They bred in the wild and began to become a nuisance to both Europeans and natives as they destroyed agricultural plants and oyster beds. livestock puts more pressure on local pastures allowing more resistant European grasses and weeds to grow. This led to a less favorable environment for plants and ultimately reduced the soil's ability to hold water. Before a century had passed, New England's ecosystem had changed permanently and would never return to normal. The ecological changes mentioned in this book, although cultural, were economic or environmental: the dandelion, the fence, the arrival of the pigs, etc., were just a way to open our eyes and bring to light the complex process and changes caused by the arrival of Europeans in America. Meanwhile these complex changes and European colonization in general cannot be well understood except through understanding the effects of New England Indians and Europeans on their ecosystem. The book also goes on to show the genesis of New England's environmental problems, such as erosion, deforestation, and climate change; which are just some of the factors we still have to deal with to this day. This book in fact realizes the author's thesis. I recommend this book because it really seems to demonstrate how what the current generation does today can influence ours