About Rancho La Brea Plants | Natural History Museum of Los Angeles

Flora at Rancho La Brea

Conservative estimates indicate more than 100,000 plant specimens have been recovered from Rancho La Brea. Most of this material comes from our recent Pit 91 excavation and Project 23 promises to yield many more specimens. Plants are represented by pollen, leaves, seeds, cones, and wood from approximately 158 species. In addition to the gymnosperms and angiosperms, over 80 species of diatoms (microscopic unicellular algae) and a single species of green algae have also been identified from Pit 91. Plants are excellent indicators of climate because they are so tightly constrained to specific temperatures, humidity, and levels of shade. Some of the fossil plants we find here are still represented locally, whereas others, such as the coast redwood (Sequoia sempervirens), currently grow outside the Los Angeles basin. In order to give visitors to Hancock Park a better insight into the vegetation that grew here during the end of the Ice Age, the Museum has grown a Pleistocene Garden. Its contents are based on the fossils recovered from Pit 91.

The climate in the Los Angeles basin during the end of the last Ice Age appears to have been a coastal maritime climate similar to that currently prevailing on the Monterey peninsula, approximately 300 miles north of Los Angeles. Evidence from pollen in deep sea cores suggests that the climate was both cooler and wetter than it is today in Southern California. However, isotopic evidence from Rancho La Brea mammals and plants indicates that that the rainfall was restricted to the winter. As the climate became cooler, so the amount of carbon dioxide in the atmosphere became smaller. Carbon dioxide is important for plant photosynthesis. Evidence from the Rancho La Brea plant material, including the 14,000 year-old fossil juniper tree from Pit 3, indicates that the late Pleistocene plants were severely stressed and plant productivity was very low. Low plant productivity would have adversely affected food supplies for herbivores.This would in turn explain why the teeth of carnivorous mammals recovered from Rancho La Brea show more wear and damage than those of modern carnivores. Because the numbers of their herbivorous prey were reduced due to low plant productivity, the carnivores had to eat more of the carcasses, including the bones, and hence their teeth became damaged and broken.

Studies of the plant materials have suggested that there were at least four different plant associations present in the area: coastal sage scrub, riparian (stream margin), chaparral, and deep canyon. 

Coastal Sage Scrub

Coastal sage scrub plants are typified by drought-resistant sages, buckwheat, morning glory, and tarweeds. The coastal plain was the primary food source for the larger grazing herbivores found here at Rancho La Brea including mammoths, bison, camel, and horse. With the abundance of these herbivores this area then attracted the carnivores like dire wolves, American lion, and sabertoothed cats. Years after the Ice Age extinctions, the landscape was used by the Chumash and the Gabrielino cultures. Various types of seeds and plants were used for food and medicine.

Stream Margin or Riparian

Riparian plants thrived on the margins of streams in the Los Angeles basin. The water would have been home to many shallow-water dependent animals including ducks, fish, freshwater snails and clams, ostracods, frogs, and insects. Large browsing herbivores such as the American mastodon and Shasta ground sloth used this habitat as their primary food source. Ripariolants and trees found in this area include sycamore, elderberry, alder, and willow. After the Ice Age, this area provided sustainable materials to the native people for housing, basketry, hunting materials, medicines, and an excellent source of protein to their diet.

Deep Canyon

Deep canyon environments occur high up in the hills and surrounding mountains. This type of ecosystem has remained almost unchanged for the past 25,000 years. During this time the area was home to small predators such as mountain lions, coyote, eagles, and hawks, as well as, to smaller prey such as rabbits, chipmunks, and squirrels. Typical plants found in this type of environment are dogwood, California bay, and redwood. 

Chaparral

Chaparral is characterized by fire dependent woody bushes and trees. Similar associations can be found in the Santa Monica Mountains today consisting of walnut, scub oak, manzanita, chamise, lilac, and coffeeberry.