Lost and Found

Its been a while since any real work was done at the prairie in Big Hollow, but there was interesting news this summer. David Hopey, a PSU student and one of the people who have really contributed to clearing brush, visited the prairie and found a few flowerless stems of Green Milkweed Asclepias viridiflora. This is a rare plant in Pennsylvania, and one that I feared had disappeared from the prairie.

As recently as the early 1990s Green Milkweed was seen during botanical surveys of Big Hollow prairie, and it is found in Pennsylvania in some other remnant xeric limestone prairies, as well as scattered locations that aren't xeric limestone prairies. Like most other milkweeds, Green Milkweed needs a lot of sun to thrive, and at Big Hollow most likely disappeared as shrubs and trees shaded out the prairie. There are patches of prairie at Big Hollow that are sunny enough for Green Milkweed to have survived, but perhaps just by chance the patches that remain didn't happen to have Green Milkweed. Another theory is that Green Milkweed might tend to grow in slightly deeper soils or moister parts of the prairie, which were more quickly taken over by trees; it may be that the parts of the prairie we have left are the driest parts with the poorest soils, and therefore least suitable for trees, but also not the places favored by Green Milkweed. Whatever the reason, when I started this project in the summer of 2006 I did not find any Green Milkweed at Big Hollow prairie.

The Green Milkweed stems that David found this summer are, I guess, shoots from a plant that was growing on the prairie for years. By 2006, as shrubs encroached, it was either hidden amid shrubs, had its stema nd leaves eaten before I started looking, or perhaps didn't produce much growth during 2006 because it was so heavily shaded. Green Milkweed is reported to be a long-lived plant with a strong root system, so it might be capable of sprouting from the roots for many years despite poor growing conditions. Alternately the 2007 stems might have come from seeds that were left behind from previous generations of Green Milkweed and were stimulated to grow by the soil disturbance or increased sunlight that resulted when we cleared brush. However, most milkweeds, in my experience, start slowly from seed, and I am sure David would have recognized first-year plants as seedlings, not adult stems. I think it is very unlikely that the Green Milkweed seeds blew in from some nearby stand of the plant. Although Green Milkweed, like others in the genus, produce seeds with tufts of white hairs that enable the seeds to fly on the wind, Green Milkweed is quite rare in our region and it is unlikely that any plants exist nearby to produce seeds to be blown into Big Hollow.

The return of Green Milkweed brings the prairie milkweed species count back to two species. Butterflyweed, Asclepias tuberosa, occurs as a few scatttered plants on the prairie, mostly under a powerline right-of-way. Butterflyweed is widespread in central Pennsylvania, occurring along roadsides, old fields, and similar places, including xeric prairie remnants. At Big Hollow I have not seen it flower. I think the few plants may produce flower buds, but the buds are eaten before they can become flowers. A third xeric prairie milkweed in central Pennsylvania is Whorled Milkweed, Asclepias verticillata. This plant has not been reported from Big Hollow, but occurs at a few of the other limestone prairies.

Several other milkweeds occur in our region, but are not present at Big Hollow Prairie. One that is a bit surprising in its absence is Common Milkweed, Asclepias syriaca, which is a common plant in most other open, not-too-wet habitats in the area. Common Milkweed seems to be fairly resistant to herbicides, and as a result often survives in cornfields, roadsides and similar places that are maintained by spraying herbicides. The dry, limestone soils at the prairie must not be suited to Common Milkweed, since it seems a sure bet that seeds blow in every fall. Poke Milkweed, Asclepias altissimum, is common in woods and woodland edges in our region, but does not occur on the prairie. This plant can closely resemble Common Milkweed, and is probably overlooked for that reason. Another common local milkweed is Swamp Milkweed, Asclepias incarnata, which as you might expect occurs in wet soils of swamps, marshes, and roadside ditches. Although Swamp Milkweed is a fairly common plant that will grow in normal (not partuclarly moist) soil if planted there, it seems a poor candidate for the very dry prairie.

Now that Green Milkweed has reappeared at the prairie, let's hope it was able to gain strength last summer. Perhaps we will see flowers on the plant(s) next summer.