Editor's Note: Bromus tectorum is a desert annual, an exotic to North America. It offers us a classical case of biotic impoverishment: it is one of those small-bodied, rapidly reproducing, hardy plants that finds a variety of open niches around the world and changes the world. In this case, in the Great Basin of North America, its chance introduction is displacing an indigenous forest and a native shrubby ecosystem.

W. D. Billings has been a lifelong student of the vegetation of the earth, extending his insatiable curiosity and capacity for new knowledge with a continuing flow of equally intense and able students. Billings has been an especially avid student of deserts and tundra, both Arctic and montane. It is his lifelong interest in deserts that we have tapped here to draw out one of the best-documented and most important case histories of how one exotic has changed a landscape, reducing its potential for support of plants and animals, including people, for all of time.

Introduction

From the tropics to the boreal forest, the destruction of vegetation by clear-cutting or fire is a common occurrence. The resultant loss of floristic and faunistic diversity is, in the main, due to direct human interference and impact. Subtle invasions by pathogens or by most exotic animal and plant species more likely result in selective loss, one species at a time, as was the case with the loss of the American chestnut, Castanea dentata (Marsh.) Borkh., from the eastern deciduous forest due to attack by the Asiatic fungus Endothia parasitica