Between three-quarters to 95 percent of tropical forest trees depend on animals to disburse their seeds, which the trees make appealing by wrapping in a tasty little packet called fruit. In the tropical forests of the Congo, the elephant is the largest consumer and distributor of tree seeds, contributing to the remarkable species diversity found there.

This phenomenon is explored in depth in the first episode of the latest installment of the The BBC Earth series "Power of Nature," which returned Tuesday for 10 new installments of four-minute episodes, available online.

The first episode, ELEPHANTS: Mega-gardeners of the Forest, takes viewers to the Congo, one of the largest and richest tropical forests in the world. The film explores how the forest elephants help sustain the Congo rainforest and contribute to its vast diversity of trees.

One of the most amazing things about tropical rainforests is the diversity of trees there, said Dr. M Sanjayan, lead scientist with The Nature Conservancy.

"You almost never see two of the same species of tree next to each other. And that's what shocks you," he said.

The forest elephant has the ability to eat "virtually every fruit nut out there," Sanjayan said. "And because they have such poor digestion, most of those seeds pass through their gut untouched. In fact, it's better than that. When it comes out, its has its own packet of fertilizer ready to grow on."

Ian Redmond, a wildlife biologist with the Born Free Foundation, said elephants are the the biggest seed dispersal agents in the forest, which he noted was vital for the health of the entire ecosystem.

Without elephants, the diversity of trees in tropical forests "absolutely goes down" Sanjayan said.

"Elephants and forests are part of the same thing," Redmond said. "If we lose the elephants, the forest will change for the worse."

Click the link to watch the complete BBC Power of Nature episode, ELEPHANTS: Mega-gardeners of the Forest.

Upcoming Power of Nature epidodes will highlight whales, wolves, sea otters, vultures, the Himalayas, salmon, coral reefs, the Sahara and the Sundarbans, which is the largest mangrove forest in the world.