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).

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