8 DERIVATION OF THE FLORA OF HAWAII 



as much. On the lee shore, southeast of Honolulu, the precipitation is 

 much less than in the town, and extremely arid conditions prevail. 



The maximum rainfall in the islands is on the windward side at ele- 

 vations of 4,000 to 6,000 feet, where some of the heaviest rainfalls that 

 have been recorded anywhere occur. The most extreme case of which 

 we have been able to obtain records is on Kauai, where on the highest 

 summit of the island, Mt. Waileale, a five-year record showed a mean 

 annual rainfall of a little over 500 inches! 4 Less than fifteen miles from 

 this station, in Waimea, a village on the lee shore, the annual rainfall is 

 not much over twenty inches, and there are other localities where it is 

 much less. 



The rainfall is almost incessant in the wettest regions, and is not 

 confined to any special season of the year. 



This extraordinary range of precipitation, and the great differences 

 in elevation and exposure, naturally have been important factors in the 

 development of the vegetation. 



Unfortunately, much of the original vegetation has disappeared since 

 the advent of the white man. During the past twenty-five years nearly 

 all of the available land at the lower elevations has been brought under 

 cultivation, and the forests have entirely disappeared. The ravages of 

 cattle, and in the drier parts of the islands, of goats, have entirely denuded 

 large areas that not many years ago were covered with forest. Through 

 these agencies there is no question that certain species have been quite 

 exterminated. Moreover, the introduction of many foreign plants, which 

 have become quite naturalized, has entirely altered the aspect of the veg- 

 etation in the lower levels. 



BOTANICAL REGIONS 



The different botanical regions have been treated recently at some 

 length by Rock. 5 



He recognizes six principal types of vegetation: 1, The Strand 

 Flora ; 2, The Lowland Region ; 3, The Lower Forest Region ; 4, The 

 Middle Forest ; 5, The Bog Region ; 6, The Upper Forest. 



The strand flora of Hawaii is poor when compared with that of 

 most tropical regions. It comprises a number of cosmopolitan species, 

 like Ipomoea pes-caprae and Hibiscus tiliaceus, but also has a consider- 

 able number of endemic species. 6 



4 See Science, Nov. 23, 1917, pp. 511-512. 



6 Rock, J. F. : "The Indigenous Trees of the Hawaiian Islands," pp. 1-87. 



McCaughey, Vaughn : "The Strand Flora of the Hawaiian Archipelago, Geo- 

 graphical Relations, Origin, and Composition," Bulletin Torrey Botanical Club, 45, 

 259-277. 1918. 



