Plants are generally not Invasive perennials within their natural range; they have evolved to grow and interact with other species in a natural way where all are part of the ecosystem. Indeed, disruption to an ecosystem – climate change, excessive grazing pressure, deforestation, pollution, etc. – can favor some species at the expense of others but not on the scale that would lead to them being called invasive.
What Are The Difficulties Linked With Them?
The problem starts when you take plants (or animals) outside their natural range and put them in a place where the climate and other conditions suit them very nicely, thank you very much, and where they don’t have active natural competitors. Purple loosestrife is a moderately pretty flower of European freshwater marshes and damp grasslands, but in North America, it grows much more significant and becomes a real menace. Rhododendron ponticum did occur in Britain before the last Ice Age but subsequently was found in Southeast Europe and Western, Southern, and Southeastern Asia. But in modern-day Britain and Ireland, it is a menace to woodlands and wetlands.
But the worst is the aquatic species because many of them can establish new colonies from bits that break off and float away. One of the worst is a Southern African species called Lagarosiphon major, famous as an aquarium species but now choking rivers and lakes around the world.
Should One Eliminate Invasive Perennials?
Prequel: For the uninitiated, the term “invasive” is useful to refer to alien, non-native species that dominate/overwhelm native populations. I make this point because non-scientific folks usually don’t realize that the term is precise and means specifically foreign, introduced plants, not just any plant that grows aggressively.
In my view, ideally, yes, they’d all be eradicated. Practically speaking, that horse left the barn long ago, and also controlling invasive species invading our wildlands is such a monumental task that it’s not going to happen.
In my part of the USA, Lonicera maackii has taken over woodland understory to such an extent. There’s little else growing there now. Like many plants, this species also not only outcompetes native flora in growth and early leaf-out/late dehiscence, it’s also allelopathic. The local herbivores don’t recognize it as a food plant, so deer are increasingly browsing yards and gardens for sustenance. Birds appreciate the red berries as food, and they spread the seed far and wide. There are god knows how many thousands of acres affected by this plague plant now. Not to mention that people *still* grow it willingly as it’s sturdy and requires no care.
Moreover, That’s just one species. Add Japanese honeysuckle, wintercreeper (Euonymus fortunei), English ivy, air potato (Dioscorea bulbifera), and stilt grass (Microstegium vimineum) as equally invasive players, and you can see the difficulty. How to clean it all up? And this is just in MY part of the world.
The problem is truly worldwide. Parts of China correspond closely to the SE USA in climate — indeed, some genera like Liriodendron are only in those two places, showing an ancient Gondwanan past — and American plants are invasive there. Australia has a HUGE lantana problem, and on and on.