I spent a good chunk of yesterday using a folding handsaw to 'fell' a whole bunch (hundreds...) of large broom bushes
which were flowering happily on a rocky knoll in our local Provincial Park. Why would I want to cut down such wonderful masses of glowing yellow blooms?
Because broom is an invasive alien plant here on the west coast, having been introduced from Europe by a sea captain,
and having subsequently spread all along the Pacific coast. We can never hope to get rid of it, but I and a few others are trying to extirpate it in our Park,
so that the native wildflowers will be able to take over their space again.
One problem is that broom is a legume: it has nitrogen-fixing bacteria in its roots, so it can grow rapidly in poor soil, thuggishly taking over the space
and out-competing the native plants, which evolved to grow in low-nitrogen soil, and are thus at a double disadvantage.
Other plants we have problems with here are English ivy, leather-leaf daphne and holly - invasive aliens all,
and hard to get rid of (I have had sweaty experiences with all of them).
Interestingly, when I was in Australia, the local biologists were complaining about invasive alien plants - but their problematic species came from South Africa.
When I was in South Africa, the locals complained about yet other invasive aliens, but these came from Australia.
Of course, plants do move around by themselves, and Humans are not to blame for all introductions.
Yet in most cases we are the villains, and those of us who care about our local floras must protect them with the sweat of our brow, and a few aching muscles..