Some Botanical and Environmental Aspects of Hawaii

Abstract

Few regions anywhere are more interesting botanically than the Hawaiian Islands. Owing to their extreme isolation, separated by 2,000 miles of ocean from the nearest land mass of any size, there is an extremely high percentage of endemic species, many of them remarkably specialized, testifying to the long period during which evolution has been going on with little disturbance from outside. Except for the almost uniformly volcanic nature of the soils, which has no doubt been a factor in the evolution of the flora, the conditions are extremely varied. Owing to the great height of some of the mountains, which in the two great cones on the island of Hawaii, Mauna Kea and Mauna Loa, rise to nearly I4,000 feet, and overtop all the mountains of Polynesia and Australasia, there is a corresponding range of temperatures, from the tropical heat of the lowlands, to regions of almost perpetual snow. The variation in precipitation is also extraordinary, ranging between an annual rainfall of 400-500 inches in extreme cases,1 to less than 20 inches in some of the dry leeward districts. These remarkable differences of elevation, temperature and moisture occurring within a quite small area afford the botanist unusual facilities for investigating a wealth of extraordinarily interesting problems in plant evolution. The writer has made several visits to Hawaii, the last in the summer of i919. Two years before, a trip was made for the purpose of collecting Hepaticae for comparison with certain East Indian species which indicate an interesting similarity in the hepatic floras of the two regions. This led to a somewhat critical study of the Hawaiian flora as a whole, which revealed an unexpected and most remarkable affinity with that of the Australasian and Indo-Malayan regions. So many were the correspondences that they led inevitably to the conclusion that these could only be explained satisfactorily by assuming the existence of some ancient land connections which have disappeared in a great general subsidence of the whole Polynesian area.