploitation of the environment. This has resulted in the depletion of large vertebrates from ecological communities, creating what has been termed "empty forest". Defaunation differs from extinction; it includes both the disappearance of species and declines in abundance. Defaunation effects were first implied at the Symposium of Plant-Animal Interactions at the University of Campinas, Brazil in 1988 in the context of Neotropical forests. Since then, the term has gained broader usage in conservation biology as a global phenomenon.
Road ecology is the study of the ecological effects of roads and highways. These effects may include local effects, such as on noise, water pollution, habitat destruction/disturbance and local air quality; and the wider environmental effects of transport such as habitat fragmentation, ecosystem degradation, and climate change from vehicle emissions.
William F. Laurance, also known as Bill Laurance, is Distinguished Research Professor at James Cook University, Australia and has been elected as a Fellow of the Australian Academy of Science. He has received an Australian Laureate Fellowship from the Australian Research Council. He held the Prince Bernhard Chair for International Nature Conservation at Utrecht University, Netherlands from 2010 to 2014.
Road expansion refers to the increasing rate at which roads are constructed globally. Increases in population size and GDP, particularly in developing nations, are the primary drivers of road expansion but transportation planning decisions also play an important role. The anticipated length of newly paved roads to be built between 2010 and 2050 would encircle the planet more than 600 times. Approximately 90% of the new roads are being built in developing nations. Africa and Southeast Asia are predicted to experience a large amount of road expansion shortly.
The barrier effect of roads and highways is a phenomenon usually associated with landscape ecology, referring to the barrier that linear infrastructure like roads or railways place on the movement of animals. Largely viewed as a negative process, the barrier effect has also been found to have several positive effects, particularly with smaller species. To reduce a road or railway's barrier effect, wildlife crossings are regarded as one of the best mitigation options, ideally in combination with wildlife fencing. The barrier effect is closely linked to habitat fragmentation and road ecology.
A roadkill hotspot or blackspot is an accumulation of roadkill along a given length of roadway with significantly more wildlife-vehicle collisions than expected to occur by chance, based on a normal distribution. Decision-makers can then authorize the construction of roadkill mitigation infrastructure based on roadkill hotspot locations, prioritizing those with the most roadkill in number or those for a particular target species for conservation. Roadkill hotspots vary spatially and temporally, depending on the scale, duration of monitoring, and both the species and season in question. They can be calculated using roadkill survey data; GPS coordinates of roadkill collected by researchers and highway maintenance personnel, or increasingly, civilian-reported data. Additionally, roadkill hotspots can be projected by using a model to ascertain probable locations; models typically use existing wildlife abundance, distribution, and mitigation data combined with landscape variables and climatic data. Models are often used to determine the probable roadkill locations of ecologically sensitive animals or during the planning stages of a new road, it is noted that these locations may not align perfectly with sites of highest animal crossing attempts. Many academics stress the combined value of animal abundance and migration data with roadkill hotspots as a more assured way to ascertain the best locations to construct roadkill mitigation structures.
Lenore Fahrig is a Chancellor's Professor in the biology department at Carleton University, Canada and a Fellow of the Royal Society of Canada. Fahrig studies effects of landscape structure—the arrangement of forests, wetlands, roads, cities, and farmland—on wildlife populations and biodiversity, and is best known for her work on habitat fragmentation. In 2023, she was elected to the National Academy of Sciences.