Environmenta1 Modifications Environmental modifications are of two types, short and long term. Short term or immediate changes in the microenvironment of a structure in the desert can be readily demonstrated by appropriate instrumentation. These are, however, only physical changes and might quickly be reversed if the modifying structures were removed. On the other hand, if these short term microenvironmental changes are permitted to continue for any length of time, they will then trigger, both directly and indirectly, longer term modifications of the ecosystem that are not so readily reversible. Long term modifications are considered to be ecological changes because not only is the microenvironment altered but the biotic components of the ecosystem are also changed. Although ecological changes may take many years to occur, the ecosystem once stabilized under new conditions will remain changed unless man again alters the overriding controlling conditions. Ecological changes resulting from construction and operation of solar collector systems are impossible to quantify without taking some actual measurements. It is possible to estimate changes in such factors as solar input, energy budgets and soil moisture using equations based on hypothetical structures and environmental processes, but every ecosystem is variable and it is this variability that will cause hypotheses based on theoretical calculations to be in great error. Other ecological factors such as wind movement, soil erosion and biotic processes are impossible to predict. One can draw hypothetical conclusions based on the literature and the theoretical calculations of variations in physical processes, but this is only a preliminary step. From these early predictions one must design tests to prove or disprove established hypotheses.
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