Aspen tree decline in West due to cattle grazing

March 15, 2021 5:30 am

A stand of wild aspen trees (Courtesy Mike Garrity/Alliance for the Wild Rockies)

The Forest Service has been proposing logging and burning projects to promote the growth of more aspen. But aspen regenerates by putting out shoots, not through seeds, and it’s extensively documented that the major cause of aspen decline in the West is cattle browsing and trampling the young aspen, thus greatly limiting regeneration.

Despite the many excuses the Trump administration used to promote more logging, aspens and conifers have existed together for millennia before cattle were introduced in the West and logging is not the answer. If the Forest Service really wants to regenerate aspen stands it is imperative to follow the science and actively minimize cattle grazing in aspen groves.

Unfortunately, the Middle Fork Henry’s project would increase grazing, not reduce it. Yet, instead of considering viable alternatives that would lighten the grazing pressure, the agency chose to destroy existing habitat for lynx and grizzly bear as well as other old growth-dependent species such as the Flammulated owl.

The Caribou National Forest’s Revised Forest Plan’s Final Environmental Impact Statement identifies aspen as a “habitat-at-risk” and specifically notes that aspen was “historically overgrazed” — which likely contributed to aspen decline due to the loss of regeneration. It is also notes that aspen need a “diversity of seral stages,” putting the loss of tender aspen shoots to cattle grazing in direct contradiction to the Forest Plan’s management recommendations. The document goes on to say aspen is at high departure from historic conditions in part due to heavy grazing which eliminates regeneration.

Cattle grazing is what’s killing aspen.

While it’s true there’s an ongoing aspen ecological crisis in the Intermountain West, the decimation of aspen stands is well-documented to be caused by cattle grazing. Unless the new shoots are protected, aspen are unable to successfully regenerate due to the continued browsing/trampling/rubbing by cows and eventually die over time due to this repeated browsing.

The problem of over-grazing and trampling by livestock has been repeatedly identified. For example, only one of 40 aspen stands surveyed on Montana’s Beaverhead-Deerlodge National Forest had healthy, surviving aspen suckers due to a failure of Forest Service programs to limit grazing of aspen stems by livestock.

The standard claim made that the heavy browsing of aspen suckers is due to wildlife, including mule deer instead of cattle grazing, was specifically monitored recently. This monitoring program documented 4.5 times the amount of cattle grazing on aspen in two weeks than mule deer use during the course of  six months. Moreover, forage utilization by mule deer prior to livestock grazing was unobservable. But when livestock grazing was added to the mule deer use during the two weeks of monitoring, a stunning 70 to 90 percent of the understory vegetation’s annual production was consumed. This report also noted that trampling of soils by livestock may also play a role in depressing aspen recruitment on allotments.

As in the Middle Fork Henry’s project, mixed aspen/conifer stands are a natural condition on the landscape, and clearly do not represent “unnatural” conditions that need management intervention. The Forest Service even notes that succession of conifers into aspen is common as long as a conifer seed source exists, but that succession to only conifers may take hundreds of years. Simply put, there is no scientifically-supported ecological reason to remove conifers from aspen stands – particularly in Inventoried Roadless Areas.

Controlling livestock use is the obvious management intervention needed, not cutting out
conifers. We would support a Forest Service project  limiting cattle grazing to restore aspen stands since it’s a scientifically-proven methodology.

Mike Garrity is the Executive Director of the Alliance for the Wild Rockies

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