Joshua trees bloomed earlier than usual – and it spells trouble for iconic succulent

Southern California’s famed Joshua trees are flowering months ahead of schedule, baffling scientists and raising fears about the future of the species.

The Mojave Desert succulents typically bloom between February and April, timing their flowers to the arrival of the yucca moth — the only insect capable of pollinating them.

The moth lays its eggs inside the flowers, producing fruit whose seeds are later spread by rodents.

This year, however, the trees’ familiar white-and-yellow blooms began appearing on late October, sparking concerns that the early flowering could disrupt the delicate relationship between the trees and their sole pollinator — and threaten the species’ ability to reproduce.

The troubling shift comes as Joshua trees are already under pressure from wildfires, drought and extreme weather.

California State University, Northridge associate biology professor Jeremy Yoder told SFGate that the premature bloom could spell trouble for the yucca moth, whose life cycle has evolved to match the trees’ predictable flowering window.

Yoder said the moths deposit pollen while laying eggs, and their larvae grow inside the fruit, eating some of the seeds before they ‘chew their way out of the mature fruit, drop to the ground, and burrow into the sand and form a cocoon’ until the next flowering season.

”The moths are totally dependent on the trees. The trees have no other pollinators because the moths are so good at their job,” Yoder said. ”And so the real question when the trees flower super early like this is: Are the moths going to show up? And what I think we’re seeing so far is that they’re not.”

Yoder suspects this year’s early rains may have triggered the premature bloom. His Yoder Lab is now asking members of the public to help document the phenomenon by uploading photos of Joshua trees in bloom to iNaturalist, allowing scientists to gather data on whether the early flowering affects fruit production.

”We’re looking for as many folks out there as possible to help observe this phenomenon,” Yoder said.

A similar early bloom occurred in 2018, but it was largely confined to Joshua Tree National Park, the southernmost edge of the species’ range.

This year, Yoder said, early flowering is happening everywhere Joshua trees grow.

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Scientists hope that comparing public photos from 2018 with new images from this year will help clarify whether repeated early blooms could weaken the trees over time.

”If the trees are flowering more frequently, but the moths don’t show up to match that, then the trees are spending energy and effort,” Yoder said. ”That might make them less resilient to stress — and that spent effort doesn’t result in new seeds and new Joshua trees to replenish the population.

”But that’s the possibility. That’s what we don’t know.”