Mine Revegetation

in Nevada: The

State of the Art in

the Arid Zone

by Christopher Ross, PhD.

Physical Scientist/Reclamation

BLM, Nevada State Office

920 (Minerals)

Background

Revegetation of mined lands,

including cyanide leach heaps, is an

evolving technique in the arid

intermountain west. At the Bureau

of Land Management (BLM) Salt

Desert Shrub Symposium in 1966,

noted desert plant ecologist A. P.

Plummer commented that the

success rate of revegetation efforts

where annual precipitation was

under ten inches was less than one

percent. Now, thirty years later,

successful vegetation is the norm in

even the driest and hottest parts of

Nevada. There is no area where

perennial native species have not

been re-established after mining

disturbance at cover and density

equal to or far exceeding that of

undisturbed areas. Areas which

have not been intentionally revegetated are uniformly dominated by

exotic annuals.

Discussion 

The keys to successful revegetation

are site preparation, species choice,

and timing. Site preparation consists of reduction in slopes to 2.5 or

3:1, application of suitable growth

medium and creation of a roughened seeding surface. Because

extremely arid soils rarely have

significant A and B horizons, topsoil may be either unavailable or

too salty and/or silty to be useful.

Most mines move ample supplies

of Tertiary or Quaternary alluvial

overburden material in the process

of accessing the ore bodies. This

can be salvaged as growth medium.

Because the nutritional requirements of native plants are rarely

known, and because the growth

medium is assembled one truckload

at a time, soil chemical testing is not

indicated unless problems with

excessive salt or boron are anticipated. It is only necessary to assure

that the medium contains a mix of

coarse and fine material that will

allow creation of an uneven surface

with adequate safe sites for seedling

establishment.

Upon application of the material to

a depth of 18 inches or more, the

surface should be shallowly ripped

with heavy equipment to roughen

it. Numerous observers have concluded that smooth surfaces are the

leading cause of failed revegetation

efforts on mined sites in Nevada

(This is consistent with much

experience with desert seeds that

suggests that safe sites which provide a good microclimate and

ensure seed-to-soil contact and

perhaps water harvest are vital to

germination). A diverse mix of siteadapted native shrubs, forbs, and

grasses is then broadcast at a rate of

20 - 30 seeds per square foot. The

mix should include at least three or

four species from each of the three

plant forms. Where the use of nonnative species is required, the documentation of their need is required

by BLM policy.Observation of the

surrounding terrain may suggest

suitable species, although fire and

grazing regimes may have degraded these areas so severely that

they are dominated by annuals or

undesired perennial. In such cases,

consultation with local managers

and observations of past successful

revegetation efforts can guide

species choice. It is important that

seeding be done in late fall or early

winter to take advantage of seasonal

precipitation — summer seedings

are rarely successful in Nevada

except at higher elevations. After

seeding, the surface should be

immediately dragged with some

device to cover the seed. A piece of

chainlink fence weighted with scrap

iron or large tires is often used.

Joint state and federal guidelines

for release of revegetated disturbances on public lands in Nevada

allow evaluation of efforts after

three or more growing seasons

have elapsed. Evaluation consists

of comparison with a reference area

or standard, usually an adjacent

undisturbed area. Ecological Site

Indices, test plots, or other reference standards may also be used.

Comparison is by aerial cover of

vegetation, usually measured by the

line intercept methods described in

Sampling Vegetation Attributes

(Interagency Technical Reference

BLM/RS/ST-96/002+1730, 1996,

BLM National Science and

Technology Center, Denver,

Colorado) or other vegetation

analysis references. Nevada guidelines require that the cover be as

close as possible to that of the reference site, with evidence of site

stability, species reproduction, and

no noxious weeds.

Sampling must be adequate to provide 80% assurance that the samples

are within 20% of the true mean

cover of both the reference and

revegetated sites. This typically

requires 7 to 10 intercept transects

on each site. A simple equation for

determination of sample adequacy is

included below:

N = (T)2 x (S)2

/(mean x 0.2)2, 

RESOURCE NOTES

NO. 36 DATE 08/07/00

Range

Range
where, N = minimum number of

samples required to give 80% probability of being within 20% of the

true mean

T = two tailed t value at (n-1)

degrees of freedom and alpha=0.80

(from a standard table)

S = standard deviation of preliminary samples

Typically six intercepts comprise a

satisfactory preliminary sample. If

fewer are used, the equation will

provide an incorrectly high number

of required samples to achieve the

required adequacy.

Conclusion

Hundreds of examples of successful

revegetation at diverse elevations,

site conditions, and locations have

proven that there are few if any

arid sites in the intermountain west

which cannot be simply and economically revegetated. In most

cases, the species choice results in a

far more productive post mining

land use than was present on

degraded sites before the mining

disturbance. However, the use of

vegetation to intercept meteoric

water before it can penetrate

cyanide leach heaps should be

approached very cautiously. Most

proposals for this to date have

incorporated serious flaws. These

include uncertainty about rooting

depth of planted or invading

species, no acknowledgement of

the fact that grazing or fire may

remove the vegetation at undetermined times, and general ignorance

of the fact that in many areas the

precipitation occurs in winter when

plants are not actively transpiring

significant amounts of water.

Enthusiasm for the potential of

revegetation success should not lead

to inappropriate applications of the

technology or uncritical application

of modelling techniques developed

in other regions.

Contact

Christopher Ross, PhD.

Physical Scientist

BLM, Nevada State Office 920

P.O. Box 12000

Reno, Nevada 89520-0006

Phone (775) 861-6571

Fax (775) 861-6711

email clross@nv.blm.gov

Range

Resource Notes are intended to be early

announcements of technical and informational topics for

Bureau of Land Management personnel and some of their customers.

Information in this Resource Note is based on the opinion and

experience of the author and has not been peer-reviewed. Conclusions

and opinions expressed herein do not

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Thank you for your interest in Resource NoteS.

Reclaimed haul road: The green, grassy are is a 120 foot-wide haul road three years after reclamation. This is an extremely harsh site where temperatures range from well below zero to over 100F,

while the saline soils receive approximately 4 inches of precipitation annually.