Showing papers by "Thomas D. Brock published in 2009"
TL;DR: Ecological observations of permanently marked stands made over a ten-year period have shown that growth is highly variable from year to year, and flowering and seed set are sporadic and unpredictable, and may partly explain the rarity of this species.
Abstract: Purple milkweed (Asclepias purpurascens) is a relatively rare member of the flora of oak savannas and open oak woodlands. It is endangered in several states and has been the subject of special conservation efforts. A number of native populations of this species arose spontaneously at Pleasant Valley Conservancy State Natural Area in south-central Wisconsin after oak savanna restoration was initiated in 1997. Ecological observations of permanently marked stands made over a ten-year period have shown that growth is highly variable from year to year, and flowering and seed set are sporadic and unpredictable. Germination studies have determined that seed viability is very high. Greenhouse-raised plants have been successfully transplanted to the field and followed for three years. Transplants have also been used in a forbs garden, where plants could be monitored more effectively. Pod formation and seed set are highly variable, both in the field and in the forbs garden, and may partly explain the rarity of this species.