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

WOODY VEGETATION
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example, point bars along rivers, drying oxbows,
and near springs and seeps. New experimental
exclosures such as described under the aspen
research recommendations would probably be
necessary for this research; such a study could
greatly help to sort out the relative influences of
ungulates, climate change, and geomorphic
processes in the decline of woody riparian vegetation
during the past century.
In the late 1980s, a group of 18 riparian
scientists reviewed the state of knowledge concerning
the status, condition, and trends of riparian
ecosystems in Yellowstone, and made recommendations
(Anderson et aJ. 1990). They concluded
that the issue of riparian system changes has been
recognized by virtually all involved, and that
preliminary research has been completed by
scientists from within the park and from outside
institutions. Resource managers and scientists
from throughout the west formulated a set of
hypotheses that should be tested. In brief, they
recommended that studies be directed as follows:
I. Test the hypothesis that the riparian
ecosystem maintains a dynamic equilibrium with
climate and geology and thus is responsive to
climate changes past, present, and future.
2. Test the hypothesis that ungulates are the
biotic dominants regulating the riparian system,
3. Test the hypothesis that natural disturbance
events (e.g., fire, flood, etc.) profoundly affect the
riparian systems.
4. Test the hypothesis that the riparian
environment is an important mediator of aquatic
systems.
5. Test the hypothesis that the riparian
environment may mediate processes in upland
areas through its effect on the movement of
ungulates, nutrient loss, and plant species movement
along aquatic corridors.
Each of the above hypotheses contained
many subquestions too numerous to detail here,
Because of cuts in research funding, little riparian
research was initiated in the 1990s, but some funds
were made available for work to begin with the
first topic listed above, beginning in 1997, with the
prospect of expanding to include the other hypotheses
in the next few years. See Chapter 5.
QUAKING ASPEN
Aspen is an especially popular part of the
western landscape. Because of its beauty, and
because it contributes to the ecological diversity of
a landscape, aspen is of great interest both to the
public and to the scientific community. Aspen has
been described as an "insignificant component" of
the Yellowstone region for the past 20,000 years
(Mullenders and Coremans 1996, Mullenders et aJ.
1996), but, like willows, aspen has disproportionate
effects on the ecological communities of the
northern range,
Barmore (1980) mapped northern range
vegetation and estimated that about 2,8 percent of
the vegetation was aspen. Based on remapping of
the northern range and compruison with historic
photos, Houston (1982) agreed:
Compared to 2-3% of the winter
range now in aspen, I estimate that 4-
6% was in aspen in the original photos.
A vegetation map of the winter range
made in the early 1930s supported this
estimate,
Kay (1993) disagreed, estimating a 95
percent decline in area occupied by aspen since the
park's establishment in 1872. The spectacular
disparity in estimates of this decline is some
indication of the uncertainty still surrounding aspen
on the northern range, and lead to calculations that
suggest how far astray scientific discourse can
occasionally go. Consider Kay's (1993) statement
that aspen have "declined by approximately 95%"
since 1872. This means that roughly 5 percent of
the 1872 aspen disuibution remains. But
Houston's (1982) estimate that aspen currently
occupy 2 to 3 percent of the northern J;ange seems
to be widely accepted, From these two figures
(aspen now occupying 2 to 3 percent of the
northern range, and that being 5 percent of their
historic distribution), it would follow that in 1872
aspen must have occupied 40 to 60 percent of the
northern range, which the photographic evidence
does not support (Meagher and Houston in press.)
While there is disagreement over the extent
of the decline, it is certainly true that the number of
tree-sized aspen standing on the northern range has