U.S. Geological Survey, Western Ecological Research Center, 160 N. Stephanie Street, Henderson, Nevada 89074, USA.
Am J Bot. 2012 Oct;99(10):1647-54. doi: 10.3732/ajb.1200099. Epub 2012 Oct 1.
The future of long-lived stand-forming desert plants such as Yucca brevifolia (Joshua tree) has come into question in light of climate variation and landscape-scale disturbances such as wildfire. Understanding plant establishment dynamics is important for mitigating the impacts of disturbances and promoting revegetation. •
We placed Y. brevifolia seeds in shallow caches and manipulated granivore access, nurse shrub effects, and the season of cache placement to determine conditions for seed germination and seedling establishment. •
Greatest seedling emergence occurred during spring and summer, when increased soil moisture was accompanied by warm soil temperatures. Late winter-spring emergence for cached seeds was enhanced beneath shrub canopies, but seedling survival declined beneath shrubs as temperatures increased in spring. Germinability of seed remaining in the soil was reduced from 50-68% after 12 mo residence time in soil and declined to <3% after 40 mo. Following dispersal from parent plants, seeds are either removed by granivores or lose germinability, imposing substantial losses of potential germinants. •
Specific germination and establishment requirements impose stringent limits on recruitment rates for Y. brevifolia. Coupled with infrequent seed availability, the return rates to prefire densities and demographic structure may require decades to centuries, especially in light of potential changes to regional desert climate in combination with the potential for fire recurrence. Demographic patterns are predicted to vary spatially in response to environmental variability that limits recruitment and may already be apparent among extant populations.
由于气候变化和野火等景观尺度干扰，长寿直立沙漠植物（如丝兰）的未来受到质疑。了解植物建立动态对于减轻干扰的影响和促进植被恢复很重要。
我们将丝兰种子放在浅藏处，并操纵食草动物的获取、护理灌木的影响以及藏种的季节，以确定种子发芽和幼苗建立的条件。
种子的最大萌发发生在春季和夏季，此时土壤水分增加，土壤温度升高。藏种在树冠下的早春萌发得到增强，但随着春季温度升高，幼苗在灌木下的存活率下降。在土壤中停留 12 个月后，种子的发芽能力从 50-68%降低到 40 个月后<3%。从母株传播后，种子要么被食草动物移除，要么失去发芽能力，从而对潜在的发芽体造成大量损失。
特定的发芽和建立要求对丝兰的繁殖率施加了严格的限制。再加上种子的供应不频繁，恢复到火灾前密度和种群结构的回归率可能需要几十年到几个世纪，尤其是在考虑到区域沙漠气候可能发生变化的情况下，以及火灾再次发生的可能性。在限制繁殖的环境变化的影响下，预测人口模式会在空间上发生变化，并且这种变化可能已经在现存种群中显现出来。
