The problem in America of invasive species rapaciously displacing native flora is weird. How did we get here? Is it like this everywhere in the world? Why? And logistically: what can we do?
Invasive Natural History
When you read the American naturalists (Walt Whitman, Henry David Thoreau, Ralph Waldo Emerson and others), quite a different American landscape is expressed. Their world was full of native flora and existed pre-urbanization. The invasive species that plague our roadsides, forests and wetlands were not even here yet. It happened slowly and/or quickly.
Each unique species has a unique story. The process of how an innocuous introduced garden plant makes the jump to become pervasive in the landscape is mysterious and sometimes surprising. Often people’s egos are involved. For 80+ years in America, Japanese Honeysuckle was an innocuous garden plant. Having it growing in a garden indicated a worldliness: travel, prestige, wealth. Could we see a similar jump in the future with plants we think of in docile terms? Like a Hosta, Daylily, Spirea or Butterfly Bush? Possibly. A few nuanced degrees of increased temperature or a secret change in rainfall are all that need happen before a new ecological problem begins.
The best thing gardeners can do is learn to identify and remove invasive plants when the specimens are young. The next best thing for environmental conservation is to only plant native species. Who knows what introduced species will make the category jump and begin wreaking havoc next? Plant native and fix the problem before it starts.