The impacts of mineral development and of recreational uses are
increasing on alpine ecosystems in the western United States. Such
activities threaten to disrupt these fragile ecosystems and are already
causing serious deterioration of aesthetic, watershed and wildlife
habitat value in some areas. This paper discusses some of the results of
interventions for rehabilitation purposes, which were carried out on the
McLaren Mine, located on the Beartooth Plateau, near Cooke City, Montana.
The McLaren Mine is an example of a site severely disturbed due to
mining. Thus, it was found to be a suitable demonstration site for
reclamation studies.
The geology of the Beartooth Plateau is characterized by an uplift
Pre-Cambrian granitic mass from which extensive sedimentary materials
have been eroded (Beven 1923, Loverling 1929). Most of the highly
mineralized zones lie on the flanks of the main Beartooth uplift, as is
exemplified by the Stillwater complex on the north and the Cooke City
Mining District on the southwest. McLaren Mine is located about 8km (5
miles) north of Cooke City, Montana, at the elevation of about 3000m in a
subalpine-alpine transition zone. This shallow open-pit mine was
operated for the extraction of copper, silver and gold, on a site that
now occupies a disturbed area of about 13.5 ha. It has essentially been
abandoned since the early 1950's except for sporadic exploration. In
addition to adverse visual impacts, soil erosion and sedimentation are
occurring as a result of the near total lack of a vegetation cover. The
oxidation of heavy concentrations of pyritic materials is causing severe
off-site water quality problems. Acid drainage is killing the native
vegetation adjacent to the mine and has already resulted in the complete
destruction of the aquatic ecosystem in the upper Stillwater River.
A series of studies were initiated on the McLaren Mine by Ray W. Brown
and Robert S. Johnston, plant physiologist and research hydrologist
respectively, who were attached to the Forest Science Laboratory, Logan,
Utah. The studies have since been incorporated into the SEAM (Surface
Environment and Mining) Program of the USDA Forest Service. The intended
goal of the projects was to find out what kinds of interventions could
help return a disturbed alpine site to a self-sustaining system with
natural successional processes as soon as possible. This included
providing protection and surface stability to the disturbances, as well
as providing aesthetic appeal and site productivity. Techniques such as
shaping and contouring the site, fertilizing, mulching, seeding and
planting were used in the hope of accomplishing this objective. These
techniques of amending the site can alter the extreme conditions of the
disturbed land so the edaphic and microclimate factors are commensurate
with the physiological tolerance limits of plants adaptable to the
region. The primary hydrologic objective was to reduce runoff and
erosion while providing for the movement of water. Establishing
protective plant cover was adopted as the principal means of achieving
this hydrologic objective. This paper will discuss three out of the many
experiments carried out on the McLaren Mine. Two of the studies were
carried out in the field. The other one was carried out in a greenhouse.
mixture of seeded introduced species without fertilizer
The fertilizer used was a 16-16-16 granular mixture applied at an equivalent
rate of 100 lb N per acre. Plots were broadcast seeded in the fall and fertilizer
was applied. Plots were then thoroughly raked and packed.
At the same time that the plots
were seeded, 76 transplants of native species collected from road cuts near
the mine were also established. Whole, dormant plants were transplanted in
rows between the subplots. Among the species that were transplanted were Deschampsia
caespitosa and Carex paysonis.
In 1976, another experiment was
conducted on a site of about 1.0 ha (2.4 acres) in an area with a west aspect
and a 15% slope, on the north edge of the mine. The rehabilitation plan for
this study area included shaping and contouring the spoil and revegetation
(seeding, transplanting and associated treatments). The spoil materials and
topography of the site were characteristic of the entire disturbed site, and
was selected so as not to interfere with future mineral exploration or other
rehabilitation activities.
Before the experiment was carried
out, the entire 1.0 ha of the site was shaped and contoured with a crawler-mounted
D9 dozer as site preparation. The spoil materials with the lowest pH and the
highest concentrations of toxic substances were used to fill depressions,
and were covered with the best growing medium available on site. The entire
area was rough-graded and contoured to conform to the natural topography of
the area using only the materials available on the site.
After site preparation, experiments
which included soil amendments, seeding, planting and mulching were carried
out. Amendments were applied to ameliorate the limiting edaphic factors where
feasible. Lime was applied at the rate of 2200 kg per ha to increase the spoil
pH from about 3.0 to 5.0, and provide increased nutrient availability to plants
in the acid soils. A granular fertilizer with an N-P-K ratio of 18-46-5 with
0.8% zinc was applied at the rate of 672 kg per ha. Dried steer manure was
then applied to the surface at the rate of 2200 kg per ha. These three amendments
were incorporated into 15cm of the soil surface.
Two revegetation studies were carried
out on the prepared and amended site. One study focused on seeding whereas
the other study focused on transplanting. The revegatation plot studies (Brown
and Johnston 1976) which were carried out in 1974 showed that most commercially
available introduced species were not suitable for seeding in the McLaren
Mine. Therefore, only a mixture of native species was used for seeding. The
seed was applied uniformly over the surface with a seeder-packer pulled by
a dozer at a bulk rate of 83 kg per ha. The seeder-packer ensured intimate
contact between the seed and soil particles and firmed the seedbed. About
0.7 ha of the study area was seeded.
The study on transplanting was carried
out on the remaining 0.3 ha of the study site. Grass transplant plugs which
were grown from seed collected the previous year were planted in this area.
Both native and introduced species were used in this experiment (the adaptability
of introduced species used as transplants had not been tested previously on
this site). These plants were grown from seed in plant tubes by the U.S Forest
Service, Coeur d'Alene Nursery, in northern Idaho. The plants were allowed
to harden-off on the site for about three weeks prior to planting. Among the
native plants used were Deschampsia caespitosa and Poa alpina. Alopecurus
pratensis and Festuca arundinacea were among the introduced species
that were used.
A surface mulch consisting of 2500
kg per ha of straw, tacked down with water soluble asphalt emulsion, was blown
onto the site with a power mulcher. The entire seeded area was covered with
the mulch. An effort was made to avoid thick accumulations of straw on the
site that might act as an excessive heat trap and barrier to seedling emergence.
GREENHOUSE EXPERIMENT
Revegetation research in the alpine
zone stressed the essential role of fertilization as an amendment (Brown and
Johnston 1976). Virtually no documentation was available of the role played
by other common amendments such as lime and organic matter. In order to extend
the rather limited scope of small plot studies that have been done in the past
to large scale revegetation, quantitative evaluations of such amendments were
needed. This was particularly important since so little was known about the
growth and development responses of native species to revegetation methods.
A study was carried out on the effects
of various soil amendments on plant growth and development. Representative spoil
material was collected and sieved to separate out the large rocks. The sieved
material was then separated into 7 equal fractions to which various amendments
were incorporated. A total of 7 treatments, each replicated 4 times, were prepared.
These included:
- Control: no amendments added to the spoil material
- Fertilizer: a granular 18-24-6 N-P-K ratio fertilizer was incorporated
into the spoil at the equivalent rate to provide 0.005% N (100lb) per acre.
- Fertilizer-Lime: fertilizer was added as in 2 above, plus hydrated lime
was incorporated at an equivalent rate of 2000 lb per acre, to raise soil
pH.
- Fertilizer -Lime-Straw: fertilizer and lime amendments were added as described
above. Straw was added at an equivalent rate of 5% by volume.
- Fertilizer-Straw: fertilizer and straw were added as described above.
- Fertilizer-Lime-Manure: fertilizer and lime amendments were added as described
above. Manure was added at an equivalent rate of 5% by volume.
- Fertilizer-Lime-Manure: fertilizer and steer manure were added as described
above.
Seeds of two species that seem to have broad adaptability for revegetation
of high elevation disturbances; a native tufted hairgrass (Deschampsia
caespitosa L.) and an introduced species, Garrison meadow foxtail (Alopecurus
pratensis L.), were planted in equally spaced rows in different containers
that contained the different soil amendments. These containers were placed
in a greenhouse, with the environmental conditions controlled.
ASSESSMENT
Assessment of success for all the
studies was mostly based on the results and Assessment of success for all the
studies was mostly based on the results and observations made during the study
period. The results of the first study in the field (carried out in 1974), studying
native species versus introduced species showed that native species were apparently
better adapted for revegetation compared to introduced species. The density
of native species was significantly higher than introduced species under all
treatments. Plant densities were generally higher on fertilized plots under
all treatments, illustrating the importance of fertilizer application. However,
introduced species on the topsoil plot showed no appreciable differences between
the effects of treatments with or without fertilizer. Native species were more
responsive to fertilizer than were introduced species on both soils. The native
plants were at least climatically adapted and were more capable of surviving
periods of environmental stress. Fertilizer was found to improve plant growth
and survival of first-year seedlings. However, the degree of plant development
after one growing season was minimal due to the severe nature of climate and
soil environments.
Transplants of native species appear
to offer a successful alternative to seeding. The mature plants selected for
transplanting were capable of tolerating greater micro-environmental stress
than were seedlings. Thus, the use of transplants may ensure rapid plant establishment
and development on alpine disturbances. If native species are to be used extensively,
however, there is a need to develop nurseries for the large-scale production
of plants and seeds.
The results of the second field experiment
(carried out in 1976) suggested several conclusions. Shaping and contouring
appeared to be a vital step in the program. The shaping and contouring eliminated
wind-swept ridges that tend to scour during the winter and become parched barrens
during the summer. It also removed depressions and other irregularities that
might become pockets of deep snow accumulation and ponds of acid water that
frequently wash out and spill onto the natural plant communities downslope.
Snow distribution on the study site was very homogenous early in the spring,
which appeared to promote uniform infiltration of snow-melt water, a more regulated
rate of runoff and evenly distributed plant emergence and development.
This study showed that for the native
species used, certain treatments were essential to alter conditions of the spoils
sufficiently to support plant growth and development. These treatments included
lime, organic matter, fertilizer and a surface mulch. The assessment was done
by comparisons of these results with results of previous revegetation plots.
Previous revegetation plots essentially used the same species but treatments
that did not include lime, organic matter or a surface mulch. Average plant
cover for the plots with additional treatments were ten times greater than the
plots without those treatments.
As for the transplants, the average
survival of all species was 65%, but there was a substantial difference between
native and introduced species. The natives had an average of 75%, whereas the
introduced species had only 39%. Therefore, transplants of native species had
a higher average of survival compared to transplants of introduced species.
The data also showed that on the average, the native species had a higher production
per plant than did the introduced species. However, two out of the six introduced
transplants showed encouraging results. These two species were Alopecurus
pratensis and Poa compressa. Further studies need to be carried out
on the potential of these two species for revegetation purposes.
The results of the study of effects
of various soil amendments on plant growth and development (Greenhouse study)
showed that the greatest levels of plant growth and development were achieved
under the highest levels of soil fertility. Generally, amendments including
both fertilizer and manure resulted in the greatest average number of culms
and leaves, leaf area, average plant height and shoot and root production for
both the species studied. The use of lime as an amendment resulted in some unexpected
effect. Normally, spoil material from the McLaren Mine is quite acid, with a
pH range of 2.0-4.5. However, the spoil material collected for this study had
a pH of 6.1. Lime seemed to depress the growth and development of both species.
For example, the fertilizer-manure amendment resulted in larger, more developed
plants than the fertilizer-lime-manure amendment. Similar responses were noted
with the fertilizer-lime-straw and fertilizer-lime treatments. The addition
of lime may be detrimental when the pH is already relatively high. The addition
of straw resulted in relatively greater levels of growth and development than
the control or fertilizer treatments. However, straw was not as effective as
manure, presumably because of its low nutrient value and its tendency to reduce
the available nitrogen in the soil by increasing the carbon-nitrogen ratio.
The role of straw in revegetation is probably more important as a surface mulch
to retard evaporation and to reduce the incidence of frost action in the soil.
CRITIQUE
The rehabilitation research program
at the McLaren Mine, Beartooth Plateau, has come up with some very good studies
and methods on how to reclaim and enhance revegetation on this highly disturbed
site. However, there are some methods that need to be improved and further studied.
Shaping and contouring the site by
burying the toxic materials and covering it with topsoil is a good move in providing
appropriate growing medium on a site which once had toxic material on the surface.
However, no mention was made on how the toxic material was prevented from moving
upwards or downwards in the soil. If no toxic containment was installed, toxic
material may eventually seep into the soil and cause toxicity to once again
be a problem. There was also no mention on what kind of topsoil was used to
cover the toxic materials. However, the fact that only the materials available
on site were used to cover the depressions, and not "alien" soil from other
areas, was a positive step in ensuring that the site would be reclaimed to as
close as it could possibly get to how it was prior to disturbance.
The study on effects of various soil
amendments on plant growth was carried out rather well, but could still be improved.
The inclusion of a control is useful as a comparison between treated and untreated
soils in the sense that we can measure the extent of the effectiveness of the
amendments. Having replicates of each amendment helps reduce the variations
in the results by taking the average results of each amendment and making conclusions
based on this average.
The study also, however, showed unexpected
results with regards as to why it was found that liming showed detrimental effects
on plant growth and development. A conclusion was made that the addition of
lime may be detrimental when the pH of soil is already high (in this study,
the pH of the soil used was 6.1). However, although liming generally helps plant
development in soils that have low pH, no test was conducted on the soils that
were highly acid in the McLaren Mine. The soil sample in this study was of a
much higher pH (6.1), and the conclusion of lime being a retardant on soils
of high pH was made without any comparison to effects of liming on soils of
low pH.
The study on effects of various soil
amendments on plants was conducted in a greenhouse. Although the results of
experiments carried out in field studies are generally similar to results carried
out in a greenhouse, this is not necessarily always true. In a greenhouse, the
environmental conditions are controlled at an optimum level to favor and enhance
plant growth and development. In the field, environmental conditions are not
always consistent or predictable, and amendments to the soil on the field may
not show the same effects on plant growth as in the greenhouse. For example,
if the site was exposed to a extremely long and hot summer, the high increase
in the rate of evaporation from the topsoil could increase the pH significantly
enough to influence the effect of liming on plant growth. Bioassay studies are
only capable of evaluating plant responses to edaphic factors, but they are
not designed to evaluate interactions with other limiting factors such as climate
variables. Environmental conditions in the field are infinitely more complex
than those reproduced in this greenhouse study. Consequently, comparison between
these data and actual field trials may be somewhat different.
The study on revegetation was carried
out rather well. The results of the study gave clear indications on which kinds
of plants were best suited for revegetation purposes. The success and failure
of these plants to survive and develop were well documented and reported. Comparison
of plant growth and development between the seeding and transplanting methods,
and between native and introduced species, is useful in selecting revegetation
species. A commendable step in the collection of seeds that was carried out
is that all the native species seeds were collected from surrounding undisturbed
sites and all the introduced species seeds that were purchased were strains
that originated in the Rocky Mountain States. This method of obtaining seeds
was to ensure that only species that were indigenous to the area were used.
Since the rehabilitation program is still in the research phase, definite conclusions
that could hinder or prevent further studies to be carried out on other species
should be avoided. For example, since there are some transplants of introduced
species (Alopecurus pratensis and Poa compressa) that show encouraging
results on plant development, further research should be carried out on these
species to test their potential as revegetation species. This could help reduce
total dependence on native species, and these species could function as a back-up
for revegetation efforts.
The suggestion of having nurseries
for large-scale production of plants and seeds is highly recommended to ensure
the supply of readily available seeds and plants for a revegetation project.
Many alpine species can be successfully grown and encouraged to produce abundant
viable seed crops in nurseries.
CITATIONS
Brown, R.W. and R.S. Johnston, 1976: Revegetation of an alpine mine disturbance:
Beartooth Plateau, Montana. USDA Forest Service Research Note INT-206, 1976.
Brown, R.W and R.S Johnston, 1978: Rehabilitation of a high elevation mine
disturbance. Pages 116-127 in S.T Kenny, editor. Proceedings: High Altitude
Revegetation Workshop No. 3. Information series 28. Colorado Water Resources
Research Institute, Fort Collins, Colorado, USA.
Brown, R.W and R.S Johnston, 1980: An assessment of revegetation techniques
for alpine disturbances. Pages 126-144 in C.L. Jackson and M.A Schuster, editors.
Proceedings: High Altitude Revegetation Workshop No. 4. Colorado Water Resources
Research Institute, Fort Collins, Colorado,USA.
Brown, R.W and R.S Johnston, 1980: Bioassay of alpine mine spoils for plant
growth and development. USDA Forest Service Note INT-285, 1980.
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