The loss of California’s coastal sand dune habitat has reached alarming levels, according to a landmark study conducted by researchers from the University of California, Santa Barbara (UCSB) and collaborators. Published in Earth’s Future, the assessment is the first comprehensive inventory of California’s coastal dunes and reveals that approximately 60% of the state’s dune systems have disappeared since 1850. Once covering around 739 square kilometers (285 square miles) of coastline, California’s dunes now occupy less than 300 square kilometers (116 square miles).

Researchers warn that this dramatic decline threatens biodiversity, weakens natural coastal defenses, and increases vulnerability to storms and sea-level rise.

California’s Coastal Dunes Have Shrunk Dramatically

Coastal sand dunes are more than just scenic landscapes. They act as natural reservoirs of sand, helping replenish beaches while providing habitat for a wide range of plant and animal species.

According to the study, most dune loss occurred due to human activity rather than natural coastal processes. Urban expansion, infrastructure development, agriculture, and the spread of invasive plant species have transformed large portions of California’s coastline over the past 165 years.

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Urban Development Drives the Largest Losses

Researchers found the most significant declines in heavily urbanized regions such as San Francisco and Los Angeles. More than 95% of the dunes that once existed in these areas were removed to accommodate roads, housing developments, commercial infrastructure, and transportation networks.

Central California also experienced substantial losses, with approximately 60% of its coastal dune systems disappearing over time.

Did You Know?

California’s coastal dunes provide benefits that extend far beyond the shoreline:

• They support unique habitats for plants, insects, birds, and small mammals.
• Dunes act as natural barriers that help absorb storm impacts and reduce coastal flooding.
• They supply sand to nearby beaches, helping maintain shoreline stability.
• Healthy dune ecosystems can adapt and rebuild naturally after storms, making them a resilient form of coastal protection.

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A Growing Role in Climate Adaptation

The study arrives at a time when coastal communities are increasingly preparing for rising sea levels and stronger coastal storms. Researchers note that dune restoration is gaining attention as a nature-based solution because dunes can provide sustainable, self-healing protection against ocean encroachment.

However, restoration is not a one-size-fits-all solution.

• Factors such as available space, local geography, costs, and community priorities will determine where dune projects are most effective.

Another key concern identified in the research is fragmentation.

• Nearly half of California’s remaining dunes are now isolated from natural coastal processes by roads, urban development, and other infrastructure, limiting their ability to evolve and function naturally.

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Mapping the Future of Coastal Resilience

To complete the assessment, researchers combined historical maps, aerial photography, LiDAR data, machine-learning tools, site visits, and archival records to track how California’s dune systems have changed over time.

Importantly, the methodology developed through this project can be applied to coastlines worldwide. As sea levels continue to rise, the findings provide a valuable framework for identifying restoration opportunities, prioritizing conservation efforts, and strengthening natural coastal defenses.

The loss of California’s coastal sand dune habitat highlights how decades of development have reshaped the coastline. At the same time, the study offers a roadmap for restoring these critical ecosystems and improving climate resilience for future generations.

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