Last Updated on June 10, 2023

The iconic piñon pines and juniper trees of the Southwest’s desert regions are struggling to survive in the face of increasing temperatures and prolonged droughts, according to a recent study published in Functional Ecology.

The research conducted by the University of California Riverside highlights the significant impact of climate change on desert ecosystems, which have long been considered resilient to the effects of global warming. However, even the limited amount of planetary heating experienced since the 1970s has reshaped these ecosystems, and emissions continue to rise.

While desert trees are some of the hardiest plants out there, which have adapted to survive in the harshest environmental conditions, they nonetheless depend on ready access to underground water. That’s in ever-shorter supply thanks to the West’s long drought, though this year’s record rainfall has provided a brief respite.

As the land dried up in past decades, those trees had thinned out at lower elevations — to be replaced by fast-growing, quick-dying shrubs like ocotillo and brittlebush, species that can quickly root, flower and die back to take advantage of flash floods.

As a result of changing environmental conditions, the piñon pines and juniper trees have migrated to higher elevations in the deserts north of Palm Springs, leaving the former forests open for weed species to colonize. This shift towards weed species has transformed the ecosystem into a “leakier” system that is less able to capture and retain carbon than the woodlands.

Piñon Pines (left) and Juniper Trees (right)
Piñon Pines (left) and Juniper Trees (right) are struggling to survive due to climate change.

The Sensitivity of Desert Ecosystems to Climate Change

The research reveals that as temperatures increase and moisture in the ecosystem falls, not all plants migrate upwards in search of cooler temperatures, as initially expected. Instead, there is a wholesale shift towards weed species that have moved down from high elevations to colonize former forests left open by the mass dying-off of trees. This transformation of vegetation has significant implications for the ecosystem’s ability to capture and retain carbon.

The study’s findings suggest that incorporating ecologically relevant functional traits into studies of range shifts and considering multidimensional changes in species’ distributions may provide greater generalization of the impact of climate change on vegetation.

By documenting changes across a steep elevational gradient comprising a large aridity gradient, the study shows divergent patterns for plants occupying contrasting positions along the global spectrum of plant form and function, providing critical insight into how trait-mediated changes under increasing aridity will impact ecosystem functioning.

Co-author of the study, Marko Spasojevic, emphasizes the importance of cutting fossil fuel emissions to alleviate stress on desert ecosystems. The fate of these desert landscapes is a troubling indicator for the vast majority of dryland ecosystems, which must withstand both climate stress and human impacts.

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