Japanese knotweed (Polygonum cuspidatum), an invasive species across North America and Europe. Play this podcast. Is it cold yet where you live? Well, we've got a topic that's forever hot to get you warmed up: invasives. Or DownloadFrom iTunes Now, when some people describe a plant as invasive, they refer to any plant, native or non-native, that tends to be spread aggressively. Others refer to invasive species, which are specifically non-native plants (and animals) that have escaped cultivation into an ecosystem that isn't their own and spread to the point that they threaten native ecosystems. To the layperson, it's a source of confusion. Links mentioned in this podcast...Garden RantKiss My Aster at FineGardening.com Passions run high when it comes to invasives, and nowhere is that more evident than in the comments of the blog Garden Rant--including those on a post about a book by our guest in this episode, Peter Del Tredici. Garden Rant was kind enough to grant us permission to record a dramatic reading (performed by myself and FG blogger Amanda Thomsen) of some of those comments, to illustrate just how intense the invasives conversation can be. Del Tredici turns that conversation on its head. In his book Wild Urban Plants of the Northeast: A Field Guide, he argues that native and non-native plants that spontaneously colonize urban areas may actually be ecologically beneficial in the concrete jungle. "The term [ecologists] use is 'ecological services'," says Del Tredici of the benefits urban plants provide. "Urban areas are typically much warmer than non-urban areas, and so all trees--it doesn't matter whether they're from China or the United States--create shade, and they all reduce temperature." He goes on to talk about how many cities are built around rivers and wetlands, and many weedy plants happen to be experts at stabilizing soil against erosion, as well as filtering pollutants among wetlands. What's more, he's not only talking about invasive species. "Roughly 40% of the plants in the book are native to Eastern North America. Think about silver maple, or the box elder, Acer negundo," he says. "The urban environment is this cosmpolitan mix--it's not all one thing or another. [It's] 40% native, 40% from Europe, and roughly 20% from Asia." One thing that's for sure: invasives, both native and non-native, are here to stay. The biggest question, and the biggest debate, seems to be how our response, as a society, will evolve.Music from this podcast by Kevin MacLeod (Incompetech.com). View the discussion thread.