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7 February 2022 Decline in Common Milkweed along Roadsides Around Ottawa, Canada
Samantha Lalonde, Jenny L. McCune, Stephanie A. Rivest, Heather M. Kharouba
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Abstract

Over the past two decades, monarch butterfly populations have been declining. This decline has been partly attributed to the extensive loss of breeding habitat through the reduction of common milkweed (Asclepias syriaca, the larval host plant) through herbicides. While the decline of milkweed has been well documented in the US, less is known about its decline in Canada. To take a first step in quantifying its potential decline, we compared roadside milkweed abundance at sites around Ottawa, Ontario, Canada in 2018, to a county-wide estimate of milkweed abundance in 1943 and 1944. We also evaluated the effect of roadside characteristics on milkweed abundance at these sites. Current milkweed density in the Ottawa region is 33–86% lower than it was 75 years ago. We found milkweed at 67% of our 100 sites and found less milkweed at sites with a higher number of lanes in the road adjacent to the roadside. Interestingly, mowing indices were not significant predictors of milkweed abundance. Here we document the first quantitative evidence for milkweed decline over the past 75 years in Canada, which has likely contributed to the decline of breeding monarchs in Canada.

2021 Université Laval
Samantha Lalonde, Jenny L. McCune, Stephanie A. Rivest, and Heather M. Kharouba "Decline in Common Milkweed along Roadsides Around Ottawa, Canada," Ecoscience 29(1), 25-37, (7 February 2022). https://doi.org/10.1080/11956860.2021.1943930
Received: 7 December 2020; Accepted: 3 June 2021; Published: 7 February 2022
KEYWORDS
Asclepias syriaca
Asclepias syriaca
Danaus plexippus
Danaus plexippus
densité
density
fauchage
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