Browning of epidermal surfaces of saguaro cacti (Carnegiea gigantea) is associated with premature death of the species in the northern Sonoran Desert. Analyses of authentic historical photographs of mature saguaros from 1903 to 1987 demonstrated a significant (1) loss of spines, (2) decrease in apparently healthy crests, and (3) increased trough barking over the period. All three of these changes occurred to saguaros of over 115 years of age at a projected rate of 4–5% per decade. Analyses of epidermal characteristics of saguaros at the Saguaro National Monument were performed to determine if epidermal browning was related to compass direction. Results show that both scaling and barking of crests and troughs and loss of spines, all symptoms of epidermal browning, were 10 times higher on southern exposures (between 140 and 220°) compared with northern exposures (between 320 and 40°). The two troughs of a crest were evaluated separately. The results demonstrated that injury to one trough of a crest could be as much as four times greater than that of the second trough.
"The cause(s) of these scale and bark injuries are not definitive . Research has shown that (1) these injuries are more prevalent now than in the past (Evans et al. 1992); (2) identical scale and bark injuries are occurring on stems of 14 species of long-lived columnar cacti in both North America (southern Arizona, Sonora, and Baja California Sur) (Evans and Fehling 1994) and South America (central Chile and northern Argentina), which indicates that these injuries are occurring to many species over thousands of kilometers (Evans et al. 1994c "
[Show abstract][Hide abstract] ABSTRACT: Rates that stem surfaces of saguaro cacti (Carnegiea gigantea (Engelm.) Britt & Rose) accumulate scale and bark injuries and the mortality rates of cacti were determined on a population of 1149 saguaro cacti in 50 field plots over the 9-year period of study (from 19931994 until 2002). Twenty-three percent of the saguaro population had few surface injuries throughout the 9-year period while 27% showed a marked increase in stem area with scale and bark injuries. Thirty percent of all cacti had more than 80% stem areas with combined scale and bark injuries on south-facing stem surfaces throughout the study period. Finally, 20.3% of the saguaro population died over the 9-year period, a rate of 2.3% per year. Thirty-three percent of all cacti that died by 2002 exhibited few surface injuries in 19931994 while 54% of the cacti that died over the period had more than 98% stem areas with combined scale and bark on south-facing stem surfaces in 19931994. In this manner, stem scale and bark injuries on south-facing surfaces were usually associated with the death of saguaros. The annual mortality rate of 2.3% appears high considering that this species may live for more than 200 years.Key words: saguaros, Carnegiea gigantea, Cactaceae, stem areas with scale and bark injuries, mortality rates.
Canadian Journal of Botany 02/2011; 83(3):311-319. DOI:10.1139/b05-005 · 1.40 Impact Factor
"The greatest post-seedling killer is freezing events (Steenbergh and Lowe, 1977, 1983). Other climatological conditions such as drought (Brum, 1973; Parker, 1993), availability of nurse plants which saguaros rely upon (Turner et al., 1966; McAuliffe, 1984; Drezner and Garrity, 2003), other biotic factors (Lightle et al., 1942; Niering et al., 1963; Hastings and Turner, 1965; Steenbergh and Lowe, 1969), pollution (Stolte, 1992), epidermal browning (Evans et al., 1992) and fire (Rogers, 1985) also affect saguaro regeneration, mortality and survivorship. Saguaro populations naturally fluctuate because of variable regeneration and mortality patterns. "
[Show abstract][Hide abstract] ABSTRACT: Saguaro cacti (Carnegiea gigantea) are long-lived and exhibit great variability in growth that makes age estimation problematic. A few single-site studies have focused on those locales where long-term data (e.g. 85 years) are available. Using a newly developed technique, 733 saguaros were sampled in three locales (Silverbell, Harcuvar, Kofa) across Arizona and their age structure reconstructed for the last 150 years based on a mathematical model of the heights of individuals. This is the first study to compare regeneration at multiple locations across the species' range. Regression analysis for each site (years and frequency of indivi-duals established during that year) was run and residuals extracted to determine peaks and troughs in regeneration over time. Correlation was run on the residuals between sites, and chi-square analysis was employed to compare frequency of good and bad regeneration years between Kofa and Silverbell. Peaks and troughs represent regeneration as well as sur-vivorship and mortality. Several large cohorts established at Kofa and Harcuvar since 1850, while at Silverbell well over 80% of sampled saguaros established after the late 1930s. This more recent recruitment at Silverbell may be related to the major freezing event of 1937 whose impact was likely greater at the cooler Silverbell site. Despite the widely different population structures at Silverbell and Kofa, recruitment trends in both populations were statistically linked as both locales often benefited from the same favorable periods for re-generation (P < 0.001). The Harcuvar population shares some common peaks and troughs in regeneration over time with Kofa and Silverbell, but its relationship to them is not statis-tically significant. Some trends overlap in some locales, such as the favorable regeneration period in the late 1800s and early 1900s, particularly at Silverbell and Kofa as well as at other known sites. However, each population has its own signature. Silverbell is a youthful population likely shaped by severe freezing events, while Kofa has many individuals repre-senting regeneration at several different periods. Regeneration, mortality and subsequent population structure is shaped by both regional-scale influences as well as more localized conditions over the long and short terms.
"When it occurs, browning typically begins on the south side of a saguaro and advances there to a much greater extent than on the north side. In addition, taller saguaros tend to have more browning than short ones, though saguaros up to 8 m tall have been found with no browning present (Duriscoe and Graban 1992, Evans et al. 1992c ). "
[Show abstract][Hide abstract] ABSTRACT: We studied the demography and health of the saguaro cactus (Carnegiea gigantea) in Saguaro National Park, Tucson, Arizona. We gathered data on populations in both districts of the park for the years 2000-2001 and compared them to baseline collected in 45 plots during 1989-1990.
During the past decade, epidermal browning of the surviving marked saguaros increased by 6%, with greater increases in those which were browner ten years ago. We also found evidence that epidermal browning has increased in the whole population, with a mean increase of 3.7% when comparing all saguaros in 18 plots.
Among the marked population, 16.5% died during the decade. The 10-year survival rate declined with greater levels of browning and greater height.
Recruitment exceeded mortality on all but one plot, with dramatic increases among plants <1 m tall making the populations significantly younger and with higher population densities in 2000-2001 than in 1989-1990.
Based on our census efforts in 18 of the study plots, we estimate the total population within Saguaro National Park is approximately 1,625,000 saguaros, a 35% increase over the 1990 estimate. Examination of size classes suggests the park continues to recover from historic damaging influences such as grazing, mining, and wood harvesting.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.