Abstract —From 1963 to 1973, Gilbert L. Jordan at the University of Arizona conducted numerous native and exotic grass revegetation trials at four sites in central and southeastern Arizona.
Lehmann lovegrass A68 initially established best. Initial establishment was highest for most species from broadcast sowing in
March after rootplowing and pitting. Grasses did not persist at the Congress and Pima sites and density of species decreased substantially at the Bowie and San Simon sites 12 to 15 years after sowing. Revegetation projects on arid and semiarid grass/ shrublands should be evaluated over time to determine which species are adapted to persist under the long-term climatic conditions of the site.
Over the last part of the 1800’s and the first half of the
1900’s, grasses decreased and woody plants increased on desert grassland in the southwestern United States and northern Mexico. Early recognition of the loss of grass by scientists and stockmen led to an interest in developing appropriate range management practices, including grazing management, brush control, and revegetation to restore the grass. Numerous field trials were conducted to determine successful species to seed and to develop techniques to control undesirable vegetation and to catch and hold rainwater for improved revegetation (Roundy and
Biedenbender, in press).
Erosion associated with cultivation and abandonment and with uncontrolled grazing of semiarid and arid lands led to the development of a strong national consciousness for soil conservation. Scientists and others sought innovative approaches and possible “miracle plants” to successfully revegetate severely eroding watersheds.
In the Southwest, exotic lovegrasses ( Eragrostis spp.), especially Lehmann lovegrass ( E. lehmanniana ), showed great promise for revegetation of desert grassland sites
(Crider 1945). In the 1940’s Lytle Adams, a retired dentist and inventor-aviator, proposed reseeding western rangelands by broadcasting pelleted seeds from airplanes
(Roundy and Biedenbender, in press). This inexpensive approach to revegetation occurred to him in southern
In: Roundy, Bruce A.; McArthur, E. Durant; Haley, Jennifer S.; Mann,
David K., comps. 1995. Proceedings: wildland shrub and arid land restoration symposium; 1993 October 19-21; Las Vegas, NV. Gen. Tech.
Rep. INT-GTR-315. Ogden, UT: U.S. Department of Agriculture, Forest
Service, Intermountain Research Station.
Bruce A. Roundy was Associate Professor of Range Management at the
School of Renewable Natural Resources, University of Arizona, Tucson, at the time of the research. Roundy is currently Professor, Department of
Botany and Range Science, Brigham Young University, Provo, UT.
California, where he had observed small cactus plants spring up from rabbit droppings. In 1945, he interested
Congress in the idea of aerially distributing pelleted seed.
The idea was that seed could be compressed in earthen pellets with fertilizers, fungicides, and insect and rodent repellents. The weight of the pellets would allow even distribution and penetration into the soil from inexpensive aerial seeding (Jordan 1967).
This idea was appealing compared to the alternate methods of broadcasting seeds without pellets, where success was usually limited by lack of soil coverage, or mechanical seedbed preparation and sowing on the ground, which was slow and expensive considering the large acreages involved. Dr. and Mrs. Adams actively promoted the pelleted seeding program at the local and national level.
Mrs. Adams made hats with Lehmann lovegrass and devil’s claw ( Proboscidea spp.), which she presented to such prominent ladies as Mrs. Morris Udall and
Jacqueline Kennedy.
Pelleted seeding research was conducted in many western states from 1945 into the 1960’s (Hull and others 1963;
Jordan 1967). At the University of Arizona, Gilbert L.
Jordan began what was to become over 20 years of intensive, field-oriented, revegetation research by conducting pelleted seeding studies.
Jordan’s (1967) findings on a Chihuahuan desert shrub site were similar to those of other studies. Pelleted seeding produced similar or less establishment than aerially broadcasting non-pelleted seed. Mechanical seedbed preparation and sowing on the ground produced successful stands of lovegrass while pelleted seeding did not, even in years with favorable precipitation. Pelleted seeding failed partly due to a decrease in germination associated with the pelleting process (Jordan 1967). When
Adam’s advocate in Congress, Representative Ben F.
Jensen from Iowa, learned that pelleted seed research money had been used to make comparisons with other methods, he accused the University of Arizona of sabotaging the program. The pelleted seeding story is interesting because it shows the interest and concern at the local and national level in revegetating the range, and it demonstrates the need to do careful comparative research to test apparently easy solutions.
It is also interesting to note the unquestioned acceptance of introduced species, at this period in time, and that the main controversy was how, not what to seed. For Jordan and many others, it forcefully demonstrated that reseeding of lower elevational desert grassland/shrubland sites required appropriate seedbed preparation.
Appropriate seedbed preparation should be designed to increase water availability to seeds and seedlings by
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controlling competing species, covering seeds at a shallow depth, and creating depressions to catch and hold water from intense thundershowers (Roundy and Call 1988).
After the pelleted seeding studies, Jordan conducted revegetation research from 1963 to 1973 on species, seedbed preparation, and sowing methods on former desert grassland and desert shrubland sites in the San Simon and
Gila Valleys, as well as near the base of the Date Creek
Mountains near Congress, Arizona, and on the Arizona
Strip. The primary objective in southeastern Arizona was to determine successful revegetation techniques for rehabilitating the badly eroded San Simon watershed (Jordan and Maynard 1970a,b). The seeding sites are transitional between the Sonoran and Chihuahuan deserts and averaged about 250 mm annual precipitation (Table 1). Funded by the Bureau of Land Management (BLM), Jordan’s studies were representative of an extensive approach to revegetation research. He tested chemical and mechanical means of brush control and seeding techniques: seeding in fall, late spring, or summer, drilling versus broadcasting seeds, seeding at different rates, and treating seeds with fungicides. He tested at least 14 species of native grasses and seven exotic grasses, as well as a number of exotic experimental selections developed by L. Neal
Wright of the Agricultural Research Service. At the peak of his research activity, Jordan was annually seeding dozens of plots on five different sites, as well as evaluating density and forage yield of hundreds of plots from previous years. He did this for 10 years, often with a small field crew, which included a series of student employees.
He also faithfully produced annual reports documenting his progress for the BLM. The current study summarizes findings from this exhaustive revegetation research effort and analyzes the long-term success of techniques and plant materials tested by Dr. Jordan.
Characteristics for the San Simon, Bowie, and Pima sites are shown in Table 1 (Roundy and Jordan 1988).
The Congress site is approximately 21 km west of the town of Congress at the base of the Date Creek Range in west-central Arizona. Soils are deep sandy loams. Average annual precipitation is 257 mm, elevation is 914 m, and dominant vegetation includes mesquite ( Prosopis juliflora) , creosotebush ( Larrea tridentata ), Joshua tree
( Yucca brevifolia ), and wolfberry ( Lycium californicum ).
The Pima, Bowie, and San Simon sites are transitional between the Sonoran and Chihuahuan Deserts (Cox and others 1982). Summer precipitation, often as intense thundershowers, is 50 to 60% of the total annual precipitation on these sites.
Revegetation trials from 1963 through 1973 on these sites focused primarily on various methods of mechanical brush control (discing and rootplowing), seedbed preparation (roller, furrow, and disc pitting), sowing methods
(broadcasting, drilling), sowing time (March, June), sowing rate (1, 1.5, and 2 times the standard sowing rate of
1.2 million seeds per ha), and plant materials (Table 2).
Root plowing was generally at a 35 to 55 cm depth and pits were generally less than 20 to 30 cm deep. Experimental design was a randomized block, with generally three to four replications per treatment. Individual plots ranged from 10 to 30 m wide and 30 to 60 m long. Density and dry matter yield of seeded species the year of seeding and 2 to 4 years later were recorded in 10 to 20,
0.3- by 1.5-m quadrats randomly placed along the diagonal of each replication. Density of plants seeded in 1969 through 1972 were recorded 12 to 15 years later in 1984 in two belt transects, 2 m wide by 30 m long in each replication. Basal cover of seeded species was estimated in
1984 by measuring basal diameter of five plants per belt transect. Mean basal area was calculated using the formula for the area of a circle and multiplied by mean plant density to give a total plot basal area. This was divided by total plot area to give an estimated basal cover percentage. Analysis of variance was used to determine significant treatment and species differences (P ≤ 0.05) for different years. Results are based on Jordan’s progress reports and on 1984 persistence data.
Table 1 —Characteristics of three sites where Gilbert L. Jordan conducted revegetation studies in southeastern Arizona ( Roundy and Jordan 1988).
Location
Elevation (m)
Mean annual temperature ( ° C)
Average percipitation 1968-1984 (mm)
Winter (November-March)
Summer (July-October)
Total annual
25km SW San Simon
1,230
17
72
152
248
Study site
13 km NE Bowie
1,080
17
100
160
284
11 km NW Pima
990
17
79
137
222
Dominant vegetation Larrea tridentata
Soils
Flourensia cernua , Prosopis juliflora var.
glandulosa,
Larrea tridentata,
Gutierrezia sarothrae
Eba gravelly sandy loam, mixed, thermic Typic
Haplarids (Vogt 1980)
Dona Ana fine-loamy, mixed, thermic Typic
Haplargids (Vogt 1980)
Prosopis juliflora var. glandulosa,
Haplopappus tenuisectus
Sandy loam to loamy sand
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T able 2 —Names and symbols of some of the grass species sown in revegetation trials by Gilbert Jordan in southern Arizona.
Symbol Common name Scientific name
A68
L11
L19
L28
L38
A84
ERAT
CAT
BOIS
SEMA
PAAN
ERSU
SPCR
BOCU
Lehmann lovegrass
Lehmann lovegrass
Lehmann lovegrass
Lehmann lovegrass
Lehmann lovegrass
Boer lovegrass
Cochise lovegrass
Catalina Boer lovegrass
Yellow bluestem
Plains bristlegrass
Blue panic
Wilman lovegrass
Sand dropseed
Sideoats grama
Eragrostis lehmanniana
E. lehmanniana
E. lehmanniana
E. lehmanniana
E. lehmanniana
E. curvula var.
E. lehmanniana
trichophora conferta
x E.
E. curvula var. conferta
Bothriochloa ischaemum
Setaria macrostachya
Panicum antidotale
E. superba
Sporobolus cryptandrus
Bouteloua curtipendula at San Simon, Pima, and Bowie. However, established plant densities measured 12 to 13 years after initial sowing were similar for different sowing rates (Fig. 2).
Summer precipitation for this area of the Southwest is highly variable from year to year (Cox and Jordan 1983).
Also, the pattern of rainfall in time and space within a given summer rainy season is highly variable (Osborn
Rootplowing in March, pitting and broadcasting grass seeds into disturbed seedbeds was the most effective revegetation method, especially for small-seeded lovegrasses.
Not only did rootplowing effectively control the woody species, but it also loosened the soil, increased infiltration, and helped bury seeds broadcast after plowing. Jordan built a Nisbet rotary shaft seeder to permit controlled sowing rates of small-seeded species with the rangeland drill, but broadcasting into a disturbed seedbed produced similar emergence as drilling. Jordan considered that seeding in March was better than seeding in June because the small amount of residual moisture in the soil helped retain soil structure during rootplowing. Jordan concluded that pitting generally increased stand density and yield from 20 to 25% over nonpitted seedbeds and could prevent seeding failure on some sites once in every five seedings. He observed that the value of pitting for catching and holding water from intense summer thundershowers was additive to the benefits of rootplowing. Consequently, Jordan built a disc pitter that could be attached behind a rootplow to permit plowing, pitting, and broadcast sowing in one pass.
For the years 1969 and 1970, pitting increased initial density of all sown grasses at San Simon, Pima, and Bowie, but density 14 to 15 years later was generally similar on pitted and unpitted seedbeds (Fig. 1). For the small-seeded
Lehmann lovegrass, pitting increased initial density on only one out of eight site-years for which data were available for the San Simon, Pima, and Bowie sites between
1969 and 1972. Pitting did not increase persistence of
Lehmann lovegrass for any sites or years measured.
Higher sowing rates increased initial seedling density on three of seven site-years tested between 1970 and 1972
Figure 1 —Density of warm-season grasses seeded on pitted and unpitted seedbeds near
San Simon, Arizona. Densities are significantly different (P ≤ 0.05) for pitted and unpitted treatments for all years sampled except at 15 years since seeding.
Figure 2 —Density of warm-season grasses seeded at various rates near Bowie, Arizona.
Densities are significantly different (P ≤ 0.05) among rates only during the year of sowing.
Rates are 1, 1.5, and 2 times the standard rate of 1.2 million seeds per hectare.
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Figure 3 —Initial seedling density of Lehmann lovegrass sown at four sites in central (Congress) and southeastern Arizona in relation to total summer precipitation.
1983). Lehmann lovegrass A68 had consistently higher establishment than other plant materials. However, its initial establishment varied greatly with total precipitation in July through August or July through September
(Fig. 3). Although there is a general correlation of increased initial seedling density with increased precipitation, this correlation varied among sites and did not hold for some sites and years (Fig. 3). For example, initial establishment at San Simon was much higher in 1968 and
1969 than in 1966 and 1972, even though total summer precipitation was similar for these years. Initial rainfall followed by a 10- to 15-day dry period may have germinated but later desiccated seedlings in 1966 and 1972.
In the initial years of his studies, Jordan evaluated a number of native grasses. On exceptionally wet years he observed successful establishment of a number of grama grasses—blue, black, hairy, and sideoats grama ( Bouteloua gracilis , B. eriopoda , B. hirsuta , and B. curtipendula ), as well as other natives such as spike and sand dropseed
( Sporobolus contractus , S. cryptandrus ). However, since the introduced lovegrasses established more consistently from year to year, and at higher densities, he quit testing most native grasses by 1970. Perhaps it was also difficult for him to obtain quality native grass seeds. Jordan suggested that plains bristlegrass ( Setaria macrostachya ) had the highest potential of the native grasses to establish, but that most native grasses adapted to the San Simon area, for example, would establish only once in 10 years.
Due to lack of initial establishment and persistence,
Jordan quit seeding the Congress site after 1966. He felt that lack of summer precipitation (40% of annual precipitation) limited potential for revegetation of this site. Jordan
(1983) later developed a method of using average annual temperature, seasonality of precipitation, and total annual precipitation to describe the boundary between arid and semiarid, with arid sites not being suitable for revegetation.
Seedling establishment and persistence varied among sites. Seedlings initially established at high densities at the Pima site, but little persistence was observed by 1984.
Seedlings initially established at generally similar densities at the San Simon and Bowie sites, depending on the year, but persisted better at San Simon (Figs. 4 and 5).
Lehmann lovegrass A68 consistently established at higher densities than the other grass species, including droughttolerant Lehmann lovegrass selections of Neil Wright of the Agricultural Research Service (L-11, L-19, L-28, L-38).
All species and selections decreased substantially in density over time (Figs. 4 and 5). These decreases occurred in
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Figure 4 —Density of warm-season grasses sown near Bowie, Arizona.
Species names for legend symbols are in Table 2. Numbers indicate
LSD (P ≤ 0.05) for a given year since seeding.

Figure 5—Density of warm-season grasses sown near San Simon, Arizona. Species names for legend symbols are in Table 2.
Numbers indicate LSD (P ≤ 0.05) for a given year since seeding.
the absence of cattle grazing, since the original exclosures were still functional during the 1984 evaluations. Plant density varied more among species at initial establishment than 12 to 15 years later. Decreases in forage yield
12 to 13 years after seeding at San Simon indicate that revegetation for increased livestock production may not be economical (Cox and Jordan 1983). However, in some cases, grass basal cover persistence may justify revegetation for watershed protection. Grass basal cover of some seeded areas at San Simon was still high (up to 19% on some plots) and seeded species had spread to adjacent small arroyos by 1984.
Lehmann lovegrass A68 had greater persistence in terms of density than all other species at Bowie while A84
Boer lovegrass ( E. curvula var. conferta ) had greatest persistence at San Simon (Fig. 6). In terms of basal cover, blue panic ( Panicum antidotale ) had highest persistence at Bowie (Fig. 7). Seedings at Congress, Pima, and on the creosotebush site at Bowie would be considered failures after 12 to 15 years, while some seedings at San Simon could be considered successful, but not necessarily profitable. Seedings on a sand dune mesquite ( Prosopis juliflora var. glandulosa ) site at Bowie also had high persistence, but were not evaluated in 1984 due to difficulty in determining plot borders.
Rootplowed and seeded plots with limited grass persistence at Bowie were relatively bare, while those at Pima and San Simon were dominated by burroweed ( Haplopappus tenuisectus ) and snakeweed ( Gutierrezia sarothrae ), respectively, in 1985 (Roundy and Jordan 1988). Native grasses such as bush muhly ( Muhlenbergia porteri ) occur at very low densities at these sites and have not invaded rootplowed and seeded areas. The paradox of this is that bush muhly is adapted to persist on these sites but rarely establishes new plants.
Some important lessons learned from this exhaustive field research are:
• Initially successful revegetation in summer rainfall areas doesn’t necessarily indicate long-term success. It’s important to evaluate persistence in revegetation studies overtime;
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Figure 6 —Mean density in 1984 of warmseason grasses sown during 1969-1972 near Bowie and San Simon, Arizona. Species names for symbols are in Table 2.
Species are ordered from highest to lowest mean rank (left to right) over the 4 seeding years. Similar letters above bars indicate no significant difference (P ≤ 0.05).

Figure 7 —Mean basal cover in 1984 of warmseason grasses sown during 1969-1972 near
Bowie and San Simon, Arizona. Species names for symbols are in Table 2. Species are ordered from highest to lowest mean rank (left to right) over the 4 seeding years. Similar letters above bars indicate no significant difference (P ≤ 0.05).
• Native grasses are more difficult to establish on these sites than exotic grasses, but some natives might persist better than exotics on certain sites;
• Conversion of semiarid and arid shrublands back to grasslands is difficult.
Perhaps we should consider revegetation with desirable shrubs to control erosion and provide forage on these lands.
At any rate, we should remember and honor Gilbert L.
Jordan for conducting one of the most extensive and intensive revegetation research projects in the West.
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