WILDLIFE IN A SONORAN DESERT OLD- FIELD SERE IN SOUTHCENTRAL ARIZONA.
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Rautenstrauch, Kurt Robert
WILDLIFE IN A SONORAN DESERT OLD-FIELD SERE IN SOUTHCENTRAL ARIZONA
The University of Arizona M.S. 1985
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University Microfilms International
WILDLIFE IN A SONORAN DESERT OLD-FIELD SERE
IN SOUTHCENTRAL ARIZONA
by
Kurt Robert Rautenstrauch
A Thesis Submitted to the Faculty of the
SCHOOL OF RENEWABLE NATURAL RESOURCES
In partial Fulfillment of the Requirements For the Degree of
MASTER OF SCIENCE WITH A MAJOR IN WILDLIFE AND FISHERIES SCIENCE
In the Graduate College
THE UNIVERSITY OF ARIZONA
19 8 5 STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.
Brief quotations from this thesis are allowable without special permission, provided that accurate acnowledgement of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the mojor department or the Dean of the Graduate College when in his or her judgement the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.
SIGNED:
APPROVAL BY THESIS COMMITTEE
sis has been /£bproved on the date shown below:
-T- )- « L.lK. -Sowls, Ttoesis Director Coofjbrative Wildlife Reasearch Unit Leader Professor of Wildlife Ecology
19 P. R. Krausman Associate Professor of Wildlife Ecology
M. M. Ratp^&ak Research Associate (7 Office of Arid Lands Studies ACKNOWLEDGMENTS
Foremost, I would like to thank my wife, Mary, for her patience, support, and encouragement, without which this study would not have been possible.
I am grateful to Dr. Lyle K. Sowls, my major advisor, for his guidance and support. I also thank Drs. Paul R. Krausman and Martin M.
Karpiscak, who served as committee members and critically reviewed the manuscript.
This study was funded by the Arizona Cooperative Wildlife
Research Unit and the University of Arizona. TABLE OF CONTENTS
PAGE
LIST OF TABLES V
LIST OF ILLUSTRATIONS vi
ABSTRACT vii
INTRODUCTION 1
DESERT SUCCESSION 2
STUDY AREA 6
METHODS 10
RESULTS 12
Birds ...... 12 Rodents 20 Lagamorphs 21 Carnivores and other Wildlife 21
DISCUSSION 25
APPENDIX 1: LOCATION OF 16 STUDY SITES IN SOUTHCENTRAL ARIZONA . 30
APPENDIX 2: COMMON AND SCIENTIFIC NAMES OF PLANTS AND ANIMALS LISTED IN THE TEXT 31
LITERATURE CITED 35
iv LIST OF TABLES
Table Page
1. Date last farmed, percent cover of shrubs and spring annuals in May 1981, and summer annuals in August-September 1981 at 16 study sites in southcentral Arizona .... 13
2. Average seasonal bird density (#/ha), number of species, diversity, and evenness in 5 old-field serai stages in southcentral Arizona 15
3. Average seasonal density (#/ha) of bird species in 5 old- field serai stages in southcentral Arizona 16
4. Average seasonal bird density (#/ha) and species richness in 16 study sites in southcentral Arizona 19
5. Number of rodents trapped, number of species, species diversity, and evenness in 576 trap nights at 16 study sites in southcentral Arizona 22
6. Total number of cottontail rabbits and jackrabbits seen in 16 study sites in southcentral Arizona from June 1981 to May 1982. . . • . . . . . • • • • .23
v LIST OF ILLUSTRATIONS
Figure Page
1. Location of 16 study sites in Avra Valley and the Lower Santa Cruz River Valley, southcentral Arizona 7
vi ABSTRACT
Bird, rodent, lagamorph, and coyote populations were monitored from June 1981 to May 1982 in 12 retired agricultural fields representing 4 serai stages, and in 4 climax-community sites in southcentral Arizona. Fields with tall, dense stands of annual vegetation had wintering granivorous birds, cottontail rabbits, and hispid cotton rats. Fields with short annual grasses and forbs had ground foraging birds, but few rodents. The presence of ruderal shrubs did not increase avian abundance, but two of three fields with ruderal shrubs had many rodents. Climax community shrubs and spinescent trees attracted forage-gleaning and aerial-hawking insectivorous birds.
Woodrats, desert pocket mice, and round-tailed ground squirrels were most abundant in sites with climax community shrubs. Management practices that promote plant growth and succession will benifit wildlife populations on retired farmland.
vii INTRODUCTION
Rising irrigation and production costs and decreasing groundwater levels are forcing many farmers in the Southwest to retire thousands of hectares of irrigated land. In the Ogallala Aquifer region of western Texas there may be a 940,000 ha decrease in cropland by the year 2020 (High Plains Associates, 1982). In southern Arizona, 4 counties had an estimated 78,800 to 92,000 ha of farmland indefinitely retired in 1983 (Meitl, Hathaway, and Gregg, 1983) and may have 215,200 ha of retired farmland by 2020 (Anonymous, 1977).
In southern Arizona most of the retired farmland is used only for commercial development and light seasonal livestock grazing.
However, since most of this land is rural and has very low forage production, it has little economic value and may remain undeveloped indefinantly.
Farmland retirement has created tracts of serai stage plant communities that were previously uncommon or did not exist in southern
Arizona. The objectives of this study were to determine what wildlife populations are found in these serai stages and how wildlife use changes with the succession and disturbance of vegetation.
1 DESERT SUCCESSION
Relatively little is known about plant succession in the southwestern deserts. In the only series of long term studies on changes in desert vegetation, Shreve (1929), Shreve and Hinckley (1937), and Murray (1959) found few changes in a lower Sonoran plant community during 52 years of recovery from cattle grazing. Shreve (1951:21) stated that succession does not occur, or is of minor importance in the
Sonoran Desert because the same species that were present after a disturbance were also found during and after more than 50 years of recovery. Muller (1940) came to the same conclusion while studying succession on eroded clay flats in the Chihuahuan desert.
These studies have often been cited as evidence that succession does not occur or is not obvious in deserts. Beatley (1976:72) described changes in vegetation after nucleur explosions in the Mojave and Great Basin Deserts as autosuccessional because the pioneer species in disturbed areas were the same species originally found there.
MacMahon (1980) stated that succession is not obvious in deserts and tundra regions because precipitation is so low and variable that the only species able to revegetate disturbed areas are the limited number of species adapted to these extreme conditions. Whitaker (1974) described deserts as superclimaxes; areas where environmental modifications are small and succession is undifferentiated or telescoped.
2 3
Others, however, have found evidence of succession in desert regions. The serai changes most often found are from exotic and native forbs to grasses to shrubs. Shreve (1929, 1951) and Muller (1940) may not have found evidence of succession because they were studying areas with relatively minor disturbances or because many of the plants that are now found in undisturbed desert areas are exotic species that were not present at the time their studies were conducted.
In a study of 51 old fields of various ages in southern Arizona,
Karpiscak (1980) found that the first plant to invade newly abandoned fields was the exotic annual Russian-thistle. In the absence of grazing or other soil disturbances, London rocket and other exotic and native mustards replaced Russian-thistle after 2 or 3 years. These mustards were then replaced by the exotic annual Mediterranean grass. The ruderal shrubs burro-weed and desert-broom invaded some recently abandoned fields but were uncommon or absent in older fields. The dominant shrubs in undisturbed vegetation, creosote-bush and salt-bush were increasingly common in some older fields.
Other studies of disturbed desert areas have found vegetation changes similar to those described by Karpiscak (1980). Because of its prolific seed production and efficient seed dispersion, Russian-thistle is one of the first plants to invade disturbed areas in montane meadows in Utah (Cottam and Stewart, 1940), the Great Plains in Colorado
(Costello, 1944), the short grass prairie in Texas (Van Hylckama, 1979), the Great Basin Desert in Idaho and New Mexico (Piemeisel, 1951; Wagner, 4
Martin, and Aldin, 1978) and the Mojave Desert in Nevada (Wallace and
Romney, 1972).
Piemeisel (1951) reported that old fields in Idaho were dominated by large, widely spaced Russian-thistle the first year after abandonment and dense stands the second year. These dense stands were stunted and had decreased seed production because of competition for moisture. When these fields were not disturbed by fire or heavy grazing, exotic mustards, which germinate and begin using soil moisture before Russian-thistle, became the dominant plants the third year.
Mustards were replaced by the exotic annual, cheatgrass by the fifth year. Cambell (1931), Costello (1944), and Wallace and Romney (1972) also described the replacement of initial forb stages by an annual or short-lived perennial grass in arid disturbed areas.
Burro-weed and desert-broom, 2 common shrubs in some recently retired fields, are native species most often found in overgrazed and periodically flooded places, respectively. Wells (1961) suggested that the pioneering shrubs in an abandoned mining town in Nevada were adapted to natural disturbances and "play a role similar to that of successional plants of more humid regions". On disturbed grasslands in Colorado
(Shantz, 1917) and New Mexico (Cambell, 1929), snakeweed , a native shrub common on overgrazed ranges, replaced short-lived perennial grasses and weeds. Vasek, Johnson, and Eslinger (1975) also found that native shrubs adapted to naturally disturbed conditions were an important part of the early serai stages in a pipeline right-of-way in the Mojave Desert of California. 5
The rate that the common plants of the climax community become
reestablished and the rate an area returns to its predisturbance condition is quite variable. Karpiscak (1980) described old fields that
were completely bare 24 years after abandonment and others that had a substantial reestablishment of shrubs. Climax community shrubs comprised 0% to 41% of the ground cover 12 years after pipeline construction in the Mojave Desert (Vasek et al., 1975) Vasek et al.
(1975) and Wallace, Romney, and Hunter (1980) concluded that the disturbed desert areas they studied had the potential to return to
predisturbance condition, but the amount of time it will take, or
whether other areas will also return to climax condition, is unknown. STUDY AREA
I measured bird and mammal populations in 12 retired fields and
4 nonagricultural sites in Avra Valley and the lower Santa Cruz River
Basin (SCRB) in southcentral Arizona (Appendix 1). Avra Valley is located in the eastern portion of the Sonoran Desert, 25 to 40 km west and northwest of Tucson (Figure l)r. Turner (1974b) mapped three vegetation associations in this valley: grassland invaded by woody shrubs above 900 m and adjacent to the major drainages, creosote-bursage below 900 m, and riparian bosques along the large drainages. The elevation of the valley bottom ranges from 950 m at the south end to 700 m where it opens into the SCRB to the north.
Two plant associations are found in the valley bottoms of the lower SCRB (Turner, 1974a). Creosote-bush is the dominant plant on loamy soils and is found in association with bursage on sandy soils.
Desert saltbush is dominant on fine grain alluvium that is periodically flooded.
This area has hot summers, mild winters, and little rainfall.
Temperatures often exceed 38 C during the summer and are rarely below 0
C during the winter. The average annual rainfall is 24 to 31 cm in Avra
Valley and 22 cm in the SCRB. About half of the annual rainfall occurs during locally heavy thunderstorms from July through September. Winter rainfall, most common from December through March, is usually widespread and may last several days (Sellers and Hill, 1974). This biseasonal rainfall pattern causes two peaks in plant growth.
6 7
10 km Cd 4to- Eloy Mts
10
Marana Cb
2 c
Mts Cc 2b
3b ts. Ca 1e4a 10 1b 3a 2a
Figure 1. Location of 16 study sites in Avra Valley and the Lower Santa Cruz River Basin (SCRB), southcentral Arizona. 8
The retired fields studied in Avra Valley are owned by the City
of Tucson for the land's water rights. This land and the fields in the
SCRB have all been burned, disked, or mowed at some time to control the
growth of Russian-thistle.
Based on work done by Karpiscak (1980) and others, I divided old
field succession in southern Arizona into five serai stages and
monitored three fields typifying each of these five stages. A serai
stage dominated by mustards was not included because there were too few
fields in the study area dominated by these plants. Because the rate of
succession in arid regions is so variable, these serai stages should not
be interpreted as a predictable series of changes that all fields go
through in a specific time period. The vegetation in desert old fields
may advance or regress rapidly, remain the same for many years, or be
completely absent, depending on soil moisture and disturbance, seed
source, and many other factors. However, most retired fields in
southern Arizona that support vegetation can be classified as one or a combination of these five stages.
Stage 1 fields were dominated by Russian-thistle, which germinates in spring and remains in a seedling stage until the summer
rains. It then grows and matures rapidly, desicates, and begins blowing
away by November, forming large piles of skeletons around fencelines, trees, and other obstructions. Russian-thistle's phenological changes cause the structure of stage 1 plant communities to change rapidly.
Field la was typical of a newly abandoned field. Fields lb and lc had been abandoned for 9 years (Table 1), but continuous cattle grazing and mowing had perpetuated the initial serai stage. 9
The dominant plants in the second serai stage, the grassland stage, were the cool season annual, Mediterranean grass, and the summer annuals six-weeks grama, needle grama, and careless-weed. Heavy grazing by horses during the late spring of 1981 caused the reestablishment of
Russian-thistle in 2a by late summer.
Stage 3 fields had dense stands of the ruderal shrubs burro-weed and desert-broom. Because of cattle grazing and moisture from an adjacent, broken irrigation ditch, field 3c also had dense stands of annuals typical of earlier serai stages.
Stage 4 fields had been invaded by mesquite, desert saltbush, creosote-bush, and other shrubs found in the surrounding unfarmed areas.
The four nonagricultural, control, sites were representative of unfarmed, grazed plant communities in Avra Valley and the SCRB. Site Ca is in a major drainage in the riparian bosque association. Site Cb is adjacent to a large drainage in an ecotone between the grassland-shrub association and the creosote-bursage association. Site Cc is in the creosote-bursage association. Site Cd is in the SCRB in the saltbush association (Turner 1974, a & b). METHODS
In each study site a 500 m transect was established as the
baseline for all measurements. The transect was located 200 m from the corner of a field, starting at and perpendicular to one edge.
I used the line intercept method (Canfield, 1941) to measure the percent shrub cover on 10 lines, each 50 m long, perpendicular to the transect in April-May 1981. I measured the percent cover of live annual vegetation in April-May and in August-September 1981 using the point quadrat method (Levy and Madden, 1933). The first species intercepted at 100 points along each of the 10 perpendicular lines was recorded.
I censused birds monthly at each site from June 1981 to May 1982 using Emlen's (1971) line transect technique. Censuses were conducted from 15 minutes before until two and one half hours after sunrise along the 500 m transect. Coefficient of detectability values were calculated by combining sightings within each stage for each species, assuming that the detectability was equal within each stage. For species with less than 20 sightings, sightings for all stages and seasons were combined.
I obtained an index of rodent populations by snap trapping in each study site in June 1981, October-November 1981, and March-April
1982. One Museum Special and one Victor Rat Trap were set at each of 32 trap stations for 3 consecutive nights each trapping period for a total of 576 trap nights per field. The traps were checked and rebaited each morning. Trap stations were located 15 m apart along 2 parallel lines of 16 stations each. The trap lines started at the field edge, and were
10 11 located on and next to the bird transect in June and 50 m either side of
it the other 2 trapping periods.
I recorded the number of cottontails and jackrabbits seen during each monthly bird census to obtain an index of lagamorph populations.
To measure carnivore use of my study sites, I set up 3 scent-post stations (Linhardt and Knowlton, 1975) in each field for 5 consecutive nights in July 1981, October-November 1981, and March-April 1982. The stations were baited with a perforated plastic capsule filled with the fermented egg product attractant used by the U.S. Fish and Wildlife
Service for its West-wide survey of predator abundance. The stations were located 100 m further from the site than the bird transect, and were 0, 150, and 300 m from the edge of the site.
I used the Shannon-Weaver (1964) formula and the tables of Lloyd et al. (1968), with natural logarithms, to calculate species diversity
(H1). Evenness, the percent of maximum possible diversity, was calculated from Pielou's (1966) equation for J'.
I used the Kruskal-Wallace test to examine differences between serai stages in the abundance, number of species, diversity, and evenness of birds and rodents, and the Friedman Rank Sums Test for differences in bird population parameters between seasons. The significance level for all statistical tests was 0.05.
Seasons were defined as follows: summer = June-August, fall =
September-November, winter = December-February, and spring = March-May. RESULTS
Birds
Stages 2 and 4 had significantly greater bird densities than stages 1 and 3. Stage 2 also had significantly greater densities than the control sites (T = 10.76f df = 4, p = 0.030).
Stage 2 fields had the highest average densities in all seasons
(Table 2). Horned larks and vesper sparrows were abundant in open areas in all seasons. During winter and spring, large flocks of
Brewer's sparrows, lark buntings, and other wintering sparrows were found in dense stands of dead careless-weed in fields 2b and 2c (Tables
1 and 3).
Fields 3a and 3b had the lowest average densities in all seasons. Field 3c, however, which had dense stands of annuals because of cattle grazing, had much higher densities and species richness than
3a and 3b (Table 4).
Stage 4 fields and the control sites had a significantly greater number of species than the first 3 serai stages (T = 9.64, df = 4, p =
0.047). These sites had forage gleaning insectivores and aerial hawking insectivores that were uncommon or absent in earlier stages.
There were no statistical differences in species diversity (T =
9.24, df = 4, p = 0.055) or evenness (T = 5.24, df = 4, p > 0.264) between stages. However, stage 4 and the control sites had the highest
12 Table 1. Date last farmed, percent cover of shrubs and spring annuals in May 1981, and summer annuals in August-September 1981 at 16 study sites in southcentral Arizona
Study sites Stage 1 Stage 2 Stage 3 Stage 4 Stage C la lb lc 2a 2b 2c 3a 3b 3c 4a 4b 4c Ca Cb Cc Cd
Year Last Farmed 1978 1972 1972 1970 1975 1975 1975 1976 1976 1972 1937 1937
Shrubs saltbush - 1.3 1.0 7.0
desert-broom 0.1 54.0 5.7 0.4 1.9
burro-weed 41.5 22.7 6.2 0.3 1.1
creosote-bush 3.7 3.1 12.4 12.7
mesquite 0.1 1.2 10.6 8.0 2.0 16.7 2.7 0.9 1.2
other 0.3 0.5 0.4 16.3 1.5 4.3
Total Percent Cover 0.1 0.1 41.5 54.3 30.1 17.6 12.0 6.4 35.9 17.7.13.6 12.5
Spring annuals filaree 0.3 0.3 0.5 20.6 4.4 14.6 11.2
Indian-wheat 22.3 1.6 0.6 19.5
Russian-thistle 41.5 38.5 38.6 2.3 0.6 3.1 0.8 8.3 6.0 18.2 8.7
Mediterranean-grass 0.8 14.1 21.0 36.1 54.0 58.2 1.4 7.2 4.4 4.5 5.7 8.4 2.1 7.7 0.8 15.6
other 7.5 6.8 6.9 12.5 2.3 1.8 9.3 4.8 1.0 0.8 11.8 2.0 2.8 0.2
Total Percent Cover 49.8 59.7 66.5 51.2 57.4 63.1 2.2 15.5 19.7 27.5 29.0 31.4 27.0 24.3 15.4 35.3 Table 1. Continued.
Study sites Stage 1 Stage 2 Stage 3 Stage 4 Stage C la lb lc 2a 2b 2c 3a 3b 3c 4a 4b 4c Ca Cb Gc Cd
Sumner annuals careless-weed 0.4 45.1 43.8 1.7 1.2 7.2 0.1
needle grama 3.4 8.4 5.4 8.1 3.5
Bermuda grass 3.3 0.6 23.6 18.3 11.7 0.8
spurge 0.4 4.7 4.1 1.6 0.8 1.6 0.9 3.0 3.2 4.4 8.0 5.9 11.6
Russian-thistle 77.7 34.9 60.9 36.1 1.7 9.4 5.4 9.5 31.1 11.9 3.8 8.1 8.9 2.3 0.3 0.2
Johnson grass 0.4 1.0 3.1 0.5 2.8 2.9 8.6 6.0 0.9 1.4 31.4
other 0.3 2.8 0.3 5.4 13.3 2.4 2.0 1.3 14.1 12.4 2.6 62.4
Total Percent Cover 82.1 43.4 64.7 49.0 70.7 62.3 11.8 13.3 66.3 54.5 ,.9 13.9 71.6.21.0 72.2 12.6 Table 2. Average seasonal bird density (#/ha), number of species, species diversity, and evenness in southcentral Arizona.
STAGE 1 STAGE 2 STAGE 3 STAGE 4 STAGE C SP SM Ft, WW SP SH FL WW SP SH FL WN SP SM FL WN SP SH FL WN Total Density 3.45 1.65 4.93 5.72 14.11 4.14 21.24 26.92 2.89 1.17 4.26 6.53 10.35 3.40 10.32 14.23 8.15 3.78 7.32 9.38
Species Richness 2.78 2.78 4.00 3.56 4.11 3.44 5.00 5.11 4.00 2.44 4.22 5.22 8.55 5.67 7.78 8.49 7.42 6.25 6.28 5.92 Species Diversity 0.62 0.58 1.00 0.82 0.82 0.75 0.98 0.81 0.93 0.70 0.95 1.15 1.46 1.35 1.39 1.55 1.22 1.51 1.20 1.08 Evenness 0.62 0.58 0.73 0.70 0.63 0.58 0.58 0.55 0.69 0.59 0.71 0.75 0.70 0.79 0.71 0.73 0.74 0.87 0.66 0.57
1SP » spring, SM " gunner, FL » fall, WN » winter Table 3. Average seasonal bird density (#/ha), number of species, species diversity, and evenness in southcentral Arizona.
STAGE 1 STAGE 2 STAGE 3 STAGE 4 STAGE C 1SP SM FL m SP SM FL WN SP SH FL W SP SM FL HN SP SH FL wj Red-tailed Hawk 0.02 0.02
Northern Harrier 0.01 0.01 0.04 0.02 0.05 0.05 0.04 0.03 0.04 0.03 0.12 0.01 0.03 0.01 ftnerican Kestrel 0.01 0.02 0.01 0.02 0.03 Ganbel's Quail 0.24 0.03 0.39 1.07 0.11 0.33 0.18 0.15 0.03 1.19 0.24 0.09 0.47 0.74 1.00 0.58 0.22
Killdeer 0.01 White-winged Dove 0.01 0.10 0.06
Mourning Dove 0.29 0.08 0.12 0.67 1.06 0.08 0.31 0.08 0.58 1.00 0.52 0.71 0.50 0.66 0.35 0.31 Roadrunner 0.01 0.01
Burrowing Owl 0.03 0.01 0.02 0.01 Conmon Flicker 0.01 0.01 0.01 0.04 0.01 0.03 Gila Woodpecker 0.01 0.03 0.02 0.03
Ladder-back Woodpecker 0.01 0.06 0.01 Western Kingbird 0.02 0.10 0.05 0.02 0.02 0.08 0.02 0.04 0.01 0.05
Cassin's Kingbird 0.02 0.03 0.02 0.03 Myiarcbus flycatcher 0:05 0.03 0.05 0.03 0.02 0.02 0.02 0.02 0.08 0.03 0.04 Say's Ftioebe 0.02 0.02 0.03 0.02 0.05 0.03 Black Ftioebe 0.02 Horned tark 2.12 0.96 1.34 2.50 2.94 2.73 6.05 4.78 0.16 0.12 0.04 0.21 0.10 0.41 0.12 0.02
Verdin 0.03 0.03 0.06 0.03 0.03 0.40 0.09 0.21 0.19 0.37 0.30 0.16 0.25 House Wren 0.04 0.04 0.04 0.09 0.10 0.10 Cactus Wren 0.12 0.07 0.14 0.10 0.15 0.20 0.06 0.04 Table 3. Continued.
STAGE 1 STAGE 2 STAGE 3 STAGE 4 STAGE C SP SM FL WN SP SM FL WW SP SM FL WH SP SM FL WN SP SM FL WN Mockingbird Bendire's Hirasher 0.03 0.05 0.03 0.02 0.02 0.06 0.11 0.04 0.01
Curve-Billed Hirasher 0.02 0.07 0.02 0.01 0.04 0.03 0.01 Crissal's Ttirasher 0.01 0.01 Sage Thrasher 0.02 0.02 0.03 0.07 Black-tailed Qiatcatcher 0.19 0.19 0.05 0.34 0.25 0.22 0.25 0.25 Phainopepla 0.02 0.03 Loggerhead Shrike 0.03 0.03 0.03 0.01 0.01 0.01 0.01 0.03 0.05 0.05 0.04 0.05 0.03 Lucy's Warbler 0.10 0.06 Yellow-runped Warbler 0.04 0.17 0.38 0.08 0.06 0.06 0.10
Wilson's Warbler 0.25 0.08 House Sparrow 0.13 Meadowlark 0.10 0.14 0.03 0.09 0.24 0.28 0.23 0.19 0.07 0.07 0.24 0.16 0.03 0.28 0.02 0.01 Bronzed Cowbird 0.02 0.05 Pyrrhuloxia 0.02 0.05 0.07 0.07 0.09 0.07 0.02
Blue Grosbeak 0.07 0.07 Green-tailed towhee 0.10 0.09 0.43 0.38 0.58 0.62 0.43 0.58 Brown Towhee 0.03 0.06 0.06 0.06 Abert's Hjwee 0.26 0.18 0.04 0.18 0.22 0.29 0.26 0.33 0.54 0.49 0.27 0.33 0.20
Savanna Sparrow 0.08 0.15 0.07 Lark Bunting 0.09 0.24 1.01 0.59 0.09 0.30 0.48 1.30 0.33 0.83 Table 3. Continued. STAGE 1 STAGE 2 STAGE 3 STAGE 4 STAGE C SP SM FL HN SP SM FL HN SP SM FL WN SP SM FL SvN SP SM FL MJ
Vesper Sparrow 0.55 0.64 0.93 4.26 0.38 7.03 7.89 0.21 0.59 0.42 0.13 0.59 0.13 0.13 Cassin's Sparrow 0.03 0.28 0.08 0.05 Black-throated Sparrow 0.10 0.04 0.06 0.06 0.27 0.10 0.20 0.30 0.05 0.05 Sage Sparrow 0.17 0.07 0.13 0.10 0.10 0.03 0.23 0.33 0.60 0.08 0.08 Brewer's Sparrow 0.16 0.08 6.26 5.57 10.51 0.82 0.04 1.01 2.10 3.96 3.07 4.77 2.88 1.92 3.92
White-crowned Sparrow 0.18 1.40 0.58 0.18 0.40 1.52 0.90 1.23 2.38 0.89 0.04 2.67 4.27 1.13 0.16 2.33 2.86 Lincoln's Sparrow 0.10 0.23 0.10 0.62 0.18 0.15 0.15 Song Sparrow 0.03 Total Density 3.45 1.65 4.93 5.72 14.11 4.14 21.24 26.92 2.89 1.17 4.26 6.53 10.35 3.40 10.32 14.23 8.15 3.78 7.32 9.38
*SP = spring, SM - surcner, FL « fall, HN = winter Table 4. Average seasonal bird density (#/hec) and species richness of 16 study sites in southcentral Arizona from June 1981 to May 1982.
Study sites
Stage 1 Stage 1 Stage 3 Stage 4 Stage C la lb lc 2a 2b 2c 3a 3b 3c 4a 4b 4c Ca Cb Oc Gd
Density
Spring 3.38 2.84 4.11 8.52 21.77 12.09 1.13 1.20 6.37 9.64 13.21 8.22 12.63 2.96 6.75 10.31
Sunnier 1.17 1.32 2.47 7.35 1.93 3.17 0.33 0.60 2.52 4.04 2.17 3.97 6.94 1.95 4.54 1.62
Fall 5.85 4.76 4.11 21.05 24.21 18.74 1.81 1.16 9.80 19.75 6.18 5.06 17.62 3.11 4.08 4.44
Winter 6.35 5.13 5.64 18.90 36.79 25.06 2.16 4.37 13.07 21.32 13.31 8.05 16.31 7.59 8.66 4.72
Species richness
Spring 2.67 2.33 3.33 4.00 4.33 4.00 2.67 3.00 6.33 9.00 7.33 9.33 12.33 5.33 5.67 6.33
Sunnier 2.67 2.67 3.00 3.00 4.00 3.33 1.00 2.00 4.00 7.67 5.67 3.67 8.00 5.00 7.00 5.00
Fall 4.67 3.67 3.67 3.67 6.33 5.00 2.67 2.33 7.67 11.00 6.67 5.67 11.13 3.33 4.00 6.67
Winter 4.67 2.67 3.33 3.67 6.67 5.00 4.00 4.67 7.00 11.13 7.00 7.33 9.67 5.00 4.67 4.33 20 average diversity in all seasons and the highest average evenness in all seasons except winter (Table 3).
In all stages, there were significantly higher bird densities (T
= 19.35; df = 11, 165; p < 0.01), and more species (T = 5.47; df = 11,
165; p < 0.010) in winter than in the other seasons. Spring and fall had significantly higher densities and species richness than summer
(Table 2). This was due primarily to the large flocks of wintering sparrows.
Rodents
Significantly less rodents were trapped in Stage 1 fields than in the control sites. Stage 2 had significantly less rodents than stages 3, 4, and the controls (T = 10.09, df = 4, p = 0.039). There were no statistical differences in species richness (T = 6.26, df = 4, p
= 0.181), diversity (T = 2.969, df = 4, p = 0.563), or evenness (T =
4.49, df = 4, p = 0.344) between stages.
The species found in fields having a dense cover of summer annuals varied between trapping periods. All but 1 of the cotton rats trapped in stage 1 fields were caught during the fall in dense stands of mature Russian-thistle. Twenty two of the 24 deer mice caught in field la were trapped in the spring, 1 month after the previous season's
Russian-thistle had been burned off. None of the Arizona pocket mice and only 3 of the 46 Merriam kangaroo rats caught in stages 1 and 2 were trapped during the fall trapping period when Russian-thistle and other tall annual plants covered the fields.
Forty six and 73% of the rodents caught in stage 1 and 2, respectively, were trapped within 30 m of the field edge. All of the 21 wood rats and round-tailed ground squirrels in these 2 stages were trapped within 15 m of the field edge. Therefore, the number of rodents living soley within the plant communities in these early serai stages is even less than it appears in Table 5.
The only species caught in the retired fields but not in the control sites were the uncommon western harvest mouse and desert kangaroo rat. Field 4c is on the eastern edge of the desert kangaroo rat's range; this species is not found in Avra Valley (Cockrum 1960). Harvest mice are uncommon in nonagricultural areas in southern Arizona, but are not restricted to serai stage plant communities (Cockrum 1982).
Wood rats were trapped only in control sites, except for the 4 caught on the edge of stage 2 fields. However, wood rat dens were found in 4b and 4c. Round-tailed ground squirrels were trapped only in stage
4 fields and the control sites, or within 30 m of the edge in other fields.
Lagamorphs
Cottontails were most often found in very dense stands of
Russian-thistle in fields la and lc, and in other sites that had dense annual plant growth or low shrubs (Table 6).
With the exception of the riparian site Ca, jackrabbits were much more common in stage 4 fields and the control sites. Most jackrabbits observed in stages 1, 2, and 3 were seen within 50 m of the field edge and ran toward adjacent shrub vegetation when disturbed.
Carnivores and Other Wildlife
Coyotes visited scent-post stations on only 8 of 226 operative Table 5. Number of rodents trapped, number of species, species diversity, and evenness in 576 trap nights per field at 16 study sites in southcentral Arizona.
Study Sites Stage 1 Stage 2 Stage 3 Stage 4 Stage C la lb lc 2a 2b 2c 3a 3b 3c 4a 4b 4c Ca Cb Cc Cd Desert kangaroo rat 7
Merriam kangaroo rat 18 15 10 3 53 1 5 3 12 36 7 9 26 18
Wood rat 3 1 11 6 6
Southern Grasshopper Mouse 6 12 2 2 2 1
Arizona pocket mouse 4 6 8 3 3 18
Bailey pocket mouse 1 1
Desert pocket mouse 11 1 3251 10 20 785
Deer mouse 24 3 5 1 20 3 19 29 1 48 2 1
Western Harvest mouse 2 3 12
Hispid cotton rat 13 4 13 1 2 29 5 17 8
Round-tailed 5 5 1 10 46 37 1 46 10 38 ground squirrel
Total caught 45 30 39 24 5 2 92 10 61 46 60 93 107 68 68 67
Number of species 5545325576458784
Species diversity 1.16 1.19 1.29 1.33 0.95 0.68 1.18 1.51 1.36 1.22 0.66 1.28 1.54 1.10 1.74 1.78
Evenness 0.72 0.73 0.93 0.83 0.86 0.62 0.73 0.94 0.70 0.68 0.37 0.66 0.74 0.57 0.84 0.78 Table 6. Total number of cottontail rabbits and jackrabbits seen in 16 study sites in southcentral Arizona from June 1981 to May 1982.
la lb lc 2a 2b 2c 3a 3b 3c 4a 4b 4c Ca Cb Cc Cd
Cottontail rabbits
Sutmer 7 6 3 3 4 3 3 2
Fall 13 11 2 3 3 1 2 3 1
Winter 16 2 1 3 6 4 2 2 5 1
Spring 3 2 2 4 2 1 4 6 1
Jackrabbits
Sumter 6 1 2 1 3 4 5 6 7 5
Fall 5 1 1 1 4 1 2 7 2 6 2 8
Winter 3 3 8 2 2 1 2 11 2 6 6 4
Spring 2 1 4 3 4 2 6 4 5 6 6 5 24 station nights. Five of these visits were in sites Cb and Cc. Three
were in field 2a on consecutive nights in October. Fresh coyote sign,
however, was common in all stages, especially along field edges. Active
badger dens were found in fields la, 3c, 4b, and Cd.
Javelina scat and tracks were found in all stages except stage
1. Javelina sign was especially common in the growing careless-weed
stands in 2b and 2c during August and September and in the dense
vegetation in adjacent sites 4a and Ca. Mule deer sign was only
observed in sites 4a and Ca. DISCUSSION
Based on the assumption that succession is an orderly, community-controlled process, Odum (1969) postulated how 24 parameters would change during succession from a developmental to a mature stage; he predicted that species richness, diversity, and evenness will increase with succession.
In part because of Odum's (1969) predictions, most studies of wildlife populations along seres have examined how population attributes change with succession. Odum's hypotheses relating to wildlife populations have been tested many times with varing results. For a review see Anderson et al. (1980), MacMahon (1980), and Smith and
MacMahon (1981).
As an alternative to Odum's (1969) view, Drury and Nisbet (1973) argued that most changes associated with succession are the consequences of differential colonization, growth, and survival of populations of species adapted to different positions along environmental gradients.
Because the rate and direction of succession in desert regions is so variable, it may be more instructive to examine the structure of plant communities found in desert old-fields and the available wildlife species adapted to these plant communities than to search for some pervading pattern.
There were at least 4 structurally and physiognomically different plant communities in the 16 sites I examined: dense, tall
25 26
scattered shrubs and spinescent trees.
Dense annual vegetation over 0.5 m tall was found in stages 1 and 2 after the summer rains. The 2 common plants were Russian-thistle and careless-weed. Small dense stands of these plants were also found
in 3cf 4a, and Ca.
Areas with dense, tall annual vegetation had very high densities
of granivorous birds, especially white-crowned and Brewer's sparrows.
Brewer's sparrows were found in careless-weed stands but not Russian-
thistle, and appear to select less dense vegetation than white-crowned
sparrows. Gambel's quail, mourning doves, and other granivorous birds
were also common in sites with dense, tall annual vegetation.
Cotton rats were the only rodents common in dense annual
vegetation, Except for 1 immature male caught in careless-weed in 2b, cotton rats were only found in stands of Russian-thistle, and the
perennials Bermuda-grass and Johnson grass. Cottontails rabbits were
also common in this vegetation after the summer rains.
The second plant community, short annual grasses and forbs with
no shrubs, were found in Stage 1 and 2 fields before the summer rains
and after dead Russian-thistle blew away in the fall and winter.
Ground foraging granivorous and insectivorous birds were
abundant in this plant community, especially horned larks, vesper sparrows and meadowlarks. Aerial hawking insectivores such as shrikes
were occasionally perched on posts or Russian-thistle skeletons.
Twenty two deer mice were caught in la when it was covered with Russian-thistle seedlings. Merriam kangaroo rats and Arizona pocket 27
mice were common among Russian-thistle seedlings in lb, lc, and 2a, but
no rodent species colonized the short, dense grass in fields 2b and 2c.
Jackrabbits occasionally foraged near the edge of fields with
short annual vegetation during crepuscular hours , but I never found one
bedded in this vegetation during midday.
Tomoff (1974) and Vander Wall (1980) found that breeding bird
community structure in the Sonoran Desert was influenced most by the
physiognomic diversity of vegetation. The addition of spinescent
trees and cacti, even in small amounts, increased the number of species
found in their study areas by providing nest sites, observation posts,
and foraging substrates.
In this study, the addition of ruderal shrubs to the initial
weed and grassland serai stages did not increase avian abundance. The
ground foraging granivores and insectivores common in stages 1 and 2,
and the foliage foraging insectivores and aerial hawking species common
in stage 4 and the controls, did not use the ruderal shrub habitat in
fields 3a and 3b.
The density of birds in field 3c, however, was at least 3 times
as great as 3a and 3b in all seasons (Table 3). This may have been due
to the increased structural plant diversity from scattered mesquite and dense summer annual plant growth.
Fields 3a and 3c had the second and third highest abundance of
rodents of the 12 old-fields, but only 10 rodents were caught in 3b.
The 3 desert pocket mice and 2 cotton rats caught in 3b were trapped in
stands of dense annuals. Apparently, pure stands of the ruderal shrub desert-broom are not suitable habitat for desert rodents. 28
The shrubs and spinescent trees in stage 4 and the climax sites provided a foraging substrate for forage gleaning insectivores and perch sites for aerial hawking insectivores that were uncommon or absent in the earlier stages. These sites also attracted large numbers of wintering sparrows.
Wood rats, desert pocket mice, and round-tailed ground squirrels were more common in sites with climax community shrubs. Round-tailed ground squirrels were trapped only in stage 4 fields and the control sites, or within 30 m of the edge in other fields.
Wood rats were trapped only in control sites, except for the 4 caught on the edge of stage 2 fields. However, wood rat dens were found in 4b and 4c. Hoagstrom (1978) only found this species in Avra Valley in rocky or wash habitats and Olsen (1973) claimed that a primary requirement in their habitat is low, dense shrub cover for den sites.
The first 3 stages did not provide adequate den sites for this species.
Hoagstrom (1978) found that desert pocket mice were most abundant in association with large spinescent shrubs, and other studies have shown that this species selects areas with shrubs and trees and avoids open areas (Rosenzweig and Winakur, 1969; Wondolleck, 1975).
Jackrabbits were common in all stage 4 and climax sites except the dense riparian site Ca. Cottontails were occasionally seen in these sites, especially in areas with dense low cover.
The old-fields examined in this study were selected because they had vegetation representative of one of the serai stages.
Unfortunantely, many of the old-fields in southern Arizona have little or no vegetation on them, even many years after abandonment. 29
Management practices that encourage plant growth and succession will benefit wildlife populations on retired farmland. Piemeisel (1945) found that a combination of intense grazing, fire, drought, and wind erosion caused some old-fields in Idaho to be completely bare.
Livestock grazing should be closely monitored and burning should be restricted to ensure that old-fields do not become susceptible to wind erosion. Although not often economically feasible, seeding fields with native shrubs before abandonment and furrowing to concentrate water runoff would also benefit wildlife in retired fields. Plant growth and succession should be encouraged because each serai stage plant community has a set of wildlife species that may be found there. Appendix 1. Location of 16 study sites in southcentral Arizona.
Study site Location
la NE 1/4, NE 1/4, OCvCor* 15, T 11 s, R 10 E
lb NE 1/4, SE 1/4, C/ap 28, T 14 s, R 11 E
lc NW 1/4, NW 1/4, OCvCOP 27, T 14 s, R 11 E
2a SE 1/4, NE 1/4, Sec 11, T 15 s, R 11 E
2b NE 1/4, SW 1/4, Sec 33, T 12 s, R 10 E
2c SE 1/4, NW 1/4, ucuQnp 12, T 12 s, R 10 E
3a SE 1/4, SW 1/4, OCv 34, T 14 s, R 11 E
3b NE 1/4, SW 1/4, Sec 4, T 14 s, R 11 E
3c SE 1/4, Sw 1/4, OCvOop 5, T 13 s, R 10 E
4a NW 1/4, SW 1/4, OCvQoo 22, T 14 s, R 11 E
4b SE 1/4, SW 1/4, Cop 33, T 7 s, R 7 E
4c NE 1/4, SE 1/4, •CLOop 12, T 7 s, R 7 E
Ca SW 1/4, NW 1/4, Sec 22, T 14 s, R 11 E
Cb NE 1/4, NW 1/4. Sec 27, T 11 s, R 10 E
Cc SW 1/4, SW 1/4, Sec 28, T 12 s, R 10 E
ca SW 1/4, SW 1/4, UvvCop 28, T 12 S, R 10 E
30 Appendix 2. Common and scientific names of plants and animals listed in the text.
Common Name Scientific Name
PLANTS
Cheat grass Bromus tectorum
Med i terranean-grass Schismus spp.
Bermuda grass Cynodon dactylon
Six-weeks grama Bouteloua barbata
Needle grama Bouteloua aristidoides
Johnson grass Sorgun halepense
Salt-bush Atriplex spp.
Desert salt-bush Atriplex polycarpa
Russian-thistle Salsola kali
Careless-weed Amaranthus palmeri
London rocket Sisymbrium irio
Mesquite prosopis juliflora
Filaree Erodium cicutariun
Creosote-bush Larrea tridentata
Indian wheat Plantago insularis
Burro-weed Happlopappus tenuisectus
Snake-weed Gutierrezia spp.
Desert-broom Baccharis sarothroides
Bursage Ambrosia spp.
BIRDS
Red-tailed hawk Buteo jamaicensis
Northern Harrier Cirus cyaneus
31 32
American kestrel Falco sparverius
Gambel's quail Lophortyx gambelii
Killdeer Charadrius vociferus
White-winged dove Zenaida asiatica
Mourning dove Zenaida macroura
Roadrunner Geococcyz californianus
Burrowing owl Athena cunicularia
Common flicker Colaptes auratus
Gila woodpecker Melanerpes uropygialis
Ladder-back woodpecker Picoides scalaris
Western kingbird Tyrannus verticalis
Cassin's kingbird Tyrannus vociferans
Myiarchus flycatcher Myiarchus spp.
Say's phoebe Sayornis saya
Black phoebe Sayornis nigricans
Horned lark Eremophila alpestris
Verdin Auriparus flaviceps
House wren Troglodytes aedon
Cactus wren Campylorhynchus brunneicaillus
Mockingbird Mimus polyglottos
Bendire's thrasher Toxostoma bendirei
Curve-billed thrasher Toxostotna curvirostre
Crissal's thrasher Toxostoma dorsale
Sage thrasher Oreoscoptes montanus
Black-tailed gnatcatcher polioptila melanura
Phainopepla Phainopepla nitens Loggerhead shrike Lanius excubitor
Lucy's warbler Vermivora luciae
Yellow-runped warbler Dendroica coronata
Wilson's warbler Wilsonia pusilia
House sparrow Passer domesticus
Meadowlark Sturnella spp.
Bronzed cowbird Tangavius aeneus
Pyrrhuloxia Pyrrhuloxia sinuata
Blue grosbeak Guiraca caerulea
Green-tailed towee Chlorura chlorura
Brown Towhee Pipilo fuscus
Abert's towee Pipilo aberti
Savanna sparrow Passerculus sandwichensis
Lark bunting Calamospiza melanocorys
Vesper sparrow Pooecetes gramineus
Cassin's sparrow Aimophila cassinii
Black-throated sparrow Amphispi'za bilineata
Sage sparrow Amphispiza belli
Brewer's sparrow Spizella breweri
White-crowned sparrow Zonotrichia leucophrys
Lincoln's sparrow Melospiza lincolnii
Song sparrow Melospiza melodia
MAMMALS
Desert kangaroo rat Dipodanys deserti
Merriam kangaroo rat Dipodamys merriami White-throated wood rat Neatoma albigula
Southern grasshopper mouse Onychomys torridus
Arizona pocket mouse Perognathus amplus
Bailey pocket mouse Perognathus bailey
Desert pocket mouse Perognathus penniculatus
Deer mouse Peromyscus spp.
Western harvest mouse Reithrodontomys megalotis
Hispid cotton rat Sigmodon hispidus
Round-tailed ground squirrel Spermophilus tereticaudus
Cottontail rabbit Sylvilagus audoboni
Black-tailed jackrabbit Lepus californicus
Antelope jackrabbit Lepus alleni
Coyote Canis latrans
Badger Taxidia taxus
Javelina Tayassu tajacu
Deer Odocoileus hemionus LITURATURE CITED
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