Foresters once regarded trees as solitary individuals: They competed for space and resources, but were otherwise indifferent to one another.The work of the Canadian ecologist Suzanne Simard upended that, finding that while there is indeed conflict in a forest, there is also negotiation, reciprocity and even selflessness.Ms. Simard discovered that underground fungal threads link nearly every tree in a forest.On today’s Sunday Read, listen to an exploration of these links and the influential and contentious work of Ms. Simard.This story was written by Ferris Jabr and recorded by Audm. To hear more audio stories from publishers like The New York Times, download Audm for iPhone or Android.