Pitcher's Thistle: Threatened Dune-Dweller - Door County Land Trust
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National Park Service
U.S. Department of the Interior
Great Lakes Research and Education Center
Indiana Dunes National Lakeshore
Pitcher’s Thistle: Threatened Dune-Dweller
Photo by N. Pavlovic
Pitcher’s thistle, a hardy flowering plant native to the western Great Lakes, relies on ever-
changing dune sandscapes for survival. Recent declines in native populations of the thistle are
due to human and non-human activity. Both have put the plant at risk of local extinction.
Pitcher’s Thistle, its Range, along the western and southeast where storm winds erode the
and Habitat shores of Lake Huron (Pavlovic sand and carve depressions,
et al., 2015). This rare thistle or blowouts. These blowouts
Pitcher’s thistle is a silvery prefers habitats with lots of provide the exposed sand that
green, federally threatened plant exposed sand, and can be found Pitcher’s thistle needs.
that spends five to eight years as growing on beaches, foredunes,
a juvenile before flowering once, secondary dunes, blowouts, sand
producing seed, and then dying. spits, and large perched dunes Populations in the
The adult thistle, reaching three within portions of its range. Landscape and Threats to
feet in height, produces seed At Indiana Dunes National their Persistence
after it sprouts many “heads,” Lakeshore, human activity
each containing from 100 to 150 including the construction of Researchers monitor this
small cream-colored flowers harbors and industrial sites threatened thistle throughout
(Pavlovic, McEachern, & Korte, has disrupted wave action and its entire Indiana range, from
2015). In order to survive dry sediment deposition, or littoral Miller Dunes in the west to
conditions, seedlings grow their drift, causing shoreline erosion Keiser Blowout in the east –
roots first, before producing and loss of sand to replenish the a distance of over 15 miles
leaves. The roots of a mature dunes. This, in combination with along the shoreline. Despite
plant can reach up to six feet storm erosion, prevents Pitcher’s the fact that Pitcher’s thistle
in length. The plant grows on thistle from growing on is biologically well adapted to
open, wind-blown sand dunes Indiana’s beach and foredunes. tolerate the stress of life in this
from southern Lake Michigan It does grow here in other dune hot, sandy environment, close
to the south and east shores of habitats, however, and tends to monitoring has revealed the
Lake Superior. It is also observed grow on northwest facing dunes long-term decline of the plant
Pitcher’s Thistle Page 2
(Havens et al., 2010). This
population decline is likely
the result of multiple factors.
Disturbances associated with
both residential and commercial
shoreline development in
Indiana have reduced and
isolated dune habitat (Harrison,
1988). This isolation prevents
pollination between local
Pitcher’s thistle populations,
causing a decline in genetic
Figure 1. American goldfinch (Carduelis tristis) feeding on the seeds of Pitcher’s thistle
diversity and making it difficult (Cirsium pitcheri) . Photo by M. Korte
for the species to adapt and
by the Pitcher’s thistle, it also New Threats to Pitchers
survive. To a much lesser
greatly increases the risk that Thistle
degree, the natural succession of
people walking in the dunes
plant communities can further
will trample the plant’s tiny, Pitcher’s thistle was listed
exacerbate population isolation.
fragile seedlings. Trampled as threatened due to human
For example, competition with
seedlings are often killed, but activity, but now that
jack pine and oak trees has
if they are somehow able to researchers are studying
decreased the available thistle
survive, they (along with some dune dynamics and plant
habitat in Miller Dunes.
insect damaged plants) are predation, new threats are being
likely to develop into multiple discovered. After blooming,
Recreational use also has an
stemmed plants, which often the adult Pitcher’s thistle
impact. Human foot traffic can
produce fewer seeds than single closes its flower’s cluster
cause erosion in the dunes.
stemmed plants (McEachern, heads very tightly to protect
Though this can provide
1992). seed production. Despite
additional exposed sand needed
this protection, American
Figure 2. Maturing thistle (Cirsium pitcheri) seed head damaged by goldfinches trying to access the seeds inside (left) Photo by N.
Pavlovic; empty husks of seeds eaten by goldfinches (center) Photo by K. McEachern, N. Pavlovic ; thistle seed heads bagged to deter
goldfinches (right) Photo by K. McEachern, N. Pavlovic.
Pitcher’s Thistle Page 3
Figure 3. Intact Pitcher’s thistle (Cirsium pitcheri) seed head (left) Photo by N. Pavlovic, K. McEachern and M. Korte; damaged seed
head (center) Photo by M. Korte; Thistle seed head with two adult Rhinocyllus weevils embedded (right) Photo by N. Pavlovic
goldfinches are able to tear into goldfinch seed predation is to thistle from goldfinches, they
the heads for a meal and to increase the size of local thistle are discovering additional
obtain the seed hairs, or pappus, populations (Pavlovic et al., threats. Through bridal veil
for building their nests. In fact, 2015). netting, researchers discovered
goldfinches appear to have the presence of two nonnative
increased their seed feeding in As scientists and managers weevils. Both of these insects
Indiana Dunes, eating as much attempt to protect the Pitcher’s lay their eggs in the plant’s
as 90 percent of the seed from flower head and their larvae
an individual plant (Pavlovic destroy the seeds. They were
et al., 2015). To study the discovered in the Indiana Dunes
impacts of goldfinch predation, in 2012 and 2013. In 2014,
researchers put several layers weevils damaged 31 percent of
of bridal veil netting over the the observed Pitcher’s thistle,
thistle flower heads after bloom making them an important
to block the goldfinch’s ability threat.
to penetrate the developing seed
head. In 2014, seed predation by Luckily, most weevil-damaged
goldfinches was reduced to one heads are still able to mature at
percent on netted flower heads least some seed. As researchers
(Pavlovic et al., 2015). Bagging continue monitoring the
heads is time consuming, distribution of weevils, they
so other means for reducing are testing the effects of certain
goldfinch feeding have been insecticidal clays that, when
sought. Research has shown painted on the thistle, could
that larger Pitcher’s thistle deter harmful insects. At Miller
populations have proportionally and Ogden Dunes, another
less goldfinch seed predation insect pest, the sluggish weevil
compared to small populations. Figure 4. Larinus (Larinus planus )wee-
(Cleonus piger), was found
This suggests that a good vils on Pitcher’s thistle (Cirsium pitcheri) feeding on Pitcher’s thistle
strategy for mitigating native seed heads. Photo by M. Korte roots in 2013. This was the firstPitcher’s Thistle Page 4
report of the species feeding
on Pitcher’s thistle (Pavlovic et
al., 2015). Weevils are present
throughout the thistle’s range
from southern to northern Lake
Michigan and are of increasing
concern.
The Future for Pitcher’s
Thistle in the Indiana Dunes
No adult thistles have been
observed in the Miller Dunes
section of Indiana Dunes Figure 5. U.S.G.S. Ecologist Noel Pavlovic, PhD, counts Pitcher’s Thistle seedlings as
part of a climate change investigation. Photo by W. Smith
National Lakeshore for two
years (Pavlovic et al., 2015), increase local populations. managers planted thistles at
and researchers project they As scientists monitor sites varying aspects and distances
will become locally extinct in in the Indiana Dunes, they from the lakeshore to determine
this location in the near future hope to develop new ways the plant’s response to lake-
(Havens et al., 2012). to limit weevil population moderated climate. Park
Efforts continue to protect this growth across the Pitcher’s managers will continue to
threatened plant. A special thistle range. Scientists are protect Pitcher’s thistle using
“sandbox” has been built also investigating yet another the best science available.
to grow Pitcher’s thistle to human-induced threat: climate
produce seed to be used to change. Researchers and park
Citations
Harrison, W. F. 1988. Endangered and Threatened Wildlife and Plants: determination of threatened status for Cirsium pitcheri.
Federal Register, 53, No. 137, 27137-141.
Havens, K., T. Bell, M. Bowles, J. Fant, Samara Hamzè, C. Jolls, K. McEachern, N. Pavlovic, and P. Vitt. 2010. Integrating
Long-term Demographic Data and Repeated Genetic Sampling for Viability Analysis of Natural and Restored Populations of
Pitcher’s Thistle. LTREB Annual report to National Science Foundation on grant 0516058. Chicago Botanic Garden, Chicago,
IL.
Havens, K., Jolls, C.L., Marik, J.E., Vitt, P., McEachern, A.K., and Kind, D. 2012. Effects of a non-native biocontrol weevil,
Larinus planus, and other emerging threats on populations of the federally threatened Pitcher’s thistle, Cirsium pitcheri.
Biological Conservation 155: 202-211.
McEachern, A. K. (1992). Disturbance dynamics of Pitcher’s Thistle (Cirsium pitcheri) Populations in Great Lakes Sand Dune
Landscapes, University of Wisconsin-Madison: 216.
Pavlovic, N.B., McEachern, A.K., and Korte, M.K. 2015. Pre-Dispersal Seed Predation on Cirsium pitcheri by introduced
weevils, deer, and goldfinches at Indiana Dunes National Lakeshore and Dunes State Park, 2012-4.You can also read
