this principle is the same for the remaining hillsides andnd ravines. what we arare seeing here is very intereresting because it't's a line between human activity and natural systems. and in the human activity, we've been ablele to value the productivity from agagriculture and give it a monetary y value, but in the naturaral systems, we haven't een able to value the trees, the biodiversity, the w water that's absorbeded into the biomass and into the soils. and there's another vital service that trees and plants provide: photosynththesis. vegetation reduceces the grgreenhouse effect by takaking carbon dioxide out of the atmosphere. a measure of what restoring nature can do has been shown here on china's loess plateau, where farmers have continued to prosper despite the worst drought in decades. >> [singing] >> since the beginning of the project, the soil that nurtures their crops has been accumulating organic material from plants and animals. this holds the moisture and contains carbon. what's interesting about this is all these root materials, all this