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SECTOR: Transport COUNTRY:Italy

BACKGROUND
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 fragmentation.
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, 2002; 2004).
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 one.
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

LESSONS LEARNT
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 infrastructure).
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.

PROJECT CONTACT
Dr. Davide Geneletti
Dept. of Civil and Environmental Engineering
University of Trento
Via Mesiano 77
38050 Trento, Italy
Tel. 0461 882685; Fax. 0461 882672
davide.geneletti@ing.unitn.it
www.ing.unitn.it/~genelett

REFERENCES

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.