In South Dakota, rising up the ﬂanks of the Black Hills, dog-hair stands of ponderosa pine as dense as 20,000 to 40,000 stems per acre seem to provide a green wall of serenity during the day; at night, they deepen the experience of full darkness. The heavy growth results from a lack of harvesting, or an unnaturally reduced incidence of ﬁre. Such isolated forests, also known as dog-hair thickets, occur in northern Arizona and the southeastern states, as well as anywhere pine trees grow. The term is used around Yellowstone National Park to describe thick “toothpick” stands of lodgepole pine. Competition for water in these overgrown areas stunts many trees, and the woods are said to stagnate; foresters argue that if some trees are removed, the remaining trees will likely return to health. Even through growth is typically slow, the strength and persistence of many pine species are evidenced in the taproots of the young seedlings. These roots might extend ﬁve feet into the ground, while only a small shoot of growth appears above ground. Deep roots give pines the ability to survive drought, to thrive even when oppressed by surrounding trees.