In New Mexico, Kerley et al. studied the effects of cattle browsing on the flowers of the soaptree (Yucca elata), and measured inflorescence consumption and population structure in six populations protected from grazing, six grazed during the flowering season, and five grazed outside the flowering season. At sites grazed by cattle during the flowering season, 98% of current flower stalks had been consumed, significantly more than at exclosure and non-flower-grazed sites. Reduced recruitment in flower-grazed populations could not be attributed to reduced flower survival, because recruitment in non-flower grazed populations was also reduced. Cattle significantly alter population structure and plant geometry of Y. elata by selectively grazing small caudices, either ramets or genets. An alternate hypothesis is that physical soil compaction due to cattle trampling may prevent Y. elata germination and recruitment. However, recruitment of Y. elata is not a function of soil compaction, refuting this hypothesis. Cattle browsing implies a lack of genetic recruitment, possible local extinction of the yucca moth, Tegeticula yuccasella, the exclusive pollinator of Y. elata, and a reduction in animal biodiversity.
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