Yucca brevifolia

One of greatest threats to Yucca brevifolia and Y. jaegeriana subpopulations is high intensity and more frequent fires fuelled by exotic non-native annual grasses (primarily Red Brome (Bromus rubens) and secondarily Cheatgrass (Bromus tectorum)) (Brooks et al. 2013) that can kill or severely damage the plants, especially the smaller younger (shorter) individuals.

While Y. brevifolia is adapted to low intensity fires and can resprout from stems and rhizomes, the hotter and more frequent fires coupled with a unique life history strategy makes it difficult for Y. brevifolia to colonize burned landscapes (Abella 2010). Seed production does not occurs as masts (Borchert and DeFalco 2016) every year and depends on one known moth pollinator; ripe seeds must be freed from indehiscent fruits by small mammals to be dispersed and planted (Vander Wall et al. 2006, Waitman et al. 2012). The seeds germinate only under exacting rainfall and temperature conditions and quickly lose viability in soil if conditions are not met (Reynolds et al. 2012). The young plants are eaten by lagomorphs and rodents (Esque et al. 2015), so seedlings receive protection growing in association with native shrubs (Brittingham and Walker 2000), which are also decimated by fires. In conjunction with other stressors, including drought-induced increases in herbivory following wildfire and predicted higher temperatures from climate change, these factors collectively may contribute to population declines through time (DeFalco et al. 2010, St. Clair and Hoines 2018, U.S. Fish and Wildlife Service 2018).

More recent threats to this species include land clearing for energy development such as wind farms and in some areas solar farms.

For the portion of the range of the species within the Joshua Tree National Park, it has been predicted that without climate change mitigation the reduction of suitable habitat for the Joshua Tree would be such that it would go extinct by the year 2070 (Sweet et al. 2019). With moderately high and moderate climate change mitigation, refugia for 18.6% and 13.9% of the original occupied area, respectively, would remain as refugia (Sweet et al. 2019). However, this study provides evidence of the effects of climate change only in the southern (trailing edge) part of the species' range. Similar models are needed for the whole range of the species to have a complete representation of the climate variability across it and a better understanding of how the range of the species will be affected by climate change. 

This species occurs within the Joshua Tree National Monument, Mojave National Preserve, Grand Staircase-Escalante National Monument and Grand Canyon National Park.

Yucca brevifolia was determined on 2 January 2003 (and last reviewed) as having a Global Status level of G4, G5, with a Rounded Global Status of G4, being "Apparently Secure" according to NatureServe; the National Status: NNR, is N4 [note: this is the broader taxonomic concept as NatureServe does not recognise Y. jaegeriana] (NatureServe 2020).

A proposal to the U.S. Fish and Wildlife Service to consider listing the Joshua Tree (i.e. the broader taxonomic concept) under the U.S. Endangered Species Act was not successful (U.S. Fish and Wildlife Service 2019).

Yucca brevifolia and Y. jaegeriana are distinctly different species. Recognising them as such has significant implications for their management and conservation as they occupy different habitats and are mostly allopatric (W. Hodgson pers. comm. 2019).