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EFFECTS OF ROADS ON LARGE MAMMALS

An Analysis of the Effects of Roads on Large Forest Mammals

Lucas Sanchez

ENVS 190

17, May 2017


Table of Contents

Abstract and Introduction……………………………………………………………………... 1

Part I: Direct Effects……………………………………………………………………………. 2

1.1 Ecosystem Degradation and Quality of Habitat……………………………………… 3

1.2 Vehicle-Animal Collision……………………………………………………………….. 6

1.3 Ecological Barriers, Habitat Fragmentation, and Connectivity Issues……………....9

1.4 Roads as a form of Ecological Facilitation…………………………………………... 13

Part II: Indirect Effects……………………………………………………………………….. 14

2.1 Increased Human Access……………………………………………………………… 14

2.2 Induction of Further Land Use and Development…………………………………... 16

2.3 Economics and Ethical Implications…………………………………………………. 17

Part III: Mitigation Strategies and Areas for Continued Research………………………... 18

3.1 Landscape Planning…………………………………………………………………… 19

3.2 Ecological Engineering………………………………………………………………... 21

3.3 Further Research……………………………………………………………………… 22

Conclusion………….………………………………………………………………………….. 24

Referenced Figures……………………………………………………………………………. 26

References.................................................................................................................................... 29


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Abstract

Rural two-lane roads and major highways impose a number of direct and indirect impacts

on all types of wildlife. This literature review focuses on direct impacts to large forest mammals

including predators and herbivorous ungulates. Some ecosystem-wide effects include direct

habitat loss from road placement, habitat degradation via introduced synthetic chemicals, and

corridor fragmentation. Predators are prevented from using their habitat niches by fragmentation;

connectivity issues are the most harmful for large-range and migratory species. The construction

of roads introduces an ecological edge that induce a variety of complex wildlife interactions,

including a potential for positive facilitation of movement. Noise and light from passing traffic

cue species of road presence prompting learned road avoidance behaviors in bears and cervids,

creating a spatial constraint on individual predators and migrating herds. Vehicle-animal

collision remains a constant threat to endangered species in Florida and southern Europe, and

creates economic and humane issues in cases of non-immediate deaths of affected animals.

Indirect effects are more subtle and difficult to quantify, yet it is generally accepted that new

roads lead to increased human access and disturbance (including poaching) as well as further

land use development and natural resource extraction. A variety of mitigation strategies have

been proposed and practiced to address the culmination of the issues in this paper. Perhaps the

most effective mitigation practice is smart road placement and the designation of roadless areas.

Existing roads can be retrofitted with culverts, underpasses, and overpasses to allow reduced

disruptions to animal movement.

Introduction

The field of conservation biology has generated interest in wildlife interactions with

human infrastructure. The most prevalent form of such interactions occur between the extensive


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networks of roads and the various habitats that roads fragment. In the United States (U.S.) alone,

road networks amount to 6.58 million kilometers and it is estimated that 83% of land area in the

conterminous states is within 1 kilometer of said roads (Forman, et al., 2003). Studies on the

effects of roads on large forest mammals are relatively limited compared to other species types,

due to the difficulty of monitoring methods. Furthermore, a comprehensive assessment becomes

difficult when considering indirect consequences of roads such as increased human-wildlife

interaction in the form of road hunting, poaching, induction of further land use development, and

other anthropogenic disturbances.

The scope of this project will include an analysis of direct and indirect effects of roads on

large forest mammals of various functional groups. I will also evaluate the efficacy of currently

implemented mitigation strategies. This project will provide special consideration to endangered

species as classified by multiple conservation entities (U.S. Endangered Species Act,

International Union for Conservation of Nature, etc.) for which road induced disturbances and

road related mortalities are especially critical. In addition to endangered species, case studies on

bears (Ursus americanus, arctos), mule deer (Odocoileus hemionus), and several other common

cervids will be referenced as illustrations of topics and how they relate to large mammals. Some

ecosystem wide effects will be discussed within the context of focal species and their associated

communities.

Professor Richard T. T. Forman of Harvard University leads the field of road ecology in

the U.S. and will be referenced throughout as an acknowledged expert in the field. The analysis

will conclude with a brief list of recommendations for further research.

Part 1: Direct Effects


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1.1 Ecosystem Degradation and Quality of Habitat

The most immediate and apparent effects of the construction of new roads in a nonurban

setting are ecosystem degradation and reduction in the quality of habitat adjacent to roads and

the contiguous landscape. In addition to direct habitat loss and replacement, various types of

chemical and nonchemical pollutants are introduced to the surrounding vegetation, soil, and

streams, including: noise and light pollution, dust, salt, sand, heavy metals, gases, and a number

of chemicals used as de-icing agents (Spellerberg, 1998). Each of these pollutants induce unique

and complex changes to the ecosystem ranging from behavioral and health effects on wildlife to

reduction of water quality in nearby streams and their greater watershed network (Forman et al.,

2003). The cumulative effects of these various disturbances impact species at all trophic levels,

yet further investigation is required in the passage of harmful organic and inorganic toxins

between species.

Direct Habitat Loss from Land Occupation of Roads

The construction of roads impacts more than 10 hectares of land per kilometer of road

(Seiler, 2009). Rural roads are narrower than major highways and therefore require less land

area; however, there are far more rural roads and their combined effect is cumulatively greater. It

is difficult to consistently measure the overall amount of land use involved in road construction,

as an evaluation of the associated infrastructure is difficult and highly variable. Land from which

aggregate material is mined, embankments, staging areas, culverts, slope cuttings, erosion and

slope failures can all factor into total road infrastructure. If parking structures, gas stations,

sidewalks, hotels etc. are also all considered as contributing to habitat loss from roads, then the

total area becomes much greater (Seiler, 2009). Logging roads introduce forest interior erosion

and contaminate sensitive aquatic habitat like salmon spawning beds. In the U.S., the cumulative


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effects of roads expand into an area that is 19 times larger than the 1% of actual land surface that

the roads cover (Seiler, 2009).

Deicing Agents and other Chemical Pollutants

Synthetic chemicals from the construction, use of, and maintenance of roads contribute a

significant source of pollutants as a form of habitat degradation in forests. Storm water runoff

that crosses road surfaces is the primary source and conduit of chemical pollutants that spread

into the adjacent soils, plants, and streams - which eventually dilute the compounds over

distances (Forman & Alexander, 1998). Sodium from deicing agents like sodium chloride

accumulates in high densities within 5 meters of roads, changing soil structure and effectively

plant composition and growth (Transportation Research Board, 1991). Furthermore, deicing

agents facilitate the movement of heavy metals in soils which can lead to infiltration in

groundwater, aquifers, and streams. Water contamination is especially harmful in low flow or

drought conditions that lack sufficient flows of water to dilute the pollutants (Amrhein et al.,

1992). The toxic effects of deicing agents themselves and related road chemicals have had direct

negative impacts on vegetation, fish, herptile, and small mammal health and have the potential to

harm larger herbivorous grazing species as well as predators.

Edge Effects, Positives and Negatives

An inevitable effect of the construction of roads is the creation of an ecological edge, or

area in which two distinct ecosystem types converge and interact. Edges and ecotones are

characterized by species diversity and an optimal interspersion of habitats. The unique qualities

of edges tend to have bottom up effects, as an otherwise rare plant species may be the perfect

food, habitat, or refuge for an even rarer animal species, as seen in some small mammals and


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birds (Andrews, 1990). The tendency for roadside vegetation to be dominated by grassy and

herbaceous species has led to the use of roads as a movement corridor for some migratory

herbivores, which will be further discussed in section 1.5. A number of studies in Scandinavia

have attempted to quantify the extent of edge effect roads have in different settings, finding that

plant and animal diversity are affected up to 30 meters off the road in most systems (Seiler,

2009). The challenge presented by the formation of edges as habitat along roads is one of

management strategy; should maintenance practices maximize species richness and ecosystem-

wide health or be weighted towards the conservation of a threatened or endangered species?

Edges can be deleterious to biodiversity and ecosystem functioning. Increasing edge

impacts in forests is caused by logging and clear cutting practices. In the Rocky Mountains the

density of edges created by roads is twice as much as logging alone. The total area affected by

roads and deforestation is three times greater than the land area that is actual cleared from trees

and occupied by roads, meaning affects extend far into the contiguous landscape (Reed et al.,

1996).

Noise and Light as a Pollution, Road Avoidance Behavior

Noise and light from vehicles also contribute a unique form of pollution into forest

ecosystems. These types of disturbances from roads have been recognized by humans since early

highway development, inducing appropriate mitigation measures such as noise barriers and

policies for areas of human residence. Noise and light have more complex effects on wildlife.

Road avoidance is a behavioral phenomenon related to noise and light pollution in which birds

and mammals have been observed to occur less often, or use resources less often along wide

roads, especially those with high densities of traffic (Forman, et al., 2003).


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In a study that observed grizzlies (Ursus arctos) in mountain habitat in Montana, it was

found that the bears preferred utilizing resources on road edge buffers along closed roads. The

grizzles were also found to prefer roads on which less than 10 vehicles traveled per day, and

avoided roads on which more than 10 vehicles traveled per day (Mace et al., 1996). Throughout

the course of this study, eight grizzly deaths by humans (reasons not in report) were recorded

that could be attributed to access to critical habitat by roads (see section 2.1).

Road avoidance is a consequential adaptation for animals near roads as it contributes greatly

to the barrier effect (see section 1.3) that roads impose on the landscape and home range of

predator and cervid species. An animal that learns to avoid roads based on noise and light

indicators from vehicles is spatially limited. Similar road avoidance behavior has been observed

in wild reindeer (Rangifer tarandus), mule deer, and other cervid species in Scandinavia (Klein,

1971) (Seiler, 2009). A Colorado study compared the extent of road avoidance between mule

deer (Odocoileus hemionus) and elk (Cervus canadensis) by counting fecal-pellet groups and

found that the area of avoidance for these species extends 200 meters out from the road.

Avoidance behavior is more prevalent in mule deer than elk (Rost & Bailey, 1979).

1.2 Vehicle-Animal Collision

Estimates of Occurrence and International Overview

Direct fatalities by vehicle-animal collision on roads is a significant source of mortality

for mammals. These fatalities only result in population level consequences for endangered

species, large carnivores that require extensive ranges, and some local populations of otherwise

low concern species. There have been many attempts to quantify the extent of vehicle-animal

collision as a proportion of mortality for various species groups (usually at a regional or national


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level). Estimates for mortality by collision have been calculated for birds, mammals, herptiles,

and even insects. Early studies in the U.S. suggested a rate of about 1 vertebrate casualty per 10

kilometers (Forman, et al., 2003). Another study from the same era found that out of 842 animal

fatalities recorded, 24% were mammals (Ibid.). In each estimate, bird fatalities always

outnumber other species groups by a significant degree.

With use of updated sampling and estimation methods, recent studies suspect 1 million

vertebrates are killed by vehicle collision each day in the U.S. (Forman & Alexander, 1998).

Over 1 million mule deer and white tail deer (Odocoileus virginianus) are struck by vehicles on

an annual basis. 92% of result in deer fatality. This value may be up to six times greater when

accounting for unreported/unrecorded incidents (there are many cases in which injured deer

travel a short distance into surrounding forest and die away from the road). Roads rarely act as a

primary threat to thriving species yet remain a severe threat to endangered and rare species as

they kill a constant proportion of populations (Seiler, 2009)

Roadkill estimates have been calculated for various geographic areas and species. In

Australia, one mammal is found killed by traffic every 30 kilometers (Andrews, 1990). Road

ecology has become a well-developed area of research in Europe, especially Scandinavia, home

to a great number of large ungulates like elk, moose (Alces alces), and reindeer. Annually, 4

million larger vertebrates are killed each year in Belgium, 1.5 million mammals in Denmark, and

0.5 million medium sized mammals in Sweden (Seiler, 2009). Vehicle-animal collision is cause

for less than 5% of mortality in annual spring populations of red deer (Cervus elaphus), roe deer

(Capreolus capreolus), and wild boar (Sus scrofa) yet accounts for 65% of moose deaths in some

southern Sweden hunting districts (Seiler, 2009). This illustrates the regional variation of rates of

mortality roads impose on similar species perceived from a continental level. In Italy, traffic


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related deaths were estimated to account for 7-25% total annual deaths in wolves (Canis lupus)

and almost 100% of grizzlies between the years 1974-84 (Seiler & Helldin, 2006).

Florida, a Critical Case Study

The potential severity of road related issues on populations is well known for a number of

species in Florida, home to the endangered Florida panther (Puma concolor coryi). As mentioned

previously, roads are particularly a threat to wide-ranging carnivores like the Florida panther.

The Jaguar (Panthera onca) in Central and South America also requires extensive home ranges

and well-connected movement corridors to find sufficient resources and mating opportunities.

The substantial spatial requirements of these large cat predators expose them to a greater number

of roads within their home range compared to other species with more limited home ranges. Prior

to a series of studies that eventually led to successful mitigation measures in the 1990’s,

collisions by vehicles accounted for 49% of annual mortality for the endangered Florida panther

(Maehr et al., 1991). Roads continue to pose a threat to the species even after implementation of

mitigation measures. This is especially true on private lands that cannot be reliably managed in

favor of the panther. In an estimated panther population of 100 adults, 40 vehicle related deaths

occurred between the years 2000-2004 (Schwab & Zandbergen, 2011). The same study

determined that male panthers are killed by vehicles in greater numbers than female as they

require a more expansive home range to find mates (Ibid.). Females typically stay in well-

defined territories to raise cubs near consistent resources.

The Florida Key deer (Odocoileus virginianus clavium), a subspecies of the white-tailed

deer, is another endangered large mammal that is subject to a high rate of mortality due to roads.

Prior to the implementation of the major highway projects in the state of Florida, illegal hunting

and poaching practices forced a decline of the Florida Key deer to a mere 50 individuals (Lopez


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et al., 2003). Conservation efforts and enforcement of hunting legislation increased the

population to an estimated current count of 453-517 deer over the last 40 years. Habitat loss and

road related deaths now face the species. These factors are responsible for 44 deaths a year, or

75-80% of all known deaths (Forman et al., 1997). Similar to the Florida panther, the Key deer

exhibit a greater loss of males than females due to greater daily movement of males. The same

study (Lopez et al., 2003) identified a direct relationship between survival and distance from

major highways that host heavy traffic and high speeds, common on US 1 in Florida, which in

particular produces similar kill rates for male and female Key deer.

Unlisted, Locally Threatened Species

There are some cases in which local populations of otherwise unlisted species are

threatened with local extinction or extirpation due to unique regional stressors or stronger

influences of stressors (Seiler, 2009). Such is the case for mountain lions (Felis concolor) in the

Banff National Park of Alberta, Canada (Forman, et al., 1997). The park is considered the

“genetic bridge” that allows eastern and western populations of mountain lions in the Rocky

Mountains to mate and maintain their severely limited numbers. Three major highways fragment

the national park, posing a threat to mountain lions, grizzlies, deer, and smaller mammals (figure

1). Roadkill contributed 5% of total local mortality of mountain lions in Banff in a 52 year

period, at an average rate of one collision every 3-4 years (Ibid.). Other non-mammal examples

of the same severity of road mortality on local populations include the Texas subspecies of the

eastern brown pelican (Pelecanus occidentalis), royal tern (Sterna maxima), and barn owl (Tyto

alba) (Ibid.).

1.3 Barriers, Habitat Fragmentation, Connectivity Issues


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Perhaps the most important, widest reaching, and universal effect of roads is their capacity to

act as ecological barriers for large mammal populations. Forman claims that “all roads serve as

barriers or filters to some animal movement” (Forman & Alexander, 1998). Roads inhibit

movement, limit home ranges, and reduce individual’s and herd’s ability to reach necessary

resources and freely find mates. Aforementioned edge effects, road avoidance, and vehicle-

animal collisions all contribute to the barrier effect of roads. Width and volume of traffic are the

two primary factors that contribute to the barrier effect of roads (Forman & Alexander, 1998)

(Seiler, 2009).

Barriers and patch fragmentation have the potential to form allopatric metapopulations

among species where small groups are isolated from one another when a road is introduced

(Andrews, 1990). In some cases, roads are physically impossible to cross due to blocking

structures like gutters, ditches, embankments, and fences - which killed thousands of wildebeests

(Connochaetes taurinus) in South Africa as they were inhibited from migrating north to find

sufficient water sources (Andrews, 1990). Also, some blocking structures on roads are

constructed with the intention of deterring animals from entering and crossing the road (see

section 3.2).

Road Density, a Metric for Connectivity

Road density is a formal metric devised by Forman (1997) as a way to quantify the extent

of road presence per unit area, usually in kilometers per square kilometer (km/km2) (Forman &

Alexander, 1998). Road density (along with traffic density) has been identified as one of the

most impacting factors on ecosystem’s wildlife populations, hydrologic cycles, and fire patterns.

A clear relationship has been established between road density and population occurrences for

several large mammal species. Determining the maximum road density a particular species can


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tolerate is an important step in developing conservation methods concerning large mammals

affected by roads (Figure 2) (Seiler, 2009). For example, a density of 0.6 km of road per square

kilometer is considered the maximum for a landscape to sufficiently support large predator

species like wolves and mountain lions (Thiel, 1985) (Van Dyke et al., 1986).

The Jaguar in Central and South America

A study on the importance of habitat connectivity for the conservation of jaguars was

conducted via identifying movement patterns in the Southern Mayan Forest at the border of

Mexico and Guatemala. The individuals studied verified jaguar habitat preferences and indicated

an avoidance of any modified landscape, especially areas with human use (de la Torre et al.,

2017). Dense, isolated forest patches provide a diversity of predation opportunity and suitable

locations for birthing and rearing cubs. Torre and colleagues determined minimum jaguar habitat

requirements including minimal functional corridor width of 240 meters. This study also

highlighted the adverse impacts of local roads which increases large mammal mortality, induces

habitat fragmentation, and induces human encroachment to previously isolated jaguar habitat.

Fur poachers may exploit newly accessible habitat due to roads.

Metapopulations, Source and Sink Dynamics

A metapopulation is defined as “a group of local populations linked by movement” (Carr

et al., 2002). Metapopulations provide a source of resilience for total populations because they

facilitate healthy gene flow and movement between source (mating individuals emigrate from

one habitat patch to another) and sink (take in immigrating mating individuals) populations to

resist local extinction. Roads confine the capacity for metapopulations to operate at their full

potential.


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Disturbance impacts on insect, bird, and small mammal metapopulations are well

documented. For large mammal metapopulations, however, the issue is less prevalent. Roads

have the potential of interrupting important metapopulation interactions between spatially

constrained wolf packs (Canis lupus) in areas with high road density in Mexico and the Rocky

Mountains (Carroll et al., 2013). Roads and road density in the Rocky Mountains have been

identified as primary influences on the suitability of habitat for the grey wolf (California

Department of Fish and Game, 2011). Similar influences of road density on wolf populations

have been corroborated in Wisconsin, Michigan, and Ontario in which wolf packs avoid areas

with road densities that are greater than 0.58 km/km2 (Mech et al., 1988). Therefore,

metapopulation disruptions may determine the viability of wolves recolonizing California in the

near future.

Migratory Cervids – Mule Deer and Reindeer

The barrier effect of roads on cervid migratory routes is well known. A well-connected

and readily traversable landscape is required for successful migratory routes that herds embark

on an annual basis. Many cervid species migrate between summer and winter ranges in order to

access reliable resources and suitable climates. Mule deer are selective foragers that rely on the

most nutritious plant species and plant parts rather than grazing on general grasses (Mule Deer

Working Group, 2014). Other cervid species have adapted more generalist tendencies, like the

red deer which are primarily grazers and can subsist on a variety of vegetation species. In

Wyoming, a group of researchers found that areas with intense development forced migrating

ungulates to detour, travel at increased rates, spend less time at stopover areas, and overall use

historic migratory routes less (Sawyer et al., 2012). Another study compared modeled caribou

(same genus and species as reindeer, yet carries a semantic difference) winter migratory


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movements to actual movements by assessing 36 individuals fitted with GPS collars (Dyer,

2002). Dyer and his colleagues revealed a semi-impermeability of roads with moderate traffic by

determining caribou crossed roads six times less than expected by models. A study in Norway,

home to the last remaining wild population of reindeer, discovered that 78% of reindeer winter

range is within 5 km of infrastructure (roads, powerlines, and resorts). Only 13% of the reindeer

population occurred in this significant portion of their range that has been encroached on by

development (Nelleman et al., 2001).

1.4 Roads as a Form of Ecological Facilitation

The presence of roads and their connected roadsides has the potential to act as new form of

movement corridors, resources, and habitat for native and invasive species. Of species that

inhabit roadsides, most are generalists that can withstand a stochastic environment (Coffin,

2007). There are cases in which roadside habitat may be actively maintained to facilitate use by

local species to some degree of success. Monitoring studies to empirically verify roadside

population support are often not implemented, and the attraction to roadside habitat puts species

at greater risk of collision (Seiler, 2009). Ecological traps are areas of attractive resources in an

otherwise unattractive environment. This term has also been used to describe the attraction of

predator and scavenger species to roadkill only to become roadkill themselves, among other

examples (Battin, 2004). There are also recorded cases of vehicles disposing invasive plants,

seeds, and even small animals into areas previously unoccupied by such species (Mortensen et

al., 2009) (Christen & Matlack, 2009). Unique soil composition and high rate of hydrologic and

chemical runoff from roads may select against native plants and invites the colonization of

invasive species.

The Possibility for Positive Facilitation


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Infrequently traveled roads have been known to facilitate movement patterns for several

larger mammal species including: red fox (Vulpes vulpes), dingo (Canis familiaris dingo), wolf,

cheetah (Acinomix jubatus), and lion (Panthera leo) (Coffin, 2007). Forman argues that the

movement of predators along unpaved roads contributes to road avoidance behavior by prey

species that associate the two and acquire a learned behavior (Forman & Alexander, 1998). One

study suggested that while large predators avoid two or more lane paved roads, they prefer the

less rugged and easily traversable surfaces of forest service roads and trails for traveling within

their home ranges. Such behavior has been observed in mountain lions in southern California

(Dickson et al., 2005). Although roads stand as a significant source of fragmentation and barriers

to ungulate migrations, they have been recognized to facilitate movement and provide a semi-

consistent source of subsistence for deer and elk, especially during critical growth years where

resources away from roads are insufficient (Rost & Bailey, 1979). (For a graphical summary of

the direct effects of roads discussed in part I, see figure 3)

Part II: Indirect Effects

2.1 Increased Human Access

As roads expand and branch into a landscape, humans gain new access to previously

unreachable areas with intended and unintended adverse effects on wildlife populations. A group

of USFS researchers found that off road vehicle use has behavioral effects on elk, namely

increased rates of movement and an induction of a “flight” response as they perceive the noise

and presence of vehicles as a threat (Wisdom et al., 2004). Unpaved roads in Forest Service and

Bureau of Land Management (BLM) land permit dispersed camping (camping outside of

designated campgrounds), and the shooting of fire arms and hunting are also permissible in

designated areas. These activities facilitate pollution, litter, forest fires, poaching, and other


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negative interactions between irresponsible campers and animals, namely bears attracted to the

potent scents of human foods. The attraction of bears to human food is also a common problem

in designated campgrounds, parks, trails, etc. (Brody & Pelton, 1989). It is easy to imagine a

timid gun-wielding camper that resorts to lethal methods when encountering intimidating

predators. These effects have been identified by Forman throughout his catalogue of work

(Forman & Alexander, 1998). Thus, this section will focus on the effects of hunting and

poaching of bears as facilitated by road access to habitat.

Hunting and Poaching of Bears in North America

In western North Carolina, researchers declare increased vulnerability to hunting as a

primary effect of roads on bear populations (Brody & Pelton, 1989). Bears that cross roads are

especially vulnerable to road hunters. Road hunting is an unethical method that takes advantage

of back country roads, using “strike dogs” to pick up scents of nearby bears that recently

accessed resources near roadsides to then track individuals into the forest. Some of these hunters

shoot game directly from their vehicles while on roads aided by spotlights. In Brody and Pelton’s

study area, 8 of 17 monitored bear individuals were killed by hunting – 5 legally and 3 illegally.

They also found that the designation of wildlife sanctuaries has little to no effect on road

crossing frequencies by bears. Poachers disregard sanctuary laws. Tracking of bears by hounds

starting outside of sanctuaries can eventually lead hunters into them without notice.

Similar hunting activities and effects are seen in grizzlies in British Colombia, Canada,

and Montana, U.S.A. (McLellan & Schackleton, 1988). In this region, legal and illegal hunting

are a primary source of mortality for adult grizzlies. During the span of their study all monitored

deaths between the years 1979-1988 were due to hunting. A majority of these kills were traced to

road hunting incidents. Hunting for grizzlies and wolves has been largely restricted in recent


16

years in the north U.S.; however, poaching, protection of nearby livestock, and talks of a change

of legal conservation status pose a continued threat to these keystone species.

2.2 Induction of Further Land Use and Development

Deforestation and Other Resource Extraction Industry

It is debated among developers and landscape planners whether roads lead to further

infrastructure development or vice versa. This interaction is complex and has only recently been

considered as an indirect effect of roads to be investigated and quantified. In Belize, an

opportunity to monitor the economic effects of an expanding road network presented itself in

1996 (Chomitz & Gray, 1996). This analysis found that while the construction of new roads

leads to new economic opportunities for the local market, increased deforestation contributes to

the great ecological cost of habitat fragmentation. Furthermore, in areas with poor soil conditions

and small populations, the addition of new roads presents a “lose-lose” scenario in which neither

the people nor the environment benefit from their construction in any lasting way.

Other studies on long term landscape changes caused by roads have been conducted in

Central and South America which illustrate the threats of increased human presence and

deforestation on species that require large home ranges (Forman & Alexander, 1998). It is in this

same geographic area that habitat fragmentation by roads and deforestation have become

pervasive stressors on jaguar populations (see section 1.3) (de la Torre et al., 2017). The

previously mentioned study on grizzlies in southern Canada and northern U.S. (McLellan &

Schackleton, 1988) also highlighted the effects of roads used to connect various resource

industry sites, claiming that such roads are a major threat when vehicle access and firearm

restrictions are not enforced.


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2.3 Economics, Human Casualties, and Ethical Implications

Economic Impact of Vehicle-Animal Collisions

New roads impact local economies in providing access to untapped natural resources;

however, this relationship is not well studied aside from the few references (see previous

section). Another economic impact of roads involving wildlife that is indeed well studied is

property damage caused by vehicle-animal collisions. The extent to which vehicle-animal

collisions cause severe and costly property damage varies by country, but most reported numbers

are alarming. For example, in Vermont between the years 1981-1991, 94% of collisions with

deer resulted in property damage at an average of $1577 per accident (Forman, et al., 2003). In

the same sample of 720,000 reported collisions, around 29,000 resulted in human injury and 211

resulted in human fatality (0.029%). More recent reports in the U.S. show close to 390 deaths by

animal collision per year (National Highway Transportation Safety Administration). In

Newfoundland, of 5422 collisions with moose between the years 1988-1994, 14 resulted in

human fatalities (0.25%). Considering the entire continent of Europe, estimates from police

records report around a half a million ungulate-vehicle collisions per year resulting in 300 human

fatalities, 30,000 injuries, and property damage of up to the equivalent of $1 billion U.S. (Seiler,

2009). Even in cases where no significant damage is caused to property or human health, a

remaining net economic loss accumulates from deaths of game species killed by vehicles that are

left unharvested or are disposed of by highway patrol and state departments of transportation

workers.

Ethical Implications


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There is a humane aspect to the effects of roads on all sentient species they affect,

especially cases where collisions are not immediately fatal and result in a slow and painful death

for the individual. In California, it is common practice for highway patrolman to resort to a fatal

shot to the head of any injured yet immobile species that may be suffering on a roadside;

however, in cases in which it is seen as unsafe or a public disturbance to do so, the animal must

be transported to another area before being put down (Sanchez, 2016 personal communication).

In Germany, animal welfare laws require drivers to minimize animal suffering in cases of non-

fatal collisions. A study in northern Sweden surveyed train drivers on their experiences in

colliding with herds of reindeer and moose, reporting that such cases are described as

“unpleasant” (Seiler & Helldin, 2006). Ecological effects of roads are complex and subtle and

have yet to be fully realized as a pressing issue to the general public. Therefore, these economic

and humane issues may implicate a more apparent need for immediate mitigation efforts in

retrofitting existing roads and refined planning frameworks in the creation of future roads in a

manner that addresses all of the areas thus far discussed.

Part III: Mitigation Strategies and Areas for Continued Research

Mitigation is often defined as a means to make something less harsh, harmful, severe, or

painful. The term mitigation and its various applications has become more specified in the

environmental arena. A formal mitigation process was developed in the enforcement of the

California Environmental Quality Act (CEQA), passed in 1970 (California Coastal Commission ,

2017). The CEQA defines ‘mitigation’ as follows:

1) Avoiding the impact altogether by not taking a certain action or parts of an action.

2) Minimizing impact by limiting the degree or magnitude of the action and its implementation.

3) Rectifying the impact by repairing, rehabilitating, or restoring the impacted environment.


19

4) Reducing or eliminating the impact over time by preservation and maintenance operations

during the life of the action.

5) Compensating for the impact by replacing or providing substitute resources or environments.

Part III of this review will focus on the multiple strategies implemented to address areas 1-3 in

the CEQA definition of mitigation and how they relate to roads in California and beyond.

Landscape planning and the designation and protection of roadless areas is a necessary

step in the creation of new development projects. Retrofitting existing roads with the latest forms

of ecological engineering infrastructure like wildlife under and overpasses is a new and

promising way to implement area 3 of CEQA’s mitigation definition. Road removal is another

more direct and beneficial action. While California state agencies do what they can to practice

and enforce CEQA’s guidelines, not all states nor countries have the political will or funding to

enact policies of similar strength or at all. To ignore the ecological and humanitarian impacts of

roads would be irresponsible and immoral.

3.1 Landscape Planning

Minimizing Impacts in New Road Planning

In locations where the altogether avoidance of constructing a new road is not a practical

option, strategically planning the location of said road in relation to the greater landscape and

ecosystem can greatly reduce its impacts. Forman (2005) and his colleagues have devised simple

and effective ways to determine the optimal position of a road considering the biotic and abiotic

factors involved. Antiquated road construction plans largely considered topography and hazards

alone, ignoring nearby habitat patches and movement corridors altogether. Spatial arrangement,

road width and expected volume of traffic, and the size and shape of occurring habitat are the

three guiding considerations in an ecologically aware construction plan (Forman R. T., 2005). A


20

patch-corridor-matrix model posits that any spatial point in a landscape is either in a habitat

patch, along a movement corridor, or a part of the greater background matrix. It is the

responsibility of transportation planners to identify these aspects of an area and arrange roads in

a way that has a minimal impact on any one of these characteristics (Figure 4) (Ibid.)

Examples of road placement planning include arranging roads adjacent to large patches in

a way that only one side of the road is affecting the edge of the patch, rather than through a patch

in which both sides of the roads would have an impact. Arranging roads perpendicular to

corridors (perhaps with an under or overpass to facilitate movement) as opposed to along them

creates a single easily mitigated obstruction. Granted, new roads in the U.S. are now uncommon

outside of municipal district projects as most interstates were constructed in the Eisenhower era;

however, taking time to minimize the ecological impacts of roads prior to construction will be

crucial in countries currently ramping up transportation infrastructure.

Designating Roadless Areas

The designation and preservation of roadless areas is an essential part in mitigating the

impacts of roads. The USFS has contributed greatly to this effort in their management of national

forests by designating “inventoried roadless areas”. These areas make up approximately one-

third of all National Forest System land area and occur within 661 of 2,000 major watersheds in

the country (United States Forest Service , 2017). The benefits of roadless areas are many. A

study in the Siskiyou-Klamath region of northern California and Southern Oregon evaluated the

benefits of designated roadless areas by quantifying their number of “special elements”, namely

the occurrence of natural-heritage species (rare or endangered) and found four times more of

these elements than in wilderness areas alone (Strittholt & Dellasala, 2001). The researchers also

identified a wider array of habitat types are extant in roadless areas, indicating greater


21

biodiversity. In the northern Rocky Mountains, a similar comparison study investigated the

variety of land-cover types that occur in roadless areas versus protected and wilderness areas and

found an increased representation of all land-cover types as well as a positive feedback of

increased patch connectivity and size (Crist et al., 2005). Meanwhile, European conservation

biologists have been identifying the few roadless areas remaining in their connected continent

and are making these areas a conservation priority as they recognize the benefits observed in the

U.S. (Selva et al., 2011).

3.2 Ecological Engineering

Wildlife Crossing Structures

The construction of wildlife crossing structures have seen great success in Europe,

Canada, and more recently the U.S. The design and location of crossing structures depends on

the species or group of species they are intended to serve. Therefore, it is imperative to consider

the movement patterns, existing corridors, distribution of resources, and location of

metapopulations in relation to roads. There are three basic types of passing structures: culverts,

underpasses, and overpasses. Culverts are the smallest of these, and many already exist as a form

of hydrological infrastructure for the safe movement of water under roads. Culverts are most

commonly used by amphibians and small mammals when dry enough to traverse. Underpasses

are a larger and less confined structure and may be intentionally built for wildlife or occur as a

byproduct of bridge construction over water ways and as such are important to species that often

occur on or move along riparian corridors, especially mammals (Glista et al., 2009). Overpasses

are even larger structures that primarily support carnivore and ungulate movement, yet can

support a variety of species (Figure 5). They are classified by width and location relative to pre-


22

identified movement corridors, the widest and best planned claiming the title “Landscape

Connectors” (Forman et al., 1997).

The evidence for use of crossing structures by wildlife is strong and continues to grow.

Such evidence indicates the importance of continued monitoring and adaptive management in

implementing any mitigation strategy to assess successes and failures. Banff National Park

stands as an ongoing experiment in the use and success of passing structures, hosting 6

overpasses and 38 underpasses within its borders. Monitoring studies on use by mountain lions

have discovered nuanced preferences like narrower overpass structures, minimized distances

between patches of dense forest cover, and a general preference for underpasses (Schwab &

Zandbergen, 2011).

Deer are also common users of overpasses in Banff (Clevenger & Waltho, 2005). The

success of overpasses in facilitating red and roe deer movement in Europe have led to a

continental expansion of their construction and use in recent years (Glista et al., 2009). Although

promising results from the structures discussed are receiving international acclaim, they are

costly and sometimes impractical based on local budget and the nature of existing infrastructure.

Cheaper alternative strategies for keeping wildlife off roads exist, such as: olfactory repellants,

ultrasound, road lighting, population control, and habitat modification as well as fencing and

barriers intended to physically block individuals from entering high traffic volume areas (Ibid.).

3.3 Areas for Continued Research

There are several areas in which continued research is required. The understanding of

chemical effects on fauna species is fairly limited although the input of road maintenance and

deicing chemicals into the surrounding ecosystem is well known and quantified. A full


23

toxicological analysis of such chemicals and the extent to which they not only degrade habitat

but also directly affect the health of individuals may aid agency planners in prohibiting the use of

some chemicals, or find alternatives for others. Research and development in vehicle design

could possibly produce a less invasive yet equivalently safe lighting system and the expected

expansion of use of electric vehicles will reduce road noise levels. These vehicle modifications

can minimize effects of road avoidance behavior in birds and mammals. Careful monitoring on

animal responses to such technological advances in vehicle design will be required as the

opposite of the desired effect may occur – if animals lose light and noise cues for the presence of

roads they may be more prone to hunting, poaching, and collision.

Research on the effects of roads on gene flow are severely limited for large mammals. In

small mammals and herptiles, large scale trapping methods on transects along opposite sides of

major and minor roads have been implemented in order to understand the extent to which roads

influence genetic differences in separated populations. Trapping enough individuals of a large

mammal species to ascertain similar information would certainly be more difficult and

presumably impossible in some cases. Tranquilization and snare trapping are the current methods

most often used to obtain biometric information and genetic material from large mammals, or

fitting individuals with costly GPS collars for movement studies. Wildlife biologists may need to

determine a more practical method for collecting genetic information from large mammals in

order to attain a fuller understanding of how population genetics are shaped by road presence.

The use of “citizen science” initiatives is becoming a common practice in several areas of

conservation biology. Creating a network of citizen scientists to report road mortalities based on

species and location could serve as an additional source of data to aid researchers and agencies in

identifying high mortality areas. For example, an integral step in determining the best location


24

for a wildlife crossing structure is identifying the target species’ movement patterns and

corridors. When funding is limited for more formal monitoring methods (i.e. GPS collars) citizen

science reports may stand as a cheaper and simpler alternative.

Lastly, it is imperative that appropriate legislation is created and enforced in the

prohibition of hunting within a certain distance from wildlife crossing structures. Firing weapons

towards roads is already illegal in the U.S. yet a new attraction to hunters and poachers to such

structures may occur as they funnel in a large quantity of animal individuals on a daily and

nightly basis.

Conclusion

The expansion of new paved and unpaved roads in the U.S. and beyond pose a critical

challenge to conservation biologists and agency planners. The literature of road ecology has

catalogued many of the nuanced interactions between roads and their encompassing landscapes.

While direct vehicle-animal collision poses population effects on endangered species like the

Florida panther and humane concerns for wildlife at large, the barrier effect of roads is the most

intrusive on natural processes in general. As the threat of climate change continues, the

monitoring and control of roadside vegetation composition and resistance to road-introduced

invasive species is another important challenge. Roads also produce a number of indirect effects

including an increase of human access to previously inaccessible wilderness, which induces

unethical hunting practices and poaching as well as invites new resource extraction projects.

It is of utmost importance that biologists, ecologists, hydrologists, planners, engineers,

contractors etc. work together in devising mitigated transportation infrastructure to minimize and

reduce the total effect that roads have on ecosystems. Already existing roads must be retrofitted


25

and perforated appropriately to permit a return to close to normal ecosystem functioning.

Considering the whole of these challenges, researchers must go forward with new gained

knowledge from the last several decades of past failures and emerging successes. These include

diverse mitigation strategies like mindful road placement, the designation of roadless areas, and

the construction of ecological engineering structures like over and underpasses. A failure to

appropriately plan and mitigate will result in a degraded ecosystem at the least, and could also

lead to the extirpation or extinction of cherished megafauna species like the Florida panther and

Key deer.


26

Referenced Figures

Figure 1: Map of Banff National Park, Canada, Fragmented by several major highways. (map

from www.planetware.com)


27

Figure 2: Road density is a formal metric in kilometers of road per square kilometer devised by

Richard T. T. Forman as a means to quantify the total presence of roads in a

patch/corridor/matrix model and to what degree various species can tolerate various densities.

Generally, as road density increases, species richness, density, and ecosystem functioning

decreases. (Seiler, 2009)

Figure 3: “The five primary ecological effects of roads: Habitat loss and transformation,

disturbance due to pollution and edge effects, barrier and avoidance, mortality due to traffic and

predation, and the conduit or corridor effect. Together, the various primary effects lead to a

fragmentation of habitat”. (Seiler, 2009)


28

Figure 4: Forman’s schematic on road placement and related extent of affect. Generally, roads

should be placed adjacent to the borders of large patches and perpendicular to wide and narrow

corridors (fitted with appropriate under/overpass structure). (Forman R. T., 2005)

Figure 5: An overpass structure in Banff National Park, Canada. The structure permits safe

passage over the Trans-Canada Highway for many large mammal species including bears, elk,

and mountain lions. The park boasts a total of 41 wildlife crossing structures. (Image from

www.theworldgeography.com)

http://www.theworldgeography.com/


29

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