THE MICHIGAN BOTANIST
EFFECTIVENESS OF HAND-PULLING THE
INVASIVE MOSSY STONECROP (SEDUM ACRE L.)
FROM ALVAR PAVEMENTS
Winter Spider Eco-Consulting, R.R. #1, Sheguiandah, Ontario POP 1WO
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The Eurasian weed mossy stonecrop (Sedum acre L.), a tiny succulent plant of the Crassulaceae,
is present on some alvar pavements on Manitoulin Island, Ontario. This study examined the rate of
spread of mossy stonecrop on alvar pavement, and tested whether hand removal of stonecrop would
eradicate the weed or possibly cause an increase in regrowth of it or other weeds. The study also
looked at regrowth of mossy stonecrop in situ from fragments. Nine 1 x 1 m plots were given three
different treatments: no pulling; careless pulling leaving fragments; very careful pulling leaving no
fragments. Plots were observed for three growing seasons after treatment. Results show stonecrop is
capable of rapid, aggressive growth, but that this does not always occur. Stonecrops do regrow from
fragments or possibly from root remnants. Careful pulling techniques resulted in almost no stonecrop
regrowth after three growing seasons. No regrowth of other weed species occurred.
Mossy stonecrop (Sedum acre L.), a common Eurasian weed, is a fibrousrooted, much-branched perennial with stems 5-10 cm long and succulent leaves
of 2-5 mm (Cronquist 1991). The plants are mat-forming in habit, with a few
centimeters at the tip of each creeping stem becoming upright and fleshy (Figure
1). The upright stems support terminal, small, yellow flowers and eventually dry
capsular fruits. The plant has been cultivated in many forms and is widely naturalized throughout North America (Voss 1985).
On Manitoulin Island, Ontario, mossy stonecrop is a common weed of pastures and open areas of shallow soil over flat limestone bedrock. In fact, the plant
is able to grow on the surface of bare limestone in small patches of soil less than
1 cm deep (personal observation). Because it can tolerate such conditions, mossy
stonecrop finds suitable habitat in rare alvar communities.
Alvars are open, treeless ecosystems based on horizontal limestone bedrock.
The vegetation is usually dominated by graminoid herbs or dwarf shrubs. Soil
cover is shallow and sporadic, making these ecosystems fragile end easily disturbed by soil displacement. Recent work has brought attention to the rarity of
different alvar community types as well as to the high incidence of rare species
present on alvars (Brownell & Riley 2000; Reschke et al. 1999; Catling 1995;
Catling & Brownell 1995).
Efforts to protect high quality examples of alvar require long-term management strategies that include plans to cope with threats. Thus, questions have been