"The focus of shifted from simple descriptions to more detailed observations of and when Watt (1940) published the first of his many ecological studies of ' (bracken) in Britain (see Watt, 1976 for a review). Pteridium is an extremely successful colonizer worldwide and can form dense, nearly impenetrable stands. Pteridium generally contains several biochemical compounds such as high levels of s that make it health hazard when eaten by livestock or humans, although the early of New Zealand used ' s as a crop. Where it is unwanted (i.e., considered an invasive weed), Pteridium is difficult to eradicate. Pteridium therefore continues to be an important subject for ecological research (Robinson, 2007). Studies of Pteridium and other abundant ferns have helped to develop an understanding of the complex relationships between ferns and other environments."