Abstract: With the past century’s continued destruction of primary forests, secondary forests became the major forest resources in China and all over the world . There is a considerable ambiguity or confusion with regard to the conception of ‘secondary forest’ in different countries or regions, although this term has been used worldwide for more than a century. This fact is inconvenience for the researches in ecology and forest science. Additionally, the imprecise definition could be a major impediment in communicating with general public and decision-makers. Based on a wide range of literature collection on the conception of secondary forest, as well as the practices and researches of ecology and management of secondary forests, this paper analyzed the uncertainties of the conception of secondary forest, and considered that secondary forests were the forests regenerated through natural regeneration, or through natural processes with minor assisted natural regeneration after the destructive disturbances of original forest vegetations by human beings or by extremely natural causes, and the forests display significant differences in forest structure, canopy species composition, and/or functions with respect to the primary forests. However, there are still many uncertainties in the definition of secondary forest, e. g. , how to define the destructive disturbances of human beings and the extremely natural causes, what degrees of the changes of forest structure, canopy species composition or functions are the significant changes for secondary forest formation, and how to determine the contribution of human activity in the artificially assisted natural regeneration. The definition of secondary forests was put forward by the specialists on plant succession, without taking the duration of disturbance into consideration. In fact, whether the primary forests or secondary forests, they are both in some stages or states in the successional series of forest community. Therefore, if the concepts of forest disturbance degree, forest naturalness, or forest ecosystem maturity can be applied in defining secondary forest to express the state of current forests, the uncertainties of the term of secondary forest may be avoided. In order to discuss the issues related to the concepts of secondary forest with ecologists or foresters, the primary concepts of forest naturalness, forest ecosystem maturity, or forest disturbance degree were mentioned, but related research and practice still need to be strengthened.

Key words: Hibiscus cannabinus, Plant height, Stem diameter, Developmental genetics, Genetics effect