fragmentation assessment for the Trento-Rocchetta road project
case study is also available in pdf format.
SECTOR: Transport COUNTRY:Italy
Linear infrastructures are characterised by a series of common problems
in terms of ecological impact, due to the complex interactions with the
landscape they cross. A linear infrastructure represents a new artificial
element that interferes with the natural structure of the landscape: it
creates barriers, breaks natural corridors, and alters the conditions
of both the intersected and the surrounding ecosystems. Its effects are
spread over a vast area that is often difficult to delimit. Infrastructures
cutting through the landscape can cause not only a loss of natural areas,
but also a reduction in the quality of the remaining ones, due to their
Ecosystem fragmentation refers to the break-up of habitat expanses into
smaller and more isolated units. It determines a wide range of threats
to biodiversity, such as invasion of exotic species, reduction of organism
movement, reduction of genetic diversity and population viability, alteration
of ecological flowpaths. Roads, as linear infrastructures in general,
are acknowledged to be a major cause of fragmentation.
Assessing fragmentation is quite a hard task. Fragmentation itself represents
a very complex effect, whose modeling can be still considered in an experimental
phase (Bogaert et al. 2000). Increasingly common approaches to fragmentation
assessment are based on the use of landscape ecological spatial parameters,
such as ecosystem size, shape and distribution (Maurer 1999; Treweek and
Veitch 1996). These approaches aim at quantifying the impacts of infrastructures
on natural habitats by studying the relevance of the ecological structures
within an area and by predicting the changes induced by the project. This
case study exemplifies the application of similar approaches to the identification
of the most suitable alignment for the Trento-Rocchetta road project (Geneletti,
The Trento-Rocchetta road project is a new road connection to be constructed
within the Autonomous Province of Trento, in northern Italy. Five alternative
layouts have been considered for this study. The objective of the study
is to help the authorities to identify the most suitable one. The area
that will be affected by the roadway is represented by a wide alpine valley
that can be described as a man-dominated landscape, in which few natural
ecosystems remain within an agricultural matrix. Due to their rarity,
several of such ecosystems play an important role for the conservation
of biodiversity within the province.
INDICATORS AND EVALUATION
The impacts caused by each alternative in terms of ecosystem fragmentation
were studied by generating landscape scenarios and by measuring the changes
in three ecological indicators: ecosystem core area, ecosystem connectivity,
and ecosystem disturbance. All the operations were performed using a Geographic
Information System (GIS). The three indicators were first measured for
each natural ecosystems in the original conditions, i.e. without the proposed
project (alternative zero). Subsequently, the presence of the road was
simulated by overlaying a space-occupation buffer to the ecosystem map.
Figure 1 shows the five scenarios corresponding to the five road alternatives.
In particular, the Figure underlines the changes expected on the riverside
vegetation patches, which are represented in black. As it can be seen,
the different layouts are to disrupt the riverside ecosystems in different
ways, which must be studied and compared in order to identify the least-impacting
The fragmentation impact caused by the five alternatives was predicted
by computing the three indicators in each of the scenarios, and then comparing
their value with the original ones (see example in Figure 2). Such changes
were assessed by constructing value functions that relate the differences
to the expected loss of viability of the ecosystem patch (Geneletti, 2004).
This allowed comparing the fragmentation impact of the five alternatives,
and to draw a suitability ranking to be then proposed to decision-makers.
The impact scores showed that Alternative 5 performed as the least impacting,
whereas Alternative 2 appears as the most disruptive in terms of ecosystem
fragmentation. The remaining alternatives performed quite similarly.
Figure 1: Scenarios
of ecosystem fragmentation
Figure 2: Example
of connectivity computation for the scenarios of Alt.0 and Alt.1
This case provided an example of how to account for ecosystem
fragmentation, so as to orient the planning and development of new infrastructures.
In particular, the application of landscape ecology and the use of Geographical
Information Systems (GIS) were illustrated to simulate the spatial
setting of the landscape after the sitting of a proposed infrastructure.
This allowed to highlight critical areas, as well as to identify the least
disruptive location (e.g., the most suitable land corridor to host a linear
In principle, the approach is transferable to other cases and countries.
However, the meaningfulness of the proposed indicators is to be checked
in case different ecological conditions occur. Furthermore, the availability
of data play also a relevant role in determining the indicator set: if
more ecological data are available (e.g., species distribution maps),
the approach could be integrated with further indicators and analyses.
Even though the approach proposed has targeted road developments, it appears
suitable for all type of transportation systems (railways, cable cars,
etc.), as well as linear infrastructures in general (power lines, oil
pipes, etc.). Obviously, each type of infrastructure has its peculiarities.
The disturbance induced by the space occupation of a power line is bound
to be different than the one caused by a road. However, most of the guidelines
provided in this study to assess the impact of roads can be generalised
to all type of linear infrastructures.
Dr. Davide Geneletti
Dept. of Civil and Environmental Engineering
University of Trento
Via Mesiano 77
38050 Trento, Italy
Tel. 0461 882685; Fax. 0461 882672
Bogaert, J., P. van Hecke,
D.S. van Eysenrode, I. Impens, 2000. Landscape fragmentation assessment
using a single measure. Wildlife Society Bulletin, 28(4), pp.875-881.
Geneletti, D., 2004. Using spatial indicators and value functions to assess
ecosystem fragmentation caused by linear infrastructures. International
Journal of Applied Earth Observations and Geoinformatio 5(2004), pp.1-15.
Geneletti, D., 2002. Ecological evaluation for environmental impact assessment.
Utrecht: Netherlands Geographical Studies 301.
Maurer, M.E., 1999. Development of a community-based, landscape-level
terrestrial mitigation decision support system for transportation planners.
Proceedings of the third international conference on wildlife ecology
and transportation. eds Evink G.L., P. Garrett and D. Zeigle. Tallahassee:
Florida Department of Transportation.
Treweek, J., N. Veitch, 1996. The potential application of GIS and remotely
sensed data to the ecological assessment of proposed new road schemes.
Global Ecology and Biogeography Letters, 5, pp. 249-257.