Ecological Archives E094-151-D1

Susana Rodriguez-Buritica, Helen Raichle, Trevor Birt, Robert H. Webb, Raymond N. Turner, Elizabeth A. Pierson, and D. Lawrence Venable. 2013. Population dynamics of Sonoran Desert saguaro cactus (Carnegiea gigantea) at the Desert Laboratory (Tucson, Arizona). Ecology 94:1660. http://dx.doi.org/10.1890/13-0182.1


Introduction

Long-term species-specific monitoring programs are an invaluable source of information regarding how species and populations respond to short-term fluctuations and long-term trends of environmental conditions. Moreover, whenever long-term monitoring programs explicitly record the location of each individual, they can help us understand the emergence of spatial patterns and their effect on long-term population dynamics. Theoretical work on the emergence and effects of spatial patterns has focused on experimental plant populations or computer-simulated scenarios, but there is little information regarding whether theoretical expectations hold true in natural populations. Here, we describe one of the longest spatially-explicit field data sets for a single species, which could be used to explore the effect of spatial heterogeneity on long-term population dynamics.

The saguaro (Carnegiea gigantea [Engelm.] Britton & Rose) is one of the most iconic cactus species in the Sonoran Desert, commonly found throughout southern Arizona and western Sonora, Mexico (Turner et al. 1995) in areas with substantial summer rainfall (Hastings 1961, Turner et al. 1995). Its abundance and distribution make it a keystone species in the eastern Sonoran Desert communities. Many animal species depend on saguaros for water, nutrition, and nest sites, and performance of other common desert plant species is heavily influenced by proximity to saguaros (Steenbergh and Lowe 1983, Turner et al. 1995).

Saguaros have been the subject of extensive research that ranges from defining the traits that explain their success in deserts (e.g., Hastings 1961, Kee and Nobel 1986) to factors limiting their reproduction, recruitment and survival (e.g., Niering et al. 1963, Steenbergh and Lowe 1977, Brum 1973, McAuliffe and Janzen 1986, Drezner and Balling 2002). More recent work has focused on the effect of long-term local and regional changes on saguaro populations. The saguaro’s highly predictable size- age relationships (Hastings and Alcorn 1961, Steenbergh and Lowe 1983, Turner 1990, Parker 1993, Bowers et al. 1995, Bowers 1997, Pierson and Turner 1998) make them ideal for studying changes in population structure. These studies have shown that saguaro population peaks are usually linked to periods of wetclimatic conditions, (Pierson and Turner 1998, Drezner 2006, Drezner and Balling 2008, Danzer and Drezner 2010, Pierson et al. 2012).

Research on factors affecting saguaro life-history, much of it conducted at the Desert Laboratory in Tucson, Arizona, have shed light on why saguaro populations show such large fluctuations in density. Saguaros recruitment is correlated to particular climatic conditions (Shreve 1917, Steenbergh and Lowe 1977, McAuliffe 1988, 1990, Turner 1990, Parker 1993, Bowers et al. 1995). Furthermore saguaro populations, do not have persistent seed banks (Bowers 2005) and seedlings are highly sensitive to freezing conditions (Shreve 1911, Steenbergh and Lowe 1977, Nobel et al. 1986). These are some of the factors that limit saguaro recruitment at the saguaros northern limit and during cold years. With these limitations, recruitment episodes occur under higher than normal summer precipitation and lower than usual maximum summer temperature during the first years of establishment (Brum 1973, Steenbergh and Lowe 1977, Drezner and Balling 2002). In some cases, these conditions may be linked to climate changes induced by volcanic eruptions (Drezner and Balling 2008).

Beyond demonstrating the potential link between favorable climatic conditions and peaks of recruitment, the data presented here have been used to disentangle microclimatic and topographic effects on long-term fluctuations of saguaro populations. Pierson and Turner (1998) concluded that recruitment, more than growth or survival, is highly influenced by microclimatic conditions resulting from topographic differences. Recruitment is favored on slope aspects that reduce the impact of extremely low temperatures during winter months due to a faster warming in the first hours of the day. Similarly, their analyses demonstrated that although the saguaro population at the Desert Laboratory experienced episodic regeneration events that could be linked to relatively wet conditions, current poorer regeneration suggests that local factors may be paramount. Furthermore, when the Tumamoc Hill data were compared with regional data, Pierson et al. (2012) observed that populations at some sites in the Tucson Basin had experienced equal or greater variability in regeneration whereas other populations remained relatively constant.

Analyses derived from these data have been fundamental to advancing our understanding of the response of saguaro to variation in climatic conditions, our understanding of the importance of episodic recruitment events to maintain viable populations, and deciphering population-level consequences of individual response to different microclimatic conditions. This data set constitutes one of the longest spatially explicit monitoring efforts for a single species. Further collection and analysis of this system may shed light on spatially explicit population dynamics and long-term changes attributable to global change.

Metadata

Class I. Data set descriptors

A. Data set identity: Title: Population dynamics of Sonoran Desert saguaro cactus (Carnegiea gigantea) at the Desert Laboratory (Tucson, Arizona)

B. Data set identification code: NA

C. Data set descriptors

1. Originators: Raymond M. Turner -5132 East Fort Lowell Road, Tucson, AZ 85712, rayturner@cox.net; Susana Rodriguez-Buritica — Department of Ecology and Evolution Biology, University of Arizona. Tucson, AZ 85721, susanarburitica@email.arizona.edu and Elizabeth A. Pierson — Department of Horticultural Sciences, Texas A&M University, College Station, TX 7843-2133, eapierson@tamu.edu
Archivists are: S. Rodriguez-Buritica, Helen Raichle  — U.S. Geological Survey, 520 N. Park Avenue, Tucson, AZ, 85719, hraichle@usgs.gov and Trevor Birt  — U.S. Geological Survey, 520 N. Park Avenue, Tucson, AZ, 85719, tbirt@usgs.gov-

2. Abstract:

The saguaro cactus (Carnegiea gigantea) is one of the most iconic perennials in the Sonoran Desert. The ecological importance of this species has motivated studies that explored its physiological adaptations to deserts, factors controlling its recruitment and distribution, and changes in its population density and extent over time. The population of saguaros on Tumamoc Hill (Tucson, Arizona) is one of the best studied. Saguaros on and nearby Tumamoc Hill were mapped in 1908, and in 1964 R. M. Turner and J. R. Hastings established four 250-m wide plots within the original census area. Plots were established on the north, south, east, and west-facing slopes of Tumamoc Hill, and each plot extends from the top to the base of the hill. Plots were resurveyed in 1970, 1987, 1993, and between 2010 and 2012. In this data paper, we present all information associated with this monitoring program, which includes digital versions of Spalding’s original 1908 saguaro map as well as information regarding individual saguaros located in each of the four plots. Collected data include plant height, number of branches, and plant condition, as well as plant location. Starting in 1993, we also noted the identity and condition of plant species growing in close proximity to each saguaro. The archived data set described here contains information pertaining to >5800 saguaros.

Past analyses of these data include reconstructions of regeneration patterns from observed age structures and the determination of the average height-specific growth rates for plants on each slope. The findings from these studies have broadened our understanding of the relationship between saguaro regeneration patterns and climate. These data have also provided pivotal information regarding regional trends of saguaro populations throughout the Sonoran Desert. As a group, the Tumamoc Hill censuses constitute one of the longest spatially explicit monitoring efforts for a single species in the world. They provide an observational baseline for future comparisons relating individual growth and population demographics to rising CO² levels, climate change, vegetation change, or changes in other biotic or abiotic factors.

D. Key words: Carnegiea gigantea; long-term monitoring; permanent plots; population dynamics; saguaro cactus; Sonoran Desert; spatially explicit data

Class II. Research origin descriptors

A. Overall project description

1. Identity: Spatially explicit population dynamics of Sonoran Desert saguaro cactus (Carnegiea gigantea) at the Desert Laboratory (Tucson, Arizona)

2. Originator: V. Spalding, Desert Botanical Laboratory (between 1906 and 1928). Permanent plots established by R. M. Turner, 5132 East Fort Lowell Road, Tucson, AZ 85712, rayturner@cox.net and James R. Hastings. Subsequent field studies conducted by R. M. Turner in 1970, R. M. Turner (and T. L. Burgess and J. E. Bowers) in 1987, and E. A. Pierson in collaboration with Turner and J. L. Betancourt in 1993. Recent contributors include Susana Rodriguez-Buritica, Department of Ecology and Evolution Biology, University of Arizona. Tucson, AZ 85721, susanarburitica@email.arizona.edu; Helen Raichle, U.S. Geological Survey, 520 N. Park Avenue, Tucson, AZ, 85719, hraichle@usgs.gov; Trevor Birt, U.S. Geological Survey, 520 N. Park Avenue, Tucson, AZ, 85719, tbirt@usgs.gov; and Robert H. Webb, U.S. Geological Survey, 520 N. Park Avenue, Tucson, AZ, 85719, rhwebb@usgs.gov.

3. Period of Study: 1908–2012

4. Objective:To provide long-term documentation of the growth rate, branching frequency, and condition of individual saguaros and demographic parameters including density, survival, recruitment rates, and age structure of saguaro populations relative to slope aspect.

5. Abstract: Same as above.

6. Source(s) of funding:Carnegie Institute of Washington; U.S. Forest Service; U.S. Geological Survey; National Science Foundation DEB 0817121.

B. Specific subproject description

1. Site description:

a. Site type: Tumamoc Hill rises 245 m above the surrounding alluvial plain to an elevation of 960 m (a.s.l.); it is within the 3.52 km² of the Desert Laboratory owned by the University of Arizona, and it is surrounded on the west by 1.12 km² of protected land owned by Pima County and on the East side by 1.1 km² that constitutes Sentinel Peak Regional Natural Resource Park, owned by the city of Tucson. Out of the four permanent saguaro plots established in 1964 only the east most portion of the east plot is outside the Desert Laboratory (Fig. 1). Vegetation of the Desert Laboratory is characteristic of the Arizona Upland Division of the Sonoran Desert (Goldberg and Turner 1986).

b. Geography: The Desert Laboratory is located about 2 km west of downtown Tucson, Arizona (32° 13'12.281" N, 111° 0'16.098" W) on a volcanic outcrop of the Tucson Mountains. Slopes at the Desert Laboratory range from predominantly gentle on the lower north aspect (mean = 63% slope) to steep along the south (mean = 109% slope) and east (mean = 129% slope) aspects.

c. Habitat: Dominant vegetation on Tumamoc Hill includes Parkinsonia microphylla (Torr.) Rose & I.M. Johnson, Carnegiea gigantea (Engelm.) Britton & Rose, Larrea tridentata (Moc. & Sess.) Cav., Fouquieria splendens Engelm., Ambrosia deltoidea (A. Gray) Payne, Encelia farinosa A. Gray, Aloysia wrightii (A. Gray) Heller, Opuntia engelmannii Salm-Dyck, and Ferocactus wislizeni (Engelm.) Britton & Rose as dominant species.

d. Geology: Tumamoc Hill is dominated by volcanic rocks (Spencer et al. 2003), mostly Tumamoc basaltic andesite (middle Tertiary: ~23–24 Ma) along the north slopes and at the higher elevations along all other three sides of the mountain. At upper and middle slopes on the west, south, and east sides, the rocks are Tumamoc tuff (middle tertiary: ~ 26–28 Ma) and a conglomerate (~26–28 Ma). The lower slopes are dominated by Mafic volcanic rocks (early Tertiary or late Cretaceous), particularly on the west side, and basaltic andesite (~26–28 Ma). A large area of the Desert Laboratory to the west consists of colluvium and alluvium of mostly Quaternary Age dissected by washes (Webb and Turner 2010). Soils on steep slopes generally are shallow and are clay soils with petrocalcic horizons and surficial colluvial basalt boulders. Sandy soils relatively free of rocks dominate the lower slopes (Phillips 1976). In these areas, many of the soils on higher geomorphic surfaces are middle Pleistocene to late Tertiary in age and have surfaces littered with caliche rubble that originated in petrocalcic horizons.

e. Watershed/hydrology: Tumamoc Hill is drained by small ephemeral washes that form high-angle chutes on the steepest slopes of all four sides. Silvercroft Wash, with its headwaters west of the Desert Laboratory, passes across the northwestern quarter of the grounds, and one of its tributaries creates the west boundary of the west saguaro plot. The alluvial landscape that constitutes the western half of the property is mostly attributed to sedimentation by this ephemeral wash.

f. Site history: The Carnegie Institution of Washington established the Desert Botanical Laboratory (352 ha) in 1903 to explore the nature of plant adaptations to the desert. In 1907, the property was fenced in to exclude livestock grazing and prevent the extraction of rocks and vegetation (Shreve 1929), which had been occurring since 1858. The site has been a location of repeated study since receiving this protection. Thus, the Desert Botanical Laboratory grounds are among the oldest ecological study sites in the world. In 1940, the Carnegie Institution transferred the property to the U.S. Forest Service, which then sold it to the University of Arizona in 1956. At some unknown point in time, but after the University of Arizona acquired the property, the name was shortened to the Desert Laboratory. Further information about the history and other long-term projects at the Desert Laboratory can be found in Bowers (2010) and Webb and Turner (2010).

Disturbance History: Several disturbances have affected plant community dynamics on the Desert Laboratory, including direct disturbances of some of the plots that led to partial plot destruction (Fig. 1). Road construction at various times caused disturbances in and adjacent to the north plot. In 1933, 1955, 1981, 2003, and 2004, several parts on the north and west sides of Tumamoc Hill were disturbed by the installation and subsequent replacement of gasoline and natural gas pipelines, most recently in 2003. Here, we summarize the major events based on a compilation by Janice Bowers in 2002, which can be found in the files at the Desert Laboratory on Tumamoc Hill. Unless otherwise specified, saguaro permanent plots have not been directly affected by these disturbances.

  1. Evidence of human activities at Tumamoc Hill extend to ca. 2300 BP with an early agricultural period (Wallace et al. 2007). At this time indigenous people built a town at the top of the hill that was surrounded by a trinchera (massive dry-laid masonry walls). Later, the Hohokam occupied Tumamoc Hill leaving evidence of extensive residential use, farming, and ceremonial activities (A.D. 850–1300; Wallace et al. 2007). Between ca. 1450 and 1757, occupation and use of Tumamoc Hill diminished. At the end of this period, colonial settlements were established along the Santa Cruz River to the east, and the city of Tucson was founded in 1775.
  2. Cattle, horse, goat, and burro grazing occurred between 1858 and 1907. Stocking rates are unknown but considered to be light.
  3. In 1907, property was fenced and protected from grazing as well as removal of rocks and native plants.
  4. In 1933, El Paso Natural Gas installed a natural-gas pipeline with a 9.14 m wide easement across the northeast side of the property.
  5. In 1955, Southern Pacific constructed a 15.24 cm wide natural gas pipeline and a 20.32 cm wide petroleum pipeline along with a 12.19 m wide easement on the west side of Tumamoc Hill. Kinder Morgan Energy Partners (KMEP) now owns this pipeline. The west saguaro plot was cut by a section of this gas pipeline.
  6. In 1981, a flood-control dike was constructed east of Silvercroft Wash and south of Anklam Road.
  7. In 2003, KMEP installed a new 30.48 cm wide pipeline. The total construction easement was 27.43 m wide, although a narrow strip along the eastern edge of the easement was not re-disturbed. Cacti and ocotillos (O. engelmannii, Cylindropuntia versicolor (Engelm. Ex Toumey) F.M. Knuth, C. fulgida (Engelm.), C. kleiniae (DC.) F.M. Knuth Carnegiea gigantea, F. wislizeni, Echinocereus fasciculatus (Engelm. Ex B.D. Jacks) L.D. Benson, Mammillaria grahamii Engelm., F. splendens) were salvaged from the easement and re-planted in 2004 along the easement. Except for the northernmost section (approximately 200 m in length), the entire easement was hydroseeded with seeds of shrubs and short-lived perennials. This installation directly affected the previously disturbed section of the west saguaro plot. A series of repeat photographs taken in 1958, 1978, and 2003 show that considerable recovery occurred on the easement between 1955 and 2003.
  8. In August 2003, El Paso Natural gas replaced portions of the pipeline and installed a launcher station at City Gate #1. A section of easement about 192 m in length and 9.6 m in width was cleared of vegetation. F. splendens, cacti (O. engelmannii, C. versicolor, E. fasciculatus, F. wislizeni, C. gigantea, M. grahamii), and shrubs and trees (Prosopis velutina Wooton, Parkinsonia microphylla, Acacia constricta A. Gray, F. splendens) were salvaged and replanted.
  9. In January 2004, the El Paso Natural Gas revegetated the easement. Salvaged plants were transplanted along with shrubs and cacti (A. deltoidea, L. tridentata, Krameria grayi  Rose & Painter, F. splendens, O. engelmannii, C. versicolor) from a nursery. Salvaged shrubs and trees were transplanted to the outside edge of the easement. In mid-January 2004, the easement was hydroseeded with seeds of shrubs and short-lived perennials. The seed mix included warm-season and cool-season germinators. Between 2004 and 2005, El Paso Natural Gas easement was sprinkler-irrigated.
  10. In 2005, drilling was conducted along the flood-control dike, causing local, light damage; shrubs and cacti were crushed by heavy equipment, and the ground was rutted where vehicles crossed the property.

g. Climate: Mean annual precipitation at Tumamoc Hill is approximately 298 mm, with 36% of precipitation occurring between November and March and 53% occurring between June and September (Webb and Turner 2010). Considering the decadal variability in precipitation, Turner et al. (2003) identified two wet and two dry periods affecting the Desert Laboratory since 1906. The two wet periods were from 1906 to 1940 and from mid 1970s to 1998, while the drought periods were from the mid-1940s to early 1960s and the 12 years following 1999 (Turner et al. 2003).

2. Experimental design:

a. Area selection

In 1908, V. Spalding commissioned the survey and mapping of saguaros on and adjacent to Tumamoc Hill, including those located on Sentinel peak, just east of Tumamoc Hill, and a section of the lower elevation plains west of Tumamoc Hill (Fig. 1).

In 1964, R. M. Turner and J. R. Hastings established four saguaro plots that are a subset of the Spalding mapped area. The plots were established on the north, south, east, and west-facing slopes of Tumamoc Hill. The placement of the four plots was designed to explore the effects of slope aspect on saguaro growth and demography (Pierson and Turner 1998). Plots were located in areas that represented the common condition at each aspect (same mesoclimate and substrate); thus areas that experienced major disturbance were avoided (R .M. Turner, personal communication). At that time, boundaries of all plots were defined on aerial photographs (scale 1:1800). In the field, final plot boundaries were adjusted to only include saguaros that grew in areas with the specified aspect. To avoid disturbance associated with Desert Laboratory’s administrative buildings, the North plot was divided into two subplots that were established up and downslope from the main administrative areas (Fig. 1); and the lower subplot was narrowed at the top to avoid areas with predominant west and east exposures (see Table 1 for details regarding each plot).

Fig1

Fig.1. Saguaro permanent plots at Tumamoc Hill. Plots were established in 1964. Purple lines show the extent of the 1908 survey that mapped all saguaros on and immediately adjacent to Tumamoc Hill; outline to the left is from plate 16 and outline to the right is from plate 15 from Spalding (1909). The digital aerial orthophoto graph (NAIP 2010; 1 m resolution) was provided by USDA-FSA-APFO Aerial Photography Field Office.


 

b. Data collection period and frequency

In 1908, the locations of all saguaros in the census area were recorded on two maps (Fig. 1 and files for Plates 15 and 16 –Spalding 1909). The resulting two maps show the location of saguaros and prominent physical features.

In 1964, Turner and J. R. Hastings censused the four saguaro plots. These plots were re-censused at least three more times between 1970 and 2012 (summarized in Table 2). In each of the field studies (1964–2012) the following data were recorded: individual identification number, location, size (height and number of branches) and plant condition (e.g., injuries). In 1993 and 2012, the PIs of each census collected additional information relating to plant location and condition, as well as the identity and condition of associated plant species (summarized in section II.3.A).

During every census an attempt was made to include all detectable saguaros. Recently germinated or very small saguaros (saguaros smaller than approx. 5 cm) are hard to detect in the field, so these very small saguaros were likely to be underrepresented or absent from all census data. Table 3 summarizes data collected at each census.

Table 1. Geographic attributes of four saguaro permanent plots at the Desert Laboratory. Each 250 m wide plot established in 1964 includes areas with the same aspect from the top to the bottom of Tumamoc Hill. Plot boundaries can be found in the file, Boundaries.shp

 

North

South

East

West

Total area

Upper: 6.55 Ha
Lower: 6.90 Ha

14.2 Ha

10.1 Ha

15.5 Ha

Average and Range
(in parenthesis) of Slope

Upper: 108.70% (782.5)
Lower: 62.98% (376.5)

109.01% (1632.2)

128.93%
(997.9)

105.64%
(961.6)

Range of Elevation

Lower: 721.8–815.2 masl
Upper: 841.7–944.4 masl

751.7–948.6
masl

762.7–945.9 masl

735.3–942.9 masl

 

Table 2. Data collection schedules and participants for saguaro censuses at the Desert Laboratory since 1908. Census period indicates the beginning and the end of the entire census. For 2010–2012, the census period is specified for each plot with the name of the plot indicated in parenthesis (N = north; W = west; E = east; S = south). Names with asterisk (*) correspond to the principle investigator for the census. ** indicates that not all plots were censused that year, only the North plot.

Census Year

Census period

Contributors

1908

Map finished in April 1908

J. C. Blumer and M. V. Spalding*

1964

February–April

J. R. Hastings, R. M. Turner*,
R. Harris, S. A. McClanahan

1970

January–March

Turner*, D. K. Warren

1987**

May

Turner,* T. L. Burgess and J. E. Bowers

1992–1993

August 1992–July 1993

E. A. Pierson*, Turner, and Bentancourt
(other collaborators: Bowers and Burgess;
surveyors: E. Stoll and R. Neubaur)

2010–2012

December 2010–March 2011 (W);
March–April 2011 (N);
April 2011 & January–March & Jun3 2012(S);
March–May 2012 (E)

S. Rodriguez-Buritica*, T. Birt,
H. Raichle, Turner, R. H. Webb,
D. Baumgartner, S. Carmichael,
M. Snyder, J .Madsen,
T. Esque and crew; D. Swann and crew.

 

3. Research methods

a. Field methods

General field protocols

1908 Census on Desert Laboratory: In 1908, Jacob Corwin Blumer mapped all saguaros in a 700 ha area that included Tumamoc Hill by request of V. M. Spalding (Spalding 1909 and Fig. 1). Maps were drawn at a scale of 1:6000 using a plane table (Plate 15 and 16 in Spalding, 1909). There is no information regarding the minimum size of saguaros included on the map, but based on the density of vegetation and the ability of surveyor to find small plants from a distance, it is logical to assume that only saguaros larger than 30 cm in height were included. In 2011, these maps were scanned, georeferenced, and converted to shapefiles using ArcGIS v. 10. See V.B.2 for details on these procedures.

1964, 1970, and 1987 Censuses: In 1964, all saguaros located within each plot were assigned individual identification numbers and identified on the aerial photographs that were used to define plot boundaries in 1964. The relative position of each saguaro (identified by ID number) was also indicated on hand-drawn field maps. For small saguaros not visible on aerial photographs, approximate locations were recorded. The maps generated in this fashion were not georeferenced or spatially adjusted and were used in 1970 and 1987 to identify new and surviving plants (see Identity section below). In addition location data, size (height and number of branches) and overall plant condition were recorded for each plant (Table 3). Height was estimated using direct methods (measuring rod or tape measure: see Size measurements below for details). Using the same methodology, all four of the plots were re-surveyed in 1970. Only the north plot was re-surveyed in 1987. In both the 1970 and 1987, newly established or discovered saguaros were assigned combination identifiers (ID number of the closest large saguaro plus an alphabetical character, e.g., 1A— see Identity information below). Some information regarding the plant species associated with individual saguaros also was collected in both of these censuses.

1992–1993 Census: In 1992, Pierson, Turner, and Betancourt initiated a census project with the following objectives: (i) to determine whether the individual saguaros in the 1964–1987 censuses could be unambiguously identified in the field (after ~23 years in most plots) and if so, re-survey the plots providing additional census data; (ii) collect additional information regarding: the condition of saguaros (e.g., injuries and factors that may have contributed to altered growth rates, branching, or mortality), height-specific flowering frequency, and the plant species associated with each saguaro (for comparisons among plots); (iii) verify plot-specific height-growth and height-age relationship models based on the height-specific growth rates observed in each plot between 1964 and 1970 (by comparing the actual height of saguaros to their predicted height based on the models); (iv) use the plot-specific models to predict the establishment date of each plant and reconstruct population regeneration patterns from the age structure of saguaro populations on each slope at each census date; (v) summarize and publish findings from all previous studies; (vi) provide more permanent information regarding the location and identity of individual plants (including digital survey data and permanent field makers for many individual saguaros); (vii) store information in digital format until data could be archived. The 1993 project involved a series of steps/censuses that were completed over the course of nearly one year. All field work and data analyses were performed by Pierson with the aid of many field volunteers unless otherwise indicated.

Identification census: In August 1992, with the help of Turner, the boundaries of the 1964 plots were determined and Pierson began the process of identifying individual saguaros in the field. With no permanent field markings, unambiguous identification of individual saguaros initially was based on the location saguaros marked in the aerial photographs, the hand-drawn field maps showing the relative position of every saguaro by ID number, and information about the appearance of the plants (height, number of branches, injuries) recorded in the previous censuses. This basic information was substantially augmented after height-specific growth rates (1964–1970) and the height measurements recorded in the 1970 and 1964 (and 1987 north plot only) census were used to predict the heights of individual plants 23 and 29 (and 6, north plot only) years later. By the end of 1992, all living plants identified in previous censuses had been located and tagged (using aluminum write-on tags and large nails to secure tags to the ground), all newly discovered plants had been tagged, and all missing but previously identified plot members were verified as dead (by finding the corpses) or listed as missing. Additionally, notes on general saguaro appearance/condition were taken at this time.

Survey census: A total station (TS, see section Instrumentation for details) was used to provide a more permanent, spatially-corrected record of the location of individual saguaros. In 1993, the survey censuses of the west, south, east, and north plots were conducted in January–February, February–March, March, and April, respectively. During these censuses, heights of plants > 2 m (where the surveyor had a clear view) were determined trigonometrically (see section Size Measurements below for details) from the survey data; heights of visually blocked and smaller plants were measured directly (Pierson and Turner 1998). All other data except flowering information were collected at this time. In order to make the field plots more useful to current and future investigators, many of the aluminum tags were replaced with more permanent aluminum angle iron on which individual ID number were hand-stamped. These stakes were driven into the ground close to the saguaro base without risking damage to support roots (see section for Identity). These markers combined with survey data provided more permanent information regarding the location of each saguaro. The saguaro location data were georeferenced during 2010–2012 censuses (see section V.A.3.b).

Flowering census: All saguaros were revisited once during late April-June by Pierson and plants were evaluated for the presence of flowers (and/or fruit). Although a small amount flowering can occur during the late summer, no census was made during this period.

Exceptions: Although an attempt was made to revisit all parts of all plots, the upper portion of the south plot was not revisited due to an inability to unambiguously identify plants from the previous surveys and safety concerns for volunteers on the steep, unstable slope. Therefore, the plants in this part of the south plot were not measured in the 1993 census, and none of the plants were permanently staked at that time. Additionally, although an effort was made to stake every saguaro, at some locations newly discovered plants were identified only using aluminum tags (secured by nails, covered with rocks). The staking effort was terminated just prior to completion leaving a few small groups of saguaros un-staked (on the south slope and the bottom of east slope).

2010–2012 Census: Similar to previous censuses, we revisited and measured all live plants within each plot and to get a more accurate estimation of plant locations we used Real Time Kinematic (RTK) Global Positioning System (GPS) technology. (see section Size measurements and Location Information below for details). In addition, we revisited and mapped all previously dead plants and verified that each plant had an aluminum angle iron with a unique number; we replaced markers when necessary. All new recruits on West and North plots were marked with aluminum angle iron. However, in certain areas within the South and East there were either so many new recruits or they were at such high densities that it was not feasible to unambiguously mark all of the very small plants. Thus in the East and South plots, we used aluminum angle iron for all plants larger than 30 cm in height, whereas there was some variability in method used for smaller plants, which may have been staked or marked with aluminum tags (nailed to the ground and covered with a rock for protection). We revisited the top portion of South plot, and although individual identity could not be determined from 1907’s data, we tagged and measured all live individuals in this section.

During this census period, not all measurements were taken during the same field visit. During the first visits for each plot, we collected all information pertaining to the overall plant condition, and the nurse information. At this point we did an initial verification of individual identity. During subsequent visits, we collected either TS or RTK data. This field protocol demanded further verification procedures during data processing. For these, we cross-referenced individual identities and locations generated from TS and RTK instruments (See Quality assurance)

Table 3. Type of information collected and methods of collection at each of the saguaro censuses since 1908. Collected data are indicated with an “X”, with specific methods indicated by abbreviations. Location information refers to any documentation of individual locations; during each census these data may have been collected but they were not georeferenced or spatially adjusted. Location information from every census was compiled and corrected between 2010 and 2012 (see Data entry verification and Quality control for details). Abbreviations: A = aerial photographs; TS = Total Station; RTK = Real Time Kinematic GPS device; GPS = Handheld GPS; DM = Direct measurements; B = quantitative evaluation of plant condition and distinction between arms and buds; S = South plot; E = East plot.

Census Year

Location

Size
Information

Condition Information

Flowering
Information

Nurse and Associated Plants

1908

X

 

 

 

 

1964

A

DM

X

 

 

1970

A

DM

X

 

 

1987
(only North plot)

A

DM

X

 

 

1993

TS

DM;TS

B

X

X

2010–2012

TS;RTK;GPS;
Satellite imagery

DM;TS

B

 

X

Specific protocols

In the following paragraphs, we describe the specific protocols used for each type of information recorded. Table 3 summarizes when each type of information was collected.

Height was measured from the base of the stem to the tallest apex, which in most cases is on the main stem; in cases where the plant has been decapitated or the tallest branch has been seriously injured, height was measured to the tallest arm. On slopes, the base of the saguaro was defined as the midpoint between the low and high side of the saguaro (excluding rocks and holes in this determination).

Two methods have been used to estimate the height of the saguaros:

Direct measurements. Measures using a stadia rod alongside the plant or a measuring tape for short plants.

Indirect estimations. Estimates calculated from the elevation difference between two survey points given by a Total Station (TS). For each plant, two survey points are recorded: the first is the elevation to a prism placed on top of a telescoping stadia rod located at the base of each saguaro, and the second is the elevation to the tallest point of the saguaro plant. Saguaro height is the difference between the second and the first reading, as the TS automatically incorporates the rod’s height. In addition to the measurement generated by the TS, and as quality assurance, we also estimated the height using only the raw angles reported by the TS. (see sections V.A.3.a and V.B.1 for details on this procedures). Table 4 summarizes the use of different methods during our censuses; see section on Instrumentation for manufacturer details on instruments used in each census.

Table 4. Use of different height determination methods during saguaro censuses at the Desert Laboratory. For each method, the range of heights recorded, the precision estimated from duplicate records, and the years used are indicated. Precision is estimated as the mean and standard deviation of the difference between duplicate records from 2010–2012 censuses.

Method

Range of plant height recorded

Precision

Years used

Telescoping survey rod,
7.5 m height graduated every 2 cm.

Plants taller than 2 m

In combination with measuring tapes with 0.01 m gradation (mean = 0.05; s.d. = 0.101)

All Censuses, except 1993

Measuring tapes

For plants shorter than 2 m.

Records to the closest 0.01 m (mean = 0.0260;
s.d. = 0.0918)

All censuses

Total Station

For plants > 1.5 m Complete information

For plants not less than 1.5 m. Reportedly records to the closest 0.001m (mean = 0.0871 m; s.d. = 0.118)

1993 and 2010–2012 only on N, W, S plots


 

Fig2

Fig. 2. Sample of different damages evaluated on saguaro individuals during census at Desert Laboratory. We classified causes of damages on saguaro plants and ranked them depending on their extent and severity from 0 to 3. (A) A plant with basal bark production and a constriction (marked with an arrow) due to growth reduction or temporary cessation; (B) moderate rodent damage at the base of the plant and a scar (arrow) due to abrasion from wind-blown paloverde branches; (C) severe rodent damage from chewing and tunneling; and (D) a saguaro decapitated by wind, lightning, or other severe damage.


 

b.Instrumentation

The following section summarizes the specifics of the instruments used during each census (Table 5). For information about height measurements, see Table 4.

Table 5. Attributes of instruments used to census saguaro plots.

Year of usage

Instrument

Measurement

Maker

Model

Manufacturer’s Accuracy

Precision in the field

Repository of Raw data

1908

Plane table

 

Plant location

No info

 

No info

1dm

NA

2010–2012

RTK

Plant location

Trimble

R6 and 5800

2 cm

2cm

USGS, Tucson

1993

 

TS

Plant location
and height

Nikon

NTD-4

+- 6 seconds
(5mm+5ppm)

NA

USGS
Tucson

2010–2012

Leica

TPS 1200

+-1 second
(3mm+2ppm)

NA

USGS,
Tucson

2010–2012

Garmin GPS

Plant location

Garmin

76CSx

<10m and DGPS 3–5 m

3m (in 2012)

76CSx

c. Taxonomy and Systematic.

Throughout this document and in all files associated with this project, we used the accepted nomenclature reported in Taxonomic Name Resolution Service v3.0 (2012; abbreviated as TNRS for the rest of the document). In addition, file Species.csv, which summarizes the taxonomy treatment of species during the census, also includes the corresponding species codes reported in PLANTS database (USDA 2012). For more information regarding the flora of the Desert Laboratory, see Bowers and Turner (1985).

d. Permit history

No permits were required for work at the Desert Laboratory. All future field research at the Desert Laboratory must apply for a permit from the Director of Research.

e. Legal/organizational requirements

Field research must be permitted by the Director of Research, Desert Laboratory.

Project Personnel.

Table 2 summarizes the information for contributors to each census.

 

Class III. Data set status and accessibility

A. Status

1. Latest update:

January 2013

2. Latest Archive date:

January 2013

3. Metadata status:

Updated on May 2013

4. Data verification:

January 2013

B. Accessibility

1. Storage location and medium:

Table 7 summarizes the location and medium of field notes, maps, and summary tables for each census. Specific information about how these data were archived can be found in section V.E

Table 6. Storage location and medium of all material related to the saguaro permanent plots. Nomenclature: USGS = Webb project, USGS, Tucson Arizona; THL = Tumamoc Hill Library of the University of Arizona, Tucson.

Data ID

Material

Medium

Census Years

Storage locations

Update status

Census Map

Copy of Blumer’s 1908 map

Paper/Digital

1908

USGS/THL

NA

Field Notes

Original Turner field notebooks

Paper

1964, 1970, 1987
2010–2012

USGS/THL

NA

Acetate transparency maps

Maps of saguaro locations derived from photointerpretation of aerial photographs between 1964 and 1987

Transparencies

1964, 1970, 1987

THL

NA

1993 Files

Final census tables and nurse information data

*.csv files

1964–1993

USGS

This files were incorporated into 2012 files

2012 Files

All files referenced in section IV.A

*shp files for maps,
*.csv for summaries, taxonomy tables included in this document

1908–2012

USGS

Up-to-date

 

2. Contact person:

For information about the USGS collection, contact R. H. Webb (rhwebb@usgs.gov ) at USGS, Tucson, Arizona. For information regarding materials at Tumamoc Hill Library contact L. Venable (lvenable@email.arizona.edu) at the Department of Ecology and Evolutionary Biology at the University of Arizona or Webb at USGS.

3. Copyright restrictions:

The data are generally public domain.

4. Proprietary restrictions:

NA

 

Class IV. Data structural descriptors

A. Data Set File

The following table summarizes attributes of the provided files and the sections that provide further information regarding each file's content. All data files refer to data from the saguaro permanent plots, except PlotX1908.shp which pertain to the 1908 Spalding maps.

Identity

Descriptions

Size

Format and Storage

Header/Variable table

Alphanumeric attributes

Special character fields

Authentication procedures

Individuals.csv

Multiyear information regarding location, size variables, general condition, and severity of damage for individuals within each plot

88–249KB

ASCII text file, comma delimited, uncompressed

See Individuals under Section IV.B.1

Mixed

None

See Section
V.A.3 and V.B

NurseInfo.csv

Multiyear information regarding the identity and condition of nurse and associated species growing in close proximity to saguaros within each plot

42–156KB

ASCII text file, comma delimited, uncompressed

See Nurse Plant Information in Section IV.B.2

Character

None

See section V.B.3

Boundaries.shp

Shape file of the final boundary for each plot.

14.7KB

ArcGIS 10 shape file (shp) from polygon shape file

See Shape files in Section IV.B.4

Mixed

None

See section
II.B.2.a

PlotX1908.shp

Shape file of the saguaros surveyed in 1908 that fall inside the area defined by a 5 m buffered contour of each plot X.

43.9KB

ArcGIS 10 shape file (shp) from polygon shape file

See Shape files in Section IV.B.4

Mixed

None

See section
V.B.2

Species.csv

Nomenclatural information and species codes for nurse and associated species detected during censuses in 1993 and 2012

3.67KB

ASCII text file, comma delimited, uncompressed

See Plant Species in Section IV.B.3

Character

None

See section
II.B.3.c

 

B. Variable information

1. Individuals

The following tables group variables by type, although all variables are present in the single file Individuals.csv

a. Identification and survey controls

The following table summarizes the variables use to uniquely identify saguaros in the field, and to control for the existence of information about location, height and size variables and general condition, severity of damages, and nurse and associated plants.

Variables

Definition

Units

Storage type

Variable code and definition
Or range

Missing code

Collection method

Plot

Identifier for each of the four permanent plots

NA

Character

East, West, South, North

None

N/A

SaguaroID

Unique identifier within each plot of each individual censused between 1964 and 2012

NA

Character

See section Identity information at the permanent plots for details on nomenclature
Prefix SNC refers to plants that are within the plot, but have never been censused

None

N/A

Location

A ranking for the precision of the location/method of each saguaro. From 0 being the least precise to 6 being the most precise.

NA

Numeric

0 = locally georeferenced, buffered Acetate transparency
1 = locally georeferenced Acetate transparency
2 = located on aerial photograph
3 = handheld GPS
4 = Total Station coordinates georeferenced 93 or 2011
5 = RTK recorded with poor precision in the field
6 = RTK

Null = Plants without location

Quality control during archiving

YearP

Indicates the year for which the plant does not have size information although the plant was alive

NA

Numeric

Year of the census

NA

Damages

Indicates whether a plant was visited in the field in 2010–2012 census, and severity of damage was recorded

NA

Dichotomous

True = Plant was evaluated for damages
False = plant was not evaluated

Null = Plants not present in the given census

Nurse

Indicates whether a plant was visited in the field in 2010–2012 census, and nurse plant information recorded

NA

Dichotomous

True = Plant has nurse plant information
False = Nurse plant information was not collected

NA

Comment12

Compiles comments from the last two censusesUsually comments refer to ID issues that were resolved, or overall conflicts during field surveys

Field notes

Character

NT93 = Identifies comments from 1993 census

Null for plants without issues

Field notes and Quality control during archiving

 

b. Location variables

The following table summarizes the variable attributes that uniquely identify each plant in the census, or in combination uniquely identify plants across all of the four plots. Not all variable are used in all four plots; superscripts identify the plots where a variable is used whenever this variable does not apply to all plots.

Variables

Definition

Units

Storage type

Variable code and definition
Or range

Missing code

Collection method

SlopeN

Identifies in which of the four plots the plant is located

N/A

Character

Upper = Upper north plot; Lower = Lower north plot;

None

Field survey

TopS

Identifies plants at the top of South plots that were not census in 1993 and for which there is not an identity match between 1987 to 2012 data

N/A

Dichotomous

True = Plants at the top of South plot
False = Plant not at the top

None

Field survey

EastingUTM

The X coordinate in Universal Transverse Mercator Zone 12N projection. North American Datum of 1983 (CORS 96) (EPOCH 2002). Derived from RTK.

m

Double

498728.6–499995.9

Null

Field surveys and archiving process.

NorthingUTM

The Y coordinate in Universal Transverse Mercator Zone 12N projection. North American Datum of 1983 (CORS 96) (EPOCH 2002). Derived from RTK.

m

Double

3563400.3–3565242.4

Null

Elev_m

The elevation in meters above sea level derived from RTK data

m

Double

733.7–940.1

Null for saguaros without RTK reading

 

c. Variables for height

Variables

Definition

Units

Storage type

Variable code and definition
Or range

Missing code

Collection method

HeightXXM

Height in year XX (last two digits of the census year, between 1964 and 1987), measured from the base of the plant to the top of the apex of the main stem. See section II.B.3.a for the description of size measurements

meters

double

0.05–12.6

Null for individuals not measured or dead

Direct Measurements

Height93M

1993 height from the base of the plant to the top of the apex of the main stem. See section II.B.3.a for the description of size measurements

meters

double

0.05–12.6

Null for individuals not measured or dead

Direct Measurements and Calculations from raw TS data

 

Height12M

Height at last census (2010–2012). For further information see section II.B.3.a for the description of size measurements.
Values in this column also include measurements from 2010 or Actual census years is recorded in Date_Height

meters

double

0.05–12.6

Null for individuals not measured or dead

HMethodXX

When more than one method was used to measure height, this variable indicates the method used in year XX. For details on the methods see section II.B.3.a

NA

character

DM = Direct measurement
TS = Total Station
ATS = Calculated height using angles reported by TS
AvDM = average from multiple direct measurements

Null for individuals not measured or dead

NA

Date_Height

Date the height of the saguaro was measured (mmm.dd.yy or mmm.yy) during 2010–2012 census

Date

Character

Dec.2010–Jun.2012

Null for individuals not measured or dead

From field notes

Problm_Height

Categorical variable flagging records with problematic measurements of heights; that should be excluded from grow analyses

NA

Dichotomous

False = no problem detected
True = problem detected

NA

Quality assurance procedures

HProblmNotes

Details on the Height measurement problem. This includes notes on plants that could be included in analyses of grow

NA

Character

NA

Null for plants without any problem

 

d. Variables for general conditions of the plant.

The following table summarizes all other variables in this data set for which variable characteristics are constant across censuses

Variables

Definition

Units

Storage type

Variable code and definition
Or range

Missing code

Collection method

ConditionXX

Indicates structural condition of the plant in year XX. This variable influences the height measurements

NA

Short Character

A = apex eaten or damaged
B = broken top
C = constriction
D = double (branching from the base)
H = hole
I = injured
L = leaning
M = Missing; not able to find during the same census
N = Not measured but present
Q = questionable ID
S = sick; plant dying
X = dead
XNF = Not found across censuses; assumed dead
V = vandalized

Null for plants without any special conditions

Archiving field notes between 1964 and 1993 and field surveys

ArmsXX

Number of arms at year XX (See section II.B.3.a)

Arms

Integer

0–24

NA

BudsXX

Number of buds at year XX (See section II.B.3.a)

Buds

Integer

0–9

NA

FlowerXX

Indicates if plant was flowering at the time of the census

NA

Character

F = Flowering
N = Without Flowers
NA = Flowering status not evaluated or not applicable

Null for plants not checked

Archiving field notes between 1964 and 1993

 

e. Variables depicting plant injuries.

The following variables recorded in the last two censuses correspond to severity rankings in the most common injuries observed in saguaro plants. Superscripts indicate plots where variables were used, whenever they were not used in all plots.

Variables

Definition

Units

Storage type

Variable code and definition
Or range

Missing code

Collection method

ConstXX

Number of constrictions, which are the result of a halt in growth. These plants should be excluded from any growth vs. age analyses

NA

Integer

0–5

NA

Archiving and field surveys

HeightConstcm

Indicates the height at which the constriction was observed in 2010–2012 census; it was measured from the ground up. Semicolons separate multiple measurements

centimeters

character

<400; 0 representing constriction at base

Null for plants without evidence of past or current damage

Field survey

BarkXX

Indicates the level of bark production of the saguaro flesh in year X; typically (but not exclusively) bark is produced at the base of the plant

NA

Integer

0 = No current evidence of damage or recovery from previous injuries; 1 = Moderate damage; localized 2 = Severe
3 = Extreme; extensive in proportion to saguaro’s size

Null for plants without evidence of past or current damage

Archiving and field surveys

ChewXX

Severity of animal damage without tunneling, which usually is superficial. This damage is usually done by packrats, but we did not assess this explicitly

NA

Numeric

0–3
(same as for barkXX)

Null for plants without evidence of past or current damage

TunnXX

Severity of packrat tunneling

NA

Numeric

0–2 (same as barkXX)
3 = Extreme; extensive in proportion to saguaro’s size, or deep damage exposing saguaro’s ribs

Null for plants without evidence of past or current damage

AbraXX

Severity of abrasion produced by direct contact against other plants or rocks

NA

Numeric

0–3
(same as barkXX)

Null for plants without evidence of past or current damage

WoundXX

Indicates level of severity of wounds that could not be assigned to abrasion or herbivory; typically indicate damage by wind or vandalism, which is noted in the column ConditionXX)

NA

Integer

0–3
(same as barkXX)

Null for plants without evidence of past or current damage

HeightWoundcm

Height on saguaro at which wound was observed from ground up in 2010–2012; semicolons separate multiple measurements

centimeters

character

<400
When more than one wound is present, height of all wounds is listed sequentially.

Null for plants without evidence of past or current damage

Field survey

BirdHolesXX

Number of bird nests in year XX.

NA

Numeric

0–14

Null for plants that were not visited

Archiving and field surveys

FrostXX

Severity of frost damage which is evident by an extensive red to black coloration

NA

Integer

0–3
(same as barkXX)

Null for plant without damage

Field survey

DowelsN

Indicates whether the saguaro has wooden dowels impaled into it from a different study (English et al 2010).

NA

Dichotomous

0 = Plants without dowels
1 = Plants with dowels

Null for plants without evidence of past or current damage

Field survey

 

2. Nurse Plant Information

The following table summarizes the characteristics of nurse and associate plant information from the file NurseInfo.csv. This file only includes records for which this information was collected. Each column in this file has the status of a given plant species (identified with the species code) in a given year (1993 or between 2010 and 2012). This status is given by a code that is the combination of information about plant condition, size, relationship with saguaro, and location of saguaro with respect to the focal plant’s canopy. Although not all the species have the complete information; letters constituting the code are unambiguous. Plants growing in the open without any nurse or associated plant will be included in this file, but they will not have any information. For more details about the field method see section II.B.3.a.

Variables

Definition

Storage type

Variable code and definition
Or range

Missing code

Collection method

SaguaroID

Unique identifier within each plot of each individual censused between 1964 and 2012

Character

See section II.B.3.a for details on nomenclature

None

NA

CCCCXX

Identifies the survival status, association condition, size, and location (Saguaro's location with respect to the plant) of the plant with code name CCCC during the census in year XX. CCCC corresponds to the four letters species code that follows the nomenclature in Species.csv). Details vary between 1993 and 2010–2012 censuses as the former only evaluate condition of plants close to saguaros.

Character

Codes are a combination of different letters in the following order:

  1. A = Alive or D = Dead
  2. n = nurse plant or s = associated plant
  3. b = big plant with respect to the maximum size for the species in the area or s = small or immature individual
  4. R = Saguaro is located at the border of this plant canopy or U = Saguaro is located under this plant canopy.

NA = conflicting information between 1993 and 2010–2012 censuses. No evidence of reported nurse was found in latter census

Null for plants without nurse information

Archiving and field surveys

NestXX

Indicates if there was a nest (packrat or other animal) on or around the base of the saguaro.

Character

X = nest present
Null = nest not present

Null

RockXX

Indicates a rock served as nurse during saguaro establishment

Character

X = rock as potential nurse
Null = no rock as nurse

Null

Unknw

Nurse or associated plant that could not be identified to species

Character

Same code as for field CCCCXX

Null

Unknown_Comment

Comments on unknown species, usually, ID of the family

Character

Varies

Null

 

3. Plant Species.

The following table summarizes species codes and scientific plant names used during our censuses recorded in file Species.csv. See section II.B.3.c for details on taxonomy and nomenclature protocols.

Variable

Definition

Units

Storage Type

Variable code and definition
Or range

Missing code

Collection/Validation methods

Code

Four letters species code used in this project

NA

Character

ABIN-ZIPU
When Plants were only identified to genus XX is used as the last two letters in the code

NA

Combination of two first letters of genus and first two letter of species.
Although nomenclature has changed for some species since the code was first defined in 2001, we have opted not to change the code, but to report the current nomenclature instead.

PLANTS_Code

Alpha-numeric species codes used in PLANTS (USDA 2012)

NA

Character

ABIN-ZIGR

NA = Plants not included in PLANTS (USDA 2012)

PLANT Database (USDA 2012)

AcceptedName

Accepted Species names

NA

Character

Currently accepted scientific species name of any plant reported between 1906–2012

NA = name without equivalent in TNRS

Reported names are cross checked in TNRS for the current accepted name

Authority

Name or names of the scientists who first validly published the accepted name.

NA

Character

 

NA = name without equivalent in TNRS

 

Family

Species family

NA

Character

Currently accepted family

NA = Species for which family could not be determined

Validated with TNRS

Common_name

Common name as reported by PLANTS (USDA 2012)

NA

Character

Currently reported common name

NA = Species with unreported common name

Validated with The PLANTS (USDA 2012)

Habit

Species habit

NA

Character

Graminoid
Tree/Shrub/Subshrub
Forb/Herb, or some combination of the last 5 options

NA = Habit not reported

Validated with The PLANTS (USDA 2012)

Duration

Species life cycle

NA

Character

Perennial/Annual, or a combination of the two

NA = Duration not reported

Validated with The PLANTS (USDA 2012)

 

4. Shape files

The following table summarizes the variables used in the files Boundaries.shp, and PlotX1908.shp. All files were created in ArcGIS v.10 (ESRI). * Indicates variables only used in the Boundaries.shp file. See section V.B for a complete description of quality control issues associated with this information.

Specific variable names for each census

Definition

Storage Type

Variable code and definition
Or range

ObjectID

Unique sequential identifier

Integer

1–5

Shape

ArcGIS Feature type

Character

Polygon for Plot boundaries
Point for shapes coming from 1908 maps

Shape_Length*

ArcGIS estimation of plot perimeter (m)

Double

1115–1765

Shape_Area*

ArcGIS estimation of plot area (m²)

Double

65174–161297

Plot*

Identifies in which of the four plots the plant is located

Character

UN = Upper north plot; LN = Lower north plot; S = South plot; E = East plot; W = West plot

 

C. Data anomalies

Data anomalies are recorded in three columns in the file IndividualsPX.csv. The column “ConditionXX” flags plants with questionable identities as “Q”. Questionable identities might have originated from plants losing tags, or the tags being read and recorded incorrectly. These flags are the results of comparison across censuses. In addition, the column “Problm_Height” flags plants with unusually high or low heights during comparison across censuses (see sections V.A.3.a and V.B.1 for details). Finally, the column “HProblemNotes” and “Comments12” have a verbal description of any potential issues.

 

Class V. Supplemental descriptors

A. Data acquisition

1. Data forms or acquisition methods

The following table summarizes the data sources for each of the censuses.

Census

Data type

Data Source

Processing

Location

Data verification

1908

1908 maps by J. C. Blumer

Plate 15 and 16 in Spalding (1909)

High resolution scanning,
Georeferencing using Orthophotos and elevation isolines in ArcGIS 10. (ESRI) (see Section V.A.3.a)
Conversion to shapefile after classification using ArcGIS 10 (ESRI).

Spalding Original (1909) Tumamoc Hill T.
Digital version located at USGS Tucson

Verification of shape conversion using feature size

1964, 1970, 1987

Size information

Original field notebooks and files processed in 1993

Data entry and codification of condition notes

Tumamoc Hill Library

Consistency in condition codes across censuses

1993

Size, Condition, Nurse plant Information

Total Station raw data and files processed in 1993

Recalculations of Height; compilation and verification of Condition and Nurse plant information

Tumamoc Hill Library and USGS Tucson

Consistency in condition codes and heights across censuses

2011

Location,
Size, Condition, and Nurse plant

Field work

Data entry; height calculations; compilation and processing of location information in Trimble Business Center version 1.11

Tumamoc Hill Library and USGS Tucson

Consistency in condition codes, heights and locations

 

2. Location of completed data forms

Files derived from this project are located at the USGS in Tucson. See Table 6 for specific location of original maps, field notes, and additional information related to the saguaro plots

3. Data entry/verification procedures

a. Verification of data prior to 2010–2012 census.

During the 1970 and 1987 censuses, researchers compared information gathered on each saguaro during previous censuses to what they were observing in the field. Post-field work verification included checks for missing information and inconsistencies. When possible, these errors were corrected with a second visit to the plots, although there are no records of these corrections.
Between 1992 and 1993 Pierson digitized field notes from previous censuses and used these data to predict average height-specific growth rates. These data were subsequently used to predict the heights of all plants in 1993 based on their previous height and the number of years that had passed since they were measured. All of these data were verified by comparison to plants observed in the field. In 1993, height data for some plants were calculated from raw TS data using the following formula:

AHeight=

equation

where HR is the rod height (meters), D is the slope distance (meters) from the instrument to the saguaro (to the rod), and VT and VSaare the angles (radians) from the instrument to the target (T) or to the apex of the saguaro (Sa).
Data for plants less than 2 m in size and for plants with an obstructed view of the surveyor were measured directly. Comparison of survey derived heights and directly measured heights were made routinely during the course of the field census.

b. Verification of field data from the 2010–2012 census

Field data verification consisted of four distinct procedures:

  1. Prior to any measurements, we verified the identity of a plant using 1993 data (including location) and flagged any inconsistencies. When these inconsistencies could not be resolved in the field or during archiving, they were flagged and documented (see section Identity procedures)
  2. Error checking for indirect height from the Total Station (TSheight) included verifying the location of each record (using maps generated with the TS raw angles) with locations from 1993 data. The equations used were the following; X=-(D*cos((90-VT))*(cos(HT)+Xref) and Y==-(D*cos((90-VT))*(sin(HT)+Yref)  where D is slope distance (m) as before; VT is the vertical angle to the rod at the based of the saguaro, HT is the horizontal angle to the rod; and Xref of Yref are the arbitrary reference coordinates of the Total stations; we set both values to 1000. This procedure allowed us to detect erroneous height assignments. In addition, TSheights were later verified by comparing the measurements reported by the instrument and the measurements estimated with raw angles using formula described above (Aheight). This procedure allowed us to identify erroneous readings. Given that the TSheights are based on laser returns, any obstruction to the laser pulse, such as tree branches or other saguaros, could give an erroneous return. TSheights that differ more than 50 cm from their corresponding Aheights were not used, and measurements were repeated using either TS or DM.
  3. Locations from RTK were verified with maps from 1993 generated by TS angles, and georeferenced using a subsample of well-identified saguaros. Location inconsistencies were flagged and solved in the field or during archiving. Most errors in this procedure correspond to plants that lost their markers and were misidentified in the field.
  4. During archiving all information was verified for consistency and completeness; see section V.E for details on quality control procedures during the archiving process. Plants for which complete information could not be gathered are identified using appropriate columns in the file IndividualsPX.csv

c. Verification of digitized data from 1908

Digitized plates from Spalding (1909) were georeferenced using geomorphological features and elevations isolines in ArcGIS v. 10. We used a 2008 isoline layer with elevation contours every 50 feet that we derived from the 2008 DEM points provided by the Pima Association of Governments (PAG). To generate the elevation isolines, we generated a 1-m cell size raster file using the original PAG DEM file and inverse distance weighted interpolation method over 12 proximal data points.
After plates were georeferenced, we classify the raster layers using the same symbology as that on the original plates. Using this classification, we were able to extract only those features that represent saguaro plants; with these, we created a point feature class (PlotX1908.shp). We checked this file against the original map to eliminate any error during classification.

B. Quality assurance/quality control procedures

Starting in 2010 we compiled and archived all information related to the four permanent saguaro plots and the 1908 maps of saguaro locations. After the initial verification of field data generated during our 2010–2012 census, we applied the following three quality control procedures.

1. Control on height measurements

Indirect and direct height information was compiled for all years. By comparing heights across censuses for each individual, and heights from different methods, we identified and flagged erroneous records; these were not used in any further analyses. For records with more than one measurement from the same method in 2012, we estimated average heights, and used those in further analyses. Table 7 summarizes the variability associated with duplicate records. The final height of each saguaro was estimated using the following rules: Priority was given to direct measurements, unless it was obvious that this was wrong (usually due to misidentification). For plants without direct measurements, we compared TSheights and Aheights and used the latter, whenever the differences between the two methods differ by more than 50 cm, otherwise we used TSheights as the preferred measure. Mismatch between these estimations are mostly due to the lack of a clear shot from the TS base to the saguaro's apex. After final measurements were selected, we used all censuses to graphically identify outliers when heights of a year were plotted against heights of the next year. Plants with extremely high or extremely low growth were flagged for further inspection. In most negative or slow growth cases, plants were discovered to be decapitated or sick. When the reason for the extreme height could not be determined, inconsistencies were documented.

2. Control on Location measurements

Location information from different sources was compiled and compared. We ranked the precision of different coordinate sources depending on the procedures and instruments used to obtain them (see Table 5). When more than one RTK reading existed, we used the last record taken if there were no other problems (see Table 7 for the average distance difference between duplicate records). Given that RTK accuracy depends on the number of available satellites and other field conditions, we give priority to readings with good precisions. For plants without RTK readings, we used georeferenced locations derived from TS readings from either the 2010–2012 census or the 1993 census. Georeferencing was performed using RTK readings from well-identified plants spread throughout the plots and with a density of no less than 1 every 50 m². Mean precision of this procedure when TS-derived locations were compared with RTK was 0.66 cm (SD = 0.32 n = 500). For any other plant without spatial information, we used the 1963–1987 acetate transparency maps to estimate their location.
We georeferenced acetate transparency maps (OHmaps) in two steps. First we used RTK coordinates to georeference the entire OHmap for each plot. Second, we identified the saguaros without location information from 1993 or 2010–2012 censuses, and locally georeferenced the neighbors around these saguaros using any RTK or 1993 points available. For plants that were not explicitly mapped (one point marked several plants), we buffered the reference point to obtain an approximate location of the target plant by adding a random distance (from 0 to 1 m) to both easting and northing values of the reference plant. For completeness, we included plants that were never mapped or tagged, but are inside the plot boundaries. We estimated their locations using georeferenced aerial photographs taken in 2008.

Table 7. Statistics for duplicate location and height measurements during 2010–2012 census at the four saguaro permanent plots. Statistics were calculated on the distance difference for duplicate RTK readings, and on absolute difference for Total Station (TS) and Direct Measurements (DM) of saguaro heights. TS and DM duplicate measurements were not recorded for East plot; data from all plots was pooled together before this statistical analysis.

Statistic

Locations with RTK
Distance (m)

Difference in Height (m)

Height with TS

Heights with DM

Mean

0.2316

0.1034

0.0522

Std Dev

0.2682

0.1277

0.1009

Std Err Mean

0.0165

0.0202

0.0194

Upper 95% Mean

0.2641

0.1442

0.0922

Lower 95% Mean

0.1991

0.0626

0.0123

N

264

40

27

 

3. Control on condition and associated species information

Quality control on condition and associated species information for 1993 and 2010–2012 censuses include checking for inconsistencies across censuses. This includes extreme differences in arm counts, severity of damages, or nurse and associated species. Inconsistencies in this information helped to discover misidentifications that were not detected in the field. Inconsistencies were documented whenever we were not able to solve them with a second field visit.

C. Related materials

See Table 6

D. Computer programs and data processing algorithms

The following table summarizes the software used to process field data during the 2010–2012 census, and available data from previous censuses

Table 8. Software used during data processing and archiving

Computer Program

Specification

Census year applicable data

Applicable data

Description of procedures

Microsoft Excel

2010

2010–2012

Total Station Readings

Subtract Z values to get TSheight and calculate raw angles to get Aheight

Trimble Business Center

1.11

2010–2012

RTK coordinates

Process coordinates with OPUS reports to get final coordinates

ArcGIS

ESRI version 10

All years

Location Data

See section V.A

Python

Python Software foundation
Version 2.6.5

2010–2012

Location data and plot boundaries

Programmatic manipulation of shapefiles

Access

Microsoft Office 2012 version 14.0

All years

All available data

Working data base that integrates tables of location, height, condition, and nurse information for each plot

Jmp

SAS Institute version 9

All years

Height and Location data

Descriptive statistics and quality control

 

E. Archiving

1. Archival procedures

Archiving of all data related to this study was conducted in two stages: (1) In 1993, E. A. Pierson and colleagues collected and digitized information from all censuses between 1964 and 1987. Data from the 1993 census were later appended to these files. (2) Starting in 2010, we compiled all information from 1993, performed quality control on these files, and using the same format, we appended all data collected between 2010 and 2012. Data verification consisted of identifying plants with mismatching tag number, height, condition and arm count, location and nurse plant information (section V.A.3.a).

2. Redundant Archival sites

See Table 6 for location of original maps and notes. Files presented here are the most accurate and up-to-date version of the information associated with the saguaro plots.

F. Publications and Results

Hastings, J. R. 1961. Precipitation and saguaro growth. University of Arizona Arid Lands Colloquia 1959-60/1960-61:30-38.

Pierson, E. A. and R. M. Turner. 1998. An 85-year study of saguaro (Carnegiea gigantea) demography. Ecology 79:2676-2693.

Pierson, E. A., R. M. Turner, and J. L. Betancourt. 2012. Regional demographic trends from long-term studies of saguaro (Carnegiea gigantea) across the Northern Sonoran Desert. Journal of Arid Environments 88:57-69.

Turner, R. M. and J. E. Bowers. 1988. Long-term changes in populations of Carnegiea gigantea, exotic plant species and Parkinsonia floridum at the Desert Laboratory, Tumamoc Hill, Tucson, Arizona. In: E. E. Whitehead et al., eds., Arid lands, today and tomorrow: proceedings of the international arid lands research and development conference, October 1985, Tucson, Arizona, pp. 445-455. Westview Press, Boulder, CO.

G. History of data set usage

1. Data request history

NA

2. Data set update history

Date

Update procedure

Name

Contact information

July.06.2012

Publication

S. Rodriguez-Buritica
R. H. Webb

susanarburitica@email.arizona.edu
rhwebb@usgs.gov

3. Review history

NA

4. Questions and comments from secondary users

NA

Acknowledgments

Special thanks are due to the many colleagues that helped map the saguaro permanent plots in the last half century. These include R. Harris and S. A. McClanahan (1964), D. K. Warren (1970), O. Grosz and T. L. Burgess (1987), J. L. Betancourt, G. Bolton, J. E. Bowers, T. L. Burgess, M. Donofrio, I. Findley, C. Lindquist, C. Mendoza, R. Neubaur, C. Pierson, L. S. Pierson, Z. Smith, E. Stoll (1993); Don Swann and a crew from saguaro National Park, S. Carmichael, M. Snyder, T. Birt, D. Baumgartner, L. Chadwick, T. Esque and crew, and D. Boyer (2010–2012).

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