In a Warmer Yellowstone Park, a Shifting Environmental Balance

In a Warmer Yellowstone Park, a Shifting Environmental Balance By Jim Robbins. New York Times.

This is really about the spread in the Lamar Valley of what is usually regarded as a noxious weed (I certainly hate it) — the Canada thistle. It seems grizzly bears and pocket gophers love it, and the griz, ever in search of new sources of food, have learned to love Canada thistle. They eat it both fresh and stored (with the industrious pocket gophers mixed in for a little extra protein and fat).




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    In October 2004, I watched a female grizzly and two big cubs digging up thistles out in the Lamar floodplain; the area was about from lower Rose Creek to that first big pullout north of Buffalo Ranch.

    After they had moved off toward the river, I went down to see what they had been up to. I am fairly certain that what they were digging was native thistle, Cirsium scariosum, aka elk thistle or Everts thistle.

    The thistles weren’t in their erect stem form, but were in the form of a — the botany term escapes me now — a flat disc of leaves radiating out at ground level from the center of the plant. See:

    The bears had an amazing technique: they would use their claws to shear away the spiny leaves, then they would dig a very efficient little hole to extract the substantial root (the biggest would be about the dimensions of an adult’s forearm).

    I found neat little piles of thistle leaves next to holes that were maybe 6″ diameter and about 12″ deep. The bears would eat the roots almost all the way to the top, leaving behind the portion that still had spiny leaves attached. They did those over quite a few acres; I couldn’t explore fully because they were still out there about 800 yards away.

    What was unclear in the article was whether Yellowstone Ecological Research Center has an actual study underway on Canada thistle, pocket gophers, and grizzlies. Or were these just casual observations?

    Any Lamar regulars know whether they have actual populations studies underway to show a tripling of the gopher population since the 1980s?

    Based on what I saw that day in 2004, it seems that a lot of the “pockmarks” left by grizzlies could be from grizzlies digging up elk thistle instead of Canada thistle. I’m not saying they never dig Canada thistle, but those bears that day made a lot of holes digging up elk thistle.

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