Long-lived Cactus Research Articles

Algorithms predict morbidity and mortality of Saguaro Cacti (Carnegiea gigantea) from sunlight exposures

Bark coverages on stem surfaces lead to premature death of saguaro cacti (Carnegiea gigantea). Bark coverages have occurred on surfaces of more than 50 species of tall, long-lived cacti throughout the Americas. This study analyzed data of bark coverages on 12 surfaces of C. gigantea. Among 1,149 saguaro cacti, from four sampling periods over 23 years, data of four independent algorithm programs were used to predict bark coverages and cactus death. On saguaros, bark coverage originates on south-facing surfaces and progresses to north-facing surfaces, prior to cactus death. For this population, bark coverages increased over time and 45% of all cacti were dead by the end of the 23-year study period. Validate Model and WEKA 3.8 predicted bark coverages with over 96% accuracy. Random Forest predicted cactus death with 99.6% accuracy and kNN predicted cactus death with 100% accuracy. Since trough surfaces occur after crest surfaces, trough surfaces were better predictors of bark coverages and cactus death. Cactus death was best predicted (above 99%) with north-right troughs with west-facing surfaces. Taken together, the four machine programs gave complimentary results and predicted (above 99%) both increased bark coverages from south-facing surfaces to north-facing surfaces over time and death of individual cacti over an eight-year period when north-facing right troughs had more than 80% bark coverages.

Nutrient fluxes from water to land: seabirds affect plant nutrient status on Gulf of California islands.

Energy and nutrient fluxes across habitat boundaries can exert profound direct and indirect effects on the dynamics of recipient systems. Transport from land to water is common and well studied; here, we document a less recognized process, substantial flows from water to land. On hyperarid, naturally nutrient poor islands in the Gulf of California, nutrient input via seabird guano directly increases N and P concentrations up to 6-fold in soils; these nutrients enrich plants. Nutrients in a long-lived cactus, a short-lived shrub, and annuals were 1.6- to 2.4-fold greater on bird versus nonbird islands. Because plant quality affects consumer growth and reproduction, we suggest that nutrient enrichment via guano ramifies to affect the entire food web on these islands.