Landscape fragmentation caused by the transport network in Navarra (Spain): Two-scale analysis and...

Landscape fragmentation caused by the transportnetwork in Navarra (Spain)

Two-scale analysis and landscape integration assessment

Miriam Serranoa,*, Luis Sanza, Jordi Puiga, Juanjo Ponsb

aDepartment of Zoology and Ecology, University of Navarra, Apt. 177, 31080-E Pamplona, SpainbDepartment of Geography, University of Navarra, 31080-E Pamplona, Spain

Abstract

Landscape fragmentation caused by the main transport infrastructure network in Navarra (north of Spain) is analysed on

both regional and local scales. Regional scale analysis identifies the overloaded zones (cloverleaves and corridors) and the

territorial imbalance due to transportation infrastructures. In order to achieve an holistic approach, this information could be

compared to other fragmentation-related regional activities. The study of the fragmentation caused by the two northern dual

carriageways is carried out at a local scale, analysing the surrounding landscape, the potential permeability and the road-kill

rates of medium-sized terrestrial wildlife. The black spots and the funnel effect sites are identified. As both regional and local

scales are complementary, the two-scale analysis could improve landscape management. Finally, it is concluded that visual

landscape study does not guarantee a functional integration. # 2002 Elsevier Science B.V. All rights reserved.

Keywords: Fragmentation; Transport infrastructures; Scale; Road-kills; Landscape integration assessment

1. Introduction

The meaning of the term fragmentation is a constant

subject of discussion in scientific literature (Collinge,

1996; Fahrig, 1997; Bunnell, 1999a,b; Fahrig, 1999;

McComb, 1999; Rochelle, 1999). In this article, frag-

mentation is understood as ‘‘the landscape’s lack of

connectivity, the mechanisms that cause it and the

subsequent alteration of ecological processes’’.

The construction of transport infrastructures, urban

development and agriculture are the causes of frag-

mentation that are most quoted in the bibliography.

These activities alter the structure of the landscape

and, therefore, the ecological processes associated

with it (Saunders et al., 1991; Merriam and Wegner,

1992; Collinge, 1996; Fahrig and Grez, 1996; Laurance,

1997; Laurance et al., 1997; Wigley and Roberts,

1997; Laurance et al., 1998; Scott, 1999). It would,

therefore, be advisable to limit the fragmentation

caused by these activities and integrate them in the

landscape, based on scientific arguments and with

all possible legal and administrative means, which

is the case of the Strategic Environmental Assessment.

In this framework the European Union has recently

developed projects like COMMUTE (Common Meth-

odology for Multimodal Transport Environmental

Impact Assessment, 32401 1998) and INTERNAT

(Integrated Trans European Network Assessment

Techniques 48323 2001).

Landscape and Urban Planning 58 (2002) 113–123

* Corresponding author. Tel.: þ34-948-425-600x6281;

fax: þ34-948-425-649.

E-mail addresses: [email protected] (M. Serrano), [email protected]

(L. Sanz), [email protected] (J. Puig), [email protected] (J. Pons).

0169-2046/02/$20.00 # 2002 Elsevier Science B.V. All rights reserved.

PII: S 0 1 6 9 - 2 0 4 6 ( 0 1 ) 0 0 2 1 4 - 6

The impact of linear transport infrastructures on

fauna has been intensively studied in North America

and different European countries since the seventies.

In Spain, these studies have been more recently devel-

oped. The scientific community, the administration

and ecological organisations have become aware of its

importance and research has proliferated. Workshops

have been organised and manuals have been edited on

the subject (Velasco et al., 1992; A.T.C., 1999; Rosell

and Velasco, 1999).

As a result of the construction and operation of

linear transport infrastructures, ecological processes

suffer changes that have a direct and indirect impact

on fauna. Two examples are the change in the move-

ment patterns of terrestrial wildlife (Curatolo and

Murphy, 1986; Murphy and Curatolo, 1986; McLellan

and Shackleton, 1988; Trewhella and Harris, 1990;

Beier, 1995; Cameron et al., 1995; Lovallo and

Anderson, 1996; Gibbs, 1998) and the risk of accidents

(Wilkins and Schmidly, 1980; Coulson, 1982; Davies

et al., 1987; Aaris-Sorensen, 1995; Drews, 1995;

Fahrig et al., 1995; Groot-Bruinderink and Hazebroek,

1995; Ashley and Robinson, 1996; Madsen, 1996;

Romin and Bissonette, 1996a,b; Lehnert and Bisson-

ette, 1997), both results of the barrier effect caused by

linear infrastructures. The importance of accidents

must also be considered not only from the environ-

mental perspective (wildlife population conservation),

but also from the point of view of road safety, con-

sidering the social and economic consequences that

these collisions have.

The purpose of this article is to provide evidence of

how two-scale analysis and landscape integration

assessment are useful to describe the landscape frag-

mentation generated by the main transport infrastruc-

tures in Navarra, in the north of Spain (Fig. 1).

The study on fragmentation is affected by the

problem of scale. McGarigal and McComb (1999)

point out that fragmentation works at different scales.

In this context, this article intends to show the advan-

tages of studying the fragmentation caused by trans-

port networks on two spatial scales, regional and local.

On the other hand, the fragmentation cause by a

road may vary depending on its characteristics and the

landscape in which it is located. This article, will

compare the fragmentation generated by two dual

carriageways, each of which has a different relation

to its surroundings and a different level of integration

in the landscape. It should be mentioned here that, just

as this article refer to landscape with the ecological

meaning of the word (Forman and Godron, 1981;

Gonzalez Bernaldez, 1981), landscape integration is

used in more than a purely aesthetic sense.

2. A regional landscape approach

2.1. Methodology

This study starts by considering the cartography

Instituto Geografico Nacional of the transport infra-

structure network in Navarra (railway, motorways and

dual carriageways, main roads, provincial roads,

regional roads and local roads), in order to obtain a

global view of its location and distribution (Fig. 2).

Fig. 3 provides further detail of the location of the

main transport infrastructures (railway, motorways

and main roads), which will later be used to char-

acterise them and the how they are related to the

territory, by means of descriptors and indices.

Two descriptors are defined (cloverleaf and corridor

infrastructures) and one index (length in km of roads

of each category in the region) to characterise the main

transport network infrastructure.

The term cloverleaf infrastructure is used to describe

an area in which several significant transport infra-

structures (railway, motorways, dual carriageways

and main roads) come together in a more or less

radial manner, and the term infrastructure corridor is

employed to describe the stretch of land in which there

are two or more parallel significant transport infra-

structures (railway, motorways, dual carriageways

Fig. 1. Navarra’s location.

114 M. Serrano et al. / Landscape and Urban Planning 58 (2002) 113–123

and main roads). The location of the cloverleaf and

corridor infrastructures is shown on Fig. 4. Table 1

shows the total length in km of each road category in

the region.

The transport infrastructure network of the territory

is then characterised by means of two new descriptors

(primary and secondary polygons) and three indices

(length in km of internal roads by primary polygon,

Fig. 2. Transport infrastructure and settlements.

Fig. 3. Main transport infrastructure. Fig. 4. Cloverleaves and corridor infrastructure.

M. Serrano et al. / Landscape and Urban Planning 58 (2002) 113–123 115

length in km of roads on the border of each primary

polygon and density (km km�2) of roads in each

primary polygon).

The first descriptor used is what it has been called a

primary polygon, which is each of the fragments into

which the region is divided considering motorways

and dual carriageways as dividers, since they are

isolated from each other by fencing and have a daily

average traffic intensity (DATI) of over 10,000 vehi-

cles per day along most of their length. The following

indices are calculated for each of the primary polygons

obtained: length of interior roads in km, length in km

of bordering roads (see Table 2) and density of interior

roads in km km�2 (see Table 3).

In the second place, the territory is characterised in

accordance with what in this article has been called

secondary polygons (Fig. 6). These are each of the

fragments into which the territory is divided if all the

roads that have a DATI of between 4000 and 10,000

vehicles per day (which in Navarra coincides with all

the roads that belong to the general road network) are

also used as dividers. Secondary polygons analysis

permits the study of the future evolution of the trans-

port network, as some of these roads will probably be

changed to motorways or dual carriageways in the

short term.

2.2. Discussion

The main transport infrastructures cross Navarra

forming a northwest–south corridor (Fig. 4) that

divides the territory into four main fragments (primary

polygons). If the roads with a DATI of between 4000

and 10,000 vehicles per day are considered, the num-

ber of fragments (secondary polygons) increases to

seven (Fig. 6). Considering the new linear infrastruc-

tures planned, which are pending approval by the

administration (and are, therefore, not included in

the figures), the fragmentation and concentration of

infrastructures will be increasing in the short term. On

the one hand, there is a project for a high speed train,

which would form part of what it has been called a

corridor infrastructure, and another for upgrading two

main roads (dividers of the secondary polygons) into

dual carriageways (increasing the number of primary

polygons up to six). And this is without considering

other kinds of linear infrastructure, such as an irriga-

tion channel that has already been approved and will

also form part of the corridor infrastructure once it is

built.

From the location of the cloverleaves and corridor

infrastructures, it is possible to identify the most

overloaded areas, an aspect that should be taken into

consideration when new regional road plans are pro-

jected, in order to take into account that the impact of a

set of infrastructures should be greater than the sum of

the impacts of each individual infrastructure. On the

one hand, this would help to prevent the saturation of

some areas brought about by this confluence of infra-

structures, providing the reasons are not proportional

to the effects, and on the other hand, evaluate the

application of corrective measures to the areas con-

cerned (which in the case of roads, are the cloverleaf

and corridor infrastructures).

At the present time, the roads are equally distributed

within the polygons, since road density is more or less

Table 1

Length of roads by category

Category Length (km)

Motorways/dual carriageways 236.29

Motorway links 77.50

Main roads 555.53

Provincial roads 531.08

Regional roads 524.60

Local roads 2508.83

Total 4433.83

Table 2

Length (km) of roads per primary polygon

Primary polygon Interior roads Bordering roads Total roads

Polygon 1 153 61.58 214.58

Polygon 2 2405.04 167.28 2572.32

Polygon 3 1485.31 153.31 1638.62

Polygon 4 186.98 34.92 221.9

Table 3

Road density (interior) per polygon (km km�2)

Primary polygon Road density

Polygon 1 0.46

Polygon 2 0.38

Polygon 3 0.44

Polygon 4 0.52


constant (values between 0.38 and 0.52 km of road per

km2) in each of the primary polygons (see Table 3).

This means that although there are areas in which the

infrastructures are concentrated (cloverleaves and cor-

ridors) as previously described, there are no primary

polygons that are more or less overloaded as far as

transport infrastructure is concerned. To define the

level of fragmentation of the territory under study and

for the best possible land management on a regional

scale, this analysis would have to be completed with

the study of other variables that also contribute to

landscape fragmentation, such as certain use of land

(agriculture, urban development).

Since the impact of landscape fragmentation

depends both on the characteristics of the linear

infrastructures and on the territory in question (Sec-

tion 1), this general information should be completed

with specific studies for each case on a more detailed

scale.

3. A local scale approach

3.1. Methodology

The local landscape integration analysis is applied

to the two dual carriageways in the north of the region

(A-15 and N-240-A) that mark the limits of primary

polygon 1 (Fig. 5). Firstly, the characteristics of these

roads and the territory they cross are described. In the

second place, in order to evaluate the permeability

of the two roads, the structures that cross them are

analysed and data on terrestrial wildlife killed by

vehicles are provided.

Some of the characteristics of the two roads under

study are similar. In the first place, they are both of

approximately the same length (the A-15 is 26 km

long and the N-240-A is 29 km). In the second place,

traffic density is very similar (around 10,000 vehicles

per day). Thirdly, they are both four-lane roads. In the

fourth place, they have the same type of fencing, and

finally, the study area belongs to the Euro-siberian

region. Forest vegetation on the higher altitudes con-

sists of beech woods (Fagus sylvatica), with common

oaks (Quercus robur) in the valleys and white oaks (Q.

humilis) on the sunniest slopes.

With regards to other characteristics considered in

landscape integration analysis, however, the two roads

are different. On the one hand, the N-240-A goes

through a relatively wide and flat valley, next to

another regional road, the railway (part of what it

has been previously been called a corridor infrastruc-

ture) and the river Araquil. It separates to large

mountain ranges with large wood masses. The area

it crosses is quite heavily populated (see Fig. 7). On

the margins of the A-15 there are 8 settlements with a

total of 1534 inhabitants, considering a 500 m area of

influence around the two roads (according to the local

census Gobierno de Navarra, 1996), whereas in the

vicinity of the N-240-A, there are 19 settlements with

16,126 inhabitants. The number of inhabitants per km

of road, then, is 57.3 people per km, whereas for

the N-240-A it is as high as 471.3 people per km.

In the same figure, it can also be seen that the activities

Fig. 6. Secondary polygons.

Fig. 5. Primary polygons.


of the population is different in each of the areas. The

population in the towns crossed by the A-15 is more

concentrated in the primary sector, whereas the popu-

lation affected by the N-240-A is more related to the

industrial sector. In fact, the N-240-A landscape has

been altered more by man (there are more settlements,

with much more industry, and the valley is made up of

meadows and an occasional group of oaks) and the

woods from the hills only come close to the roads in

four concrete areas. In two of these four areas, the

woods are on both sides of the road.

On the other hand, the beginning of the A-15 runs

next to the river Larraun, with a complex topography

due to how narrow the valley is. This problem has been

solved by the construction of tunnels and viaducts. It

continues through some areas in which the valley is

wider, and others in which it rises half way up the

slope. Its highest point is on a long sloping stretch that

ends in a tunnel. It finally falls with the help of

viaducts until it reaches the river Leizaran. The sur-

roundings in general are less populated and more

abrupt and the landscape is more varied.

To sum up, it can be said that the two roads are also

different as far as their visual integration in the land-

scape is concerned. The N-240-A is visually better

than the A-15. While the A-15 has some sections with

bare large embankments and cuttings, the N-240-A

crosses a constant topography (a valley), and an area

with more human involvement.

To analyse the potential permeability of the roads,

all the passes that affect both roads have been inven-

toried. Their utility has then been evaluated for large

Fig. 7. Population and activities in the primary polygon 1.


and medium sized wild mammals, based on the char-

acteristics that articles and studies on the subject have

classified as important, such as the location, access,

substrate, construction materials and dimensions of

each pass (Singer et al., 1985; Velasco et al., 1992;

S.E.T.R.A., 1993; Foster and Humphrey, 1995; Yanes

et al., 1995; Rodrıguez et al., 1996; Keller and Pfister,

1997; Muller and Berthoud, 1997; Rodrıguez et al.,

1997; Rosell et al., 1997; Rosell and Velasco, 1999).

It is assumed that the passes that these animals use

will also be used by smaller fauna (S.E.T.R.A., 1993;

Muller and Berthoud, 1997; Carsignol, 1999),

although this is not the main subject of this study.

The passes have been classified in three groups. The

first consists of passes with a high level of perme-

ability (large viaducts and tunnels). The second

includes overpasses and underpasses that provide

for a certain level of potential fauna permeability,

and the third are passes that are not considered as

adequate for use by wildlife.

3.2. Results

The A-15 has a series of structures that provide it

with a high level of permeability, three tunnels and

six viaducts. There are also several overpasses and

underpasses, four of which have a certain level of

permeability. According to the study area description,

the A-15 has several large slopes that isolate the

road from the rest of the landscape, and in these areas

it is impermeable. The N-240-A has several over-

passes and underpasses, but none of them guarantee

permeability. These permeable points are identified

on Fig. 8.

The terrestrial wildlife (large and medium sized

mammals: Capreolus capreolus, Erinaceus euro-

paeus, Felis silvestris, Genetta genetta, Lepus euro-

paeus, Martes foina, Martes martes, Meles meles, Sus

scrofa, Vulpes vulpes and Mustela putorious) killed

by vehicles have been inventoried, on weekly

runs between May 1999 and May 2000. The road

Fig. 8. Permeable points and black spots in A-15 and N-240-A (primary polygon 1).


conservation service for both roads collaborated with

the research team to ensure the most accurate data

possible. The road-kill rate (number of animals killed

per km per year) and the average for each road

(number of animals killed per km per year) have been

calculated. The N-240-A road-kill rate is 4.10 animals

per km per year (119 animals killed) and the A-15

road-kill rate is 2.38 animals per km per year (62

animals killed). From these rates, black spots are

defined as the points where the number of accidents

is at least 45% above average.

Finally, it should be mentioned that the number of

traffic accidents caused by animals on the two roads

between 1993 and 1998 was 19. Most of them were

caused by domestic animals, particularly sheep.

4. Discussion

Fig. 8 shows the potentially permeable points and

the black spots of these roads. A look at this map

relates the road-kill rate to potential permeable passes

of the roads with high and certain level (Section 3.1).

In the first place, the stretches of road with no accident

black spots are generally those with the highest poten-

tial permeability. This is the case for stretches with

large tunnels and viaducts, which have the lowest

road-kill rates, and for others with overpasses or

underpasses permeable by fauna, which have no black

spots. In the second place, generally speaking there are

no black spots on stretches bordered by large slopes.

These are areas that are isolated from their surround-

ings and the road-kill rate is therefore low. Thirdly, the

areas that are not very permeable in which wildlife can

access the roads with relative ease, in spite of the

fencing, have to be considered. This happens on the N-

240-A and on some parts of the A-15. This is where

the accident black spots are found, particularly where

the road crosses rivers or other vegetation corridors.

For example, the two oak woods crossed by the N-

240-A are accident black spots, and six of the eight

black spots on this road are in the four areas where the

woods come close to the road. On the A-15 two black

spots are found next to permeable passes. This is

explained because the configuration of the landscape

leads the animals here instead of to the permeable

points, producing what it could be called a ‘‘funnel

effect’’. This shows the need to establish passes that

give roads permeability, taking the landscape elements

that wildlife makes use of into account. Thus, the local

permeability of the infrastructure would contribute to

the connectivity of the landscape.

But the economic factor must also be considered. In

an abrupt topography (such as the A-15), the con-

struction of viaducts may be preferred, in spite of their

high cost, to avoid land movement, integrate the road

in the landscape and from a road safety perspective,

for example. But for roads that cross a valley, such as

the N-240-A, the construction of large permeable

structures like viaducts is not contemplated.

The N-240-A characteristics (Section 3.1) make it

less permeable for wildlife, with a higher road-kill rate

(119 animals killed, representing 4.10 animals per km

per year) than the A-15 (62 animals, representing 2.38

animals per km per year). Therefore, the integration of

a road in the landscape cannot be considered merely

from an aesthetic perspective. Its functional integra-

tion should also be considered. This would reduce the

number of wild animals killed on the roads, and

minimise the impact of roads on the wildlife popula-

tion, improving road safety.

Finally, as the number of accidents caused by wild-

life (S. scrofa and C. capreolus) was low (Section 3.2),

it is not possible to study if there is a relation between

the spots where they occur and the surrounding land-

scape.

5. Conclusions

The many different ways in which authors describe

fragmentation is evidence of the complexity of the

problem, research on which has recently increased in

Spain. The two-scale study (regional and local) of the

fragmentation caused by communication infrastruc-

tures is seen to be very useful for improving landscape

management.

In the first place, the regional scale offers a global

view of the level of fragmentation in an area, revealing

territorial imbalance and existing infrastructure over-

loads. As for the detection of territorial imbalance, the

study of the region divided into polygons defined by

the main roads and characterised by indices is very

revealing (Section 2). For the particular case that has

been studied here, Navarra can be said to have a good

distribution of its territorial communication network.


With regards to overloads, the definition and carto-

graphy of two types is suggested: cloverleaves and

corridors. Fig. 4 shows these elements for the case

under study. The knowledge of this imbalance and

overloading could condition the future evolution of the

road network. Their identification could be useful to

define the route for new communication infrastruc-

tures in general, to make local alterations in areas

already defined in the General Road Plan, or to define

concrete local measures to be applied in an attempt to

cancel out or mitigate the cumulative impact when a

new road is built. It is seen, then, that the local and

regional scales are highly complementary.

In the second place, the regional information on the

fragmentation caused by road infrastructures is com-

parable to regional plans related to other activities that

cause fragmentation (agricultural, urban development

or forestry plans) or the network of protected natural

areas (Nature 2000 Network). The use of the regional

scale thus allows to consider all this information as a

whole, with a view to the best possible landscape

management.

On the other hand, the local scale implies a more

detailed analysis, and therefore, leads to a much

greater knowledge of the territory. The study of frag-

mentation on a local scale is centred on the two main

roads in the north of Navarra, and includes an exam-

ination of the surrounding landscape, the study of

points of potential permeability and a record of the

accidents involving medium-sized and large mam-

mals. It is, thus, possible to detect black spots of

casualties (Section 3), show how they are related to

the fragmentation of the concrete area under study

(they identify conflictive points with regards to land-

scape fragmentation and also from the perspective of

road safety, revealing causes and effects), and propose

preventive and corrective measures to effectively

mitigate them. Locating points where the so-called

funnel effect is present is also possible. This effect,

which consists of the design and fencing of the road

itself leading animals to points with low potential

permeability (with no upper or lower crossing placed)

where they have easy access to the road, should be

avoided at the design stage. Finally, a local scale

analysis provides evidence that functional landscape

integration is not guaranteed by its mere visual inte-

gration, which does not ensure the connection between

the different elements in the landscape, as shown in the

results of the study on wildlife accidents. A local

study, therefore, also identifies factors that should

be taken into account for regional planning and con-

firms that a two-scale, local and regional, study of

landscape fragmentation caused by linear infrastruc-

tures and landscape integration, is very useful.

Acknowledgements

We thank ‘‘Departamento de Obras Publicas del

Gobierno de Navarra’’ for providing us with informa-

tion. We would like to specially thank Mr. Daniel

Rodes, Ma Carmen Lizarraga and Luis Miguel Martın.

We also thank ‘‘Gobierno de Navarra’’ for the research

grants and ‘‘Universidad de Navarra’’ for the financial

support.

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