There’s only one place left on Earth where Sumatran tigers, orangutans, rhinos, and elephants all still coexist—and actor Leonardo DiCaprio was just there. Fresh off winning a best actor Oscar for his role in The Revenant, the movie star was getting his shoes muddy in Indonesia’s Leuser Ecosystem, highlighting efforts to defend the area’s wildlife against encroaching palm oil plantations.

DiCaprio’s eponymous foundation has donated millions to organizations making those efforts, among them the local Indonesian NGO HAkA and the San Francisco-based Rainforest Action Network. The latter describes the Leuser Ecosystem as a “world unto itself—a rich and verdant expanse of intact tropical lowland rainforests, cloud-draped mountains, and steamy peatlands.” It notes the encroachment by palm oil plantations continues despite much of the ecosystem being protected by Indonesian national law.

Palm oil, nicknamed “green gold” by the industry, is used in about half of all packaged products sold in the supermarket, from margarine to detergent to instant noodles. Efforts to ensure that it is sustainably produced have, many believe, fallen short.

The movie star shared photos from his trip on his social media accounts.

The ecosystem is on the island of Sumatra, where large swathes of rainforest and peatland are routinely burned down and replaced by the neatly ordered rows of palm oil plantations. The burning of dried peatland, essentially young coal, is especially destructive as it releases vast amounts of greenhouse gases.

The destruction pauses for Indonesia’s rainy season, but returns with the dry season that starts in April, along with the resultant air pollution. Last year the land-clearing fires conspired with dry El Niño conditions to create what one observer called the “the biggest environmental crime of the 21st century,” with a thick toxic haze covering large areas of Southeast Asia, closing schools in Singapore, causing deaths in Indonesia, and creating a class of climate refugees escaping cities where visibility was low and the simple act of breathing had become potentially lethal.

In his social media posts, DiCaprio focused on the threat to the Leuser Ecosystem’s mega-fauna, notably elephants.

Expansion of palm oil plantations is fragmenting the forest and cutting off key elephant migratory corridors, making it more difficult for elephant families to find adequate sources of food and water.

DiCaprio’s focus on the ills of palm oil come after he highlighted the environment in his acceptance speech for the best actor award in February: