Protecting the western Joshua tree

Candidacy for the California Endangered Species Act

The California Fish and Game Commission will decide in February 2023 whether the western Joshua tree (Yucca brevifolia) will become the first plant species to be listed as threatened in California due to climate change.

The western Joshua tree was designated as a candidate species for listing as threatened under the California Endangered Species Act in October 2020. This triggered an 18-month scientific review and interim protections for the species. In filing their petition to list the species, Brendan Cummings of the Center for Biological Diversity wrote: “…the western Joshua tree meets the definition of a ‘threatened species’ since it is ‘a native species or subspecies of a … plant that, although not presently threatened with extinction, is likely to become an endangered species in the foreseeable future in the absence of the special protection and management efforts’…” Cal. Fish & Game Code § 2067.

The Mojave Desert Land Trust supports the listing of the western Joshua tree.

Talking points: Threats to the western Joshua tree

The rationale for listing the western Joshua tree was primarily driven by climate change impacts, but a suite of other threats all pointed towards a reduction in range for this iconic species.

Rising temperatures

  • A 2012 study estimated that a temperature increase of 3°C – with no change in precipitation – would reduce suitable habitat for Joshua trees by 90% (Barrows and Murphy-Mariscal). This temperature increase corresponds with a projected high emissions scenario that is well above current levels.
  • Even under a best case scenario in which emissions are reduced to zero by 2080, the mean annual temperature within Joshua Tree National Park is projected to increase by 1.5°C (Gonzalez, 2019).
  • A temperature increase of only 1°C is estimated to reduce suitable Joshua tree habitat by one-third (Barrows and Murphy-Mariscal, 2012).

Emissions

  • A 2019 study looked at several possible outcomes for Joshua tree habitat. In the best-case scenario, major efforts to reduce heat-trapping gases in the atmosphere would save 19% of the tree habitat towards the end of the century. In the worst case, with no reduction in carbon emissions, the park would retain a mere 0.02% of its suitable Joshua tree habitat, leading to “an almost complete elimination of Joshua trees from the park”. (L. Sweet, Congruence between future distribution models and empirical data for an iconic species at Joshua Tree National Park, 2019).

Wildfire

  • Climate change presents an additional threat to the Joshua tree in the form of wildfire. Atmospheric carbon dioxide accelerates growth of invasive grasses like mustard and brome. In undisturbed Mojave ecosystems, bare soil separates vegetation with low incidence of severe wildfire. Field research in Joshua Tree National Park found that nitrogen deposition from vehicles has increased grass growth at two of four sites, significantly increasing wildfire risk.
  • One of the most evident risks of wildfire threat to the Joshua tree took place in Mojave National Preserve in the world’s largest Joshua tree forest. In August 2020, 1.3 million eastern Joshua trees (Yucca brevifolia var. jaegeriana) burned in the 43,000-acre Cima Dome wildfire.
  • The combination of increased temperatures and variable precipitation attributable to climate change, spread of invasive species, and increased human activity favor opportunities for wildfire and increased Joshua tree mortality. Young trees under one meter in height are particularly vulnerable to extreme fire temperatures as their formative plant tissue is close to the ground.

Development

  • Local jurisdictions in the western Joshua tree range have minimal protective measures in place and often provide exemption for single family homes.

Threats can be even greater on private lands, which account for 40% of western Joshua tree habitat. Only a small fraction of private land retains any kind of protections for this vulnerable species from development. With a growing list of threats stacked against shrinking population projections, virtually all suitable habitat may be lost in the coming decades without strengthened protections for the western Joshua tree.

Permitting

During the western Joshua tree’s candidacy period, it is a violation of California Fish and Game Code to trim or remove (or “take”) a tree without first obtaining a permit. Read the resources and processes for compliance with the interim regulations here.