and they are abundant in the coastal plain of the southeastern United States. 

 In addition to Atlantic white cedar, dragon's mouth is the other rare plant 

 species associated with this community. 



FACTORS OF ABUNDANCE 



The distribution and abundance of plant species are the result of natural and 

 human-related factors. Long-term changes in climate and land forms (i.e., 

 glaciation and mountain emergence) have resulted in the development of new 

 species (speciation) , the loss of species (extinction) , and changes in 

 distribution of species. Speciation and extinction are usually long, slow 

 processes. People accelerated the extinction process in the last century by 

 altering the earth's surface with advanced technology (Ayensu and DeFilipps 

 1978). 



Some plant species are naturally rare, and have evolved adaptations to permit 

 existence under conditions of low abundance. Many orchids, for example, have 

 highly specific and "faithful" pollinators that allow them to exist in 

 scattered populations. In addition, each plant produces large numbers of 

 small seeds, a practice beneficial to less dense populations. Among species 

 less-specialized than orchids, rarity is the result of a species' inability to 

 adapt to change in habitat, climate, predator pressure, or competition. 



Biotic factors affecting the distribution and abundance of plants include 

 competition with newly-evolved or formerly allopatric (species whose ranges do 

 not overlap) species, disease, damage from overgrazing by animals, insect 

 damage, loss of pollinators, destruction of seeds and fruit, and changes in 

 the soil-water regime (i.e., changes in drainage patterns, water table level, 

 and waterholding capacity of the soil). 



Plant populations have been reduced severely by human activities such as real 

 estate developing, impounding water, and lowering the water table by wells, 

 drainage, and peat mining. Populations of ginseng have been eradicated by 

 commercial plant collectors along with mountain laurel and rhododendron. 

 Orchids, and other aesthetically attractive plants, are subject to private 

 plant collecting. 



Timber removal, particularly clearcutting, directly alters plant habitats. 

 Clearcutting results in changes in the light regime of the understory, the 

 shrub and herbaceous layers, mechanical damage to the residual vegetation, 

 changes in evapotranspiration rates, and increased erosion and nutrient 

 depletion of the soil. The site preparation procedures most commonly used in 

 coastal Maine are bulldozing, burning, and herbicidal application, which 

 destroy the residual vegetation. Timber removal is likely to affect rare 

 forest-dwelling species. 



Introduced vascular plants sometimes reproduce prolifically and compete more 

 successfully for light and space than native species. Introduced species are 

 usually free of native diseases and pests, which, if present, keep them in 

 biological balance. Many introduced species are vigorous, aggressive weeds. 

 Approximately 24% of Maine's flora is composed of naturalized exotics and 

 garden escapees. The degree of competition between introduced plants and 

 rare species in coastal Maine is unknown. 



20-19 



10-80 



