Heracleum / Reuzenbereklauw

Mooi of eerder indrukwekkend is hij wel, de Reuzenberenklauw (Heracleum mantegazzianum). Ernaast kijken kan je moeilijk, want hij steekt met kop en schouders uit boven de overige vegetatie. Bovendien wordt hij druk bezocht door allerhande zweefvliegen en kevers. Wat kan je in hemelsnaam tegen zo’n plant hebben?

En toch! Het plantensap bevat chemische stoffen, de furanocumarines, die worden geactiveerd door zonlicht (fotoactivatie). Wanneer deze stoffen in contact komen met de huid kan dit in combinatie met zonlicht (ultraviolette straling), brandwonden veroorzaken. Deze fototoxische reactie zet pas in ongeveer een kwartier nadat het contact met de huid heeft plaats gevonden.

Het contact met de plant zelf is volledig pijnloos maar na een periode van 24 uur begint de huid rood te kleuren (erythema) en hoopt zich vocht op onder de huid (oedeem). Na ongeveer één week krijgt men een ongewone verdonkering van de huid (hyperpigmentatie) op de aangetaste plaats. En tot slot kan de huid nog jarenlang gevoelig blijven voor ultraviolet licht!

Mensen die via hun beroep of hun hobby in contact komen met de plant, zoals tuiniers en natuurliefhebbers vormen de belangrijkste risicogroep. Wieden zonder handschoenen of het uitvoeren van beheerswerken zonder de nodige bescherming houdt een zeker risico in. Omdat het contact met de plant zelf volledig pijnloos is, kan men urenlang doorgaan zonder zich van enig kwaad bewust te zijn!

Voorkomen is uiteraard beter dan genezen. Wanneer je de plant kent, kan je ze vermijden In geval van blootstelling aan het plantensap moet de huid zo spoedig mogelijk met water en zeep gewassen worden. Vervolgens dient de plek minstens 48 uur tegen het zonlicht bedekt te worden.

Reuzenberenklauw is mooi en fotogeniek maar in elk geval geen katje om zonder handschoenen aan te pakken.

Literatuur

Giant Alien Project (2002-2005)

http://www.giant-alien.dk/manual.html

Economic and societal effects (positive/negative)

H. mantegazzianum has been cultivated for silage in Russia and Estonia (Kull et al. 2005; Holm 2004). Fresh weight yields exceeded 90 t per hectare in the third year. A study in Hungary suggested that acetone extracts of the plant could have useful allelopathic effects on other weeds (Solymosi 1994). It is reported to be used as a spice in Iranian cooking. The most important use is as an ornamental in Europe, where it has been a garden plant especially for garden lovers and parks (CABI 2004).

Negative effects are the displacement of other species which may leave sites with dominant H. mantegazzianum stands free of vegetation in winter. Sites near watercourses are therefore endangered by erosion (Williamson and Forbes 1982). H. mantegazzianum can also be a problem for agriculture because it is an alternative host of the carrot fly Psila rosea and the fungi Sclerotinia sclerotiorum (Gray and Noble 1965, Tiley et al. 1996) but there are no records of direct impact due to increased attacking of crop plants (CABI 2004). The control of the species nevertheless needs significant financial resources, especially if its growth endangers human injuries. In Germany, the total coast is assumed to be 10 mill. €/a: 8 mill. € for the control along traffic routes, 1 mill. € for injuries and 1 mill. € to control it in nature reserves (Reinhardt et al. 2003).

In 2005 Estonia initiated a 5-year strategy for the countrywide control of alien Heracleum species (mainly Heracleum sosnowskyi, and H.mantegazzianum), in 2005 the cost of control for 235 hectares, was 1,4 mill. Estonian krooni (~90.000 €); the expected cost for 2006 is 3,36 mill.

Estonian krooni (~240.000 €) for 300 hectares (Lilika Käis pers. comm).

http://www.nobanis.org/files/factsheets/Heracleum_mantegazzianum.pdf

http://www.giant-alien.dk/pdf/Dutch%20manual_web.pdf

History of Introduction and Spread

H. mantegazzianum has been repeatedly introduced to other countries as a garden ornamental, often initially via botanic gardens, as is known for UK (Jahodová et al., 2007a). It was available as seed from Kew Botanic Gardens in 1817, presumably brought in from the Caucasus, and by 1828 was recorded as naturalised in Cambridgeshire. It was subsequently recorded in the Netherlands, Switzerland, Germany, Ireland, Denmark and, by 1862, in the Czech Republic. First records for other countries are indicated in the Distribution Table. Nielsen et al. (2005) produced a table showing the first records of H. mantegazzianum in the wild for 16 European countries, the latest being Slovakia and Iceland in about 1945. Whether it arrived directly from the Caucasus or via elsewhere in Europe is not generally known, but Jahodová et al. (2007a,b) suggested that it is likely that the current pattern of genetic diversity in Europe resulted from multiple introductions.

Spread following initial introduction is usually delayed, with a lag of 10-50 years being typical. Pysek et al. (2007d) indicated that it was first found in the wild in Czech Republic in 1877, 15 years after first introduction. Pysek and Prach (1993) and Pysek (1994), discussing the weed's spread in the Czech Republic, indicated that from 1862 up to about 1943, spread appeared to be exclusively due to cultivation as a garden ornamental but after that there was natural spread along the main rivers, and later along roadsides and railways. A genetic study from the western Swiss Alps (Henry et al., 2009) also reported anthropogenic as well as natural long-distance dispersal along rivers as main historical drivers of invasion. The role of the two mechanisms of spread appears to change with scale, with humans play a crucial role at the continental and regional scale and species traits at local level (Pyšek et al., 2008).

Uses

Buttenschøn and Nielsen (2007) commented that H. mantegazzianum has been widely grown as a forage plant in eastern Europe in the past. In invasive stands fresh weights of up to 94 t/ha have been measured and dry weights of 6-7 t/ha above ground and 2.4 t/ha below. However, its use has now declined due to problems of tainting of milk, and availability of alternatives.

Westbrooks (1991) reports that it is used as a spice in Iranian cooking.

H. mantegazzianum has been widely grown as an ornamental in Europe, thanks to its striking appearance and usefulness in flower arranging. It is still available via the Internet from commercial nurseries in Europe and North America.

A study in Hungary suggested that acetone extracts of H. mantegazzianum could have useful allelopathic effects on other weeds (Solymosi, 1994).