Abstract Sunlight exposures have resulted in periderm coverages on more than 40 species of tall, long-lived columnar cactus species in the Americas. Periderm coverages start on equatorial surfaces and eventually cover all surfaces. Periderm coverages lead to tissue morbidity and eventual cactus death. After more than 80% of periderm coverage on saguaro (Carnegiea gigantea) cacti, the probability of cactus death was greater than 95% within eight years. Periderm coverage characteristics were not similar for five species of tall, long-lived columnar cactus species endemic to the Tehuacan-Cuicatlan Valley (18° N), Puebla, Mexico. For four species, trough coverages were higher for south-facing surfaces than north-facing surfaces. For these four species periderm ratios were near 2:1, S:N. This 2:1 ratio is coincident with the ratio of direct sunlight exposures on S: N surfaces. For one species, the amounts of periderm were low so no differences in periderm coverages occur of south to north were present. Unlike cacti at other locations, crests of species of this study did not show a directional effect. The results indicate that periderm formation occurred first on south-facing surface and eventually occurred on other surfaces. Results with Random Forest, an algorithm, reinforce results of periderm percentages. Random forest was used to determine surfaces coverages that predict periderm coverages on other surfaces. As expected, neighboring surfaces were the best predictors of periderm coverages. Other surfaces were not good predictors of periderm coverages indicating that other surfaces had periderm coverage before or after the predicted surfaces. Random Forest data were the same for all five species. Although, the patterns of the five species showed some variability, they all support that hypothesis that periderm coverages start on south-facing surfaces and eventually occur on north-facing surfaces and they are caused by sunlight.

中文翻译：

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墨西哥中部五种长寿命柱状仙人掌物种的外皮覆盖率

摘要 阳光照射导致美洲 40 多种高大、长寿的柱状仙人掌物种的周皮被覆盖。外皮覆盖从赤道表面开始并最终覆盖所有表面。外皮覆盖导致组织发病和最终仙人掌死亡。在仙人掌（Carnegiea gigantea）仙人掌的周皮覆盖率超过 80% 后，八年内仙人掌死亡的概率大于 95%。墨西哥普埃布拉州 Tehuacan-Cuicatlan 山谷（北纬 18 度）特有的五种高大、长寿柱状仙人掌物种的外皮覆盖特征并不相似。对于四个物种，朝南表面的槽覆盖率高于朝北表面。对于这四个物种，周皮比率接近 2:1，S:N。这2：1 比率与 S:N 表面上直接阳光照射的比率一致。对于一个物种，周皮的数量很少，因此从南到北的周皮覆盖率没有差异。与其他位置的仙人掌不同，本研究中物种的冠没有显示出方向性效应。结果表明，周皮形成首先发生在朝南的表面，最终发生在其他表面。随机森林算法的结果加强了周皮百分比的结果。随机森林用于确定预测其他表面周皮覆盖率的表面覆盖率。正如预期的那样，相邻表面是周皮覆盖率的最佳预测指标。其他表面不是周皮覆盖率的良好预测因子，表明其他表面在预测表面之前或之后具有周皮覆盖率。所有五个物种的随机森林数据都相同。尽管这五个物种的模式显示出一些变异性，但它们都支持周皮覆盖从朝南的表面开始并最终发生在朝北的表面并且它们是由阳光引起的假设。