The remote Nāpali Coast, a beautiful region of sheer sea cliffs and lush valleys on the northwestern shores of Kaua‘i, is one of the most breathtaking landscapes in the Hawaiian Islands – and on Earth.

The Nāpali Coast spans 17 miles of shoreline and is located within the boundaries of the 6,000-acre Nāpali Coast State Wilderness Park and the smaller Hono O Nā Pali Natural Area Reserve.

It annually attracts many visitors to hike through wet gulches and open ridgelines of the well-known Kalalau Trail, which ends at the isolated Kalalau Beach. It also beckons many to experience the coast by air on helicopter tours, or by sea while aboard catamarans or Zodiac style boats to explore sea caves and snorkel or dive.

But despite all the exploration, the Nāpali Coast retains mystique and remains home to a vibrant array of animals and plants, many endemic to the area.

“This is a biodiversity hotspot,” said Scott Heintzman of the Plant Extinction Prevention Program, a statewide conservation program affiliated with the University of Hawai‘i at Mānoa.

“The beauty alone … The views and all of the unique microhabitats those rugged cliffs have is something that’s unmatched,” Heintzman continued. “I’ve never seen that anywhere else in Hawai‘i.”

The Plant Extinction Prevention Program is supported by state and federal funds, grants and donations. Heintzman is one of two program personnel based on Kaua‘i, where they work to save so-called “PEPP species,” critically endangered plant species with fewer than 50 individuals remaining in the wild. Chief threats include climate change and animals like goats, pigs and rats, which eat native vegetation and also destroy it by trampling and other actions.

The Hawaiian Islands have been dubbed “the endangered species capital of the world” and are home to 40% of all endangered plants in the United States. On Kaua‘i, Heintzman is responsible for approximately 90 PEPP species. That number fluctuates as new plant populations are discovered and others are determined to be extinct.

Heintzman spends much of his time working on the Nāpali Coast in partnership with other conservation organizations, including the nonprofit National Tropical Botanical Garden headquartered on the island’s South Shore.

Heintzman, botanical garden scientists and others use tools, helicopters and drones to monitor plant populations and collect seeds and other propagative materials.

To perform these duties, they at times rappel down the cliffs of the Nāpali Coast, which can reach dizzying heights of more than 1,400 feet at the coastline and more than 4,000 feet less than a mile inland.

“It’s interesting to [imagine] what tourists might see of these places, not knowing some of the most critically endangered species in the world occupy those spaces,” Heintzman said. “These are really jewels of creation.”

Plant species handled by Heintzman on the Nāpali Coast include Kadua st-johnii, a succulent herb in the coffee family that sprouts from cracks in cliffsides beyond the reach of goats. Farther inland, within the Kalalau Valley, he and his colleagues focus on plants like māhoe, also known as ‘ala‘alahua (Alectryon macrococcus var. Macrococcus). The tree with reddish-brown branches, which can grow to more than 36 feet tall, has been devastated by the black twig borer, an invasive insect.

Kaua‘i is the oldest of the eight major islands of Hawai‘i, which also include Ni‘ihau, O‘ahu, Molokaʻi, Lānaʻi, Maui, Kahoʻolawe and Hawai‘i Island, frequently referred to as the Big Island. Together, they make up the most isolated landmass on Earth, which began to form nearly 30 million years ago with the creation of the present-day Northwestern Hawaiian Islands, a series of small islands and atolls.

Kaua‘i, by comparison, is about 5 million years old. The Big Island is the youngest at less than half a million years old.

Both the northwestern and major Hawaiian Islands were formed by the passage of a tectonic plate over a volcanic “hot spot” spewing magma from the seafloor. This ongoing geological process is now occurring underwater off the southeast coast of Hawai‘i.

The distinctive geography of the Nāpali Coast continues to be formed by erosion caused by waves, streams and the roots of plants. But humanity also has played a role in shaping the landscape as well. Hikers on the Kalalau Trail today will pass overgrown agricultural terraces constructed by ancient Native Hawaiians who once lived in ahupuaʻa, or land divisions, set within the region’s narrow valleys.

The main focus of the Nā Pali Coast ʻOhana, a nonprofit organization formed in 1995, is the preservation and restoration of the archaeological site Nuʻalolo Kai. Access is controlled: Most individuals may only visit the former Native Hawaiian village through a permitted tour operator.

“It shows how … the Hawaiians’ lifestyle did not detract from the ecosystem,” Mike DeMotta, a Nā Pali Coast ʻOhana advisor and retired curator at the National Tropical Botanical Garden, said of Nuʻalolo Kai.

“It actually enhanced ecosystem function, because Hawaiians understood how important that was to their own survival,” DeMotta continued. “Everybody benefits in the long run.”

Nu‘alolo Kai is believed to have been continuously occupied for 800 years, from the 12th century through the 20th century.

Most of Kaua‘i is surrounded by fringing coral reefs that buffer adjacent shorelines from high surf conditions. The Nāpali Coast is different. Its nearshore waters are largely home to deeper reefs that offer little protection from incoming waves, which grow in size during the winter, often cresting at 25 to 30 feet in height.

Corals here tend to be flatter and are hardy species. Despite this, the area is known to support large fish populations that subsistence fishers depend on, such as ʻakule that school within Nāpali Coast sea caves, according to Kaua‘i district biologist Heather Ylitalo-Ward of the Hawaiʻi Division of Aquatic Resources.

“We do see some interesting species in that area that we don’t generally see in other areas around Kauaʻi,” Ylitalo-Ward said.

These species include knifejaws, large schools of mū and more kāhala than Ylitalo-Ward and her colleagues see elsewhere around the island.

“This might be because we are closer to Papahānaumokuākea than the other main Hawaiian Islands and therefore have more species overlap,” said Ylitalo-Ward, who was referring to the protected marine national monument located in the Northwestern Hawaiian Islands.

Spinner dolphins are often seen along the Nāpali Coast. Local tour operators often advertise a “dolphin guarantee.”

“They tend to like areas with clear, calm water when they are resting during the day, and in Kauaʻi those places can be few and far between,” Ylitalo-Ward said.