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Use of Native Species in
Revegetation of Disturbed Sites (Arizona)
Richard D. James1
ABSTRACT
Seeding disturbed sites to establish native species in desert and
desert grassland areas of Arizona has been shown to be
successful. A growing awareness of and appreciation in the role
native species play in ecosystem functioning is a major factor in
their use. There is also an increasing interest and acceptance of
arid lands as valuable beyond livestock production. Land values in
. term of esthetic appeal, wildlife, fisheries, watershed, tourism and
other forms of recreation are of significant public importance.
Native flora and fauna contribute immeasurably to the value of
these entities. Using native species for revegetating to closely
approximate the original pre-disturbance, or contiguous native flora
will best meet restoration goals. This can often be accomplished
using certain simple technologies of site preparation and direct
seeding.
The practices described in this paper are involved with acutely or drastically disturbed sites as
considered by Box, (1978). These are sites such as deep construction cuts and fills where
vegetative communities have been removed and the natural surface soils have been lost, altered,
or buried. These sites are ones which do not typically restore themselves in reasonable time.
Adequately applied common soil surface modifications combined with the appropriate materials can
dramatically accelerate the process of secondary succession.
There has been a phenomenal increase in drastically disturbed sites due to construction
activities in recent years. This coupled with increased environmental awareness has created a
demand for restoring natural vegetation. Erosion control has been a major objective and still is on
many projects. However, esthetics are of greater perceived importance due to land values based
on visual appeal of real estate.
Traditional landscaping solutions have often been used. Drip irrigated landscape container
plantings and transplanting are relatively expensive often running in excess of $30,000.00 per acre.
Using small containerized plants Bainbridge, et. al. (1995) reported planting costs alone of $0.50
to $3.00 per plant. This was for installation only not indicating plant costs or irrigation and
subsequent management costs. Direct seeding is much less costly. A greater density and variety
of plants can be realized for less than 1/10 the cost of containerized plants.
1
Western Sod/Western Sere, Casa Grande, Arizona.
297
Species Use
Until very recently there has been resistance to the use of native species. It was believed that
native species primarily grasses were difficult or impossible to establish. Cox, et. al. (1982)
reviewed the history and literature of revegetation activities in the Chihuahua and Sonoran Deserts.
Most research focused on restoring grasses, not necessarily native grasses, to overgrazed ranges to
promote livestock production. Treatments were typically minimal because of the large land areas
which were degraded. Less regard was given to other entities such as floral and faunal diversity.
Seeding failures were common. Introduced exotic grasses such as Lehmanns lovegrass, Eragrostis
lehmanniana, and bufflegrass, Pennisetum ciliare appeared to give easier initial success prompting
their extensive use. Roundy, (1995) in a review of G.L. Jordan's revegetation work indicates that
Jordan stopped testing natives not only because of failure but likely also because of the lack of
quality native seed. It is probable that other researchers had difficulty obtaining quality native site
specific seed.
Even though Cox, et. al. (1982) recognized success of eighty-three species their conclusion was
that only fourteen should warrant general use. This included 11 non-native species. Their
widespread use is considered to be ecologically detrimental (D'Antonio and Vitonsek, 1992).
Typically differing from past projects is the use of a relatively high variety of native species
combined with good soil surface modification. It appears that this "shotgun" approach to species
use particularly suits many of these arid lands due to the unpredictability of environmental factors
such as weather and the resultant dynamic plant communities as elucidated by Burgess (1995).
Although other factors resulting in success may be attributed to using diverse seed mixes. Miller,
et. al. (1983) showed that mycorrhizal colonization was more likely to occur with interspecific
associations. This may give greater long term success.
The southwestern deserts and desert grasslands have a wide variety of plant communities.
Many diverse species are found here on many diverse soils. Some of the grasses found here are
grasses usually associated with prairies such as plains bristle grass, Setaria macrostachya, and side
oats grama, Bouteloua curtipendula. These are likely arid-adapted ecotypes. Other species are
more specialized desert types found in unique habitats such as big galleta, Hilaria rigida, often
associated with sandy desert areas such as dunes. This high diversity makes for a great selection
of species for revegetation. Table 1 shows the variety of species commercially available for seeding
use in desert grassland areas of Arizona. Most of these species have been used with a high degree
of success in revegetation seeding since the mid 1980's.
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Grasses
Side oats grama, Bouteloua curtipendula
Blue grama, Bouteloua gracilis
Squirrel tail, Sitanion hystrix
Purple three awn, Aristida purpurea
Green sprangletop, Leptochloa dubia
Plains lovegrass, Eragrostis intermedia
Curly mesquite, Hilaria belangeri
Sand dropseed, Sporobolus cryptandrus
Plains bristle grass, Setaria macrostachya
Vine mesquite, Panicum obtusum
Alkali sacaton, Sporobolus airoides
Arizona cottontop, Trichachne califomica
Tangle head, Heteropogon contortus
Indian ricegrass, Oryzopsis hymenoides
Forbs
Firewheels, Gallarciia pu/chella
Prairie aster, Machaeranthera tanacetifolia
Mexican poppy, Escholtzia mexicana
Firecracker penstemon, Penstemon eatonii
Sonoran penstemon, Penstemon parryi
Palmer penstemon, Penstemon palmeri
Desert globemallow, Sphaeralcea ambigua
Desert marigold, Baileya multiradiata
Shrubs & Trees
Four wing saltbush, Atrip/ex canescens
Apache plume, Fallugia paradoxa
Squawbush sumac, Rhus trilobata
Wait-a-minute bush, Mimosa biuncifera
Cat claw acacia, Acacia greggii
White thorn acacia, Acacia constricta
Velvet mesquite, Prosopis velutina
Desert willow, Chi/opsis /inearis
Table 1
ARIZONA NATIVE SPECIES FOR ELEVATION OF 3,500' - 5,500'
A greater probability of success can be attained when certain technologies are used in dryland
revegetation seedings. Three basic phases should be considered; 1) site/soil preparation, 2)
seeding, 3) surface mulching. All three done with specific techniques and materials will interact to
give a greater probability of success.
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Soil Preparation
Soil properties such as erosiveness, compaction, surface roughness, structure, fertility, and
water capture and retention capacity can be modified to increase plant establishment and growth.
These factors are often interacting and can be significant determinates in plant establishment. The
effect of good soil preparation techniques prior to seeding has been well documented. Soil surface
modifications to relieve compaction, reduce runoff, and capture and retain moisture is generally
considered to be of benefit to plant establishment (Verma and Thames 1978, Packer & Aldan,
1978, Wright, et. al. 1978). Most projects we have worked on show a marked increase in plant
establishment and growth when contour ripping is done. This simple technique can be
accomplished with widely available equipment. A minimum of four inches depth of ripping on 1020 inch centers is recommended. On steeper slopes or more heavily compacted sites, crawler
tractors are employed. The resultant roughened or furrowed surface helps to stabilize the surface,
reduce runoff and infiltrate moisture. Ripping also provides an improved environment for root
growth. Soil should not be pulverized with discs or rototillers.
In general, very little is known on the mineral nutrient requirements of native arid land species.
Standards for soil fertility testing in the arid southwest are based on land used for agricultural crops
such as cotton. Native drought tolerant species likely utilize nutrients very differently compared to
field crops. Interacting effects of microbial symbioses further complicate the picture. However, it is
well known that arid land soils are typically deficient in nitrogen and available phosphorus (Bauer,
et. al. 1978). Subsoils and drastically disturbed sites are even lower in these nutrients. We have
noticed a great benefit to plant growth by the supplementing of these nutrients. It is common
practice to add 200 to 400 lbs per acre of ammonium phosphate (16-20-0) preferably tilled into
the soil during tillage. It appears that supplements of organic soil conditioners such as compost
high in humus compounds are also of benefit. However, because of complicated interactions,
especially regarding soil microbes, an accurate identification of what is happening remains elusive.
It has been shown that mycorrhizal fungi improve plant survival (Miller, 1987). However,
commercially available mycorrhizal symboints for practical addition to revegetation projects have
been restricted to container plantings until recently. We have established many species without the
artificial addition of microbe symbionts.
If inoculation is occurring on these sites, it may be that symbionts such as mycorrhizal fungi are
occurring naturally by wind (Warner, et. al. 1987), or as spores in organic residue during the
addition of organic matters applied as surface mulching. Supplementing a site with chemical
fertilizer may allow for initial growth of desirable species until natural symbiosis can occur.
However, St. Johns, (1987), suggests that chemical fertilizer strongly favors weeds and the
resultant detrimental competition limits establishment of desirable later successional species. He
suggest a method of anti-fertilization whereby carbon:nitrogen ratios are increased thereby,
reducing nutrient availability by microbes resulting in less nutrient availability for weed growth. We
have never tried anti-fertilization on our projects, but it could be a solution on sites heavily infested
with the non-mycorrhizal Russian thistle, Sa/so/a spp. or wild mustards, Brassica spp., Sysimborum
spp. among others.
Nutrient modification is likely occuring with the addition of high carbon mulches, such as straw
and wood fiber. It is recommended that drastically disturbed sites be prepared and seeded before
weedy species can colonize. This is one reason we feel that newly disturbed sites should typically
not be left fallow anticipating a preferred seeding season.
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Seeding Methods
The objective is to place seed in a stable environment conducive to germination and
emergence. A stable environment is one in which soil movement is limited, in which rainfall will not
wash the seed away, in which wind will not blow the seed away, and in which moisture and
temperature variations are relatively low. Birds, insects, and other animals should not have easy
access to the seeds. An environment conducive to germination and emergence is one that retains
available moisture, that does not form a hard, crusted surface, and that allows relatively low
fluctuations in moisture and temperature. Most of the revegetation seeding being done now in
Arizona employs hydroseeders. The hydroseeder is very versatile and can far exceed the limitations
of drill or dry broadcast seeding.
The hydroseed slurry, if composed of specific types and quantities of materials and sprayed over
well prepared roughened sites with loose surface soil, meets many of the criteria that define a
stable environment conducive to germination and emergence. The slurry sprayed over loose soil
combines mulch and soil to a depth of one-half inch. This mulch/soil layer is resistant to erosion.
If quality materials are used, it will move very little with rainfall and virtually not at all with wind.
Tackifiers are used in the slurry as adhesives to increase the mulch's resistance to erosion. Birds,
insects, and other wildlife have difficulty finding and removing the seed. The mulch material
reduces surface crusting caused by rainfall impaction. Moisture softens the mulch/soil layer,
allowing water percolation and seeding emergence. Seed placement is excellent, in that the
surface soil/mulch layer meets the depth requirement for nearly all desert seeds.
The basic materials used in hydroseeding, other than seed, are mulch, tackifier, and fertilizers.
Mulch materials produced solely for the hydroseed industry are highly engineered; some are
more effective than others. Among the better hydromulches are wood fibers from the byproduct
wood chips of the lumber industry. Other materials, such as waste paper, sawdust, wood shaving,
and grass clippings, have proven to be only about sixty percent as effective in creating a
germination environment. Waste paper tends to flatten, wash out, and compact; the other types in
this group lack integrity and wash out easily.
Tackifiers, too, come in a wide range of material types. Some have very effective adhesive and
cohesive qualities. Two of the better materials are plantago mucilage and guar-based mucilage.
Plantago mucilage is derived from the Indian wheat, Plantago insularis. It is a powder that, when
mixed with water, forms a sticky, gel-like glue. Tackifiers should be applied to impart good binding
characteristics to the slurry as it sets up.
Surface Mulching
Many studies have shown that surface mulching increases soil moisture, and stabilizes the soil
temperature. Kay (1978, 1987), compared the effectiveness of a variety of surface mulching
materials in terms of temporary erosion control and eventual plant establishment.
Hydromulch used in the seeding process is considered a surface mulch. Hydromulch is in
intimate contact with the soil and seed. This is of definite benefit to seed germination but of less
benefit in modifying moisture and temperature fluctuation in the soil profile. Hydromulch, therefore,
is very good for germination but less so for seedling establishment. During the cool season,
hydromulch used as the sole mulch material generally gives as good a result in terms of seedling
establishment as straw mulch. Added quality grade tackifiers greatly improve effectiveness. Used
together, hydromulch and straw mulch give an excellent combination of erosion control and
301
germination and seedling establishment. It is one of the most cost effective techniques.
Long lived stands of diverse native species have been established using good tillage, diverse
site specific seedmixes, and well affixed surface mulching of hydromulch and/or straw mulch. Table
2 lists a seed mix which was used employing some of the techniques outlined here establishing
native vegetation along a pipeline corridor where surface soils were drastically altered. After
pipeline construction, ammonium phosphate (16-20-0) was broadcast at 200 lbs/Acre. The site
was tilled with crawler tractors leaving a roughened furrowed surface. Seed was immediately
broadcast. Straw mulch was applied at 2 tons per acre and crimped on 8 inch centers. Today the
site is dominated by the species which were seeded. The stand appears as dense as adjacent
natural undisturbed areas.
With improved methods and materials and attention to detail, many disturbed sites have been
dryland seeded using native species with a long term measure of success. The costs are very low
compared with landscaping solutions but higher compared with most past attempts at restoring
desert grassland.
Species
PLS rate lbs/Acre
Grasses
Side oats grama, Bouteloua curtipendula
Blue grama, Bouteloua gracilis
Green sprangletop, Leptochloa dubia
Plains lovegrass, Eragrostis intermedia
Sand dropseed, Sporobolus cryptandrus
Plains bristle grass, Setaria macrostachya
3.0
1.0
3.0
1.0
1.0
3.0
Shrubs
Four wing saltbush, Atriplex canescens
Apache plume, Fal/ugia paradoxa
White thorn acacia, Acacia constricta
Cat claw acacia, Acacia gregg;;
Velvet mesquite, Prosopis velutina
3.0
1.0
1.0
2.0
1.0
Forbs
Sagewort, Artemisia ludoviciana
Desert globemallow, Sphaeralcea ambigua
1.0
1.0
Table 2
MULESHOE RANCH SEEDMIX (Seeded -August, 1986)
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