Previous research has shown that identical scale and bark injuries occur on stems of 16 species of columnar cacti in North and South America. For all 16 species, areas with scale and bark injuries on stems were greater on equatorial-facing surfaces than on polar-facing surfaces. Moreover, percentages of stem areas with injuries were well correlated with relative amounts of annual sunlight exposure. Cacti with high levels of scale and bark injuries had high levels of mortality. Previous data have shown that at the Equator, about 1.4 times more incident light occurs on west-facing and east-facing surfaces (equatorial surfaces) than on north-facing and south-facing (polar-facing) surfaces. Herein we determined the percentages of stem areas with scale and bark injuries on equatorial-facing (east and west) and polar-facing (north and south) surfaces of four species of columnar cacti in Ecuador (near the Equator). Specifically, percentages of trough areas with scale and bark injuries were determined for stems of Armatocereus cartwrightianus, Pilosocereus lanuginosus, and Praecereus euchlorus on mainland Ecuador and for Jasminocereus thousarii on the Galapagos Islands, Ecuador. For our analysis, data from all four cactus species were pooled. Chi-square tests showed that average injuries on equatorial surfaces were greater than average injuries on polar surfaces. For the pooled data, injuries on equatorial-facing surfaces were 1.4 times greater than on polar-facing surfaces. Therefore, the 1.4 times greater injuries on equatorial-facing surfaces compared with polar-facing surfaces was coincident with the 1.4 times greater incident light on equatorial surfaces than on polar surfaces for cacti at the Equator. Taken together with previous data, the data of this study show that at least 20 species of long-lived columnar cactus species in the Americas have almost identical scale and bark injuries even though they exist from 32° N to 32° S. Ratios of equatorial vs. polar injuries are well correlated with ratios of PAR (photosynthetically active radiation) for equatorial and polar surfaces. Moreover, the ratio of injuries on equatorial vs. polar surfaces were highly correlated with the latitudes of this study.
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Vol. 135 • No. 4