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U. S. Forest Service
Research Paper RM- 22 )

THE SANTA RITA EXPERIMENTAL RANGE

A Center for Research on Improvement and
Management of Semidesert Rangelands y

DEC 161S

by S. Clark Martin

\a Ljj - i. , jrj& .

COOPERATORS

Many agencies and individuals cooperate in
conducting research on the Santa Rita Exper-
imental Range. Among those currently in-
volved are:

The University of Arizona
Agricultural Research Service
Soil Conservation Service
Bureau of Sport Fisheries and Wildlife
Arizona Department of Game and Fish
Keith S. Brown
H. H. Robinson
Feliz Ruelas

U. S. Forest Service Research Paper RM-22 1966

THE SANTA RITA EXPERIMENTAL RANGE >

- <=. J

& Center for Research on Improvement and
Management of Semidesert Rangelands^,

2 by
S. Clark Martin, Principal Range Scientist
Rocky Mountain Forest and Range Experiment Station1

1 Central headquarters maintained in cooperation with Colorado State
University at Fort Collins; author is located at Tucson in cooperation
with the University of Arizona.

CONTENTS

Page

DESCRIPTION OF THE RANGE . 1

Climate 1

Vegetation 3

RESEARCH 4

Forage Production 5

Grazing Management 9

Mesquite Growth « 13

Mesquite Control 16

jumping Cholla 20

Burroweed 21

Range Reseeding . . 22

Rodents and Rabbits . 2 3

EDUCATIONAL OPPORTUNITIES . 24

COMMON AND SCIENTIFIC NAMES USED ...... 24

THE SANTA RITA EXPERIMENTAL RANGE

A Center for Research on Improvement and
Management of Semidesert Rangeiands

S. Clark Martin

DESCRIPTION OF THE RANGE

The Santa Rita Experimental Range, 30
miles south of Tucson, Arizona is maintained
by the Forest Service, U.S. Department of
Agriculture, for research on semidesert ranges
grazed by cattle. The 50, 000-acre Experimen-
tal Range, established in 1903, is representa-
tive of about 20 million acres of semidesert
grass-shrub range in southern Arizona, New
Mexico, and Texas (fig. 1). Research is con-
ducted in cooperation with State and other
Federal agencies, and with cooperating cattle-
men.

The Range lies on a broad, sloping plain
cut by many shallow, dry washes. The eleva-
tion rises from less than 2,900 feet at the north-
west corner to over 4,500 feet along the
foothills of the Santa Rita Mountains.

CLIMATE

Average yearly rainfall increases with ele-
vation from 10 inches at 2,900 feet to almost
20 inches at 4,300 feet (fig. 2). About 60
percent of the rain comes between July 1 and
September 30 (fig. 3). No effective rainfall
is expected in April, May, or June.

ARIZONA

Santa Rita
Experimental Range

NEW MEXICO

OKLAHOMA

TEXAS

SEMIDESERT RANGE

Figure 1. — General distribution of the semidesert area with
range sites or conditions similar to those on the Santa
Rita Experimental Range.

- 1 -

Figure 3 . —Monthly -gve-

- 2 -

100

^80

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MEAN MAXIMUM

Figure 4. — Average daily maxi-
mum and minimum temperatures
by months at the Santa Rita
MEAN MINIMUM Experimental Range Head-
quarters.

Oct Nc^

Dec

Jan Feb

Mar

Apr May Jun

Jul

Aug Sep

Average daily maximum temperatures at
the Range headquarters exceed 90° F. in June
and July. Daily mimimum temperatures aver-
age below 40° F. in December, January, and
February (fig. 4). The frost-free period is about
8 months, but growth of herbaceous plants
usually is limited by lack of moisture to about
8 weeks.

20,

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VEGETATION

The perennial vegetation is dominated by
mesquite,2 cactus, and other shrubs. Mesquite,
burroweed, and cholla cactus reach their high-
est average densities between 3,200 and 3,600
feet elevation(fig. 5); mesquite andpricklypear
cactus are major species even above 4,000
feet. Other shrubs, including Acacia, Mimosa,
and Calliandra, make up only 21 percent of
the shrub cover below 3,200 feet but comprise
65 percent of the shrub cover above 4,000
feet.

^Common and scientific names of plants
mentioned are listed on page 24.

Figure 5. — Crown cover of major shrub
species and total shrub cover as a
function of elevation.

< 3200

3200-
3600

3600-
4000

4000-
4400

ELEVATION (FEET)

- 3 -

The abundance of perennial grasses in-
creases with rainfall and elevation (fig. 6). The
species composition of the perennial grass
stand also changes with elevation and rainfall.
The tall three-awns are common at all eleva-
tions (fig. 7). Santa Rita three-awn, Arizona
cottontop, and Rothrock grama are major
species at the middle and lower elevations but
are minor species above 4,000 feet. Bush
muhly makes up a greater part of the grass
stand at the lower than at the middle eleva-
tions, and is scarce at the upper elevations.
Other gramas including black, side-oats,
slender, sprucetop, and hairy, make up over
60 percent of the stand at the upper eleva-
tions and are relatively scarce at the middle
and lower elevations.

RESEARCH

The objective is to learn how to attain
maximum sustained forage and beef produc-
tion on semidesert range with reasonable costs.
The research program includes many kinds of
studies. Most important of all is research to '
develop grazing practices that meet the long-
time needs of the forage plants and the soil,
as well as the immediate needs of the cattle
and the rancher. Detailed studies of the growth
requirements of desirable and undesirable
range plants and their reactions to various
kinds of grazing, climate, and soil are basic.
Learning how to improve rundown ranges
rapidly and economically by controlling un-
wanted plants, reseeding, or other cultural
practices is another important area of re-
search.

The Federal government owns the land and
improvements; cattle for grazing experiments
are furnished by private ranchers operating
under cooperative agreements. The cattlemen
furnish the kind, number, and class of cattle
needed, and manage them according to a
written management plan. Under this arrange-
ment, grazing studies are carried out on a
practical scale, thereby eliminating the need
for pilot testing.

Figure 6. —

Vegetation on the Santa Rita
Experimental Range at:

Upper elevation

Intermediate elevation Lower elevation

FORAGE PRODUCTION

Rainfall during both summer and winter
makes possible two growth periods— a minor
one during early spring when temperatures
become favorable, and the major one during
summer when rains begin after the late spring
drought. Perennial grasses, browse, and an-
nuals each react to this climate with their
own characteristic growth pattern.

Perennial grasses are the most reliable
forage. Most begin growth soon after the start
of summer rains, and grow rapidly as long as
effective rains continue. Growth rarely starts
before July 1 and usually stops before Septem-
ber 30. In favorable years, some grasses also
produce a little growth intermittently from
February through June. However, more than
90 percent of perennial-grass growth is pro-
duced after summer rains begin. Height growth
of flower stalks of Rothrock grama, slender
grama, and Arizona cottontop illustrate the
rapid growth during the brief summer growing

period (fig. 8). Perennial grass production
increases with increasing elevation and rain-
fall, as would be expected (fig. 9).

14 28 11 25 8 22

JULY AUGUST SEPTEMBER

Figure 8.— Height growth of flower stalks of
slender grama, Rothrock grama 3 and Arizona
cottontop during 1 summer on the Santa Rita
Experimental Range.

- 5 -

Figure 9. — Perennial grass production is greater at the higher elevations:

On brushy 3 low-rainfalls low-elevation parts
of the range 3 perennial grass yields less
than 20 pounds of herbage per acre.

Annual grasses produce 80 percent of
the grass herbage on brushy, low-
rainfall ranges

At the higher elevation where the rainfall
is greater and the brush has been removed^
perennial grasses produce almost 450 pounds
of herbage per acre.

Perennial grasses produce 70 percent
of the grass herbage on mesquite-free
ranges where annual rainfall is 16 inches

Grass production fluctuates extremely from
year to year on brushy, low-rainfall range
(fig. 10). Here, perennial grass yields may
average less than 20 pounds per acre. Still,
the perennial grasses are more stable than the
annuals, which may produce several hundred
pounds of herbage in a wet year and nothing
at all in a year of drought (fig. 11).

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Annual grasses
Perennial grasses

Year-to-year fluctuations in forage produc-
tion are marked at the upper elevations, but
substantial amounts of forage are produced
even in the poorest years (fig. 12). Average
annual perennial grass production on the most
productive pasture on the Santa Rita was
443 pounds per acre for the 1954— 1964 period
(fig. 13), 26 times the average yield for the
least productive pasture a few miles away.
Yields of annual grasses on the best pasture
averaged only three times as great as on the
poorest pasture, but production of annual
grasses in dry years was negligible at both
locations. Some forage is obtained from mes-
quite and other browse plants on the poor
range, but perennial grasses are the key to
higher and more stable forage production on
all parts of the range.

Figure 10. — Where average annual rainfall is less
than 13 inches and the mesquite cover is heavy 3
perennial grass production averages only 17

pounds per acre. Total
grass production varies
greatly from year to
year due mainly to
changes in the yield of
annual grasses. Average
total grass production
is 89 pounds per acre.

Figure 11. — Grass yield and general
appearance in September . Year-to-
year ehanges in herbage production
are dramatic.

LOW-ELEVATION 3 LOW-RAINFALL RANGES

800,-

1 9 5 9 - -

Good summer
growing season

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1 9 6 2 - -

Exceptionally
poor summer
growing season

Cs
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400 -

Fvgwre 12.— Grass yield and general
appearance in September .Fluctuations
in yield are much less for perennial
than for annual grasses.

HIGH-ELEVATION, HIGH-RAINFALL RANGES

1600. 19 5 9

Exceptionally
good summer
growing season

Perennial
grasses

1600r

1 9 6 3 - -

Good summer
growing season

800 -

Figure IS. —

Where annua 1 ra in fa I I
averages 16 inches or
more and the mesquite
has been killed 3 aver-
age yields of perennial
grass and total grass
are 44S and 633 pounds
per acre3 respectively.
In years of low rain-
fall and low total grass
production (19563 1957 3
1960 3 and 1962) the
annual grasses produce
very little.

1956

1958

1960

1962

Grazing capacities of semidesert

range vary from 5 to 25 head per section

The number of cattle that can be supported
on semidesert grass-shrub range depends on
the basic potential of that range and its con-
dition. In the Southwest in general, rainfall
increases with elevation, so the higher eleva-
tions have a higher potential for forage produc-
tion. On the Santa Rita, ranges below 3,300
feet receive an average of 12 inches annual
rainfall or less. Those above 4,000 feet usually
receive 16 inches or more. Approximate graz-
ing capacities of the upper, middle, and lower
elevation ranges are listed in Table 1.

Table 1 . --Estimated average yearlong stocking
rates, by elevation and condition class,
Santa Rita Experimental Range

Elevation

Range condition

(Feet)

Good to
excellent

Fair to
good

Very poor

Animal units per square mile

Upper

(Above 4, 000)

20-25

15-20

< 15

Middle

(3, 300-4, 000)

15-20

10-15

< 10

Lower

(Below 3, 300)

8-10

6- 8

< 6

GRAZING MANAGEMENT

Perhaps the most persistent factor that
contributes to the improvement or decline of
semidesert ranges is the grazing use. The
season of grazing, the number of animals, and,
to some extent, the intensity and distribution
of grazing use can be controlled. Without such
control, cattle graze forage from the best forage
plants on the most accessible parts of the
range 365 days per year. The natural end
result of this process is that the most produc-
tive parts of the range eventually become the
least productive. By forcing cattle to graze
less on favorite parts of the range and more
in areas where they ordinarily would not go, a
higher percentage of the total forage crop
can be harvested without damage to the most
accessible areas. Improved grazing manage-
ment probably is the most effective and econ-
omical tool for improving the productivity of
semidesert cattle ranges.

Moderate grazing maintains
range productivity

Grazing too closely or too frequently weak-
ens perennial grass plants and cuts down seed
production. Approximate standards of proper
use developed for several important perennial
grasses on the Santa Rita are as follows:

- 9 -

Herbage removal

(Percent by weight)

Arizona cottontop 40

Bush muhly 35

Curlymesquite 40

Dropseed 35

Grama:

Black 45

Hairy 45

Rothrock 55

Side-oats 45

Slender 50

Sprucetop 40

Tanglehead 40

Three-awn 50

Wolftail 40

Cattle select the more
nutritious forage

The quality of range forage, as measured
by crude protein content, is highest during
the summer growing season and lowest during
the May-June drought. The protein content
of hand-picked grass samples usually is less
than 6 percent, except during the summer
growing season. Even so, cattle selected plants
and plant parts in such a way that the crude
protein content of their diet was 9 percent
or higher, an amount considered adequate for
range cattle, in all months but January, May,
and June (fig. 14).

20r

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10-

RUMEN SAMPLE
LEHMANN L0VEGRASS
ARIZONA COTTONTOP

About half of the grass plants should

be ungrazed at the end of the grazing year

Tests show that the percentage of plants
that remain ungrazed at the end of June can
be used to estimate the degree of utilization
(fig. 15). The stocking rate is about right if

Plants

ungrazed

(percent)

Weight of
herbage used
(percent)

Figure 15. —

Line scale showing
relationship between
■percent of plants
ungrazed and percent
of perennial grass
herbage consumed.

10-

20 —

30.

40.

50-

60.

70.

A S
196 1

F M

1962

Figure 14. —

Crude protein content
of Arizona cottontop,
Lehmann lovegrass3 and
of herbage samples taken
from steer rumens at in-
tervals of about 1 month
from May 1961 to April
1962.

80.

- 10 -

40 percent of the herbage produced by peren-
nial grasses is used each year. This level of
use has been achieved if 46 percent of the
perennial grass plants remain ungrazed when
effective summer rains introduce the new for-
age year. This level of use also leaves an
appreciable quantity of herbage on the ground
(fig. 16).

Moderate to heavy yearlong
grazing reduces number of
seedlings of taller grasses

Seedlings or sets of 11 perennial grass
species studied for 17 years became estab-
lished every year. Species were black, hairy,
side-oats, Rothrock, sprucetop, and slender
gramas, Arizona cottontop, mesa three-awn,
tanglehead, wolftail, and curlymesquite. More
seedlings of tanglehead, black grama, and
side-oats grama were established in exclosures
than on grazed areas, but the grazed areas
produced more seedlings of wolftail, Arizona
cottontop, Rothrock grama, curlymesquite,
sprucetop grama, and slender grama (fig. 17).
The number of seedlings per year on meter-
square plots ranged from 0.5 for Arizona
cottontop on ungrazed areas to 29 for Rothrock
grama on grazed plots.

Yearlong grazing shortens life

of mid-grasses, lengthens life

of grasses with dense basal foliage

Black grama, mesa three-awn, Arizona
cottontop, and sprucetop grama are long-lived

grasses, with some plants living 10 years or
more (fig. 18). Rothrock grama, with maximum
age of 5 years and average age of 1.3 years,
is the shortest lived perennial on the Santa
Rita. Except for Arizona cottontop, the species
that lived longer on grazed plots were short
grasses with mostly basal foliage. On the other
hand, the plants that lived longer under pro-
tection were mainly mid-grasses. These differ-
ences in response to grazing help explain why
the percentage of mid-grasses increases in
response to moderate to light grazing, and
decreases under heavy grazing.

Moderate stocking and alternate-
year summer deferment improve
rundown ranges

In 1954, the mesquite was killed on two
pastures and was left undisturbed on two
others. Since 1957, each pasture has been
deferred during the summer growing season
every other year and utilization of perennial
grasses has averaged around 40 percent when
measured in June. Grazing capacities have
increased on both pairs of pastures (fig. 19).
The estimated number of animal units required
to graze 40 percent of the perennial grass
crop increased by 169 percent between 1954
and 1961 on the mesquite-free pastures, an
average of 2.5 head per section per year.
Where the mesquite was alive, grazing capa-
city increased 62 percent, an average of 1.1
head per section per year during the same
period.

Figure 16. — Appearance of the range near the end of June varied with the level of use.

In 1960 3 use was moderate In 1964 3 use was heavy

(35 percent) (58 percent)

Tanglehead

Black grama

Side-oats grama

Wolftail

Hairy grama

Mesa three-awn

Arizona cottontop

Rothrock grama

Curlymesqui te

Sprucetop grama

Slender grama

^(2.9)
(3.1)

3'6.9)

^/y^// Grazed
|#ff::i:;:j Ungrazed

(6.4)

• ■ 1(6.2)

(3.1)

m (2-6)

(2.4)

Figure 17. — Average number of grass seedlings
established per year over a 17-year period
on meter-square quadrats on yearlong cattle
range and inside exelosures.

] (0.9)
(0.5)

15.7)

ITiu)

. 1(5.2)

10 20
SEEDLINGS PER SQUARE METER

30 r

— 20

1954

1956

Figure 19. — Changes in number of
animal units required to graze
40 percent of the perennial
grass crop.

1958

1960

- 12 -

Tanglehead

Black

grama

Side-oats grama

Wolftai

Hairy grama

Mesa three-awn

Arizona cottontop

Rothrock grama

Curlymesquite

Sprucetop grama

Slender grama

V////////AW

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(6)

Grazed
Ungrazed

(14)

(7)
(7)

Figure 18. — Ages of oldest plants
recorded on grazed and ungrazed
plots.

1(6)

1(13)

'///■'A--////// /,■■'// ///-/A ^

(8)

A/A/A/AA (5)

(3)

WAVAAAAAA/A7\ («)

(4)

AAAAAAAAA/AAAZ\ no)

AW^////^

4 8 12

AGE OF OLDEST PLANT (YEARS)

MESQUITE GROWTH

Mesquite now covers almost twice as much
southwestern rangeland as it did in 1900.
Where mesquite has taken over, forage produc-
tion has declined (fig. 20). Mesquite produces

some forage, but mesquite leaves and beans
will feed fewer cattle than would the grass it
crowds out. When mesquite completely re-
places perennial grasses, forage production is
reduced to less than one-third of capacity
(fig. 21).

Figure 20. — Changes that accompany mesquite invasion.

In 19 03 s this relatively brushfree In 19643 the same spot supported
area had enough perennial grass to only scattered tufts of perennial
cut for hay. grasses 3 with most of these pro-

tected by crowns of mesquites
burroweedj or cactus.

Vigorous grass stands retard
spread of mesquite

Dense, vigorous stands of deep-rooted
perennial grasses can almost prevent the
spread of mesquite. Grasses reduce the num-
ber of seedlings that are established during
the summer, and eliminate additional plants
during the period October through July of
the first year (figs. 22 and 23). In small plot
tests, Arizona cottontop, black grama, and
bush muhly inhibited the establishment of
mesquite seedlings, bush muhly most effec-
tively. Grasses retarded the development of
lateral roots on the mesquite seedlings. Early
mortality was attributed to shading as well
as to competition for moisture.

Cattle spread mesquite seeds

It is well known that mesquite seeds are
distributed in the droppings of livestock and
other animals (fig. 24). A single cow chip
may contain 1,500 or more mesquite seeds,
of which y2 to % are viable. Obviously the
rancher who is trying to clear mesquite from
his range should avoid bringing such quanti-
ties of new mesquite seed to cleared range.
It takes about 8 days to clear mesquite seeds
from the digestive tract of cattle. This means

that cattle should be kept on a mesquite-free
ration for a week before they are put on
cleared range.

Some mesquite seeds live at
least 10 years in the soil

Just how long mesquite seed will remain
alive in the soil is uncertain, but 60 percent
of a 50-year-old lot of seeds from a herbarium
sheet at Tucson germinated. Seeds buried
in the soil for 2, 5, and 10 years showed
rapid declines in the percentage of sound seeds
recovered, but the viability of the apparently
sound seed did not decrease greatly with time
(fig. 25). A recently germinated seed dug up
at the end of 10 years was evidence that mes-
quite seed could remain in the soil for many
years and still germinate naturally. Thus,
any mesquite control program must reckon not
only with existing mesquite plants and seed
carried from other areas, but also with dormant
seed in the soil.

Favorable growing conditions do not always
increase height growth of mesquite in first year

A comparison of field-and nursery-grown
mesquite seedlings showed that the more fav-
orable conditions of the nursery were ex-

- 14 -

KIND OF GRASS

None

Arizona cottontop
Black grama
Bush muh I y

MESQUITE SEEDLINGS

7.3

2.2

1 ^

50.0

0 10 20 30 40 50 60

Figure 22. — Number of live mesquite
seedlings in October -per 100 seeds
planted in July.

KIND OF GRASS
None

Arizona cottontop

Black grama
Bush muhly

MESQUITE SEEDLINGS

2 77

(0)

Figure 23. — Number of live mesquite
seedlings on July T per 100 seed-
lings present the preceding October.

0 10 20 30 40 50 60 70 80

Figure 24. — Mesquite seeds are distributed

Cattle have a marked preference for mature
a.nd nearly mature velvet mesquite pods3
and graze them avid.ly even in the presence
of grass.

in the droppings of livestock and other animals.

In a dense mesquite forest where little other
forage was available 3 partially disintegrated
cow chips were composed mainly of undigested
pod segments and contained up to 13 670 seeds
per chip.

Apparently sound seed

MESQUITE CONTROL

100

£ 60

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40 1-

Viability of apparently
sound seed

YEARS AFTER BURIAL

Figure 25. — Percent of mesquite seeds stilt

apparently sound 23 53 and 10 years after

burial 3 and viability of apparently sound
seed.

pressed in additional height growth of mesquite
seedlings beginning in the second growing
season. Slow height growth during the first
growing season, even with adequate moisture,
accounts in part for the susceptibility of mes-
quite seedlings to competition from perennial
grasses. Because of frequent dieback and
browsing, mesquite seedlings on the range may
gain little height for many years (fig. 26).

Figure 26. — This mesquite seedling 3 established
in 1949 3 was only 9 inches tall when photo-
graphed in December 1964.

Costs depend on
size of trees and job

The most efficient method for controlling
mesquite depends on a number of considera-
tions. The number of trees per acre, their
size and growth form, and the number of
acres to be treated are all important (fig. 27).
Costs vary greatly from job to job for many
reasons. Approximate average costs for sev-
eral methods are listed below:

Treatment

Equipment Chemical
and and
labor materials

Total

Costs per tree

Grubbing $ 0.015 $ 0.015

Diesel oil 035 $ 0.015 .05

Costs per acre

Cabling and chaining 4.00 4.00

Foliage spraying

(two treatments) 3.00 2.00 5.00

Small mesquites are
easily grubbed

Plants 1 inch in diameter or smaller at the
root crown can be easily killed by hand grub-
bing at any season of the year. Plants cut
off 1 or 2 inches below the root crown do not
sprout. Fewer plants will be overlooked if the
range is traversed in marked strips and if
grubbing is done in May and June when the
new mesquite leaves contrast sharply with the
dry grass. Grubbing is especially adapted for
dense clusters of small mesquites around wa-
ter, and for widely scattered seedlings on other-
wise mesquite-free range. The cost of hand
grubbing depends on the density of the mes-
quite, the wage rate and efficiency of the
labor, and the relative stoniness of the soil.

Large machinery works
best on large mesquite

Large bulldozers, with or without "stinger"
attachments, are well adapted for uprooting
scattered stands of relatively large trees.

THAN
INCH

GRU8B ING

S3:

LESS
ONE

I—

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DIESEL OIL

■ CLA

FORTIFIED OIL

FOLIAGE

ISI

SPRAY

DOZ ING

>
z

THAN
INCHES

CABLING AND CHAINING

MORE
THREE

i ■ i I 1

50 100

150 200 250

300 4

MESQUITE

TREES PER ACRE CNUMBER)

Figure 27. — The most efficient method for
controlling mesquite depends on the size
and number of plants per acre.

Dense stands of relatively large trees can be
effectively opened up by chaining or cabling.
However, chaining and cabling usually result
in dense stands of mesquite sprouts from small
mesquites that are broken off or roughed up
but not uprooted by the chain or cable.

Large bulldozers are not recommended for
small mesquite because too many are missed.
Cabling and chaining usually require followup
to kill sprouts from small plants that are
not killed.

Large tractor-drawn root plows have not
been used enough to determine their best place
in mesquite control. More data are needed on
costs, degree of mesquite control, and on the

short- and long-time effects of root plowing on
important forage grasses.

The cost of mechanical mesquite control
varies so much due to so many factors that
each job requires independent negotiations
between the rancher and the contractor.

Diesel oil applied to stem bases
is effective on trees of all sizes

Low-grade diesel oil or kerosene will kill
mesquite at any time of year. Oil should be
sprayed against the bark just above the ground
line (fig. 28). Enough oil should be used to
saturate the bark and flow down into the soil

Figure 28. — Treatment of mesquite with diesel oil.

dormant buds are numerous in the root- stem
transition zone. Oil is applied to "kill
these buds and to chemically girdle the
tree.

A 2- to 4-gallon compressed-air sprayer
equipped with a 3-foot piece of 1/4-inch
copper tubing is a good device for apply-
ing the oil.

on all sides of the stem and in the crotches
of low-branching trees. Trees with two or three
stems up to 3 inches in diameter require about
a pint of oil per tree. Diesel oil works well
on mesquite that has a single stem or from
two to four branches arising at or above the
soil line. Results are best on sites where there
has been no deposition of soil around the stem
base.

Diesel oil is not recommended for flood-
plain sites where the sprout buds are deeply
buried by silt, or for the multiple-stemmed,
low-growing form of mesquite that has no defin-
ite trunk.

The cost per tree of killing mesquite with
diesel oil depends on the cost of the oil, the
wage rate and efficiency of the labor, and the
size and density of the mesquite. In mesquite
stands of about 100 plants per acre, where
plants range in size from seedlings to stems 5
inches in diameter, a good worker should treat
40 trees per hour, and a gallon of oil will
treat 6 to 8 trees.

Airplane spraying with 2,4, 5-T
controls dense, extensive
mesquite stands economically

Under ideal conditions, airplane spraying
with 2,4,5 — T (2,4,5— trichlorophenoxyacetic
acid) in an oil-water emulsion top-kills more
than 90 percent of the mesquite, and kills up
to 50 percent of the plants outright (fig. 29).
The most effective formulation is 1/3 to 1/2
pound acid equivalent per acre of a low- volatile

Figure 29. — Low-yielding mesquite

Unimproved range.

ester of 2,4, 5-T in 1/2 gallon of diesel oil and
enough water to make 4 gallons of spray mix-
ture. Continuous agitation of the mixture is
essential. Two applications are necessary, 1
or 2 years apart.

The proper time for spraying is between
April 15 and July 15. Mesquite should be
sprayed when the new leaves are full-size,
twig elongation has stopped, and developing
pods are about one-half inch long. It is better
to be a few days late than a few days early.

For jobs of 100 acres or more, the cost for
herbicide and flying for two sprayings would
range from $3.00 to $5.00 per acre at rates
charged commercially in 1964.

Burning to kill mesquite most
effective on small plants in June

Broadcast burning experiments in Febru-
ary, June, and November resulted in kills of
4, 29, and 10 percent respectively for mes-
quite of all size classes. The June burn was
most effective for all sizes of mesquite, and
mortality was much higher on small plants
than larger ones (fig. 30). The percent kill
on plants less than 0.5 inch in diameter was
almost twice as great as for plants with stems
between 0.5 and 1.0 inch, and three times as
great as for plants 1.0 to 2.0 inches in diam-
eter. These results suggest that burning to
control mesquite should be done in June, and
that results are best when the plants are
small.

covered range can be improved.

Range improved by spraying with 234}5-T to
control mesquite 3 then seeding to Lehmann
lovegrass .

on
LLI
X

I/O

LU
O

en
<

CxL
LU
h-
LU

_l
<

V//////////A™

Up to 0.5

0.5 to 1.0

1.0 to 2.0

2.0 to 5.0

Over 5.0

Average
All sizes

(60)

21:

15)

(33)

15)

(0)

:20)

(7)

Burning Date

(0)

15)

:5)

— February

— June

— November

Figure SO. — Mortality of mes quite
by size classes after burning
in February 3 June3 and November .

(0)

. (0)

:4)

:29)

10)

PERCENT KILL

Perennial grasses recover quickly from a
June burn if grazing is deferred during the
summer rainy season immediately after the
burn, and if the amount and distribution of
rainfall are favorable. If summer drought or
heavy grazing follow burning, the mortality of
perennial grasses may be severe.

Mesquite control

increases benefits of reseeding

Range that was seeded to Lehmann love-
grass by airplane in 1954 improved more
rapidly where the mesquite was controlled by
aerial applications of 2,4, 5-T in 1954 and 1955

than where the mesquite was not controlled.
Spraying killed about 90 percent of the top
wood and over half of the plants. The cost of
seeding was $3.00 per acre; the cost of seed-
ing and mesquite control combined was $9.50
per acre. The sprayed range showed the great-
est advantage in grass production during the
second, third, and fourth seasons after spray-
ing (fig. 31a). Cumulative net returns on the
sprayed range returned more than the cost of
spraying and seeding within 3 years (fig. 31b).
Cumulative net returns on unsprayed range
did not exceed the cost of seeding until the
fourth year. These results show that rundown
mesquite-grass ranges can be improved by
seeding and management alone, but that the
rate of recovery can be greatly increased by
controlling the mesquite.

- 19 -

a:
u
<

a: 1000

h-
U
ID
Q
O

LU
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(«")

Sprayed
Range

Unsprayed
Range —

1954

1956

1958

I/O

or
<

LU
LU

16-

> 0

-4 -

-8

(b)

Sprayed range-^.''

Unsprayed range

J _J L

1954

1956

1958

Figure 31. — One range was sprayed with 2S 43 5-T in 1954 and 1955 to control mesquite; an adjacent
range was not sprayed. In 19543 both ranges were seeded by airplane to Lehmann lovegrass.

Figure 32. — Changes in jumping cholla cactus.
A3 1905; B. 1941; C3 1962.

JUMPING CHOLLA AS A RANGE PROBLEM

Jumping cholla is a nuisance on the range.
It may not seriously reduce grass production,
but it does interfere with the handling and
movement of livestock. Cattle do eat some
cholla fruits when green forage is scarce, but
it is doubtful whether the food value obtained
offsets the discomfort and injury involved.

New cholla plants rarely become estab-
lished from seed, but dense stands of new
plants are frequently established from scat-
tered joints. Jumping cholla is not a fixed or
ever-increasing component of the vegetation
on any part of the Experimental Range. In-
stead, stands become established, develop
rapidly for a few years, mature, and then
decline (fig. 32 ). The decline may be dramatic,
with 90 percent of the plants dying in 2 or
3 years.

Cholla can be killed with chemicals now on
the market, but only if high rates of material
are used. Completely wetting sprays of 2,4, 5-T
or TCA (trichloroacetic acid) will kill individual
plants. Low-volume aerial applications, as
applied tomesquite, are completely ineffective.
Burning in June kills about one-third of the
cactus, if there is enough fuel to carry a fire.
Within a year or two after burning, however,
large numbers of young cholla plants may
become established from joints dropped off the
partially burned parent plants. Mechanical
measures such as chaining or cabling knock
over and uproot most of the large cactus, but
numerous new plants usually start from scat-
tered joints. Studies to test the feasibility of
controlling cholla by combinations of mechan-
ical treatment and fire are in progress.

BURROWEED AS A RANGE PROBLEM

Invasions of grassland by burroweed have
concerned cattlemen in southern Arizona since
the turn of the century. Mature burroweed is
a long-lived, woody half-shrub with a strong
taproot. Occasional severe livestock losses
from burroweed poisoning have been reported,
but most of these have involved either a
shortage of forage or cattle that were not
familiar with burroweed. No cattle losses from
burroweed poisoning have been recorded on
the Experimental Range, where moderate to
heavy stands of burroweed have persisted for
many years. Cattle that grow up with burro-
weed apparently learn to leave it alone.

Invasion varies with
cool-season precipitation

Burroweed does not invade grassland at
a steady rate. Large numbers become estab-
lished only in years of high winter and spring
precipitation. Burroweed stands fluctuate
greatly and sometimes quite rapidly (fig. 33).

Figure 33. — Burroweed stands become established
in years with favorable winter- spring mois-
ture, then decline from natural mortality
until conditions permit the establishment of
a new crop of seedlings : A_3 1920, before burro-
weed invasion; 19353dense mature burroweed
stand; 0,1958 3the old stand is about gone3but
new seedlings are evident; D, 1962 3 the new
crop of burroweed is approaching maturity.

Burning is more effective
than chemical control

No satisfactory chemical method of control
is available for burroweed. In years when there
is an adequate supply of grass herbage, how-
ever, 90 to 100 percent of the burroweed may
be killed by broadcast burning in June. Most
of the burroweed that survives such fires is
found in unburned or lightly burned islands.
Burning is reasonably effective from mid- April
to mid-September (fig. 34).

Burroweed control increases
yields of annual grasses

Average yields of annual grasses during
a 10-year period were higher on burroweed-free
plots than where the burroweed was not re-
moved. Burroweed control increased annual
grass yields in the presence of mesquite as
well as on plots where mesquite was killed
(fig. 35). Yields of perennial grasses, on the
other hand, were greater in the presence of
burroweed. It is suspected that heavier grazing

on the burroweed-free plots was responsible
for the decrease in perennial grass production.
Whatever the cause, the results of this study
do not justify controlling burroweed to increase
perennial grass yields.

RANGE RESEEDING

Range reseeding studies began on the
Santa Rita soon after the Range was estab-
lished in 1903. Studies to date have indi-
cated that: (1) grasses should be seeded in
May or June immediately before the start
of the summer rainy season, (2) burroweed,
mesquite, cactus, or other competing brush
should be removed before seeding, and (3)
the chances for success are improved by pre-
paring a good seedbed.

The best sites for reseeding have produc-
tive, medium-textured soils, are above 3,500
feet elevation, and receive 14 inches or more
rainfall annually. On these sites, Lehmann and
Boer lovegrasses are the best species to use.

Figure 34. — Percentage of burroweed after burning at 4-week intervals
from October 21, 1942 3 to September 213 1944. Each point marked by
a dot represents a burn on the date indicated but at a different
location and usually in a different year.

- 22 -

Annual Grasses

Mesqui te
Alive

Mesqui te
KiMed

Mesquite
Alive

Mesquite
Ki I led

:59)

Burroweed
present

Burroweed
removed

127)

(122)

J u

Perennial Grasses

Figure 35. — Effects of burroweed
control on yields of annual and
■perennial grasses on mesquite-
infested and mesquite-free range.

0025)

103)

(290)

[210)

80 160 240

PRODUCTION (POUNDS PER ACRE)

320

Lehmann is easier to establish, but Boer is
more palatable and longer lived. Arizona cot-
tontop and black grama are more difficult to
establish. Weeping lovegrass and side-oats
grama are suitable for the more moist sites.
Wilman lovegrass can be used where tempera-
tures do not fall below 10° F.

On upland areas receiving less than 14
inches of rainfall, Lehmann lovegrass is the
only species that can be generally recom-
mended. Reliable species and methods have
not been developed for reseeding ranges that
receive less than 11 inches of precipitation
yearly.

RODENTS AND RABBITS

Rodents and rabbits use vegetation that
would otherwise be available for livestock,
and thereby lower the overall grazing capacity
of the range. In 1937, it was estimated that
rodents and rabbits consumed about two-fifths
of the total forage. Animal numbers for the
Experimental Range, and their forage con-
sumption, were as follows:

Species Animals

(no.)

Allen jackrabbit 10,300

California jackrabbit 620

Arizona cottontail 3, 530

Roundtail grounds quirr el . 29,780
Bannertail kangaroo rat. . 87,125
Merriam kangaroo rat . . . 42,025
Total

Forage con-
sumed per

animal
per

year year

(lbs.)

175.20
120.45
54.75
8.21
5.53
2.41

(lbs acre)

2
56

Rodents and rabbits can be more detri-
mental than cattle to range vegetation, be-
cause they graze much closer and may even
dig up root systems during dry periods. Also,
certain species, particularly kangaroo rats,
help establish unwanted shrubs by storing
seeds in small caches about 1 inch below the
soil surface. Seeds not used by the rodent
are planted at an ideal depth, and thus fre-
quently give rise to new plants. Jackrabbits
and some kangaroo rats are more abundant
on ranges in poor condition, where their ac-
tivities tend to perpetuate the undesirable
condition of the range. A relatively small
rodent population can consume the entire seed
crop of forage grasses on low-rainfall range
in poor condition.

- 23 -

EDUCATIONAL OPPORTUNITIES

The facilities of the Santa Rita Experimen-
tal Range are often used for training schools,
for undergraduate field work, for field meet-
ings of range management and conservation
groups, and for training programs of the For-
eign Agricultural Service.

Opportunities for graduate students to
undertake fundamental research in the ecology

and management of semidesert ranges are
excellent.

Visitors are always welcome. To obtain
more detailed published information about
the experimental work, ask the resident tech-
nicians, or send a request to the Director,
Rocky Mountain Forest and Range Experi-
ment Station, Fort Collins, Colorado.

COMMON AND SCIENTIFIC NAMES USED

Acacia

Burroweed

Cactus

Jumping cholla
Pricklypear

Calliandra

Cottontop
Arizona

Cur lymes quite

Dropseed

Grama

Black

Hairy

Side-oats

Slender

Sprucetop

Rothrock

Lovegrass
Boer
Lehmann
Weeping
Wilman

Me s quite
Velvet

Mimosa

Muhly

Bush

Tanglehead

Three-awn
Mesa

Santa Rita

Acacia spp.

Aplopappus tenuisectus (Greene) Blake

Opuntia

fulgida Engelm.

Principally engelmannii Salm-Dyck

Call iandra spp.

Trichachne

californica (Benth.) Chase

Hilaria belangeri (Steud.) Nash

Sporobolus spp.

Bouteloua

eriopoda Torr.
hirsuta Lag.

curtipendula (Michx.) Torr.
filiformis (Fourn.) Griffiths
chondrosioides (H.B.K.) Benth.
vothvockii Vasey

Eragrostis

chloromelas Steud.
lehmanniana Nees
cuvvula (Schrad.) Nees
supevba Peyr .

Pvosopis

juliflora velutina (Woot.) Sarg.

Mimosa spp.

Muhlenbergia

porteri Scribn.

Heteropogon contortus (L.) Beauv.

Aristida

hamulosa Henr.

glabrata (Vasey) Hitchc.

Wolftail

Lycurus phleoides H.B.K.

Agriculture — CSU, Ft Collins

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