Why do invasive species have to dominate their environment? Why can’t they just live happily with other species in a balanced way? The majority of plants live quite happily in their natural setting and don’t feel the need to strangle, kill and poison their neighbours – so why do the likes of Japanese knotweed behave so aggressively?

A statement that I read recently seemed to cover this question – ‘given the slightest opportunity invasive species…must fulfill their purpose…’ this was a description of a new infestation of Japanese knotweed on a development site. ‘Must fulfill their purpose’ – this seems a great way to describe what these plants are doing – their purpose in life being to reproduce and spread…

The reason that these plants reproduce and spread so aggressively comes down to the strategies that have enabled them to survive in their natural environment, where they are predated and reduced in numbers by the environmental factors that surround them. If you use the human reproductive system as an analogy – the male of our species produces millions upon millions of sperm which go into a fairly hostile environment –and the majority of them die. Imagine if you took those sperm and put them in a different environment where they all survived!!

With Japanese knotweed, its natural setting is on the sides of volcanic terrain in Japan where it has produced strategies that enable it to survive in the most difficult of conditions. We have then uprooted it (literally) and placed it in environments where it has little or no factors mitigating against its total domination.

Nobody has told Japanese knotweed that it doesn’t need to be so aggressive. Nobody has told Japanese knotweed that nothing is going to eat it or infect it with rust pathogens…so as far as Japanese knotweed is concerned…it’s still living in an environment where it will struggle to survive – so it’s still in ‘rapid spread’ mode. It still thinks the majority of its efforts to reproduce will fail…so it produces as many new shoots and new areas of growth as it can …expecting to lose the majority of its new progeny to predation.

Maybe some sort of Newsletter or public service announcement would help –

‘Hello – Japanese knotweed – please calm down…you are not living on a volcano so you can stop spreading so quickly’

Maybe not?


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