I'm reviving this thread because the topic's fascinating to me. And I didn't want to take over another thread about getting rid of pampas grass to talk about a lot of discussion points that are already taking place here. I like taking the ecological point of view when it comes to invasive species. As an observer, avid reader, and science teacher, I take the stance that they're not good or bad.
Repeating some of the previous responses here--it's curious that for every one invasive poster child that's reviled and accused of potential world domination, there's a dozen more that go relatively unnoticed or even loved (some wisteria and lily of the valley, in my neck of the woods). I think in some cases it has to do with their niche, what their role is in their native range, and what they do when that niche presents itself for the filling. I’m talking about the invasive plants that take over disturbed land that a lot of people are likely to see, along highways and roadsides, in little snippets of land between roadways, in small parks surrounded by houses in dense neighborhoods--they get a lot of the press. A lot of the “bad guys" are the pioneers that are really good at gaining footholds in disturbed (land that has significant changes in nutrient retention or biomass, e.g.) or fragmented ecosystems or simply places where nothing is growing. Like garlic mustard in my area--you would think it's on a rampage judging by some people's descriptions and responses to it. To my eye, it's not--it's growing on roadsides and under pine trees (and it's growing in a bare patch of yard where I hacked down some barberry--ironic), and it happens to make a delicious pesto. Even native
pioneers are labeled “invasive” by farmers and homeowners--but just because it “invades” the backyard or cornfield or apple orchard doesn’t make it a bad guy. The land has been disturbed--this is nature’s response.
Like the pampas grass argument--the meadow being invaded in the example I was shown
doesn’t look like a meadow to me. It’s a clearing at the end of a sliver of woodland/shrubland hedged in by thousands of houses and buildings and streets in a large suburb of San Francisco. That does not constitute an ecosystem disturbance by an invasive species (it’s in a small city) because that ecosystem is seriously fragmented--native grasses in wild places are established along a timeline of natural succession, and in natural succession all those factors like biomass and primary production and soil properties are changing from one stage to the next. If you want something different to grow other than pampas grass, let it grow and die and change the niche parameters so something different will thrive (probably the trees that are growing there in the middle of the sliver).
I taught in northern CA about invasive species in biology class and discussed pampas grass a lot in that unit. I was reminded of the first attempt to reign in pampas in the other thread--how a lot of people took it upon themselves to spray the grass that had started growing on canyon soil disturbed by loggers that was eroding away. Many kids asked why that was bad--why not let the pioneers settle and stop the erosion? I silently agreed with them in that debate. They’re (pioneers) the first line of succession, and in succession there is no one way to reach the climax community. The invasive plant isn’t “exploiting” because only predators and parasites exploit in ecological terms--they live at the expense of others; the invasive plant is competing
with native plants for the resources in its niche. In interspecific competition, whether between native species or native and invasive species, one species inevitably outcompetes the other (lots of times the invasive isn’t competing with anything because there’s nothing to compete with in some disturbed areas). Interactions may or may not be redefined, niches may or may not be affected. If they are, it just means that the change may lead to divergence in the morphology of competing species--natural selection. Evolution. Wow, what a mouthful. Not good or bad, just par for the course, because even though a landscape may seem eternal, it’s not. It’s always changing--just on a much different timescale than we’re capable of perceiving most of the time.
A lot of the students ended up asking if we humans were an invasive species--a fair question. And unlike pampas grass, which grows according to its growth habit in places that accommodate that habit, humans actually change their environment. Pampas still “plays by the rules,” just like all other plants, even though it’s a fairly new introduced player on the field; humans are players but they're also capable of changing the entire field.
Just one point of view. Now I have to get myself back outside and cut back some damn Rosa multiflora ;)