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2016 update: Cirsium hillii fire and fitness

This experiment assesses effects of fire on the fitness of Cirsium hillii (Hill’s thistle) plants at Hegg Lake WMA. Like Echinacea, C. hillii inhabits dry prairies, but Hill’s thistle is listed as a Species of Special Concern in Minnesota and little is known about how it responds to fire. Burn and non-burn units were created prior to an experimental fall burn conducted by the DNR in 2014. That year, we mapped 28 C. hillii rosettes (basal and flowering).

We revisited the locations this year, a non-burn year, and found three flowering rosettes. Several of the rosettes we found in previous years weren’t present this year. We weren’t sure if this was an indication of mortality since C. hillii is clonal, and it’s possible that each rosette is not a unique individual. Last year, Abbey White, a masters student in the Plant Biology and Conservation program at Northwestern, she analyzed the genetic diversity of tissue samples from each rosette. Based on a conservative delineation of genotypes, she found that there was only one individual in our C. hillii “population!” If she uses a more liberal approach, there are two individuals. We don’t know of any other C. hillii populations in Douglas County and are possibly monitoring the last individual in the area.

The distribution of Cirsium hillii, a rare endemic to the Great Lakes region

The distribution of Cirsium hillii, a rare endemic to the Great Lakes region (yellow counties are where C. hillii has been found)

Start year: 2014

Location: Hegg Lake WMA

Overlaps with: fire and flowering at Staffanson Prairie Preserve

Data collected: We measured the length of the longest axis of a basal rosette and the corresponding perpendicular axis. These data were recorded electronically in a memo and are backed up in Handspring.

Products:

You can find more information about our experiment on how fire affects the fitness of Cirsium hillii and links to previous flog posts regarding this experiment at the background page for the experiment.

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