Narrator: A hundred years ago, there were one-and-a-half billion people on Earth. Now, over six billion crowd our fragile planet. But even so, there are still places barely touched by humanity. This series will take you to the last wildernesses and show you the planet and its wildlife as you have never seen them before.
Mark Linfield: This is amazing. This is absolutely amazing.
Narrator: forest covers only 3 percent of the planet's surface, but it contains more than 50 percent of all its plants and animals.
Narrator: [about polar bears] She's leading her cubs into a dangerous new world. Nearly half of all cubs die in their first year out on the ice.
Narrator: As we travel south, so the Sun's influence grows stronger, and at 50 degrees of latitude a radical transformation begins. Summers here are long enough for broad leaved trees to replace conifers. Broad leaves are much easier to digest, so now animals can collect their share of the energy that has come from the Sun. It's summer and these forests are bustling with life.
[birds, butterflied, wrestling antelope]
Narrator: But the good times will not last.
[green transforms to white]
Narrator: Broad leaves must be shed in winter, for they are damaged by frost. As they disappear, so the land become barren, with little for animals to eat. The inhabitants must migrate, hibernate, or face months of near-starvation.
Narrator: One season hands over to another. Some organisms thrive on decay.
[time lapse of growing mushrooms]
Narrator: But most must make special preparations for winter, and life with little sun.