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

THE NORTHERN RANGE
38
grazed and ungrazed sites (Merrill et al. 1994a,
1994b,1996). In other words, grasses grazed in
winter and spring "caught up" with their ungrazed
counterparts by the end of the growing season.
Singer and Harter (1996) studied the effects
of long-term protection of plants from elk grazing,
"at 8 large ... exc1osures constructed in 1958 and
1962:"
Winter grazing by elk resulted in
less standing crop biomass of grasses
only in 1986, following a drier than
normal spring. Total grasses were not
influenced by grazing in any other year,
and total forbs were not influenced by
grazing in any year ....
Use of exc10sures (that is, ungulate-proof
fences) to study plant communities on the northern
range has been quite productive, but it has also
caused considerable confusion. Critics of park
management sometimes publish photographs of
these exc10sures showing that inside the fence the
plant growth is taller; if the exc10sure contains
shrubs and other woody vegetation, the difference
is even more dramatic. These exclosures are easily
seen at several locations along the road from
Mammoth Hot Springs to the Lamar River Valley,
on the northern range. The implication of the
publishers of the photographs is that the vegetation
condition inside of the fence is what a "healthy"
range should look like, when in fact the vegetation
inside the fence only shows what the range would
look like if it had no large mammals grazing it at
all. As already noted, at least one researcher (Kay
1994a) believes that there were very few if any
large animals on the northern range prior to 1872;
if that were the case, then it might be argued that
the exclosures represent the "natural" condition of
the range. However, until evidence is presented to
demonstrate such a paucity of grazers prehistorically
(evidence that will have to overcome a
mounting body of documentation indicating that
grazers were present and abundant), the exclosures
must be regarded as maintaining the artificial
protection of plants from all large, native herbivores.
Last in the discussion of grassland production,
Pearson et al. (1995) concluded that in the
first few years after the fires of 1988, elk preferred
to graze in burned areas, "presumably because
burning had enhanced the abundance of forage,"
but that "fire effects on northern Yellowstone
ungulates are likely to be relatively short-lived, and
in the long term, may have minimal impact on
population dynamics compared to winter conditions."
Tracy (1997) found increased aboveground
net primary productivity and forage consumption
on transitional and winter range sites used by elk.
But, results suggested that burning effects, if
present at all, persisted for no more than three
years postfire in most Yellowstone grasslands. Fire
had either positive or neutral effects on
aboveground production and the cycling of
nutrients.
FORAGE QUALITY
Grazing enhanced the protein content of the
three most common native northern range grasses
(bluebunch wheatgrass, Junegrass, and Idaho
fescue) between 10 percent and 36 percent (Singer
1996a). Grazing enhanced nitrogen content of
forage plants in three other independent studies
(Coughenour 1991, 1996; Mack and Singer 1992a;
Merrill et al. 1994a, 1996). Grazing slightly
enhanced other nutrient concentrations (calcium,
phosphorus, magnesium, and potassium) in
selected grasses.
NUTRIENT CYCLING
The nutrient dynamics of wildland ecosystems
are quite complex. They are influenced by a
variety of forces, including climate, soils, and the
plant and animal species that inhabit the setting.
Frank et al. (1994) examined the mechanisms
surrounding the sustainability of grazing ecosystems
such as the northern range through the study
of nitrogen cycling. They reported that ungulates
were a "particularly important component" of the
nitrogen budget of the northern range, noting that
the nitrogen flow from the animals to the soil was
about 4.5 times that found in senescent plants.
Their results suggested that herbivores increased
both aboveground and belowground production.