RELATIONS AMONG SPECIES 



373 



4. Deciduous Forest, a temperate forest dominated 

 by deciduous, broad-leaved trees and actually a group 

 of elements, is south of the Boreal Forest in the east- 

 ern United States. It occupies all of the east except 

 for Florida. Included in the Deciduous Forest is a 

 somewhat aberrant, probably fire-maintained, sub- 

 unit, the Southern Evergreen Forest. This evergreen 

 forest inhabits the Atlantic Coastal Plain from Vir- 

 ginia to Texas except for southern Florida. Charac- 

 teristic evergreen forest plants include live oak, bald 

 cypress, long-leaf pine, magnolia, gums, and short- 

 leaf pine. 



5. Easl Asian, an additional fossil element, also was 

 present. Despite its name, modern derivatives of the 

 East Asian element are found in both Boreal and 

 Deciduous forests in eastern Asia; in eastern Asia 

 and eastern United States; or in eastern Asia, western 

 United States, and eastern United States, typically in 

 the form of deciduous trees. Strictly speaking. East 

 Asiatic species now include the dawn redwood and 

 the ginkgo, or maidenhair tree. Plants of eastern Asia 

 and eastern North America include hornbeans, hick- 

 ories, chestnuts, beeches, liquidambars, and elms. 

 Those in eastern Asia and the western and eastern 

 United States include maple, birch, dogwood, ash, 

 Walnut, spruce, pine, plum, oak, rhododendron, rose, 

 willow, and arborvitae. 



Madro-Terfiary Geoflora. Named for the Sierra 

 Madre Mountains area of northern Mexico where 

 many relicts now live, this geoflora apparently evolved 

 mostly from the Neotropical-Tertiary, but also from 

 the Arcto-Tertiary, and assumed definite but poorly 

 developed form by the Middle Eocene. Its vegetation 

 was much different from that of the broad-leaved 

 evergreen Neotropical-Tertiary or the hardwood de- 

 ciduous and coniferous Arcto-Tertiary Geofloras. 

 Rather, the plants were and are small-leaved, often 

 deciduous and/or sclerophyllous (having leaves with 

 very thick, often waxy-walled cells in the epidermis), 

 drought-resistant plants. These adaptations imply 

 an arid climate group of plants, but the flora now 

 extends from warm temperate to dry tropical areas. 



The Madro-Tertiary Geoflora now includes three 

 elements of woodland, two elements of chaparral, and 

 one of thorn scrub. 



1. The California Woodland Element contains 

 madrone, walnut, digger and pinyon pines, live oaks, 

 Catalina ironwood, cottonwood, and bay. It can be 

 further subdivided into the maritime climate Insular 

 Woodland of the islands off the southern coast of 



California, the cold-winter Digger Pine Woodland of 

 central coastal California, and the warmer climate 

 Oak-Walnut Woodland of southern California moun- 

 tains. 



2. The Sierra Madrean Woodland Element includes 

 madrone, juniper, avocado relatives, locust, cotton- 

 wood, soapberry, holly, and oak. It now survives in 

 areas of summer rain from Arizona to west Texas and 

 south into Mexico. 



3. The Conifer Woodland Element has pinyon pine, 

 juniper, service berry, plum, hard tack, cream bush, 

 snowberry, and antelope bush. It is found in cold 

 semiarid places from eastern California to the Rock- 

 ies. 



4. The California Chaparral Element of manzanita, 

 ceanothus, hard tack, bush poppy, silk tassel bush, 

 Christmas berry, plum, oak, coffeeberry, redberry, 

 and lemonade berry and its relatives now dominates 

 the California Chaparral. 



5. The Southwestern (chaparral Element consists of 

 much the same genera as California Chaparral, but 

 different species now occur from Arizona and east- 

 ward and southward into Mexico in locales of sum- 

 mer rain. 



6. The Thorn Forest Element was found in southern 

 California during warmer periods. Now it forms the 

 arid subtropical scrub vegetation of northeastern and 

 northwestern Mexico. 



Subtropical Scrub and Grassland Elements. The 

 Subtropical Scrub is here treated for convenience as 

 an element, but its element status is in question. It 

 could have been only an early stage of the Grassland 

 Element. It did consist of scrub and herbaceous vege- 

 tation, and probably originated in eastern Mexico 

 and the Great Plains during the abrupt climatic 

 change at the end of the Eocene and very beginning of 

 the Oligocene. Throughout the Oligocene and into 

 the Miocene it was the vegetation of our country's in- 

 terior, probably a semiarid habitat. In any event, it 

 was in the mid-continent during a period of cooling 

 and drying. However, with further cooling and per- 

 haps increased moisture, the scrub was replaced by, 

 or evolved into, the grassland. 



The Grassland Element is of major significance. 

 This flora formed very rapidly after the Oligocene. 

 By the Late Miocene it had become well developed 

 and generally assumed its present distribution in the 

 Great Plains. Its origin is rather indefinite, but it 

 probably has components from both Arcto-Tertiary 

 and Madro-Tertiarv elements. 



