A botanist by training, Mary O’Brien was working with a small organization in Oregon in the 1980s to propose alternative techniques to successfully replant Douglas fir trees that had been clear-cut on federal lands. Aerially sprayed herbicides aimed at helping the conifers grow have not only been linked to health problems in humans but were also killing another species of tree, red alders, that were beneficial to the fir saplings, O’Brien said.