Pavlik B M, Enberg A
Department of Biology, Mills College, Oakland, California 94613, USA.
Environ Manage. 2001 Aug;28(2):225-42. doi: 10.1007/s002670010220.
The geysers panic grass [Dichanthelium lanuginosum Spellenberg var. thermale (Bol.) Spellenberg or DILA] is exclusively associated with surface geothermal manifestations in Sonoma County, California, USA (38 degrees 46'N, 122 degrees 38'W). Steam extraction by power plants could alter the subsurface distribution of heat and water to the site, potentially impacting subpopulations of this rare plant. The purpose of this study was to use demographic monitoring to determine: (1) temporal and spatial patterns of soil temperature in relation to the distribution of established DILA individuals at Little Geysers, (2) in situ response of experimental populations of DILA to spatial variations in soil temperature, and (3) habitat requirements of DILA as an indicator of its tolerance to variations in surficial geothermal features. Thermocouple transects and a datalogger provided data for characterizing the spatial and temporal patterns of soil temperature in four microhabitats (fumarole, DILA stand, Andropogon stand, and cleared). Experimental populations were established by precisely sowing and monitoring DILA seeds in these microhabitats. The results indicated that spatial and temporal variations in soil temperature had significant effects on the processes of germination, growth, survivorship, and reproduction, thus producing a readily observed metapopulation patch dynamic in relation to geothermal activity. Seasonal depressions of soil temperature near the fumaroles by cold air and prolonged rainfall events also promoted the emergence and survival of DILA seedlings in a microhabitat that was previously too hot to occupy. Over longer periods of time, DILA metapopulation dynamism reflected climatic and geothermal variation. Drought years inhibited germination for lack of water, but more importantly for the lack of requisite soil temperature depressions in the fumarole microhabitat. Wet years promoted subpopulation expansion into transition areas that were once too hot and dry. There have also been shifts in the underground distribution of steam into areas distant from known geothermal features. The demographic responses of DILA to spatial and temporal variations in soil temperature indicate that heat is an absolutely essential component of the steam resource. In its absence, germination, seeding survivorship, growth, and maturation are significantly inhibited even if soil conditions are favorable and potential competitors are controlled. Ultimately, persistence of the species depends on maintaining the ecosystem dynamic of colonization and extirpation in response to variations in surficial geothermal features over long spatial and temporal scales. This should shift management perspective from its narrow focus on individual plants to a wider focus on monitoring the essential habitat component of steam.
间歇泉恐慌草[Dichanthelium lanuginosum Spellenberg var. thermale (Bol.) Spellenberg或DILA]仅与美国加利福尼亚州索诺马县（北纬38度46分，西经122度38分）的地表地热活动有关。发电厂抽取蒸汽可能会改变该地点地下热量和水的分布，从而可能影响这种珍稀植物的亚种群。本研究的目的是通过种群统计学监测来确定：（1）与小间歇泉已定植的DILA个体分布相关的土壤温度的时空模式；（2）DILA实验种群对土壤温度空间变化的原位响应；（3）DILA的栖息地需求，以此作为其对地表地热特征变化耐受性的指标。热电偶样带和数据记录器提供了数据，用于描述四个微生境（喷气孔、DILA群落、须芒草群落和空地）中土壤温度的时空模式。通过在这些微生境中精确播种和监测DILA种子来建立实验种群。结果表明，土壤温度的时空变化对发芽、生长、存活和繁殖过程有显著影响，从而产生了与地热活动相关的易于观察到的集合种群斑块动态。冷空气和长时间降雨事件导致喷气孔附近土壤温度季节性下降，这也促进了DILA幼苗在一个以前因温度过高而无法占据的微生境中的出现和存活。在更长的时间尺度上，DILA集合种群动态反映了气候和地热变化。干旱年份因缺水抑制了发芽，但更重要的是喷气孔微生境中缺乏必要的土壤温度下降。湿润年份促进了亚种群向曾经过热和干燥的过渡区域扩张。蒸汽的地下分布也发生了变化，进入了远离已知地热特征的区域。DILA对土壤温度时空变化的种群统计学响应表明，热量是蒸汽资源的绝对必要组成部分。在缺乏热量的情况下，即使土壤条件适宜且潜在竞争者得到控制，发芽、种子存活、生长和成熟也会受到显著抑制。最终，该物种的持续存在取决于在长时间的空间和时间尺度上，响应地表地热特征变化维持定殖和灭绝的生态系统动态。这应该将管理视角从狭隘地关注个体植物转变为更广泛地关注监测蒸汽这一基本栖息地组成部分。
