It’s great having Alba to assist with our Invasive species research. The only trouble is that she keeps producing more and more data!

Seriously, she is fantastic and a real asset.  I’ve summarised some of her latest findings that I thought blog followers may find interesting. This follows on from last weeks post about GHW roots. This is Alba’s work, I’m only summarising it and correcting some minor grammatical errors for her. If the roles were reversed and I was working in Spain, I’d  manage a quick ‘Ola’ and ‘Sangria por favor’ and  that would be me finished. She really puts us to shame with her language skills. Anyway here are some key facts from her research at the Dobbie’s site.

Overall, we estimate more than 530 seeds, 630 surface seedlings and 440 buried seedlings in just one square meter (1600 in total). We know that mostly of these seeds or seedlings, will not germinate nor survive next year, but the size of these taproots, 1 cm diameter and about 5 cm long, raised new questions about the timescale of seedling development and seed viability. We must take into account that no plants survived and produced seed in 2011; hence we are finding viable seeds and seedlings that arise from plants that grew on the site no later than 2010.

These results help to understand the enormous reproductive capacity of the weed, but actually, these numbers are relatively small compared to its seed potential. How many seeds can a big Giant Hogweed plant produce? What are we risking if we allow just one flowering plant to disperse its seeds?

Counting the main flower's seeds

To answer this question, we decided not to spray a big plant (around 3 meters tall) and allow it to produce seeds, and thus be able to count them. We counted the number of flower heads, the florets per flower head, and finally the number of seeds per floret. We did the maths, and we counted about 4000 seeds in the main flower head, 28000 in the 12 flower heads from the sides, and 21000 seeds in smaller flower heads, resulting in a total of 53000 seeds in just one plant. The average plant reputedly produces 10 – 20,ooo seeds but what is average? The plant we looked at was certainly not uncommon or unusual in any way.

Each floret produced a mass of seeds

Around 15% of the seeds could be viable next year, which show us the high dispersal capacity of this plant. Furthermore, seeds produced by self-pollination are viable, meaning that even a single isolated plant is capable of founding a new population.Understanding the incredible reproductive  capacity of this species and its biology will help us to improve our control methods and management strategies.