Exotic Species Succession 



Secondary successions by exotic 

 species include five types of com- 

 munities: 



(1) Cajeput colonization of saw- 

 grass marsh; 



(2) Brazilian -pepper/cajeput/ 

 Australian pine colonization 

 in muhly prairies; 



(3) Brazilian pepper/Australian 

 pine colonization of hammock 

 and bayhead recovery commu- 

 nities; 



(4) Cajeput monocultures; and 



(5) Australian pine monocul- 

 tures. 



Cajeput colonization of saw- 

 grass marshes is quite variable, 

 reflecting the variable, but natural 

 distribution of site disturbances, 

 chiefly soil fires, drought mortal- 

 ity, ORV use patterns, and seed 

 availability. 



Mature cajeput is known to be 

 quite resistant to the environmental 

 extremes that are typical of the 

 southern Florida ecosystems, namely 

 flooding, fires, freezes, and 

 droughts. Seedlings and saplings 

 are probably more susceptible to 

 these extremes, but to an unknown 

 degree. The presence of this exotic 

 tree species within what is other- 

 wise a natural community, is sig- 

 nificant and probably indicates a 

 similar outcome for this newly colo- 

 nized area that is clearly present 

 in other sawgrass marsh areas to the 

 north and east of U.S. 41 and Fla 

 S.R. 27. 



The Brazilian pepper/cajeput/ 

 Austrialian pine colonization of 

 muhly prairies successional communi- 

 ty has significant ecological bear- 

 ing upon the management approaches 

 relating to the marl rocky glade- 

 lands along the eastern boundary of 

 Everglades National Park and those 



north and south of the Chekika 

 hammock region of the study area. 

 Three exotic tree species, Brazilian 

 pepper ( Schinus terebinthifolius ) , 

 cajeput ( Melaleuca quinquenervia ) , 

 and Australian pine ( Casuarina 

 equisetifolia ) , in conjunction with 

 the native species, red bay ( Persea 

 borbonia ) , blolly ( Guiapira dis - 

 color ) , dahoon holly ( Ilex cassine ), 

 poisonwood ( Metopium toxiferum ), 

 bayberry ( Myrica cerifera ), and coco 

 plum ( Chrysobalanus icaco ), comprise 

 a "guild" of hardwood species that 

 are colonizing vegetationally intact 

 muhly grass prairies throughout the 

 East Everglades. This colonization 

 process appears to be occurring at 

 an increasing rate that is inversely 

 proportional to the length of the 

 effective hydroperiod prevailing at 

 the site. As the effective hydrope- 

 riod decreases, the rate of hardwood 

 colonization increases according to 

 some constant proportionality. 



These observations suggest that 

 the 3 most abundant and ubiquitous 

 exotic tree species in southern 

 Florida are also common in the East 

 Everglades study area, and appear to 

 be increasing in frequency through- 

 out the rocky gladelands and marl 

 prairies. Because these communities 

 are essentially continuous with 

 those along the eastern boundary of 

 Everglades National Park, it appears 

 that the probability of the coloni- 

 zation of park lands by these 3 

 exotic species is increasing. 



Some severely fire-damaged tree 

 island communities are currently 

 dominated by the exotic trees Brazi- 

 lian pepper ( Schinus terebithifo- 

 lius ) and Australian pine ( Casuarina 

 equisetifolia ) , and the native suc- 

 cessional species saltbush ( Baccha- 

 ris halimifolia ) and Florida trema 

 ( Trema micrantha ). The understory 

 vegetation consists primarily of 



121 



