264 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



Plant Invaders 



A further effect of the activities of man has been the introduction 

 of numerous foreign plant species on each of the islands. These have 

 often become more abundant than the native species and grow so vigor- 

 ously under the existing conditions that the native plants can only rarely, 

 and with difficulty survive the competition. Such species as Mesembry- 

 anthemum crystallinunij Hordeum murinum, Avena jatua, Bromus 

 mollis J A triplex semibaccataj and Medicago hispida, dominate many 

 extensive areas to the almost complete exclusion of the indigenous flora. 

 Only a few of the more vigorous, suffrutescent perennials, shrubs, or 

 bulb plants can withstand the competition. 



No adequate attempt can be made to list all of the plant species 

 that have been introduced since the discovery of the islands by Juan 

 Rodriquez Cabrillo in 1542. Four centuries represent a period during 

 which many of the species arriving during the first two or three hundred 

 years may have become thoroughly naturalized. Many species reached 

 the islands from Europe by w^ay of the United States, while others 

 may have come from Siberia or northwestern North America during 

 the days of Russian sea otter hunting, or may have been brought from 

 Mexico or South America by the early Spanish, English, and American 

 voyagers. Holder (1910) considers it highly probable that such explorers 

 as Drake, Woodes, Rogers, Shelvocke, and the adventurers and buc- 

 caneers of the latter part of the sixteenth or the early part of the seven- 

 teenth may have visited the islands during their journeys along the 

 west coast of North America. Following Vizcaino's visit in 1602, during 

 the next two and one-half centuries many Spanish vessels must have 

 stopped at the islands. Early American mechants made the islands bases 

 for smuggling activities during the Mexican regime, landing their 

 cargoes on the islands to be transferred to smaller boats for surreptitious 

 landing on the mainland. As these cargoes had often been earlier landed 

 in Chile, it is possible that many of the plants now reported as common 

 to both Chile and the islands have reached them through this agency. 



Most of the introduced plants have come directly or indirectly from 

 southern Europe or northern Africa where similar climatic conditions 

 prevail. Most of these plants not only come from the semi-arid regions 

 of the world, but come from regions where grazing has been practiced 

 for many centuries, and possess life forms that enable them to success- 

 fully withstand the activities of grazing animals. 



