Micro environmental factors must influence individual plant survivability

Soil column moisture AND degree of exposure???

We have had a couple of instances where the same species of plants have had individual plants wither and die (I am assuming due to loss of soil moisture) while other plants of the same species near by, have survived .... I am assuming that the degree of individual exposure to sunlight is also a contributing factor to these death rates .... shade may play an important role in promoting plant survival!