Introduction

For several reasons, historical data on the occurrence of Heracleum mantegazzianum Sommier & Levier are fairly detailed, especially in countries with a strong floristic tradition. Such data allow a retrospective analysis of this species' spread. This species is attractive enough to be recorded by botanists, because of its alien origin and tendency to spread, and above all its conspicu-ousness (Fig. 3.1). In parts of the continent, such as Central Europe, it is also taxonomically unproblematic, hence easily recognizable by amateur botanists who are the main collectors of floristic data (Pysek, 1991). The taxonomic problems referred to earlier (see Jahodová et al., Chapter 1, this volume) are of little significance in the Czech Republic as the vast majority of the observations concern this species (Holub, 1997).

Probably the most systematically gathered data on the occurrence of H. mantegazzianum in Europe are those for the Czech Republic (Pysek, 1991, 1994; Pysek et al., 1998a) and the UK (Collingham et al., 2000), countries with a strong floristic tradition (Preston et al., 2002; Pysek et al., 2002). Such data allow the invasion dynamics of H. mantegazzianum over the last 150 years to be reconstructed. These two data sets are complementary because they: (i) come from climatically different geographical areas of Europe (continental and oceanic climate); and (ii) were collected using different methods, i.e. collation of localities from the literature in the Czech Republic, and repeated

42 © CAB International 2007. Ecology and Management of Giant Hogweed (Heracleum mantegazzianum,). (eds P. Pysek, M.J.W. Cock, W. Nentwig and H.P. Ravn)

ij Other o

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Fig. 3.1. Sources of floristic data for H. mantegazzianum differ from those for other neophytes, based on a sample of 76 neophytes recorded in the Czech Republic (based on 28,330 floristic records). The percentage of literature sources is very similar (55.6% and 52.2% of all records of H. mantegazzianum and all neophytes, respectively). However, H. mantegazzianum is avoided by herbarium collectors because of its large stature, which accounts for why only 4.1% of the records (25 of the 603 in total) are from herbaria, compared to 38.4% for an average neophyte. Interestingly, 245 unpublished records (40.6% of the total) were supplied by botanists, which greatly exceeds the average number for other neophytes (35.2 records).

■ Heracleum mantegazzianum i ! Other neophytes (n = 76)

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Herbaria Unpublished

Fig. 3.1. Sources of floristic data for H. mantegazzianum differ from those for other neophytes, based on a sample of 76 neophytes recorded in the Czech Republic (based on 28,330 floristic records). The percentage of literature sources is very similar (55.6% and 52.2% of all records of H. mantegazzianum and all neophytes, respectively). However, H. mantegazzianum is avoided by herbarium collectors because of its large stature, which accounts for why only 4.1% of the records (25 of the 603 in total) are from herbaria, compared to 38.4% for an average neophyte. Interestingly, 245 unpublished records (40.6% of the total) were supplied by botanists, which greatly exceeds the average number for other neophytes (35.2 records).

mapping in different periods in the UK. That these different approaches yield similar results, as shown below, is an indication that conclusions drawn about the history of invasion at regional/geographical scale are robust.

Furthermore, floristic data not only make it possible to reconstruct the invasion, and describe the pattern of species abundance in the landscape and its development over time, but also provide information on species ecology and the temporal changes in the spectrum of habitats occupied during the course of the invasion (Pysek, 1991). The present chapter reviews information on the historical dynamics of H. mantegazzianum and aims to: (i) describe the dynamics of the invasions of the Czech Republic and UK; (ii) compare the pattern of spread at local and regional/geographical scales; and (iii) place the invasion potential of H. mantegazzianum into a wider context of plant invasions by comparing its rate of spread recorded in these two countries with that recorded for important invasive species elsewhere.

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