GREENSBORO, Vt. — In the snowy woods of northern New England and other forested parts of the country, the lumberjack is an endangered species. As high-tech machinery replaces chain saws, which themselves replaced the ax, a generations-old way of life is disappearing, one that historically saw fathers pass on to their sons their love and knowledge of the woods and the independence that came from working for oneself. Ken Davis feels this keenly as he reaches retirement age after a half-century career with no one to pass the torch to. Davis once employed 19 people full-time to cut the wood, haul it and then truck it, sometimes to his log yard, other times directly to the now-disappearing mills across Vermont, New Hampshire, Maine and upstate New York that would turn it into lumber or process it into paper.