Yellowstone's Northern Range - Greater Yellowstone Science ...

THE NORTHERN RANGE
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channels in these reaches, it would be necessary to
re-establish the woody species, primarily willow."
Rosgen attributed these "out of balance" situations
to what he regarded as historical increases in elk
numbers beyond what had existed in the park area
prehistorically.
Rosgen's interpretations appear to fall under
the category described earlier in this report, under
the WIllows discussion, of presuming a full
understanding of how a particular setting "should"
look. The Colorado streams he used for comparison
and contrast (that is, the streams he believes
northern range streams "should" resemble) are
managed by humans to look a certain way. Rosgen
concluded that changes in climate over the past
century did not cause the changes he measured in
Lamar River drainage, but did not introduce any
climate data to support his position. He presented
no riparian data to support his interpretations,
which appear to have been based on undocumented
assumptions about ungulate effects on this watershed.
Rosgen also based his interpretations of
current sediment conditions in the Lamar Valley on
the elToneous conviction that "large herds of elk
did not inhabit the greater Yellowstone ecosystem
until the late l800s." As the present volume
demonstrates, large herds of elk were in fact
present in the park area prior to the late l800s. As
the present volume also has explained, willow, elk,
and willow thrived together in this setting in the
late 1800s. This means that another explanation
must be found for what Rosgen describes as the
"dramatic conversion" of willows to grass communities
along some Lamar Valley streams.
CONCLUSIONS
Soils normally erode in wildland settings,
and often do so on a grand geological scale. The
Yellowstone we see today is a relatively young
landscape. Flowing water, wind, gravity, and other
forces still carve the park's canyons, shift stream
channels, and relocate soils. One look at the Grand
Canyon of the Yellowstone River would convince
most observers that this is true. As well, ungulates
do move soil, and at times contribute to sediment
loads in park streams. But even if there were no
ungulates at all on the northern range, the rivers
would become muddy, especially during the period
of spring snowmelt, during high-intensity summer
thunderstorms, and following fires when vegetative
cover is reduced or eliminated. The sedimentation
process is clearly geologically and climatically
driven. Dire interpretations of erosion processes
on the northern range, such as given by Rosgen
(1993), are not yet persuasive because they so
totally reject any factor being involved other than
ungulates.
RESEARCH
RECOMMENDATIONS:
EROSION AND SEDIMENTATION
To date, studies of erosion and its role in
northern range ecological and hydrological
processes have concentrated on the grand scale of
entire watersheds, starting on the highest, steepest,
and most easily eroded slopes and working down
the drainages to the dver valleys. Research has
now resolved that most of the material that
muddies park streams originates in steep and
geologically unstable areas where the activities of
ungulates are not a significant factor in movement
of material. However, as Rosgen's study suggests,
important questions remain, especially involving
local conditions along park streams. As already
explained, grazing increases percentage of bare
ground exposed to erosive processes, and in other
ways may dispose soils to higher rates of erosion
than would occur without grazing; ungulates
unquestionably contribute to erosion.
As mentioned earlier, documented changes in
willows and other riparian vegetation may affect
stream processes, which in turn can have a variety
of effects, including increased movement of
sediment and erosion of stream banks and beds.
Riparian areas occupy only a small percentage of
the northern range, but ecologists have long
recognized that riparian areas are disproportionately
significant in the processes of large ecosystems
because so much energy and activity is
focused in or near them. There is a need for more
information on the localized riparian areas associ-