Coastal Uplands 



Conceptually, the upland ecosystem is composed of two primary systems - 

 the abiotic system and the biotic system. The biotic system, in turn, is a 

 complex composed of three equivalent subsystems (communities): the maritime 

 woodland subsystem, the coastal grasslands subsystem, and the brush-grass sub- 

 system. In the field, the biotic component will express itself as a particular 

 subsystem or community functioning under the regulatory influence of the 

 abiotic system. The abiotic system operates directly on the plant itself and/ 

 or indirectly through competition by other plants. The convention of separat- 

 ing the abiotic system from the communities is justified by the similarities 

 of physical and chemical processes which operate in each community, which pro- 

 vide support for each community in the form of storage of various limiting 

 factors, and which act as connecting links between adjacent ecosystems. Thus, 

 four ecosystems are easily recognizable and will be analyzed separately, though 

 in reality each system is inseparable from the others. 



On the coastal plain uplands where grasslands and forests blend, the impor- 

 tant regulatory factors that determine the existence and nature of the plant 

 communities are fire and soil moisture (Wells, 1928; Costing, 1956; Powells, 

 1965; E. Odum, 1971). The major consequences of the presence, absence, and 

 availability of these, as well as other components and the regulating factors 

 .Mich affect them, are important aspects that are addressed below. 



Particular references are made to the Aransas NWR, but it should be recog- 

 nized that the upland model is applicable to most coastal uplands and chenier 

 ridges. 



Abiotic system . The abiotic system describes (1) the physical and chemi- 

 cal processes and components which are common to the different aspects of the 

 upland system and (2) microbial activity. The soil microbiota are more inti- 

 mately associated with the abiotic system than with any particular community 

 (Wiebe, 1971). 



The abiotic system receives external inputs (driving forces) in the forms 

 of sunlight, atmospheric water and gases, surface water from upland drainage, 

 groundwater flowing down a hydrologic gradient, and gulf salt spray (E. Odum, 

 1971; Au, 1974). Additional system inputs such as nutrients and detritus are 

 received from the particular community supported by the site. The abiotic 

 system provides outputs as flows to the biotic components, flows that regulate 

 community development. Such abiotic outputs include soil moisture, fire, soil 

 salts, plant surface salts, nutrients, and soil heat. Finally, certain out- 

 puts of the abiotic system are lost from the system, at least temporarily, to 

 become potential inputs of adjacent ecosystems, such as brackish or fresh 

 marshes. Such system losses include evaporated water, eroded soils, leached 

 nutrients and salts and surface-water runoff. 



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