Giant Hogweed - Heracleum mantegazzianum 

This relative of Scotland’s native cow parsley (Anthriscus sylvestris), giant hogweed (fig. 1) can grow to 5m tall (Booy, Wade and White, n.d.). In Scotland, the species commonly grows in low-lying areas and along riverbanks (Keating, 2022). 

Range and Introduction:
The native range of the giant hogweed is Western Greater Caucasus, Southwest Asia (NNSS, 2019). The species was intentionally introduced to the UK in the 1800s, first planted in gardens as an ornamental feature. By 1828, the first wild growing giant hogweed plant was recorded in Cambridgeshire (NNSS, 2019). Since then, it has spread throughout the UK.

Scottish Distribution:
Figure 2 shows just how commonplace the species has become in the UK, even reaching as remote a place as Shetland. Data from NESBReC (2022) demonstrates the distribution of this species around the Northeast Coast from 2000-2022 (fig. 3). It appears common along rivers nearer to their mouth, such as along the Don, the Dee and the Deveron. While on this map Giant Hogweed appears less prevalent further South, this is due to the scope of data collection and is not reflective of real patterns – the NESBReC operates mostly in the Aberdeenshire and Cairngorms area (from Draft Document). 

Reproduction:
The rapid spread of giant hogweed was facilitated the plant’s efficient reproductive process. They can self-fertilise and produce as many as 50,000 seeds each (SISI, n.d.). These seeds are often transported by water, resulting in clusters of giant hogweed around river mouths. 

Impacts and Risks:
Giant hogweed poses risks to both humans and plantlife. The size and density to which stands of giant hogweed can grow will dominate and shade out native species (SISI, n.d.). Additionally the sap of the giant hogweed is ‘phototoxic’, meaning if the sap gets onto human skin and is then exposed to the sun it will cause burns and blistering - an effect potentially lasting for years (Brunning, 2017; Keating, 2022). The toxin is most concentrated in the leaves of the plant, making the removal process especially difficult (Brunning, 2017).

Management:
For the last 45 years it has been illegal to promote the growth of giant hogweed in the UK (Royal Horticultural Society, n.d.). However, for the giant hogweed which has already established, various measures can be taken to reduce its spread. Current control techniques include herbicide application, cutting of flowering heads, and digging up from the roots (SISI, n.d.). Additionally, recent trials have shown the success of sheep grazing in infested areas – sheep are not affected by the sap toxicity and seem to enjoy grazing on the plant (NatureScot, 2023).