30-year thistle experiment shows seeds can rebuild rare populations
Pavlovic NB, Fant JB, McEachern AK
Native Plants
If you've ever donated to or volunteered with a native plant restoration, this study is proof that a single planting event isn't enough: even successful reintroductions need follow-up seed additions for decades to keep the genetics healthy.
Scientists planted seeds of Pitcher's thistle, a rare plant found only on Great Lakes sand dunes, at three new sites back in 1994 and then checked on them for 30 years. Two of the three plantings survived and even spread a bit on their own, but the plants showed signs of inbreeding because there still weren't enough of them reproducing. The big lesson: starting a new wild population from seed can work, but you often need to come back and add more seeds or plants later to keep the gene pool strong.
Key Findings
Two of three reintroduced populations persisted for 30 years after a single 1994 seeding event using 4,200 seeds from 54 maternal lines.
Direct sowing produced three times more seedlings than broadcasting seeds, though seed source didn't affect germination rates.
Reintroduced populations had higher genetic diversity than native regional populations but still showed moderate inbreeding, indicating a need for repeated seed or plant additions.
chevron_right Technical Summary
A 30-year experiment reintroducing an endangered Great Lakes thistle shows that carefully planted seeds can rebuild wild populations, but the new colonies still need more genetic diversity added over time to stay healthy long-term.
Abstract Preview
Original paper
The interface between rare plant management and genetics: conserving Pitcher's thistle (Cirsium pitcheri) in the Great Lakes region, USA.
Tools showing best conservation practices are becoming critical for rare plant conservation as populations become isolated through habitat fragmentation and changing ecosystem processes. We illustr...
open_in_new Read full abstractAbstract copyright held by the original publisher.
Species Mentioned
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Cirsium pitcheri, sometimes called Pitcher's thistle or dune thistle, is a species of thistle native to sand dune shorelines along the upper Great Lakes. It is native to Indiana, Illinois, Michigan, Wisconsin, and Ontario. It is listed by the U.S. Fish and Wildlife Service as a threatened species.