| Plant Stewardship Index |
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Plant Stewardship Index Bowman's Hill Wildflower Preserve, a 134-acre public garden in Bucks County, has a free, new online tool that will measure just that by assessing the kinds of plants growing on a particular tract. The Preserve's "Plant Stewardship Index" rates 3,400 plants based on their value in native plant communities. Gardeners and landowners check off which plants they've got growing on their land, and the index computes a score that tells them how much — or how little — the site has been impacted by human activity. By reassessing scores from year to year, landowners are able to determine if their plant conservation efforts are working. "The index is free, and anybody can use it," says Jeannine Vannais, the PSI coordinator for Bowman's Hill. "We're already seeing landowners make use of it for things like assessing the health of their meadows." To set up an account to use the index and its plant lists at no charge, visit www.bhwp.org/plant-stewardship-index.htm. "It's designed to assess the naturalness of an area," says Miles Arnott, executive director of Bowman's Hill, which is Pennsylvania's official wildflower preserve located 2½ miles south of New Hope along the Delaware River. "With the PSI, you can get a good idea of the quality of an ecosystem ... The presence or absence of a particular plant tells us a lot about the nature of a habitat." That's because some plants, such as white trout lilies and dwarf crested iris, will grow only in very particular and undisturbed areas. In other words, they're picky. Then there are plants such as pigweed, bindweed and dandelions that will grow just about anywhere, including roadside ditches, cracks in curbs and those heavily graded clay fields masquerading as residential yards. Rating plants On the Plant Stewardship Index scale, plants are rated from 0 to 10. Plant thugs and other undesirables rate a 0. "Generalists" that aren't exactly unwelcome but that tend to show up even in highly disturbed sites rate somewhere between 1 and 3. Scores rise along with each plant's demand for increasingly pristine conditions, up to a 9 or 10 for plants you're only likely to find in sites unblemished by human activity. "Just because a plant gets a 9 or 10 doesn't mean it's endangered or rare," says Arnott. "But it does mean it's indicative of a good quality ecosystem." A team of botanists from Pennsylvania and New Jersey rated the 3,400 plants, so this index is local to the Piedmont region. Vannais says plans are to convene a second team of botanists that will rate plants for the rest of Pennsylvania. The online tool calculates two different scores. One — a "coefficient of conservatism" — is a measure of how close the land is to what would have existed before roads, buildings and other human impact occurred. The second — a "Floristic Quality Assessment Index" — is a measure of how far nonnatives have elbowed their way into the native plant community. "This gives you a numerical sense of the impact of nonnative plants," says Vannais. The online plant list itself will help gardeners and landowners determine exactly what's a native plant and what's not. Natives show up in green type online while nonnatives are in black. "That information can be used to help people identify appropriate choices for a restoration," Vannais says. One thing the index doesn't do is assess how worthy a plant is for a home garden. Putting it in perspective Just because a plant has a high PSI rating doesn't mean it's a "good" one that everyone should plant, and just because a plant scores a 0 or 1 doesn't mean it's a "bad" one to be shunned. For instance, all plants that are not native to the Piedmont region are automatically assigned a 0. It doesn't matter whether the nonnative is a horrible imported weed like the mile-a-minute weed or a garden center favorite like a lilac, Japanese spirea or purple coneflower. If it was introduced here by man, it's not something you should find in a natural setting and therefore is of no value in your site's naturalness rating. That will throw you a few curveballs if you're looking at this from a pure gardening standpoint. Even some nasty plants that most of us would call weeds outscore plants we buy for their ornamental value. For example, giant ragweed (Ambrosia trifida) might be a sneeze hazard, but it's a native that manages to rate a 1 on the PSI scale. By comparison, the nonnative butterfly bush rates a 0. Wild strawberries (Fragaria virginiana) might plague our lawns, but they're natives that score a 2 on the PSI scale. By comparison, the white-blooming groundcover sweet woodruff (Galium odoratum) — a nonnative here — rates a 0. Even the dreaded but native poison ivy (Toxicodendron radicans) comes away with a 1 while Japanese maples, Japanese hollies and bearded irises — all nonnatives — score zeroes. Remember, the point is to assess the naturalness of a site, not the garden-worthiness of plants. Arnott says it's important to get a handle on what's out there and how to preserve it because so many of our native habitats are being lost to development. Also a big problem is how nonnative invasive plants are increasingly displacing native species — an immigration problem of a botanical sort. The usefulness of the index will depend on a gardener's ability to correctly identify the plants on their property. That's especially critical because even two closely related species may have markedly different scores, such as Hibiscus moscheutos (the native rose mallow) that rates a 7 vs. Hibiscus syriacus (the nonnative rose-of-sharon) that rates a 0. To score a site, the owner jots down the names of as many species as he or she can identify. (See below for sources of help identifying plants.) "You don't have to count everything," Arnott says. "Just write down what you have. You don't need to do an inventory. Even if you count 30 to 40 percent of the species you have, it'll give you a good reading." "This lets you see what you have and where the trouble spots might be," says Vannais. "And it'll show you over the years if what you're doing is working." Once your plants are logged in on the site, you can call up that list later, make changes and quickly get a new reading instead of having to re-enter everything from scratch. "It's not a magic bullet or an end-all," says Arnott, "but it's a very important piece that we haven't had before." Sources to help identify the plants on your property: * County Extension offices, local Master Gardener clinics and some garden centers have staff that can identify plant clippings. (insert image here) Dwarf crested iris (Iris cristata) How 40 common landscape plants rate on Bowman's Hill Wildflower Preserve's new Plant Stewardship Index. Plants with higher numbers on a scale of 0 to 10 are indicative of a healthy, native ecosystem. "N" stands for plants that are native to the United States. "I" stands for plants that were introduced here after European settlers arrived. * American dogwood (Cornus florida) (N): 5 Ten plants that score a 0 on the Plant Stewardship Index — ones you would NOT want to see in a healthy, native Pennsylvania ecosystem: 1. Tree-of-Heaven (Ailanthus altissima) Ten plants that score a 9 or 10 on the Plant Stewardship Index — ones you would WANT to see in a healthy, native eastern-Pennsylvania ecosystem: 1. White trout lily (Erythronium albidum) |
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