Esque Todd C, Medica Philip A, Shryock Daniel F, DeFalco Lesley A, Webb Robert H, Hunter Richard B
U.S. Geological Survey, Western Ecological Research Center, 160 N. Stephanie St., Henderson, Nevada 89074 USA.
School of Natural Resources, University of Arizona, Tucson, Arizona 85719 USA.
Am J Bot. 2015 Jan;102(1):85-91. doi: 10.3732/ajb.1400257. Epub 2014 Dec 24.
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Accurate demographic information about long-lived plant species is important for understanding responses to large-scale disturbances, including climate change. It is challenging to obtain these data from desert perennial plants because seedling establishment is exceptionally rare, and estimates of survival are lacking for their vulnerable early stages. Desert wildfires, urbanization, and climate change influence the persistence of the long-lived Yucca brevifolia. Quantitative demographic attributes are crucial for understanding how populations will respond to disturbances and where populations will recede or advance under future climate scenarios.•
We measured survival in a cohort of 53 pre-reproductive Y. brevifolia at Yucca Flat, Nevada, USA, for 22 yr and recorded their growth, nurse-plant relationships, and herbivory.•
Herbivory by black-tailed jackrabbits (Lepus californicus) caused severe losses of plants during the first and second years (45% and 31%, respectively). Surviving plants experienced <2.5% annual mortality. Survival for the population was 19% over 22 yr. Plants <25 cm in height had lower life expectancy. Average growth rate (± SD) for plants that survived to the last census was 3.12 ± 1.96 cm yr(-1), and growth rates were positively associated with precipitation. Thirty-year-old Y. brevifolia had not yet reproduced.•
A rare establishment event for Y. brevifolia during 1983-1984, triggered by above-average summer rainfall, provided a unique opportunity to track early survival and growth. Infrequent but acute episodes of herbivory during drought influenced demography for decades. Variability in survival among young Y. brevifolia indicates that size-dependent demographic variables will improve forecasts for this long-lived desert species under predicted regional climate change.
研究前提：关于长寿植物物种的准确人口统计学信息对于理解其对大规模干扰（包括气候变化）的反应至关重要。从沙漠多年生植物中获取这些数据具有挑战性，因为幼苗建立极为罕见，而且缺乏对其脆弱早期阶段存活情况的估计。沙漠野火、城市化和气候变化影响着长寿的短叶丝兰的存续。定量人口统计学属性对于理解种群将如何应对干扰以及在未来气候情景下种群将在何处衰退或扩张至关重要。
方法：我们在美国内华达州丝兰平原对53株未生殖的短叶丝兰进行了为期22年的存活情况测量，并记录了它们的生长、伴生植物关系和食草情况。
主要结果：黑尾长耳大野兔的啃食在第一年和第二年造成了严重的植物损失（分别为45%和31%）。存活的植物年死亡率低于2.5%。22年间该种群的存活率为19%。高度小于25厘米的植物预期寿命较短。存活到最后一次普查的植物平均生长速率（±标准差）为每年3.12±1.96厘米，且生长速率与降水量呈正相关。30岁的短叶丝兰尚未繁殖。
结论：1983 - 1984年期间，由高于平均水平的夏季降雨引发的一次罕见的短叶丝兰幼苗建立事件，提供了一个追踪早期存活和生长情况的独特机会。干旱期间不频繁但严重的食草事件在数十年间影响了种群统计学。幼年短叶丝兰存活情况的变异性表明，在预测的区域气候变化下，与大小相关的人口统计学变量将改善对这种长寿沙漠物种的预测。
