. >> reporter: not far from the soy fields raimundo maniwari and other members of the munduruku tribe take motorbikes deep into their 400 square mile forest reserve to harvest brazil nuts. >> ( translated ): since i was a child, my father harvested the brazil nut, and we would tag along.ba then we learned how to work with the brazil nuts. we would gather moreiv seley, just to eat. we would pick only the big ones for ourselves. >> reporter: maniwari says since then farms have surrounded the munduruku's forest on all sides, clearing the trees right up to the edge. things haven't been the same since. >> ( translated river, the wind, the weather.ll it's aifferent now. in the past, what we call summer used to come earlier. and today the wind is hot and dry, it doesn't bring that yslmness that it used to. >> reporter: he few years ago the brazil nut trees didn't produce any nuts at all for the first time. these changes are worrying scientists who say deforestation, combined with rising temperatures and the droughts and fires they encourage, is taking a heavy toll on the forest. carlos nobre