National Park Service

U.S. Department of the Interior

Natural Resource Program Center

A History of Saguaro Cactus Monitoring in 

Saguaro National Park, 1939–2007

Natural Resource Report NPS/SODN/NRR—2009/093
ON THE COVERS

Front: Saguaro cacti, Tucson Mountain District, Saguaro National Park. NPS/E. Ahnmark.

Inside Back: Saguaro cacti, Saguaro National Park. NPS photo.
A History of Saguaro Cactus Monitoring in 

Saguaro National Park, 1939–2007

Natural Resource Report NPS/SODN/NRR—2009/093

Authors

Eric B. Ahnmark

Don E. Swann

Saguaro National Park

3693 South Old Spanish Trail

Tucson, Arizona 85730-5601

Editing and Design

Alice Wondrak Biel

Sonoran Desert Network

7660 E. Broadway Blvd., Suite 303

Tucson, Arizona 85710

February 2009

U.S. Department of the Interior

National Park Service

Natural Resource Program Center

Fort Collins, Colorado
ii National Park Service

The Natural Resource Publication series addresses natural resource topics that are of 

interest and applicability to a broad readership in the National Park Service and to others in the management of natural resources, including the scientifi c community, the 

public, and the NPS conservation and environmental constituencies. Manuscripts are 

peer-reviewed to ensure that the information is scientifi cally credible, technically accurate, appropriately written for the intended audience, and is designed and published 

in a professional manner.

Natural Resource Reports are the designated medium for disseminating high priority, 

current natural resource management information with managerial application. The 

series targets a general, diverse audience, and may contain NPS policy considerations 

or address sensitive issues of management applicability. Examples of the diverse 

array of reports published in this series include vital signs monitoring plans; “how 

to” resource management papers; proceedings of resource management workshops 

or conferences; annual reports of resource programs or divisions of the Natural 

Resource Program Center; resource action plans; fact sheets; and regularly-published 

newsletters.

Views, statements, fi ndings, conclusions, recommendations, and data in this report 

are solely those of the author(s) and do not necessarily refl ect views and policies of 

the U.S. Department of the Interior, National Park Service. Mention of trade names or 

commercial products does not constitute endorsement or recommendation for use by 

the National Park Service.

Printed copies of reports in this series may be produced in limited quantity, and are 

only available as long as the supply lasts. You may send a request to: 

 Sonoran Desert Network 

 7660 E. Broadway Blvd., Suite 303

 Tucson, Arizona 85710

This report is also available electronically from the Learning Center of the American 

Southwest (http://www.southwestlearning.org) and the NPS Natural Resource 

Publications Management website, http://www.nature.nps.gov/publications/NRPM. 

When original printed copies are exhausted, copies can be obtained from: 

 Technical Information Center (TIC)

 Denver Service Center

 National Park Service 

 P.O. Box 25287

 Denver, CO 80225-0287

Please cite this publication as:

Ahnmark, E. B., and D. E. Swann. 2008. A history of saguaro cactus monitoring in 

Saguaro National Park, 1939–2007. Natural Resource Report NPS/SODN/NRR—

2009/093. National Park Service, Fort Collins, Colorado. 

NPS D-182, February 2009
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 iii

Contents

Figures ................................................................................................................................ v

Photos ................................................................................................................................ v

Acronyms ......................................................................................................................... vii

Acknowledgements ......................................................................................................... ix

Introduction .......................................................................................................................1

The State of Saguaros, 1910–1939 ...................................................................................1

Surveys of Forrest Shreve ...........................................................................................................1

Surveys of C. S. and J. C. Wilder ................................................................................................4

Identifying the Agent of Decline, 1940–1960 .................................................................5

The U.S. Department of Agriculture: Section 17 ......................................................................5

Gill and Lightle: The 5-acre plots ..............................................................................................7

Gill and Lightle, Alcorn, and Orum: The 10-acre plots ............................................................7

Continued work in Section 17 ...................................................................................................9

Return to the Census, 1961–present ..............................................................................10

Turner and Hastings: The 9.2-acre plots .................................................................................10

Steenbergh and Lowe: Resurvey of Gill and Lightle’s 5-acre plots .......................................11

Duriscoe and Graban: 45 new plots ........................................................................................12

Orum et al.: The Saguaro Cactus Virus surveys ......................................................................16

The Mother’s Day Fire assessment ..........................................................................................16

Turner and Funicelli: Resurvey of Duriscoe and Graban’s 45 plots .......................................18

Funicelli and Turner: Resurvey of Gill and Lightle’s 5-acre plots ...........................................18

Holden and Swann: Gap Census .............................................................................................19

Conclusions ......................................................................................................................19

Notes ................................................................................................................................23
iv National Park Service
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 v

Figures

Figure 1. Combined plot locations in Saguaro National Park, Rincon Mountain District. ...........2

Figure 2. Combined plot locations in Saguaro National Park, Tucson Mountain District. ...........3

Figure 3. Map of the USDA experimental test area, “Section 17” .................................................6

Figure 4. Gill and Lightle’s original six 10-acre plots within Section 17 in the present-day 

Rincon Mountain District. .................................................................................................................8

Figure 5. Timeline showing the relationships between long-term saguaro monitoring 

projects, Saguaro National Monument/Saguaro National Park. ..................................................12

Figure 6a (above) and 6b (below). Steenbergh and Lowe’s 11 plots from 1971 and 1975. .......14

Figure 7. Duriscoe and Graban’s 45 plots from 1988–89, resurveyed by Turner and Funicelli 

in 2000. ............................................................................................................................................17

Photos

Homer L. Shantz, President of the University of Arizona, in the Cactus Forest, 1930. .................1

Saguaros in snow, 1937. ....................................................................................................................4

Young saguaro under cover of a mesquite “nurse tree” (Prosopis velutina) in the Rincon 

Mountain District, Saguaro National Park. ......................................................................................5

Juvenile saguaro. .............................................................................................................................10

Cactus Forest, Saguaro National Monument, 1935. ......................................................................11

Cactus Forest, same view, 1998. .....................................................................................................11
vi National Park Service
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 vii

Acronyms

ha hectares

NPS National Park Service

RMD Rincon Mountain District

SCV Saguaro Cactus Virus

TMD Tucson Mountain District

USDA U.S. Department of Agriculture

USGS U.S. Geological Survey
viii National Park Service
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 ix

Acknowledgements

This report highlights only long-term saguaro plot monitoring surveys completed within 

Saguaro National Monument (since 1994, Saguaro National Park) as recognized by the 

National Park Service (NPS) and contained within its archives. Many independent and 

short-term studies have been done on the saguaro cactus and other Sonoran Desert vegetation in and near the present-day borders of Saguaro National Park since the dawn of the 

twentieth century. This report by no means covers every one of those surveys. In addition 

to the researchers and scientists mentioned herein, individuals such as W. V. Turnage, A. L. 

Hinckley, W. A. Niering, W. T. McDonough, E. E. Snyder, C. Steelink, W. H. Earle, L. Benson, D. C. Bertelsen, and others have completed many short-term and periodic surveys on 

saguaros. Current work on saguaros owes much of its foundation to these and other individuals for their work and dedication. These lesser-known—but no less signifi cant—studies ranged from the carbon dioxide exchange of saguaros, to determinants of growth, to 

the characteristics of saguaro tissue fl uids. For more information on these surveys, see the 

literature-cited pages of any of the three installments of Steenbergh and Lowe’s “Ecology 

of the Saguaro” series, or browse sources in the NPS NRBIB-SAGU master fi le. 

Over the past decade, Saguaro National Park has made a great eff ort to re-locate original 

plots and data, map plots, digitize the data, and preserve the original work—and to use 

this work in developing long-term monitoring at the park. The goal is to make these data 

available for future researchers and managers, so that Saguaro National Park can learn 

from the work of the past in order to better understand its resources and make informed 

decisions in the future. Much of the data for this “research atlas” project, preserved with 

great care by generations of researchers, is now in digital format on the Saguaro National 

Park network drive. 

This report was supported by the Western National Parks Association and the National 

Park Service. The park is very grateful for the many researchers who have done work at 

the park over the years and whose work in cited in this report. We are particularly grateful 

for the ongoing work and support of researchers Ray Turner, Tom Orum, Nancy Ferguson, 

Carianne Funicelli, and Dale Turner, as well as the summary work of Joseph McAuliff e. We 

also thank Ray Turner, Tom Orum, Larry Norris, Jeff Balmat, Meg Weesner, Matt Daniels, 

and Natasha Kline for reviewing this manuscript, and Andy Hubbard of the NPS Sonoran 

Desert Inventory & Monitoring Network for help in bringing it to publication.
x National Park Service
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 1

Introduction

Saguaro National Monument was established 

in 1933, with the aim of preserving the majestic 

saguaro cactus (Carnegiea gigantea) and other 

plants unique to the Sonoran Desert.* At that 

time, research on the saguaro had been underway for nearly 30 years, and some evidence already existed that the saguaro population in the 

Tucson, Arizona, area was declining. Many factors may have been responsible for the decline, 

including cattle grazing, which led to trampling 

of both young saguaros and the brush and trees 

that provided the cover necessary for them to 

survive. As Tucson and its mining and agricultural-based economy grew, so too did the need 

for land and wood for homes. Loss of saguaro 

habitat and the deforestation of local timber 

increased through the early and middle decades of the twentieth century. Even after the 

monument’s establishment, both grazing and 

illegal collection of fi rewood continued within 

its borders for many years. In addition, major 

freezes during the winters of 1937, 1940, and 

1941 damaged or killed many of the older and 

larger saguaros (Steenbergh and Lowe 1983). 

In response to the obvious saguaro decline observed throughout the monument in the late 

1930s, eff orts to establish saguaro monitoring 

plots commenced in 1941, with the assistance 

of the U.S. Department of Agriculture (USDA) 

Agricultural Research Service. From these early “cactus-disease investigations” blossomed a 

multi-faceted network of saguaro monitoring 

projects, several of which continue today. Collectively, data from these studies have revealed 

a great deal about the decline and recovery of 

the saguaro population at the park, and have 

provided insight into some of the factors that 

aff ect the park’s signature cactus. 

The main purpose of this report is to summarize, clarify, and relate the comprehensive and 

often convoluted web of saguaro research and 

monitoring undertaken at Saguaro National 

Park since its founding (see timeline, Figure 5). 

This report is by no means a complete summary 

of every study carried out within the park, nor 

does it highlight much of the work performed 

on saguaros outside park boundaries. The focus here is on long-term studies for which data 

are currently available, with the objective of 

summarizing the methods, goals, location, history, personnel, and results of each monitoring eff ort. This document can also be used as a 

literature review to facilitate future monitoring 

projects. Figures 1 and 2 illustrate the locations 

of all plots from each major long-term monitoring project. Each separate project and corresponding plot spread is then discussed in more 

detail, in chronological order.

The State of Saguaros, 

1910–1939

Surveys of Forrest Shreve

In 1909, Forrest Shreve’s surveys on the rate of 

establishment of the saguaro became the fi rst 

recorded and published monitoring project 

concerning this unique giant cactus. Shreve’s 

work focused chiefl y on the saguaro population on Tumamoc Hill, a site just east of the 

Tucson Mountains and the present-day Tucson 

Mountain District (TMD) of Saguaro National 

Park. His surveys focused on growth rates and 

recruitment. According to his report, Shreve 

took “an exact census . . . of some 240 giant 

cacti, which formed the entire population of a 

portion of the northern slope of Tumamoc Hill, 

including easterly and westerly slopes. All the 

unbranched individuals less than 5 m. in height 

were measured.”1

 Shreve’s fi ndings represent 

*The monument became Saguaro National Park in 1994. 

Homer L. Shantz, 

President of the 

University of 

Arizona, in the 

Cactus Forest, 

1930.

SHANTZ COLLECTION, UNIVERSITY OF ARIZONA HERBARIUM
2 National Park Service

Figure 1. Combined plot locations in Saguaro National Park, Rincon Mountain District. Section 17, where saguaro experiments took place in the 1940s, is located immediately north of Loop Drive, directly under the “notch” in the park’s northwest corner.
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 3 Figure 2. Combined plot locations in Saguaro National Park, Tucson Mountain District.
4 National Park Service

some of the fi rst preliminary data on density, 

growth, and duration of saguaros. 

The individuals under 5 m in height—which 

is to say, those less than 60 years old—formed 

36% of the total population, which would indicate an average life expectancy of 175 years 

for the giant cactus in this location and habitat. There was a noticeable lack of young and 

middle-aged plants, and an abundance of fallen 

skeletons, on the steep, rocky, fl anking slopes 

of the hill. The number of younger plants was 

greater on the gentle slopes facing east and 

west, which indicates that erosion may have 

been one of the most important factors in limiting the length of life.2

In addition to collecting establishment and 

density data, Shreve did a great deal of work on 

the eff ects of freezing temperatures and frost 

on saguaros. In his 1911 report, “The Infl uence 

of Low Temperatures on the Distribution of 

the Giant Cactus,” Shreve concluded that successive hours of freezing temperatures were the 

saguaro’s most signifi cant limiting factor. This 

consensus was reached through a series of laboratory tests in which saguaros were exposed 

to varying hours of frost conditions, and also 

through fi eld observations of the saguaro stand 

near Tumamoc Hill. 

Shreve’s work, although performed at a time of 

limited technology and botanical knowledge, 

represented a momentous leap forward in the 

study of Sonoran Desert plant life. His research, 

in the early decades of the twentieth century, 

provided a strong foundation of data on saguaro growth, establishment, and limiting factors 

upon which future scientists could base their 

research. Shreve was also fi rst to note a decline 

in saguaro recruitment rates: “The striking fall 

in the establishment rate of the Giant Cactus . . 

. compels the conclusion that it is not maintaining itself. A fuller knowledge of its germination 

and the behavior of its seedlings, together with a 

more complete knowledge of the periodicity of 

certain climatic elements within its range, will 

be sure to throw light on the fall in its rate of 

establishment.”3

 The recommendations within 

this statement would come to embody the evolution and maturation of saguaro monitoring 

throughout the following century. For more 

information on Forrest Shreve’s initial rate-ofestablishment and limiting-factor surveys, see 

Shreve (1910) and Shreve (1911).

Surveys of C. S. and J. C. Wilder

Following the establishment of Saguaro National Monument, a survey similar to that of Forrest 

Shreve was performed in 1939, by Carleton S. 

Wilder and Judith C. Wilder. Their study focused primarily on saguaro population density 

and recruitment. Their survey area comprised 

three separate locations, each representative 

of the habitats upon which saguaros are found 

(lower desert fl oor, upper desert pocket, and 

foothill). The quadrant locations were not randomly selected. Instead, “The quadrants were 

selective; however, in the choice of the general 

area for counting and in consciously tending, 

once the line was started, to make counts where 

small saguaros were seen.”4

Saguaros in the “lower desert fl oor” section 

were found to be taller and denser, on average, 

than anywhere else in the park. Observations 

were also recorded about the relative occurrence of saguaro cacti and palo-verde, a plant 

that would later be identifi ed as one of the saguaro’s preeminent nurse plants. The location 

for this portion of the survey was listed as near 

the public campground, approximately two 

miles from the north entrance gate in the present-day Rincon Mountain District (exact location unknown).

The “upper desert pocket” habitat was “formed 

by the abrupt Observatory Hill [near the northern junction of the park’s current Loop Road 

with the Cactus Forest Trail], rising about a 

mile north and west of the curving base of the 

Tanque Verde mountains.”5

 Here, the saguaros 

were not observed as being clumped around 

palo-verde, as they had been in the lower desSaguaros in 

snow, 1937.

NPS HISTORIC PHOTOGRAPH COLLECTION
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 5

ert terrain. Instead, mature saguaros stood 

alone, and small saguaros (those less than 6 ft 

in height) were plentiful and located predominately beneath or near palo-verde and other 

desert scrub.

The “foothill” observations were made at the 

north end of the Skyline Loop Road, where 

steep slopes transcend to the Tanque Verde 

ridge. The greatest abundance of small saguaros 

(those less than 6 ft in height)—many of which 

were growing beneath the granite boulders that 

composed the rocky slope—were found here.

The conclusions of the Wilder study generally complemented those of Shreve’s Tumamoc 

Hill survey 30 years prior: the saguaros in the 

densest location (lower desert fl oor) were not 

replacing themselves as effi ciently as the populations at the other two test locations. According to the Wilders, “the number of young plants 

indicates the possibility of a denser stand of 

mature trees in the future than exists on these 

areas at the present time.”6 Such results were 

alarming to park staff , in that the park’s esteemed Cactus Forest was not displaying suffi -

cient levels of recruitment. These fi ndings from 

the Shreve and Wilder surveys played a major 

role in fueling a panic about saguaro extinction 

at the monument that lasted nearly 50 years. For 

more information on the Wilder census survey, 

see Wilder and Wilder (1939).

Identifying the Agent of 

Decline, 1940–1960

The U.S. Department of Agriculture: 

Section 17 (1940)

Long-term monitoring of saguaros at Saguaro 

National Monument began in 1940, at the request of the USDA Bureau of Plant Industry, 

whose offi cials initiated cactus-disease investigations after noting an increase in the spread of 

bacterial necrosis (epidermal rot) on mature saguaros. For this experimental survey, a portion 

of the northwest corner (S17, R16E, T14S) of 

Saguaro National Monument (Rincon Mountain District; RMD) was chosen (see Figure 1). 

This so-called “Section 17” was divided into 

northern and southern halves, each of which 

covered approximately 320 acres, for a total test 

area of 640 acres. The objective of the USDA 

project was to test the eff ectiveness of sanitation measures at deterring the spread of necrosis. The plan called for all infected saguaros and 

saguaro limbs from the southern “half” to be 

removed, burned, and buried, while the “data 

from the north half [were to] serve as a check or 

means of judging the eff ectiveness of the sanitation work.”7

 The progress of each half was 

then to be checked annually for the following 

fi ve years. Figure 3 shows the 640-acre USDA 

test area. 

Each half was divided into 10-acre quadrants, 

and each quadrant was subsequently labeled. 

According to a 1942 report on the project, 

“The staking [for the southern half] was begun 

in September 1941 and completed in January 

1942; 12,968 living saguaros were thus identifi ed.”8

 Data on saguaro height, mechanical injuries, and disease condition were gathered at 

the time of staking. Similar information was 

gathered for the northern half from February through March 1942. Infected plants that 

Young saguaro 

under cover of a 

mesquite “nurse 

tree” (Prosopis 

velutina) in 

the Rincon 

Mountain 

District, Saguaro 

National Park.

NATIONAL PARK SERVICE
6 National Park Service

Figure 3. Map of the USDA experimental test area, “Section 17” (Gill 1942). Individual saguaros, mapped 

using a detailed aerial photo, are represented by a single black dot. A copy of this map is available at the 

Western Archeological and Conservation Center and a digital copy is on the Saguaro National Park server.
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 7

warranted removal were felled and removed 

from February 16 to 20, 1942, with more than 

313 diseased plants removed.9

 Sanitation work 

was executed simultaneously: “Cacti marked 

for removal were felled, bucked, loaded on 

trucks, and dumped into one of four pits which 

had been previously excavated on the area. The 

cacti in the pits were fumigated with a concoction of paradichlorobenzene and kerosene and 

then covered with at least a foot of earth.”10

Over the course of the two years for which data 

were recorded, a striking decrease was found in 

the origination and spread of bacterial lesions. 

However, over a longer period, there was no 

diff erence in mortality between the treated and 

untreated sections (Gill 1951). For more information on the USDA cactus-disease investigations, including methods, results, photographs 

of the investigations and necrosis progression, 

as well as recorded data from similar investigations at Organ Pipe Cactus National Monument 

and the Tucson Mountain Park, see Gill (1942).

Gill and Lightle: The 5-acre plots 

(1941)

The fi rst permanent plots intended for repeated 

and long-term monitoring were established in 

the fall of 1941, in tandem with the USDA cactus-disease investigations. Researchers Lake S. 

Gill and Paul C. Lightle established the plots, 

while simultaneously spearheading the Section 17 project. The goals of this survey were 

(1) to learn to recognize the developing stages 

of bacterial necrosis, (2) to observe the progress and behavior of bacterial lesions and the 

cactus’s healing abilities, and (3) to determine 

the cause(s) of the disease.11 As with the USDA 

study, Gill and Lightle performed similar research at Organ Pipe Cactus National Monument. The long-term objective was “to establish 

permanent observation plots in the Saguaro 

and Organ Pipe Cactus National Monuments 

on which detailed case histories shall be kept. 

Thorough reexamination will be made at stated 

intervals.”12

Monitoring began in April 1941, and consisted 

of six 5-acre (2-ha) plots in and near the Cactus Forest of today’s Rincon Mountain District. 

These plots were numbered 41A–F and marked 

by a wooden stake in the southwest corner (see 

Figure 6a).13 Data were recorded on saguaro 

density, height, estimated age, and health (mechanical injuries, disease condition). The six 

plots were revisited three times after their initial 

establishment in 1941, and although they were 

originally intended for regular study, their existence was nearly forgotten; 34 years passed before they were resurveyed. In 1975, W. F. Steenbergh and C. H. Lowe discovered data from Gill 

and Lightle and revisited all but one plot, collecting critical and unprecedented data on growth, 

mortality, and recruitment that spanned nearly 

40 years. Gill and Lightle’s 5-acre plots were resurveyed again in 2002, by C. S. Funicelli and D. 

S. Turner. More information on these resurveys 

is discussed later in this report.

Little information is known about the precise 

data recorded at Gill and Lightle’s 5-acre plots 

in 1941–42, other than the rudimentary height, 

density, and recruitment fi gures listed in Steenbergh and Lowe’s resurvey in 1975. Data from 

these plots were recorded in Steenbergh (1980 

and 1986). 

Gill and Lightle, Alcorn, and Orum: 

The 10-acre plots (1941)

In addition to their six 5-acre plots, Gill and 

Lightle also established six 10-acre plots. 

These were also located in the Cactus Forest 

area (present-day RMD), in and around the 

vicinity of Section 17. Figure 4 shows the exact locations of these plots. It is not known for 

certain why Gill and Lightle established these 

plots simultaneously with their six 5-acre plots, 

nor why they showed diminishing interest in 

their 640-acre site and all but abandoned their 

5-acre plots, yet continued annual resurveys 

of their 10-acre plots. However, statements in 

Gill (1951) on saguaro mortality lend to the notion that the 10-acre plots (comprising 60 acres 

compared to 640 acres) were established to enable a more intimate study of each saguaro and 

its immediate environment. 

Impressively, with the exception of 1955, these 

same six plots have been surveyed annually 

since 1942, “and their condition, including 

mortality, noted. In addition, a search is made 

for young saguaros, their location is noted on a 

map, and their height measured. The heights of 

all saguaros under six feet tall are measured each 

year. Heights of taller saguaros are estimated in 

6 foot height classes and, periodically, are estimated using a clinometer.”14 Gill and Lightle, 

in association with S. M. Alcorn, recorded data 

on the six 10-acre plots from 1942 through the 
8 National Park Service

Figure 4. Gill and Lightle’s original six 10-acre plots within Section 17 in the present-day Rincon Mountain District 

(Orum and Alcorn 1991). For reference, note the park headquarters and Cactus Forest Loop Drive. 
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 9

mid-1950s, when Alcorn took over.

S. M. Alcorn became one of the saguaro’s most 

prolifi c and dedicated researchers, publishing a 

great number of reports that focused predominantly on the pollination and germination of 

the giant cactus. One of Alcorn’s more elaborate long-term studies ran from January 1942 

through January 1961, and was summarized 

in the report, “Attrition of a Saguaro Forest” 

(Alcorn and May 1962). This mortality survey 

reported on diff erent causes of saguaro death, 

with an emphasis on bacterial necrosis. Alcorn’s 

conclusions were grim. Not only had bacterial 

necrosis accounted for 29% of saguaro mortality over the course of the 20-year survey, but 

the combined eff ects of grazing (not eliminated 

on monument property until 1958) and wind 

also resulted in soil erosion that seriously impeded the growth of seedlings. These fi ndings 

led Alcorn to conclude that “the sparsity of juvenile plants indicates that this saguaro forest is 

failing to maintain an adequate rate of natural 

repopulation. . . . the continual attrition of this 

forest by BN [bacterial necrosis] and wind is . . . 

eroding the base for repopulation.”15 For more 

information on this long-term mortality survey, 

see Alcorn and May (1962). 

In 1979, Alcorn passed his monitoring of the 

six 10-acre plots on to researcher Tom Orum, 

Alcorn’s former research technician who, with 

his wife, Nancy Ferguson, have continued to 

monitor these plots for almost three decades. 

With the change in leadership came a change 

in direction; whereas in earlier years, the surveys had tended to focus on mortality and the 

progression of bacterial necrosis, both the latter years of Alcorn’s surveys and Tom Orum’s 

resurveys reverted toward study of saguaro 

density and recruitment. Orum avers that it is 

inevitably the saguaros, not the researchers, 

who deserve the credit for the change in focus 

(T. Orum, pers. comm.); saguaro recruitment 

increased so prolifi cally during the late 1970s 

and early 1980s that Nancy Ferguson even suggested changing the name of the project from 

“mortality surveys” to “annual saguaro census.” 

To date, this set of surveys represents the longest ongoing saguaro-monitoring eff ort in the 

park. Although the methods have remained relatively consistent over the past 60 years, survey 

focus and results have changed signifi cantly. 

While earlier fi ndings, from the Gill-and-Lightle era, exhibited a steady and alarming decrease 

in the saguaro population—“between 1942 and 

1972, almost no new saguaros were found”—a 

recent infl ux of growth and recruitment over 

the past 20 years has largely diff used concern 

for the saguaro’s immediate future.16 Orum 

has noted that after reaching an apparent low 

point in 1982, by 1985, “the observed original 

population seem[ed] to have deviated slightly 

in the positive direction from the predicted decline.”17 By 1990, the number of young saguaros 

in the 10-acre plots outnumbered members of 

the original population for the fi rst time since 

recording began in 1942.18 Much to the satisfaction of all those concerned with the fate of the 

saguaro, the results published in Orum and Alcorn’s 1991 “Report on the Long-term Saguaro 

Mortality Study” found saguaro recruitment to 

be on the rise. Orum, Mihail, Alcorn, and Ferguson also published supplemental reports in 

1998 and 1999, both of which confi rmed his 

encouraging results from 1991. More information on the ongoing Gill-and-Lightle/Alcorn/

Orum surveys can be found in Orum (1991, 

1998, 1999). 

Continued work in Section 17 

(1944–1960)

While focusing on their six 10-acre plots, Gill 

and Lightle also continued intermittent research 

and follow-up at the Section 17 site. A February 

1944 report on the progress of treated saguaros 

from the 1941–42 sanitation procedures led to 

encouraging and intriguing results. From the 

time the study began in 1941 until the resurvey 

in 1943, some 587 additional saguaros had died 

on the entire 640-acre test area. Of these, only 

187 (32%) were on the southern (sanitized) section, whereas the remaining 400 (68%) were on 

the untreated northern section.19 In addition, 

by this time, the bacteria were presumed to 

be transmitted through a certain moth larvae, 

making the felling and burial of diseased saguaros unnecessary. Additional studies showed 

that many lesions could be eliminated simply 

by removing them from the cacti and allowing 

the plant’s natural healing process to take over. 

Further data from the 1943 survey led to Gill 

and Lightle’s 1946 resurvey and publication 

on mortality. They discovered that, overall, 
10 National Park Service

mortality seemed to be decreasing since the 

study’s beginning, six years prior. However, 

due to the slow growth and regeneration of saguaros, it was unclear whether or not this decrease could be attributed, in part, to the USDA 

sanitation eff orts. This uncertainty, combined 

with the brevity of the survey, led to the absence of any long-term mortality predictions. 

Gill resurveyed the area again in 1951, for a 10-

year reconnaissance. Using data from 1943 and 

1946, he found there to be no signifi cant diff erence between the treated and untreated areas.20

Gill also concluded that stem rot was positively 

associated with cactus height (and presumably 

age). This, combined with the general absence 

of stem rot on younger specimens (those less 

than 12 feet in height), led to the consensus 

that bacterial necrosis was not as threatening a 

disease as once perceived, and was unlikely to 

obliterate the saguaro as a species. Gill’s 1951 

fi ndings eff ectively brought an end to bacterial 

sanitation eff orts. More information on these 

two surveys, as well as their results and fi ndings, can be found in Steenbergh (1986), Gill 

and Lightle (1946), and Gill (1951).

In 1945, Alice M. Boyle conducted a survey that 

looked deeper into the causes and spread of bacterial necrosis. Her search focused on how the 

disease was spread through the larvae of a common moth, Cactobrosis fernaldialis, whose young 

carry the bacterium and infect the cactus. 

Finally, another one of Alcorn’s studies, led by 

Ray Turner, ran from July 1957 to July 1967. 

This study took place on the USDA test area, 

but encompassed more than the aforementioned six 10-acre plots. In this survey, young 

saguaros “were transplanted into 80 plots within a 4-ha tract on level terrain . . . on July 8–10, 

1957.”21 Sixteen treatment combinations were 

surveyed; some plots were caged to deter rodents, some plots were watered, others shaded. 

More than 1,800 saguaros were planted, 1,600 

of which were less than 5 cm in height. The 

results from the plots varied signifi cantly. All 

plants in the unshaded and uncaged plots died 

or vanished within months of planting. Survival 

in the caged, although not rodent-proof, plots 

was more than twice as high as the uncaged 

plots.

The study changed slightly in 1958 and 1963, 

when the researchers added the element of rodent-proof cages and included plots at varying 

altitudes. The cages, buried to a depth of 15 cm, 

completely inhibited rodent access; interestingly, these sites experienced the highest rate 

of mortality by insects. Results from the plots 

at diff erent altitudes were inconclusive, other 

than that average mortality was highest in the 

“mountain plot,” and lowest in the “lowland 

plot.” For more information on this 10-year 

mortality and transplant survey, see Turner et 

al. (1969). 

Return to the Census, 

1961–present

Turner and Hastings: The 9.2-acre 

plots (1961–2006)

In the 1960s, a large-scale eff ort for long-term 

saguaro monitoring was initiated by researchers R. M. Turner and J. R. Hastings, authors of 

the well-received book on long-term vegetation 

change, The Changing Mile. Turner and Hastings established a set of ten 400 × 1000-ft (9.2-

acre) plots throughout southern Arizona and 

Sonora, Mexico. Of these ten, one was located 

in each of the two districts of Saguaro National 

Monument. The plots were reexamined fi ve 

times up until 1989; they were most recently reJuvenile 

saguaro. By the 

1990s, increasing 

numbers 

of younger 

plants began 

to quell fears 

of a saguaro 

“extinction.”

NATIONAL PARK SERVICE
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 11

mapped and resurveyed in 2005–2006.22

The plots have been monitored at intervals averaging about 10 years, during which data on 

mortality, growth, and recruitment have been 

recorded.23 One of the important fi ndings of 

these plot studies has been the marked increase 

in new recruitment that has occurred during 

the past 20 years, within the area of the original 

RMD Cactus Forest. This abundance of young 

cacti represents a “phenomenal population 

surge,” and has the potential to become a new 

saguaro forest in the next century.24

Turner and Hastings also discovered that although mortality in the RMD plot was signifi cantly higher than in its TMD counterpart, 

recruitment in the RMD was also signifi cantly 

higher than in the denser, healthier TMD plot. 

This suggested that the widespread fear of saguaro attrition and extinction in Saguaro National Monument was unfounded; the RMD 

Cactus Forest was not, in fact, “dying out.” 

Rather, the old, mature cacti were dying due 

to natural causes. Turner and Hastings felt that 

the fear of saguaro extinction existed simply 

because not enough consideration was given 

to life cycles—specifi cally, recruitment. In the 

latter stages of this survey, “attrition” had given way to an unprecedented surge in recruitment—such that by 1989, 76% of the RMD 

plot population had been established since 

the beginning of the study in the early 1960s.25

Conversely, the “younger” TMD saguaro stand 

was slowing in recruitment levels, and represented a diff erent level in the saguaro’s episodical cycle of growth. It is now generally believed 

that if present trends continue, the now-majestic saguaro stands in the TMD will resemble 

the present-day RMD stands in 50–100 years, 

and the now meager RMD Cactus Forest may 

return to its 1940s splendor. 

Aside from quelling the extinction panic, Turner and Hastings’s survey also played a signifi -

cant role in advancing the eff ects of prolonged 

drought as one of the principal limiting factors 

of saguaro growth. According to their survey, 

amidst the 20-year “population surge” there 

was a single year of variance, 1976, which was 

defi ned by extremely low levels of recruitment. 

This year also corresponded with one of the 

most severe droughts in the Tucson area since 

the beginning of the twentieth century.26 As 

such, this survey not only shed encouraging 

light on the saguaro’s life cycle, but also provided further insight into the giant cactus’s limiting 

factors. For more information on other studies 

of the saguaro’s limiting factors, see McAuliff e 

(1993). A full report of Turner and Hastings’s 

results from the TMD and RMD plots can be 

found in Turner (1989). In 2006, Ray Turner 

and his colleagues completed another round of 

surveys on these plots, but the results were not 

published as of this writing.

Steenbergh and Lowe: Resurvey of 

Gill and Lightle’s 5-acre plots 

(1971–1975)

Among the major contributors to modern 

knowledge of the saguaro were Warren F. 

Top: Cactus 

Forest, Saguaro 

National 

Monument, 

1935.

Bottom: Cactus 

Forest, same 

view, 1998. If 

present trends 

continue, this 

area may return 

to its former 

splendor in 

50–100 years, 

representing 

a period of 

episodic growth.

NATIONAL PARK SERVICE NATIONAL PARK SERVICE
12 National Park Service

Figure 5. Timeline showing the relationships between long-term saguaro monitoring projects, Saguaro National Monument/

Saguaro National Park.

Steenbergh, of the National Park Service, and 

the eminent ecologist Charles H. Lowe, from 

the University of Arizona. Steenbergh and 

Lowe, who did a number of studies in both Saguaro and Organ Pipe Cactus national monuments, published their fi ndings in three books: 

Ecology of the Saguaro I, II, and III, published 

in 1976, 1977, and 1983, respectively. In 1971, 

the two researchers established a single, 2-ha 

(100 × 200-m) plot, labeled 71G, near Kinney 

Road in the TMD, in which all living saguaros 

were tagged, recorded, and surveyed annually through 1975, when four additional 2-ha 

plots were established.27 One additional 2-ha 

(100 × 200-m) plot, labeled 75M, was established in 1975, approximately one mile east of 

the Madrona Ranger Station, to provide longterm data on saguaros growing on south-facing slopes.28 Also in 1975, the two researchers 

stumbled upon information that led to the relocation of Gill and Lightle’s 5-acre RMD plots 

from 1941. Of the original six, only fi ve were reestablished and resurveyed: plots 41A–F, with 

the exception of plot 41E. 

Data retrieved from these 11 plots, primarily 

height and density information, documented a 

34-year period of change (see Figure 5). Overall 

results from this resurvey were consistent with 

other density conclusions from the time: the 

saguaro was continuing to decline, although 

some areas were beginning to show increased 

recruitment of young saguaros. More information and data from this 1975 resurvey, including copies of original fi eld maps and data on 

saguaro height and density, can be found in 

Steenbergh (1986) and Steenbergh and Lowe 

(1983). 

Following the 1975 resurvey, these 11 longterm plots were not studied again for another 

27 years. However, Steenbergh and Lowe left 

behind documentation of their work, and the 

plots were resurveyed in 2002 by Carianne S. 

Funicelli and Dale S. Turner. Figures 6a and 6b 

show the locations of the 11 long-term plots 

from Steenbergh and Lowe’s 1975 establishment and survey. Plots 41A–F represent Gill 

and Lightle’s original six 5-acre plots from 1941 

(again, plot 41E was not relocated). More information on Funicelli and Turner’s 2002 resurvey 

will be discussed later in this report.

Duriscoe and Graban: 45 new plots 

(1988–1989)

The next major step in long-term saguaro monitoring came in 1988–89, when researchers Dan 

M. Duriscoe and Sandra L. Graban established 

a completely new set of forty-fi ve 4-ha plots 

throughout both districts of the monument. 

This project was carried out at the request of the 

1910: Forrest Shreve’s surveys 

on saguaro growth rate,

recruitment, and limiting

factors fuel concern about

possible extinction.

1940: USDA initiates cactus 

disease investigations

on the 640-acre Section

17, in the present-day RMD.

1941: Gill and Lightle 

establish six 5-acre plots

intended for long-term 

monitoring.

1941: Gill and Lightle 

establish and annually

resurvey six 10-acre plots.

S. M. Alcorn takes over 

operations on the six 

10-acre plots and conducts

mortality surveys, with 

grim results. 

Turner and Hastings

establish ten 9.2-acre

plots, quell extinction

fears with encouraging

results on life cycle and

limiting factors.

1910–1939 1940–1941 late 1950s 1961 

1939: C. S. and J. C. Wilder’s

findings on saguaro population

density and recreuitment cause

further alarm.

A. Boyle investigates 

the moth, Cactobrosis

fernaldialis, as a 

possible cause of 

saguaro decline.

R. Turner conducts

transplantation 

experiments (1957–1967)

to study several possible

agents of decline.

1945

Phase I: State of the Saguaros Phase II: Identifying the Agent of Decline
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 13

NPS’s Air Quality Division, due in part to recommendations from a study done the previous 

year by researcher K. W. Stolte, who found that 

epidermal browning, a brown scale on the skin 

of the plant, was a widespread phenomenon, 

and found in greatest concentration in areas of 

high saguaro mortality. Stolte’s recommendations for a more complete, long-term survey on 

the eff ects of epidermal browning led directly 

to Duriscoe and Graban’s study, which began 

months before Turner and Hastings published 

the encouraging census results from their TMD 

and RMD plots. 

The focus of the study was to “identify the extent of epidermal browning on giant saguaro 

cacti and to initiate long-term studies of population dynamics.”29 The survey’s objective was 

to “establish a system of relocatable plots that 

represent an unbiased, independent sample of 

the population and of suffi cient size and number to describe the condition of the population 

in 1989–90 in terms of incidence and severity 

of epidermal browning, population density and 

structure, and the occurrence and importance 

of associated plant species.”30

In terms of the level of consistency, data analysis, and ease of repeatability, no previous study 

compared to that of Duriscoe and Graban, 

which set the stage for a new era of long-term 

saguaro-plot monitoring at Saguaro National 

Monument. Of Duriscoe and Graban’s 45 

plots, 25 were located in the RMD, and 20 in 

the TMD. The plots were selected by fi rst dividing the environment into 45 quadrants, 

each containing approximately 1.5 square kilometers of “saguaro-type” habitat. One 4-ha 

plot was then chosen from each quadrant. This 

method provided for an even, arbitrary spread 

of plot locations throughout both districts that 

was also representative of the diff erent altitude 

levels and terrain in which saguaros are found. 

The plots were two-tiered, each being 200 × 

200-m (4-ha) square and containing a smaller, 

10 × 10-m ecological plot, from which precise 

data would be recorded, not only on saguaros, 

but also on all vegetation species present. 

In each 4-ha plot, 30 saguaros of 2 m and taller 

were selected for long-term monitoring, while 

all saguaros of 10 cm and taller were marked 

and tallied. Each 10 × 10-m ecological plot contained one of the selected saguaros at its center. 

Plots were mapped via compass, and the selected saguaros were mapped, photographed, 

and measured. All hand-drawn fi eld maps were 

digitized using AutoCAD software.31 In addition, Duriscoe and Graban noted “a need . . . 

to augment this plot system with a number of 

saguaro cactus mortality transects to add the 

Steenbergh and Lowe establish six new plots

and resurvey five of Gill and Lightle’s six 5-acre

plots, documenting 34 years of change and 

reporting a bleak outlook for mortality and

recruitment.

T. Orum takes over 

operations on the six

10-acre plots. He 

conducts annual resurveys 

at least through 2006.

Funicelli and 

Turner resurvey

11 plots, obtain

encouraging results,

and organize study 

for future resurvey.

1988–1989: Duriscoe and

Graban, studying

epidermal browning, 

survey 45 newly 

established long-term

plots, set new 

standards for 

methodology, offer

hopeful findings on

recruitment.

Funicelli and Turner 

resurvey the 45 Duriscoeand-Graban plots, results 

strengthen positive outlook.

Holden and Swann

lead census to 

retrieve data not

gathered in 2000, 

obtain encouraging 

recruitment results.

1971–1975 1979 1988–1994 2000 2002 2006–2007

1994: USGS studies 

effects of Mother’s 

Day Fire.

Phase III: Return to the Census
14 National Park Service

Figures 6a (above) and 6b (below). Steenbergh and Lowe’s 11 plots from 1971 and 1975. Gill and Lightle’s original six 5-acre plots are shown in 6a (Plot 41E was not relocated). 

6a
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 15 6b
16 National Park Service

dimension of a shorter time frame for observation of cactus death in relation to browning. . . . 

the placement of transects along washes where 

predominantly green saguaros are found and 

on adjacent bajadas where high densities of the 

brownest cacti reside will permit the detection 

of diff erent mortality rates between brown and 

green groups.”32 The establishment of these six 

mortality transects in both districts was due, 

in part, to prevailing knowledge that the mature saguaro population in the Cactus Forest 

area was in decline. Findings were as expected: mortality of the “browner” specimens was 

signifi cantly higher than that of the “greener” 

specimens. More information on Duriscoe and 

Graban’s mortality transects can be found in 

Appendix A of Duriscoe and Graban (1991).

Duriscoe and Graban generally found that the 

severity of epidermal browning was positively 

associated with height and negatively associated with spine retention, and that the condition tended to be more severe on south-facing 

slopes—suggesting that the process is worsened or expedited by more direct sunlight. Another interesting fi nd, and one that reinforced 

the fi ndings of Turner and Hastings in 1989, 

was that an “infl ux of young saguaros into the 

Cactus Forest population of the past 10 or 20 

years was documented by the fi nding of signifi -

cant numbers of plants less than 0.5 m in height 

in many plots.”33 This information helped lead 

researchers, in the early 1990s, to conclude that 

the monument’s saguaro population was making a surprising comeback. Figure 7 illustrates 

the locations of Duriscoe and Graban’s 45 

monitoring plots. 

Orum et al.: The Saguaro Cactus 

Virus surveys (1966–2000)

In 1966, S. M. Alcorn and Merritt Nelson discovered a saguaro-infecting virus. The strain, 

named Saguaro Cactus Virus (SCV), continues 

to baffl e researchers and park scientists to this 

day. The virus is diffi cult to detect, and Merritt and Alcorn eventually sought the advice of 

Dr. Zhongguo Xiong, a plant virologist at the 

University of Arizona. Together, the team discovered that the virus was related to Carnation 

Mottle Virus, a more common disease, transmitted by pollen. This led led the team to suspect that SVC was pollen-transmitted, as well. 

In 1991 and 1993, Tom Orum, together with 

Merritt Nelson and Donna Bigelow, sampled 

every fl owering saguaro in each of the original 

six 10-acre plots established by Gill and Lightle 

in 1941. In each plot, the team recorded a “high 

incidence of the virus” (T. Orum, pers. comm.). 

In most plots, a higher percentage of older saguaros was found to be infected compared to 

younger specimens (those 6–12 ft in height). 

Additionally, in 1999 and 2000, as part of a Sonoran Desert-wide study, Orum and Nelson 

completed similar research on several of Duriscoe and Graban’s plots from the 1990 epidermalbrowning study. Incidence of SCV was found to 

be higher in the RMD than in the TMD, and the 

virus was again observed to be more pervasive 

among the older specimens. Thus, according to 

Orum, “The interesting question is whether the 

virus will be transmitted to the new generation 

of saguaros that are coming along and beginning to fl ower, or if it will die out with the older 

generation” (T. Orum, pers. comm.). For more 

information on the SCV surveys, see Milbraith 

and Nelson (1972), Weng and Xiong (1997), or 

Sun et al. (2000).

The Mother’s Day Fire assessment 

(1994–2000)

In May 2004, the catalytic converter of a vehicle 

ignited a blaze in the RMD Cactus Forest area 

that burned approximately 1,200 acres of park 

land. Several park-led surveys occurred in the 

following years to assess the vegetation loss 

caused by the fi re. The eff ort was eventually led 

by Todd C. Esque and Cecil Schwalbe, from the 

U.S. Geological Survey (USGS), and ran from 

1994 to 2000. Beginning one month after the 

fi re and lasting until February 1995, the team established transects within the burned area and 

selected 436 saguaros to be monitored for fi re 

eff ects. In a research paper, Esque et al. (2004) 

stated that the “goal of setting up the transects 

was primarily to identify saguaros to monitor 

their survival over time, throughout the burned 

and unburned areas.”34 In May 1996, the USGS 

added an additional 13 transects and selected 

496 saguaros from an unburned section just 

north of the burn area. Saguaros on both the 

burned and unburned sections were resurveyed 

annually until 2000, except for 1999. The study 

also surveyed associated vegetation, although 

the primary focus was the saguaro. Included in 

the burned study area was plot #13 from Duriscoe and Graban’s 1988–89 survey.
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 17

Figure 7. Duriscoe and Graban’s 45 plots from 1988–89, resurveyed by Turner and Funicelli in 2000.
18 National Park Service

Results from this six-year study indicated 

that nearly 25% of monitored saguaros on 

the burned section were dead by 2000. However, the study also found that mortality on the 

burned section was highest in the fi rst year and 

eventually tapered off , until mortality rates on 

both the burned and unburned sections were 

nearly equal by 2000.35 The USGS has most of 

the data from this study, but some of the 1994 

plot and transect data (original data sheets, or 

copies of originals, plus GPS coordinates) are in 

the Saguaro National Park NR-Bib master fi le, 

under “Esque, T.C. et al. 2004. Saguaros under 

siege: Invasive species and fi re: Supplemental 

Data).” For more information on the Mother’s 

Day Fire saguaro assessment, see Esque et al. 

(2004). 

Turner and Funicelli: Resurvey of 

Duriscoe and Graban’s 45 plots 

(2000)

The fi rst resurvey of Duriscoe and Graban’s 

45 plots was completed in 2000, by researchers 

Dale S. Turner (no relation to R. Turner) and 

Carianne S. Funicelli. The study, sponsored 

in part by Canon USA, Inc., made area headlines and was broadcast on national television 

through a series of interviews (recordings of 

these interviews and news coverage of the 

study are available at the Western Archaeological and Conservation Center in Tucson, Arizona). Turner and Funicelli turned in two separate reports. One focused on the larger, 200 × 

200-m plots (Turner and Funicelli 2000); the 

other focused on the smaller, 10 × 10-m plots 

(Funicelli et al. 2000). Condensed versions of 

both reports were published in October 2000 

and April 2001, respectively.

Turner and Funicelli’s resurvey, in 2000, used 

Duriscoe and Graban’s study as a template for 

gathering information, allowing them to recover vital data that might have been lost had the 

resurvey not followed its predecessor so closely. 

The protocol and structure of the studies were, 

in eff ect, identical, except for a slight advancement in the technology used (the use of compass-and-grid orientation to locate plots and 

specifi c saguaros gave way to GPS coordinates, 

and digitized backups of plot maps on 51⁄4-inch 

fl oppy disks were replaced by CD-ROMs). 

Individual saguaros tagged in 1988–89 were 

relocated, studied, and rephotographed. Original plots were relocated and rephotographed, 

and precise information on vegetation growing within each 10 × 10-m ecological plot was 

recalculated. The end result was an astonishing 

collection of previously undocumented data 

on the eff ects of epidermal browning as well 

as saguaro growth, cohabitation, density, and 

recruitment. The results from 2000 confi rmed 

those from 1988–89: percent cover of epidermal browning increased with saguaro height 

(and presumably age), and was most intense on 

south-facing slopes. 

Turner and Funicelli also planned to record saguaro census data for all original forty-fi ve 200 

× 200-m plots but, for undocumented reasons, 

only recorded such data for 18 plots. From 

those 18 plots, Turner and Funicelli recorded 

encouraging results, with a mean saguaro increase of 32%.36 In 2006 and 2007, volunteers 

and NPS personnel returned to 10 of the 27 

plots not surveyed since 1988–89. Details of 

those 2006–2007 census are explained later in 

this report.

Turner and Funicelli’s 2000 resurvey represented a critical 10-year period of change, coming 

at a time when encouraging saguaro census results had been recently presented by Turner and 

Hastings, Tom Orum, and Duriscoe and Graban. Fortunately, Turner and Funicelli’s 2000 

resurvey only strengthened these results, and 

helped lead to a more positive outlook on the 

saguaro’s future. A similar resurvey of Duriscoe 

and Graban’s original 45 plots is scheduled to 

be completed in 2010. For more information on 

Turner and Funicelli’s 2000 resurvey of Duriscoe and Graban’s 45 plots, see Turner and Funicelli (2000) and Funicelli et al. (2000).

Funicelli and Turner: Resurvey of 

Gill and Lightle’s 5-acre plots (2002)

This resurvey, “Relocation and Restudy of Historic Saguaro Plots at Saguaro National Park,” 

represented a second resurvey of Steenbergh 

and Lowe’s 11 plots from 1971 and 1975 (including fi ve of Gill and Lightle’s original six 

5-acre plots). Results from this 2002 resurvey were very diff erent from Steenbergh and 

Lowe’s 1975 results, which had shown an overall decline in all age classes on combined plots 

and attributed them to the eff ects of a series of 

catastrophic freezes (though some plots in the 

Cactus Forest did show increased recruitment 
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 19

of young saguaros in 1975). The results of Funicelli and Turner’s 2002 resurvey, however, were 

similar to those of their 2000 resurvey of Duriscoe and Graban’s plots: saguaro recruitment 

was on the rise. This conclusion was reached 

due to the relatively high density of young saguaros (those less than 6 ft in height) discovered throughout the relocated plots. 

The plots were located by using a hand-drawn 

map from W. F. Steenbergh, and were studied 

from February 2001 through May 2002. Saguaro density and recruitment data were then 

collected and placed in historical perspective: 

“The current project provides a unique opportunity to put the results of Turner and Funicelli (2000) into a longer ecological time frame 

through the comparison of these data with data 

from the 11 plots that were established in 1941, 

1971, and 1975 by Gill and Lightle (1942) and 

Steenbergh and Lowe (1983).”37 Funicelli and 

Turner’s 2002 resurvey was a signifi cant step 

toward organizing this specifi c set of plots for 

future study. The fi nal report contained plot locations via GPS coordinates as well as their data 

in comparison to previous results. As of yet, 

there is no scheduled resurvey for these plots. 

For more information on Funicelli and Turner’s 

2002 resurvey, see Funicelli and Turner (2002). 

Holden and Swann: Gap Census 

(2006–2007) 

In the springs of 2006 and 2007, Saguaro National Park personnel and volunteers, led by 

Mark Holden and Don Swann, returned to 

seven plots in the TMD (plots 27, 28, 29, 32, 35, 

37, and 44) and three plots in the RMD (plots 1, 

9, and 20) that had not been surveyed for census data since Duriscoe and Graban’s survey of 

1988–89. The main purpose of the 2006–2007 

census was to “fi ll in the gaps” left by Turner 

and Funicelli’s 2000 resurvey. Whereas the 

1988–89 and 2000 studies focused primarily on 

the extent of epidermal browning, the 2006–

2007 census was concerned almost entirely 

with gathering data on saguaro density and recruitment. In addition, the 2006–2007 census 

intended to see how much (if any) growth had 

occurred across all plots (average) since 2000. 

The 2006–2007 census yielded encouraging 

results. Young saguaros (those <.5m) had increased 157% in the surveyed TMD plots, and 

an astounding 542% in the surveyed RMD plots 

since 1990. Additionally, total saguaro density 

had increased 93% across the TMD plots and 

217% across the RMD plots since 1990. When 

seedling-growth data were compared with 

fi ndings from the 2000 resurvey, fi ndings were 

congruent with those of past surveys. While 

the RMD was characterized by an increase in 

recruitment levels, TMD plots showed a slight 

decrease in average recruitment levels since 

2000. For more information on the 2006–2007 

census, see Ahnmark et al. (2007). 

Conclusions

The history of saguaro monitoring in Saguaro 

National Park can be thought of as comprising three diff erent phases (see Figure 5). These 

phases are by no means exclusive or rigid, but 

more general in nature. Each is distinct, yet 

all three are interwoven. Those phases are (1) 

the initial fi ndings, i.e., the “state of saguaros,” 

1910–1939; (2) identifying the agent of decline 

(and gaining a better understanding of the saguaro itself) and implementing a cure, 1940–

1960; and (3) ecological studies, the second 

round of census results, and the population 

surge, 1961–present.

The fi rst phase is characterized by the Shreve 

and Wilder surveys that focused on saguaro 

population density, establishment, and recruitment. Their reports constituted the foundation 

of the park’s saguaro monitoring, and their 

grim conclusions largely prompted the second 

category. 

The initial disease investigations by the USDA 

and Gill and Lightle focused predominantly 

on the causes, spread, and cure of bacterial necrosis. Other studies centered on climatic and 

anthropogenic (grazing, deforestation, and air 

quality) factors. Also included in the second 

category are the Alcorn studies on the science of the saguaro itself—its respiratory and 

circulatory systems, germination tendencies, 

cell structure, and root system. This second 

category represents the realization of Forrest 

Shreve’s 1910 call for a “fuller knowledge” of 

the saguaro. 

The third and fi nal phase is characterized by a 

focus on ecological studies and conserving the 

saguaro within its overall environment. Encouraging census results gathered by Turner 
20 National Park Service

and Hastings, Orum, Duricoe and Graban, and 

Turner and Funicelli have all confi rmed that the 

future of the saguaro in Saguaro National Park 

is looking more positive. Additionally, results 

from the 2006–2007 census helped confi rm 

that saguaro recruitment and overall population density are increasing—most notably in 

the RMD, where fears of saguaro extinction 

were greatest. 

Thus, despite immense changes in methodology and technology, the overriding purpose 

of saguaro research remains clear: to scrutinize and study the giant cactus in its respective 

habitats in order to better understand its nature 

and, therefore, provide proper and successful 

measures of preservation for its future. 
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 21

Literature Cited

Note: All sources except Steenbergh (1980) 

are available in the NPS NRBIB-SAGU master 

fi le, fi led alphabetically by author. Steenbergh 

(1980) is located in the SAGU-RMD library, 

call number QK 495.C115 U72.

Ahnmark, E., M. Holden, and D. E. Swann. 

2007. 2006–2007 saguaro cactus census, 

Saguaro National Park. Unpublished report to the Friends of Saguaro National 

Park and the National Park Service. 

Alcorn, S. M, and C. May. 1962. Attrition of 

a saguaro forest. Plant Disease Reporter 

46:156–158.

Duriscoe, D. M., and S. L. Graban. 1991. Epidermal browning and population structure 

of giant saguaro cactus (Carnegiea gigantea) in Saguaro National Monument, Arizona. Eridanus Research Associates, California. 23 pp.

Esque, T. C., C. R. Schwalbe, D. F. Haines, 

and W. L. Halvorson. 2004. Saguaros under siege: Invasive species and fi re. Desert 

Plants 20:19–55.

Funicelli, C. S., and D. S. Turner. 2002. Relocation and restudy of historic saguaro plots 

at Saguaro National Park. National Park 

Service. 16 pp.

Funicelli, C. S., P. J. Anning, and D. S. Turner. 

2000. Long-term vegetation monitoring at 

Saguaro National Park: The fi rst decade of 

change. Report to Saguaro National Park. 

Tucson, Arizona. 

Gill, L. S. 1942. Cactus disease investigations. 

U.S. Department of Agriculture, Bureau of 

Plant Industry. 23 pp.

Gill, L. S. 1951. Mortality in the giant cactus at 

Saguaro National Monument, 1941–1950. 

U.S. Department of Agriculture, Bureau of 

Plant Industry. 8 pp.

Gill, L. S., and P. C. Lightle. 1946. Analysis of 

mortality in saguaro cactus: A progress 

report on the experimental area (Section 

17 R16 ET14S) established in the Saguaro 

National Monument in 1941 for the study 

of bacterial rot. Saguaro National Park. 15 

pp.

McAuliff e, J. R. 1993. Case study of research, 

monitoring, and management programs 

associated with the saguaro cactus (Carnegiea gigantea) at Saguaro National Monument, Arizona. National Park Service. 50 

pp.

Mielke, J. L. 1944. Summary of results of control experiments on saguaro disease, Saguaro National Monument. National Park 

Service.

Milbraith, G. M., and M. R. Nelson. 1972. Isolation and characterization of a virus from 

saguaro cactus. Phytopathology 62:739–

742.

Orum, T. V., and S. M. Alcorn. 1991. Report 

on the long-term saguaro mortality study, 

Saguaro National Monument, Rincon 

Mountain Unit, Section 17. Department of 

Pathology, University of Arizona. 8 pp.

Orum, T. V., J. D. Mihail, S. M. Alcorn, and N. 

Ferguson. 1998. Tracking the next generation of saguaros in the cactus forest of 

Saguaro National Park. First conference 

on research and management in southern 

Arizona National Park Areas: Extended 

abstracts. 2 pp.

Orum, T. V., S. M. Alcorn, and N. Ferguson. 

1999. Changes in the population of saguaros in the cactus forest of the Rincon Mountain District of Saguaro National Park since 

1942. Second conference on research and 

management in southern Arizona National 

Park Areas: Extended abstracts. 2 pp.

Shreve, F. 1910. The rate of establishment of the 

giant cactus. The Plant World 13:235–240.

Shreve, F. 1911. The infl uence of low temperatures on the distribution of the giant cactus. The Plant World 14:136–146.

Steenbergh, W. F. 1980. USDA Bureau of Plant 

Industry cactus disease investigations: Reports and related correspondence, 1941–

1951. National Park Service. 

Steenbergh, W. F., and C. H. Lowe. 1976. Ecology of the saguaro I: The role of freezing 

weather in a warm-desert plant population. Pages 49–92 in Research in the parks: 

Transactions of the National Park Centennial Symposium. National Park Service 

Symposium Series No. 1. 232 pp.
22 National Park Service

Steenbergh, W. F., and C. H. Lowe. 1977. Ecology of the saguaro II: Reproduction, germination, establishment, growth, and survival 

of the young plant. National Park Service 

Scientifi c Monograph Series No. 8. 242 pp. 

Steenbergh, W. F., and C. H. Lowe. 1983. Ecology of the saguaro III: Growth and demography. National Park Service Scientifi c 

Monograph Series No. 17. 228 pp.

Steenbergh, W. F. 1986. Saguaro population 

study plots at Saguaro National Monument: 1941–1975. National Park Service. 

22 pp.

Sun, X., T. V. Orum, Z. Xiong, J. C. Guerrero, 

and M. R. Nelson. 2000. A survey of the 

spatial distribution of saguaro cactus virus 

in the Sonoran Desert in 1999. Program 

abstracts. Third Conference on Research 

and Resource Management in the Southwestern Deserts. May 16–18, 2000. Tucson, 

Arizona.

Turner, D. S., and C. S. Funicelli. 2000. Ten-year 

resurvey of epidermal browning and population structures of saguaro cactus (Carnegiea gigantea) in Saguaro National Park, 

Arizona. National Park Service. 74 pp.

Turner, R. M. 1989. Long-term saguaro population studies at Saguaro National Monument. National Park Service. 11 pp.

Turner, R. M., S. M. Alcorn and G. Olin. 1969. 

Mortality of transplanted saguaro seedlings. Ecology 50:835–844.

Weng, Z., and Z. Xiong. 1997. Genome organization and gene expression of saguaro 

cactus carmovirus. Journal of General Virology 78:525–534.

Wilder, C. S., and J. C. Wilder. 1939. Re-establishment of saguaros. Southwestern Monuments Special Report No. 26. National 

Park Service. 8 pp.
 A History of Saguaro Cactus Monitoring in Saguaro National Park, 1939–2007 23

Notes

1

 Shreve, F. 1910. The rate of establishment of 

the giant cactus. The Plant World 13:237.

2 Ibid., 237.

3 Ibid., 240.

4

 Wilder, C. S., and J. C. Wilder. 1939. Re-establishment of saguaros. Southwestern Monuments Special Report No. 26. National 

Park Service, 155.

5 Ibid., 155.

6 Ibid., 158.

7

 Gill, L. S. 1942. Cactus disease investigations. 

U.S. Department of Agriculture, Bureau of 

Plant Industry, 1.

8 Ibid., 2.

9 Ibid., 3–4.

10 Ibid., 3.

11 Ibid., 17.

12 Ibid., 17.

13 Ibid., 5.

14 Orum, T. V. and S. M. Alcorn. 1991. Report 

on the long-term saguaro mortality study, 

Saguaro National Monument, Rincon 

Mountain Unit, Section 17. Department of 

Pathology, University of Arizona, 1.

15 Alcorn, S. M, and C. May. 1962. Attrition of 

a saguaro forest. Plant Disease Reporter 

46:158.

16 Orum and Alcorn, Report on the long-term 

saguaro mortality study, 1.

17 Ibid., 1.

18 Ibid., 1.

19 Mielke, J. L. 1944. Summary of results of control experiments on saguaro disease, Saguaro National Monument. National Park 

Service, 1.

20 Gill, L. S. 1951. Mortality in the giant cactus at 

Saguaro National Monument, 1941–1950. 

U.S. Department of Agriculture, Bureau of 

Plant Industry, 1.

21 Turner, R. M., S. M. Alcorn and G. Olin. 1969. 

Mortality of transplanted saguaro seedlings. Ecology 50:837.

22 Turner, R. M. 1989. Long-term saguaro population studies at Saguaro National Monument. National Park Service, 3.

23 McAuliff e, J. R. 1993. Case study of research, 

monitoring, and management programs associated with the saguaro cactus (Carnegiea 

gigantea) at Saguaro National Monument, 

Arizona. National Park Service, 20–21.

24 Ibid., 21.

25 Turner, R. M., Long-term saguaro population 

studies, 3.

26 Ibid., 21.

27 Steenbergh. W. F. 1986. Saguaro population 

study plots at Saguaro National Monument: 1941–1975. National Park Service, 

1–2.

28 Ibid., 2.

29 Duriscoe, D. M., and S. L. Graban. 1991. Epidermal browning and population structure 

of giant saguaro cactus (Carnegiea gigantea) in Saguaro National Monument, Arizona. Eridanus Research Associates, California, 2.

30 Ibid., 3.

31 Ibid., 8–10.

32 Ibid., 31.

33 Ibid., 2.

34 Esque, T. C., C. R. Schwalbe, D. F. Haines, 

and W. L. Halvorson. 2004. Saguaros under siege: Invasive species and fi re. Desert 

Plants 20:50.

35 Ibid., 51.

36 Turner, D. S., and C. S. Funicelli. 2000. Tenyear resurvey of epidermal browning and 

population structures of saguaro cactus 

(Carnegiea gigantea) in Saguaro National 

Park, Arizona. National Park Service, 12.

37 Funicelli, C. S., and D. S. Turner. 2002. Relocation and restudy of historic saguaro plots 

at Saguaro National Park. National Park 

Service, 2.
24 National Park Service
The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides 

scientifi c and other information about those resources; and honors its special responsibilities to American Indians, Alaska 

Natives, and affi liated Island Communities.

NPS D-182, February 2009
Natural Resource Program Center 

1201 Oak Ridge Drive, Suite 150 

Fort Collins, Colorado 80525

www.nature.nps.gov

National Park Service

U.S. Department of the Interior

EXPERIENCE YOUR AMERICATM