On the Age and Growth Rate of Giant Cacti: Radiocarbon Dating of the Spines of Cardon (Pachycereus Pringlei)

Abstract

Age estimation has been a limiting factor in the study of giant columnar cacti. In order to test the feasibility of using radiocarbon methods to estimate the age of the giant cardon cacti (Pachycereus pringlei), we selected six sites spanning the latitudinal and precipitation range of the species in the Baja California peninsula. In each site, we selected four individuals of different heights and sampled a spine from the lowest areole in the stem. The age of the spine was estimated using 14C dating, and the mean annual growth rate of the plant was calculated dividing the height of the lead shoot by the plant’s age. Mean annual growth rate was 0.098 m/yr, with values varying between 0.03 and 0.23 m/yr. Within the range of plants sampled, mean annual growth rates were significantly correlated with the height of the plant (r2=0.82, P<0.0001), and no other site-specific variable such as precipitation or latitude was a significant predictor of mean annual growth rates. A model integrating mean growth rate versus height showed that relatively small differences in growth rates between plants accumulate during the plants’ lifetime, so that plants of similar size may have very different ages. We conclude that 14C dating provides a robust method to explore the growth and demography of columnar cacti.

Gas exchange characteristics of giant cacti species varying in stem morphology and life history strategy

“…Relative stem growth rates are generally higher in Sonoran Desert giant cacti species that produce many, relatively short-lived basal stems compared to co-occurring single-stemmed giant cacti species that do not produce secondary arms from its main stem until several decades after establishment (Parker, 1988;Delgado-Fernández et al, 2016). For example, age-height relationships measured on the multi-stemmed L. schottii and S. thurberi plants in the northern Sonoran Desert found that a stem 5 m long had a mean age of 37 and 35 yr, respectively (Parker, 1988).…”

“…For example, age-height relationships measured on the multi-stemmed L. schottii and S. thurberi plants in the northern Sonoran Desert found that a stem 5 m long had a mean age of 37 and 35 yr, respectively (Parker, 1988). In contrast, a C. gigantea plant 5 m tall in the northern Sonoran Desert would have an expected mean age of 65-110 years, depending on location and mean annual precipitation (Pierson et al, 2013), while a 5-m-tall plant of P. pringlei would be expected to have a mean age of 45-90 yr, depending on location and mean annual precipitation (Delgado-Fernández et al, 2016). Stem growth rates are an important fitness trait in giant cacti species because in most species, flowers and fruits are produced primarily from recently constructed areoles near the apex of the stem.…”

“…The stems of L. schottii and S. thurberi rarely persist for more than 40 yr (Parker, ) and therefore take on a life history strategy that prioritizes rapid areole production over stem longevity. Conversely, the large single‐stemmed C. gigantea and P. pringlei can persists for well over 100 yr (Pierson et al., ; Drezner, ; Delgado‐Fernández et al., ), but do not produce secondary arms for decades after establishment. These species maximize stem longevity by constructing stems with low S:V ratios that prioritizes resource storage over rapid growth.…”

“…Large single-stemmed species, including C. gigantea and P. pringlei have stem volumes per unit surface area that can be 5-fold or more higher than co-occurring multi-stemmed cacti species, including L. schottii and S. thurberi (Hultine et al, 2016). Variation in stem S:V reflects apparent trade-offs between stem relative growth rate and longevity where the slow-growing single-stemmed species, with low S:V can persist for at least 100 years and possibly up to 200 years (Pierson et al, 2013;Drezner, 2014;Delgado-Fernández et al, 2016), while the faster-growing, high S:V stems of L. schottii and S. thurberi likely only persist for 40 years or less (Parker, 1988).…”

Reconstruction of past climatic events using oxygen isotopes in Washingtonia robusta growing in three anthropic oases in Baja California Sur

“…Although the isotope curves of W. robusta exhibited some relationship with historical climate events, the utility of the data might improve if a methodology to estimate the age of formation of stem cellulose were to be developed. Approaches for calculating the ages of plants using 14 C in species without growth rings, such as Pachycereus pringlei (Delgado-Fernández et al, 2016), Carnegiea gigantea (English et al, 2007), and tropical trees such as Otoba gracilipes and the palm Oenocarpus bataua (del Valle et al, 2014), have been developed. Similarly, it will be important for future research to calculate the relationship of the whole hydrological cycle, including precipitation, humidity, temperature, and evaporation that is involved in the absorption of water by W. robusta palms, to obtain more reliable assessments of δ 18 O in this species.…”