LAX Leader

Los Angeles—Scientists at the La Brea Tar Pits have successfully identified a previously unknown juniper species as Juniperus scopulorum, commonly referred to as the Rocky Mountain Juniper. This identification, alongside the first radiocarbon dating of these fossil plants in Southern California, enhances understanding of past environmental changes and emphasizes the vulnerability of junipers amid modern climate change. The findings are published in the journal New Phytologist.

The junipers were significant components of Ice Age Los Angeles landscapes, where mammoths and saber-toothed cats roamed. They served as keystone shrubs for over 47,000 years before disappearing during a major extinction event that also affected megafauna.

Previously, researchers recognized two different juniper species at the Tar Pits: J. californica (California juniper) with large seeds and an unidentified small-seeded mystery juniper. Fossilized junipers are crucial for studying past climate conditions and predicting future survival prospects under climate change scenarios. However, the identity of this mysterious seed remained unresolved until now.

"We set out to identify this mystery juniper, and in the process, we found a number of exciting things," says Dr. Jessie George, postdoctoral researcher at La Brea Tar Pits and lead author on the study. "Number one, we identified this juniper as Rocky Mountain juniper, and it is one of the most extreme examples of a plant going extinct locally. It’s not present anywhere in California today."

Radiocarbon dating led to another intriguing discovery: “In the process of radiocarbon dating these juniper species, we found this really interesting pattern of reciprocal presence—either California juniper only or Rocky Mountain juniper only.”

Dr. George noted that each plant's presence acts as a proxy for specific climatic conditions due to their survival requirements. "California juniper is a much more drought-tolerant species," she explained. "Through these back-and-forth occurrences of the two species from the Tar Pits, we have this really fascinating record of aridity and drought that was previously undetected."

The small size of the unknown seed made identification challenging without DNA extraction from fossils; instead, researchers compared seed structures using advanced microscopy techniques until they reached a conclusion.

While climate played a role in their local extinction, human-induced fires may have contributed further stress on already drought-adapted plants like these non-fire-resistant conifers.

“We're seeing a really dramatic decline of these trees in the southwest today because of warming temperatures and increased wildfire caused by modern climate change,” says George. “It gives us a better framework to understand baseline climates and environments necessary for contextualizing changes affecting other flora-fauna interactions during significant historical shifts."

The study was authored by Jessie George along with Monica Dimson; Regan E Dunn; Emily L Lindsey; Aisling B Farrell; Brenda Paola Aguilar & Glen M MacDonald - published December 10th via New Phytologist journal

La Brea Tar Pits offers insights into ongoing urban Ice Age excavations globally unique due its consistent activity within city limits providing both research opportunities while educating visitors onsite about various paleontological discoveries ranging from large predators down through smaller botanical specimens spanning roughly fifty millennia worth data contributing towards broader ecological understanding worldwide facilitated further via collaborative initiatives spearheaded under Natural History Museums umbrella encompassing three locations throughout greater Los Angeles region fostering engagement public science outreach endeavors bridging gap between academia general populace alike.