tikal has been interpreted as meaning place of the voices. nowadays, the barks of howler monkeys dominate the forest. it's unclear what caused the downfall of the maya about 1000 years ago. there are many theories -- disease, wars, climate change. >> they had a culture for almost 2000 years. there's a lot of people, many people, and obviously they lived to some extent in harmony, and i think that is something we can learn from the past. >> jaap schorl is a biologist whose aim is to bring the rainforest into harmony with people today. together with local conservation organizations, he's developing sustainable concepts for protecting the forest. the breadnut tree -- the mayas used its seeds long ago. here they are called maya nuts and harvested twice a year. the people from the forest village of uaxactun go out to collect the seeds. the seeds had long been forgotten, but nowadays, they're being eaten and traded again. >> the forest means an income for me. if the harvest is good, our family alone can deliver up to 90 kilos a day, which means alm