By Kathrin Olson-Rutz1, Clayton
Marlow1, Kathy Hansen2, Leonard Gagnon1, and Rick Rossi3
The need to manage wilderness or
wildlands has been recognized for many years (Krumpe
and McLaughlin 1987). Policy makers and managers of
wildlands are faced with the paradox of protecting unique
ecosystems or areas with little human development while
allowing recreational use (Kuss and Graefe 1985, Cole
1987, McClaran 1989). WildIand ecosystems may be used
by humans or domestic animals without altering the processes
that sustain the native plant and animal communities.
One impact of wildland recreational use is packstock
grazing.
Traditional range management practices
have been developed to enhance or maintain rangeland
productivity, therefore, many principles of livestock
grazing may be similar to those of packstock grazing.
However, grazing effects on high elevation plant communities
have received little study. Also, management objectives
of wildland areas may be very different from those of
livestock production systems. Management mandates of
these areas may be to maintain species diversity or
to protect specific organisms. The ideal may be to manage
for no change, yet limits of acceptable change should
be defined (Krumpe and McLaughlin 1987). Grazing management
research in wildland areas needs to address how these
areas respond to use, and which community responses
can be used to indicate acceptable or unacceptable change.
Our objective was to determine the level of packstock
grazing that a dry subalpine meadow can tolerate without
changing ground cover, soil compaction, and plant growth.
Such information will help land managers develop guidelines
for packstock grazing.
Methods
We are working on the Burntfork of
the Bacon Rind drainage in the Lee Metcalf Wilderness
Area in southwestern Montana The site is a dry upper
timberline (8500 ft) meadow classified as a Festuca
idahoensis/Agropyron trachycaulum habitat type (Mueggler
and Stewart, 1980). The area receives little recreational
horse use because hunting and fishing opportunities
are limited. However, it is used frequently by elk.
We picketed horses on 25 foot ropes
for three durations (4, 8, and 18 hours) and had a control
(0 hours) in each of three months (early July, mid-August,
mid-September). The 4-hour circles were grazed for four
continuous hours either in the morning or evening. The
8-hour circles were grazed four hours in the morning
and evening, and the 18-hour circles were grazed nine
hours a day for two consecutive days. We had four replicate
pickets per month for each duration. One set of picket
circles was grazed in 1988. A second set was grazed
in 1989 on a different area of the meadow. The 1989
circles were regrazed in 1990.
We used a 0.75x2 inch sampling frame
(Morris 1973) to estimate percent cover of mineral soil,
rock, moss/lichen, litter, and basal vegetation, and
to determine grass and forb stem densities, height classes
of the tallest plant material, and grazed plant frequencies,
before grazing (n=76 per circle). Plant height class
and grazed plant frequency were remeasured after grazing.
We also measured penetration resistance in the top 0.5
inch soil layer with a pocket ring penetrometer (N=1
6 per circle in 1988, N=76 in 1989). In September 1988,
it snowed six inches before we could measure the circles
before grazing. Therefore, those data are incomplete.
To determine the impact of packstock grazing one year
on the subsequent year, all of the variables were remeasured
in August 1989 on the circles treated in 1988, and in
July 1990 on the circles treated in 1989.
Results and Discussion
The immediate change in soil penetration
resistance due to picketed horse grazing was influenced
by soil moisture. When the soil was very dry, the soil
surface was scuffed and loosened by hooves, thereby
reducing soil surface compaction. Wet, muddy soil was
also not compacted by their hooves. With intermediate
soil moisture there appeared to be some compaction in
the soil surface. However, the soil surface recovered
from these immediate impacts within one month after
grazing. We did not measure impacts to lower depths.
Longer term changes in soil compaction may result from
repeated grazing and indirectly through changes in soil
cover and plant species composition. The horses consistently
grazed a greater proportion of grasses than forbs (Table
1). There was a measurable increase in grasses grazed
the longer the horses were on picket. However, the proportion
of forbs grazed was only increased with horses on the
pickets 18 hours. The control circles (0 hours) indicate
wild animal use, which was mostly elk on this meadow.
Forage removal was measured indirectly
through changes in plant height class distribution.
Plant height classes were not recorded separately for
grasses and forbs in 1988. In 1989 and 1990 grazing
reduced grass more than forb heights (Fig.
1), especially after 8 and 18 hours on picket. Forb
heights were reduced less in 1990 than in 1989, even
after 18 hours grazing. Plants were taller before grazing
in 1990 than 1989 (Fig.
1, 0 hours), therefore the horses were not forced
to graze the forbs.
Although fewer forbs were grazed
than grasses, they were trampled or bent by the picket
rope. This affected the appearance of the meadow, but
since the plants were usually not severed, the height
class distribution did not reflect this impact. However,
if areas are to be managed under aesthetic guidelines,
hobbling horses or containing them with electric ribbon
fence may be more desirable.
From a visual perspective the immediate
impact of grazing and trampling may appear harsh. From
an ecological perspective the impacts cannot be evaluated
until the following growing season. The picket locations
differed in ground cover, stem counts, and plant heights
before grazing. Therefore, treatment effects were evaluated
by comparing changes from before grazing to the following
year.
The meadow we worked on appears,
at first, to be resilient to one time moderate to heavy
grazing. Yet, trends in the results indicate the picketed
horses may be causing some changes on the picket circles.
Eighteen hours grazing in August 1988, and four, eight,
and eighteen hours grazing in August 1989 appeared to
reduce vegetal cover the following year (Fig.
3). Conversely, bare soil increased on the same
treatments. Bare soil also appeared to increase with
eight and eighteen hours grazing in September 1989 with
a concomitant reduction in litter rather than vegetal
cover.
The decrease in basal vegetal cover
was partially reflected in reduced stem counts. On the
meadow grazed in 1988, circles grazed in July appeared
to have more forb stems than the ungrazed circles the
following year (Fig. 4a).
In contrast, grazing for 18 hours in August appeared
to reduce grass and forb stem counts the following year
(Fig 4a,b). September 1988
pregrazing data were missing. Mid-summer 1988 was extremely
dry (NOAA 1988) and the grasses were flowering in July.
Grasses grazed during flowering produce fewer tillers
per unit area (Stout et al. 1980, Stout et al. 1981)
or have lower tiller replacement (Olson and Richards
1988) than ungrazed plants. Like grasses, forbs produce
fewer inflorescences when defoliated just before or
during flowering (Blaisdell and Pechanec 1949, Mueggler
1967, Edwards 1985). By August the forbs were either
flowering and thus sensitive to defoliation, or dried
and brittle and thus broken by trampling. The grasses
were more resistant. After 18 hours of grazing both
were grazed or trampled and produced fewer stems the
following year.
Responses from the meadow grazed
in 1989 supported these trends. Grazing for 8 and 18
hours in July increased the number of forb stems, but
forbs were not affected by grazing in August and September
(Fig. 4c). In contrast,
grazing for 18 hours in July, and any grazing in August
and September, reduced grass stem counts in 1990 (Fig.
4d). Grasses flowered in July and August of 1989,
and were therefore sensitive to grazing. By mid- to
late summer the grasses were still being grazed more
than the forbs and therefore had fewer stems the following
year. The forbs were also flowering at this time. Since
the forbs were at a sensitive phenological stage (flowering),
they did not have a competitive advantage over the grasses
and did not have more stems the following year.
Several studies have shown that defoliation
just before or during flowering reduces leaf (Mueggler
1972 and 1975, Edwards 1985) or stem lengths (Mueggler
1967 and 1972, Trlica et al. 1977, Stout et al. 1980,
Stout and Brooke 1987, Olson and Richards 1988) the
following growing season. Yet, our plant heights did
not reflect an effect of the previous years grazing.
This could be for several reasons. Blaisdell and Pechanec
(1949) and Mueggler (1972, 1975) found culm length to
underestimate the impact of defoliation on plants. We
probably did not measure maximum heights of all species,
because we measured all plants at only one time during
summer. Also, our height class categories were rather
broad. Plant height changes following defoliation in
other studies (Mueggler 1972, 1975, Trlica et al. 1977,
Stout et al. 1980, Stout and Brooke 1987) would not
have resulted in placing the plants in lower height
classes used in our study.
Conclusion
Trampling and grazing by packstock
have an immediate impact on an area's appearance. They
can also alter plant community composition by changing
an individual plant's status within the community (Grime
1979, West et al. 1979, Lovett-Doust 1981, Bryant et
al. 1983, Crawley 1983). Changes in stem counts, plant
heights, or ground cover, are indicators of potential
community change (Cook and Child 1971). However, measures
of plant status which best indicate plant response to
grazing vary among species (Cook and Child 1971, Mueggler
1975). As with evaluating traditional livestock grazing,
such measures may be useful indicators of the effects
of packstock grazing on wildland plant communities.
They integrate all the direct and indirect effects of
grazing on a plant species or vegetation type.
To determine how packstock may be
managed to meet desired wildland management objectives
we are continuing to control when, how long, and how
frequent packstock graze a meadow. There are few differences
between grazing by horses, cattle, sheep, or elk, other
than their management. In principle, people have greater
control over packstock than other livestock grazing,
because packstock handling is intensive. The challenge
of managing wildland packstock use is agreeing on objectives
and having the recreationists handle their stock to
accomplish those objectives.
Acknowledgements
The project could not have been done
without advice from David Cole, (U.S.Forest Service,
Missoula, MT) and the help of all the field helpers
who persevered through snow and sun. We thank Bret Olson,
Robyn Tierney, and Carl Wambolt for helpful review of
this manuscript.
The project is funded by the U.S.
Forest Service and the Montana Agricultural Experiment
Station.
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Figures
Figure 1. Grass and forb height
class distribution one year after grazing, by year and
duration grazed. Height classes were as follows; class
1 = >0.75 in, 2 = 0.75-1.5 in, 3 = 1.5-4.5 in, 4
= 4.5-9.5 in, 5 = >9.5 in. Lines depict one standard
error.
Figure 2. Change in ground cover
from before grazing to the following summer.
Figure 3. Change in stem counts
(following year minus initial year) per 1.5 in cm2 by
year, month and duration grazed. a) Forb stems from
pregrazing 1988 to 1989, b) grass stems from pregrazing
1988 to 1989, c) forb stems from pregrazing 1989 to
1990, and d) grass stems from pregrazing 1989 to 1990.
Lines depict one standard error.
