Habitats Invaded by Heracleum mantegazzianum

H. mantegazzianum occurs in a variety of habitat types in its invaded range in Europe. Among the most common habitat types of H. mantegazzianum are linear structures along traffic routes (roadsides, railway margins) and flowing waters (Fig. 8.1; Pysek and Pysek, 1995; Thiele, 2006). These habitats can be completely open or partly shaded by tree lines, single trees or shrubs. Furthermore, H. mantegazzianum can often be found at fringes and margins of woodlands and grasslands. In terms of area covered by stands of H. mantegazzianum, abandoned grasslands are the most represented habitat type, followed by tall-herb stands which can be found at long-abandoned former grassland sites or at other disused sites. Moreover, ruderal places, i.e. sites that recently have been severely disturbed by human activities, are suitable habitats (Neiland et al., 1986; Pysek, 1994; Ochsmann, 1996). Examples are sand pits, building sites and rubbish dumps. Closed tree canopies prevent invasion and growth of H. mantegazzianum, but it can occur beneath sparse canopies or in light gaps. Managed grasslands are a marginal habitat type for H. mantegazzianum in which the species sometimes can establish if there is a high pressure of H. mantegazzianum seeds from adjacent stands. However, regular mowing or grazing with adequate intensity (e.g. mowing twice a year) adversely affects the performance of H. mantegazzianum (lower height, prevention or reduction of fruit set, slower life cycle). As a result, occurrences of H. mantegazzianum in managed grasslands are not invasive as long as regular management is applied. In addition to rural habitat types, H. man-tegazzianum also occurs in urban areas, gardens and parks (Pysek, 1994; Pysek and Pysek, 1995).

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O Point-like stands

□ Linear stands

■ Dominant stands

Fig. 8.1. Frequencies of habitat types invaded by H. mantegazzianum in 20 study areas in Germany. Number of stands recorded in each habitat, based on 738 records from Germany, is shown and representation of different stand types within habitat types indicated. Stands exceeding 25 m2 in size were classified into dominant (with more than 50% cover of H. mantegazzianum) and open (with less than 50% cover). Other categories distinguished are point-like (smaller than 25 m2) and linear (narrower than 1 m) stands. Data from Thiele (2006). 'Open' habitat types are virtually treeless and shrubless, while 'shaded' habitat types had more than 10% tree or shrub cover. 'Abandoned grasslands' are former agricultural grasslands which are currently disused. 'Woodland margins' are the outer 5(-10) m of copses, forests and shrubland. 'Woodlands' refers to the interior of copses and shrubland but not to forest interiors. 'Grassland and field margins' are marginal parts of grassland and arable fields, which are not used agriculturally. 'Tall-forb stands' can be found in long-abandoned sites of former agricultural grasslands or other long disused sites. 'Ruderal areas' are recently disturbed sites, such as sand pits, building ground and rubbish dumps, which are in an early stage of secondary succession.

O Point-like stands

□ Linear stands

■ Dominant stands

Fig. 8.1. Frequencies of habitat types invaded by H. mantegazzianum in 20 study areas in Germany. Number of stands recorded in each habitat, based on 738 records from Germany, is shown and representation of different stand types within habitat types indicated. Stands exceeding 25 m2 in size were classified into dominant (with more than 50% cover of H. mantegazzianum) and open (with less than 50% cover). Other categories distinguished are point-like (smaller than 25 m2) and linear (narrower than 1 m) stands. Data from Thiele (2006). 'Open' habitat types are virtually treeless and shrubless, while 'shaded' habitat types had more than 10% tree or shrub cover. 'Abandoned grasslands' are former agricultural grasslands which are currently disused. 'Woodland margins' are the outer 5(-10) m of copses, forests and shrubland. 'Woodlands' refers to the interior of copses and shrubland but not to forest interiors. 'Grassland and field margins' are marginal parts of grassland and arable fields, which are not used agriculturally. 'Tall-forb stands' can be found in long-abandoned sites of former agricultural grasslands or other long disused sites. 'Ruderal areas' are recently disturbed sites, such as sand pits, building ground and rubbish dumps, which are in an early stage of secondary succession.

H. mantegazzianum develops stands of varying extent and density. In our field studies, we recognized point-like stands (smaller than 25 m2), linear stands (narrower than 1 m) and extensive stands (larger than 25 m2). Extensive stands were classified into dominant (with more than 50% cover of H. mantegazzianum) and open (with less than 50% cover). Of all extensive stands found during our field studies in Germany, 36% were dominant. The highest proportions of dominant stands (among extensive stands) were found in open roadsides where inadequate maintenance was applied, in abandoned grasslands, and in neglected grassland and field margins (Fig. 8.1). Particularly extensive invasions by H. mantegazzianum in abandoned pastures and former settlements are currently present in the Slavkovsky les region, Czech Republic (see Pysek et al., Chapter 3, this volume; Pysek and Pysek, 1995; Mullerovâ et al., 2005) and by H. sosnowskyi Manden. in abandoned agricultural land in Latvia (see Ravn et al., Chapter 17, this volume).

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