U.S. Geological Survey, Western Ecological Research Center, 160 N. Stephanie Street, Henderson, Nevada 89074 USA.
Am J Bot. 2010 Feb;97(2):243-50. doi: 10.3732/ajb.0900032. Epub 2010 Jan 22.
Extreme climate events are transforming plant communities in the desert Southwest of the United States. Abundant precipitation in 1998 associated with El Niño Southern Oscillation (ENSO) stimulated exceptional alien annual plant production in the Mojave Desert that fueled wildfires in 1999. Exacerbated by protracted drought, 80% of the burned Yucca brevifolia, a long-lived arborescent monocot, and 26% of unburned plants died at Joshua Tree National Park by 2004. Many burned plants <1 m tall died immediately, and survival of all but the tallest, oldest plants declined to the same low level by 2004. Postfire sprouting prolonged survival, but only at the wetter, high-elevation sites. During succeeding dry years, herbaceous plants were scarce, and individuals of Thomomys bottae (pocket gopher) gnawed the periderm and hollowed stems of Y. brevifolia causing many of them to topple. Thomomys bottae damage reduced plant survivorship at low-elevation, unburned sites and diminished survival of burned plants in all but the driest site, which already had low survival. Accentuated ENSO episodes and more frequent wildfires are expected for the desert Southwest and will likely shift Y. brevifolia population structure toward tall, old adults with fewer opportunities for plant recruitment, thus imperiling the persistence of this unique plant community.
极端气候事件正在改变美国西南部沙漠中的植物群落。1998 年与厄尔尼诺-南方涛动（ENSO）相关的丰富降水刺激了莫哈韦沙漠中异常丰富的外来一年生植物的产生，这导致了 1999 年的野火。由于持续干旱的加剧，2004 年约书亚树国家公园 80%的已燃烧的丝兰（一种长寿命的木本单子叶植物）和 26%的未燃烧植物死亡。许多高度小于 1 米的燃烧植物立即死亡，到 2004 年，除了最高和最古老的植物外，所有植物的存活率都下降到相同的低水平。火灾后的萌发延长了存活时间，但仅在较湿润、高海拔的地点。在随后的干旱年份，草本植物稀缺，而 Thomomys bottae（囊鼠）啃食丝兰的表皮和空心茎，导致许多丝兰倒伏。Thomomys bottae 的损害降低了低海拔、未燃烧地点的植物存活率，并降低了除最干旱地点以外的所有燃烧植物的存活率，而最干旱地点的存活率已经很低。预计沙漠西南部的 ENSO 事件会更加频繁和剧烈，这可能会使丝兰种群结构向高大、古老的成年植物倾斜，减少植物繁殖的机会，从而危及这种独特植物群落的持续存在。
