The Cittadella of Alessandria, north-west of Italy (44,9197° N; 8,6082° E), is one of the best preserved military fortifications present in Europe. Built in XVIII century it extendeds on an area of 60 hectares. In 2014 the citizen’s movement “Europa nostra” has included the Cittadella in the “7 Most Endangered”(http://www.europanostra.org/2014-list/) program, which identifies the monuments and sites at risk in Europe. Since the abandonment by the Italian Army in 2007, the fortress underwent a gradual degradation. In this condition several herbaceous and wooded species colonized most of the buildings, increasing damages. A. altissima is the most troublesome among these species because of the high ability of the root system to infest building elements (roofs, walls) and roads, causing severe deterioration of the structures. The invasive potential of A. altissima is due to its abundant seed production by female individuals and high germination ability, its fast growth, the numerous suckers and the release of allelopathic compounds limiting the growth of other plants. In 2013 a survey of the A. altissima presence in the Cittadella fortress was carried out to determine the level of infestation. The number of A. altissima plants present at Cittadella was assessed on three distinct areas: the bastions and curtain walls, the courtyards and internal roads, and the building roofs. The infestations were sorted in isolated plants, small groups of plants, linear infestations along the curtain walls, and large areas of infestation (\textgreater5m2). Overall, 32 isolated or small groups of plants, 26 linear infestations, and 8 large areas were identified. Linear infestations summed about 730m, while large areas were spread on about 7200m2, with an average infestation of 10-13 stems/m2. Male plants represented the majority of the infestations, and few female plants were present on the bastions. In order to prevent the spread of A. altissima and preserve the buildings from other damages, the eradication is undelayable. Different control strategies have been suggested and consist of an integration of mechanical (cutting, girdling) and chemical means. Hand pulling of young seedlings and suckers should be avoided on the buildings to prevent further damages on the structures. Considering the high level of infestation detected and the high risk of resprouts, the chemical control should be preferred. Stem injection, cut stump and basal bark application of systemic herbicides are the most suitable options.
The destructive invasion by Ailanthus altissima (Mill.) Swingle of the eighteenth century fortress “Cittadella” of Alessandria
VIDOTTO, Francesco;FOGLIATTO, SILVIA;MILAN, MARCO;FERRERO, Aldo
2015-01-01
Abstract
The Cittadella of Alessandria, north-west of Italy (44,9197° N; 8,6082° E), is one of the best preserved military fortifications present in Europe. Built in XVIII century it extendeds on an area of 60 hectares. In 2014 the citizen’s movement “Europa nostra” has included the Cittadella in the “7 Most Endangered”(http://www.europanostra.org/2014-list/) program, which identifies the monuments and sites at risk in Europe. Since the abandonment by the Italian Army in 2007, the fortress underwent a gradual degradation. In this condition several herbaceous and wooded species colonized most of the buildings, increasing damages. A. altissima is the most troublesome among these species because of the high ability of the root system to infest building elements (roofs, walls) and roads, causing severe deterioration of the structures. The invasive potential of A. altissima is due to its abundant seed production by female individuals and high germination ability, its fast growth, the numerous suckers and the release of allelopathic compounds limiting the growth of other plants. In 2013 a survey of the A. altissima presence in the Cittadella fortress was carried out to determine the level of infestation. The number of A. altissima plants present at Cittadella was assessed on three distinct areas: the bastions and curtain walls, the courtyards and internal roads, and the building roofs. The infestations were sorted in isolated plants, small groups of plants, linear infestations along the curtain walls, and large areas of infestation (\textgreater5m2). Overall, 32 isolated or small groups of plants, 26 linear infestations, and 8 large areas were identified. Linear infestations summed about 730m, while large areas were spread on about 7200m2, with an average infestation of 10-13 stems/m2. Male plants represented the majority of the infestations, and few female plants were present on the bastions. In order to prevent the spread of A. altissima and preserve the buildings from other damages, the eradication is undelayable. Different control strategies have been suggested and consist of an integration of mechanical (cutting, girdling) and chemical means. Hand pulling of young seedlings and suckers should be avoided on the buildings to prevent further damages on the structures. Considering the high level of infestation detected and the high risk of resprouts, the chemical control should be preferred. Stem injection, cut stump and basal bark application of systemic herbicides are the most suitable options.
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