Data from large scale field experiments are clearly highly relevant to the development of a new system for radiological protection of the environment. Therefore, an actuality and severity of population-level effects within radioactively contaminated areas are among key problems today. The results of long-term field studies in the Bryansk Region, Russia, affected by the Chernobyl accident, and at the Semipalatinsk Test Site, Kazakhstan are discussed. The results of these studies clearly indicate that plant populations growing in areas with relatively low levels of pollution are characterized by the increased level of both cytogenetic disturbances and genetic diversity. Genetic processes in exposed populations lead to increasing of phenotypic diversity and rapid selection of novel phenotypes favoured in changed environment. In particular, radioactive contamination of the plants' environment activates genetic mechanisms, changing a population's resistance to exposure. However, in different radioecological situations, genetic adaptation to extreme edaphic conditions in plant populations could be achieved with different rates. Such evolutionary effects are of special concern because they are able to negatively affect population dynamics and local extinction rates. A development of a system for protection of the environment from ionizing radiation should be based on a clear understanding of these effects and their contribution to biological response.