james kimani njuguna goes into the forest daily. he knows how to harvest the bark without hurting the trees. dorothy also profits from the natural healer's knowledge. >> this tree won't die because i've only taken the bark from one side. otherwise, it would dry out. >> james treats people from all over the region in his natural healing practice. the knowledge about the muiri tree has been passed down in his family over generations. scientists are now also benefitting from it. >> it only uses water to get the effective ingredients out of the bark. we use different solvents -- in addition to water, we use oils. that way we can filter out a larger number of ingredients. >> back in mary's village, she gets a visit from a member of the kenyan environmental group the green belt movement. the organization supports mary in setting up her nurseries. it is also one of the main consumers of young trees. their aim is -- together with village residents -- is reforestation. the green belt movement has been promoting native species such as the mui