George Jessie, Dimson Monica, Dunn Regan E, Lindsey Emily L, Farrell Aisling B, Aguilar Brenda Paola, MacDonald Glen M
La Brea Tar Pits & Museum, Natural History Museums of Los Angeles County, 5801 Wilshire Blvd, Los Angeles, CA, 90036, USA.
Department of Geography, University of California, Los Angeles, CA, 90095, USA.
New Phytol. 2025 Feb;245(4):1746-1761. doi: 10.1111/nph.20324. Epub 2024 Dec 10.
Juniperus spp. are keystone shrubs in western North America and important climatic indicators in paleo-records. However, a lack of taxonomic resolution among fossil species limits our ability to track past environmental changes. Plant macrofossils at Rancho La Brea (RLB) allow for reconstructions of juniper occurrence to species across 60 000 yr. We use microscopy, image analysis, species distribution modeling (SDM), and radiocarbon dating to identify an unknown Juniperus species at RLB and put it into chronological context with fossil Juniperus californica at the site to infer past environmental conditions. We identify the unknown taxon as Juniperus scopulorum Sargent, 1897. The Pleistocene occurrence of this species in California expands its known distribution and documents its extirpation. Temporal ranges of the two fossil junipers alternate, revealing a pattern of differential climatic sensitivity throughout the end of the Pleistocene. Occurrence patterns suggest sensitivity to temperature, moisture availability, and the presence of two mega-droughts at c. 48-44.5 ka and c. 29.3-25.2 ka. Extirpation of both taxa by c. 13 ka is likely driven by climate, megafaunal extinction, and increasing fire. The extirpation of fossil junipers during these past climatic events demonstrates vulnerability of juniper species in the face of global change.
刺柏属植物是北美西部的关键灌木，也是古记录中的重要气候指标。然而，化石物种之间缺乏分类分辨率限制了我们追踪过去环境变化的能力。拉布雷亚牧场（RLB）的植物大化石有助于重建6万年以来刺柏属植物的出现情况及物种信息。我们使用显微镜检查、图像分析、物种分布建模（SDM）和放射性碳测年法来识别RLB的一种未知刺柏属物种，并将其与该地点的加州刺柏化石置于时间序列中，以推断过去的环境条件。我们将这个未知分类群鉴定为1897年萨金特命名的石崖刺柏。该物种在加利福尼亚州更新世的出现扩展了其已知分布范围，并记录了其灭绝情况。两种化石刺柏的时间范围交替出现，揭示了整个更新世末期不同的气候敏感性模式。出现模式表明它们对温度、水分可利用性以及约48 - 44.5 ka和约29.3 - 25.2 ka时两次大干旱的敏感性。到约13 ka时，这两个分类群的灭绝可能是由气候、大型动物灭绝和火灾增加所驱动。在这些过去的气候事件中化石刺柏的灭绝表明了刺柏属物种在面对全球变化时的脆弱性。
