Trees in forests are linked together by a network of mycorrhiza (symbiosis between plants and fungi). One reason why it is important to maintain those networks is because they are involved in carbon sequestration. In order to maintain the below-ground fungal network, harrowing (plowing) should be avoided. See the TED talk "The networked beauty of forests" by Professor Suzanne Simard, Department of Forestry, University of British Columbia:
Quote from the presentation: "The whole world wipes its nose on our old-growth forests". Read more about the author at her university website.