If orangutans went extinct, Southeast Asian rainforests would lose one of their most important seed dispersers, triggering a chain of ecological consequences that would reshape forest composition, reduce carbon storage, and push dozens of plant species toward decline. The effects wouldn’t be immediate or dramatic like a wildfire or flood. They would unfold over decades, quietly degrading some of the most biodiverse forests on Earth.
Why Orangutans Matter to the Forest
Orangutans are the largest tree-dwelling animals on the planet, and their diet revolves around fruit. A single orangutan eats hundreds of fruit species, swallowing seeds whole and depositing them far from the parent tree as it travels through the canopy. This process, called seed dispersal, is how many tropical trees reproduce. Seeds that fall directly beneath their parent tree face intense competition for light and are more vulnerable to species-specific diseases and insects. When an orangutan carries a seed a kilometer or more away and drops it in its dung, that seed has a far better chance of growing into a mature tree.
Many large-seeded tropical trees depend specifically on big-bodied fruit eaters for this service. Smaller animals like birds or bats can’t swallow or carry seeds above a certain size. Orangutans fill a niche that very few other animals in Borneo or Sumatra can replicate. Hornbills handle some of the same fruits, but they cover different distances and deposit seeds in different patterns. Without orangutans, certain tree species would see their seeds pile up beneath parent trees with nowhere else to go.
Forest Composition Would Shift Over Time
The most significant ecological consequence would be a gradual change in which trees dominate the forest. Trees that rely on large fruit eaters for dispersal would slowly decline as fewer of their seeds successfully germinate in suitable locations. Trees with wind-dispersed seeds or those spread by smaller animals would fill the gaps. This isn’t hypothetical. Research across the tropics has documented this pattern wherever large fruit-eating animals have disappeared: forests become less diverse and increasingly dominated by a narrower set of tree species.
This shift matters because tropical rainforests are not interchangeable collections of trees. Different species support different insect communities, provide food at different times of year, and create different microhabitats. A forest that loses its large-seeded hardwood trees and replaces them with lighter-wooded, wind-dispersed species is a fundamentally different ecosystem, even if it still looks green from above.
Carbon Storage Would Decline
One of the less obvious consequences involves climate change. Research published in Scientific Reports found that tree species dependent on seed dispersal by large-bodied fruit eaters account for nearly one-third of total carbon biomass in Southeast Asian tropical forests. These tend to be large, dense-wooded trees that store enormous amounts of carbon in their trunks. If those species gradually disappear and are replaced by lighter-wooded alternatives, the forest’s ability to pull carbon dioxide out of the atmosphere drops.
The same study estimated that a complete loss of large fruit-eating animals would reduce forest carbon storage by 2.4% to 3.0%. That number sounds small until you consider the scale involved. Borneo and Sumatra contain some of the most carbon-dense forests on Earth. A 3% reduction across millions of hectares translates to significant additional carbon in the atmosphere, worsening the same climate change that already threatens these forests through drought and fire.
Other Species Would Feel the Ripple Effects
Orangutans don’t just move seeds. Their daily activities shape the forest in ways that benefit other species. When they build sleeping nests each night by bending and breaking branches, they create small gaps in the canopy that let light reach the forest floor, encouraging new plant growth. They also spread fungal spores and invertebrates as they move between trees. Their partially eaten fruits feed smaller mammals, birds, and insects below.
The decline of tree species that depend on orangutan dispersal would reduce food availability for other fruit-eating animals, creating a cascading effect through the food web. Insects that specialize on those tree species would lose habitat. Predators that rely on those insects would follow. Tropical ecosystems are built on dense, interconnected relationships, and removing a keystone species pulls threads throughout the web.
How Close This Scenario Already Is
This isn’t a distant thought experiment. All three orangutan species are critically endangered. The Bornean orangutan population has declined by an estimated 86% between 1950 and 2025, driven by habitat clearance, logging, and killing. Sumatran orangutans number around 14,000, and the Tapanuli orangutan, discovered as a distinct species only in 2017, has fewer than 800 individuals left. The Tapanuli is considered the most endangered great ape on Earth.
The primary threat is deforestation for palm oil plantations, logging, and agriculture. Between 1973 and 2010, habitat clearance alone reduced Bornean orangutan numbers by 39%, with an additional 37% decline projected through 2025 from continued clearing. Fires, often set to clear land, destroy vast areas of peat swamp forest that orangutans depend on. Hunting and the illegal pet trade compound these losses.
In many areas, orangutans are already functionally extinct, meaning their numbers are too low to perform their ecological role even though a few individuals remain. The seed dispersal services and forest-shaping behaviors described above are already diminished across large portions of their historical range. The ecological consequences of orangutan extinction are not a future scenario in these places. They are already underway.
What No Other Animal Can Replace
A common question is whether other animals could step in and fill the orangutan’s role. The short answer is: partially, but not fully. Sun bears eat fruit and disperse some seeds, but they are smaller, travel shorter distances through the canopy, and are themselves declining. Gibbons disperse seeds but handle a different size range. Elephants in Sumatra move large seeds on the ground but occupy different habitat zones and are also critically endangered.
The problem is compounded by the fact that orangutan extinction wouldn’t happen in isolation. The same deforestation driving orangutans toward extinction is simultaneously reducing populations of hornbills, gibbons, sun bears, and elephants. The backup dispersers are disappearing alongside the primary ones. When an entire guild of large fruit eaters collapses at once, the forest has no redundancy left, and the ecological changes accelerate.