The primary cause of shriveled tree leaves in Yosemite is prolonged environmental stress, particularly due to drought and nutrient depletion. Secondary factors include pest infestations and soil degradation.

Yosemite's ecosystem faces significant challenges from climate change, including reduced precipitation and higher temperatures. From 2012 to 2023, California experienced its worst multi-year drought, with average annual rainfall decreasing by 20% in the Sierra Nevada region. This water scarcity directly impacts tree hydration, leading to desiccation and leaf shrinkage. Data from the U.S. Geological Survey (USGS) shows that soil moisture levels in Yosemite fell below 10% of capacity during the 2021–2022 dry season, exacerbating stress on vegetation.

Pest infestations, such as bark beetles and aphids, further weaken trees by disrupting nutrient transport. A 2023 report by the California Department of Forestry and Fire Protection (CDFP) documented a 35% increase in bark beetle activity in Yosemite’s coniferous forests since 2018. These pests create entry points for fungi, which consume plant cells, reducing water absorption. For example, the mountain pine beetle infestation in the Mariposa Grove area caused 40% of sugar pine mortality between 2019 and 2022, per National Park Service (NPS) surveys.

Soil degradation from erosion and foot traffic also plays a role. Heavy visitor use in Yosemite leads to nutrient runoff and compaction, reducing microbial activity. A 2022 study in Environmental Management found that trails near major viewpoints had 60% less organic matter compared to remote areas, impairing root function. Combined, these stressors create a feedback loop: drought weakens trees, making them more susceptible to pests and diseases, which further deplete resources. Mitigation efforts, such as controlled burns and pest monitoring, are critical to restoring balance.

In summary, Yosemite’s shriveled leaves result from interconnected environmental stressors, with drought being the dominant factor. Addressing these requires integrated conservation strategies to address water scarcity, pest control, and soil health.