||Urban forest recreation environments have their particular rhythms, not only natural periodicities, but also periodicites of their human members (vistors, rangers,...). A human forest ecosystem as a basic unit of analysis can be defined as an interaction between the population, the organization of forest and the technology in response to the environment. In order to manage such forest ecosystems information about the recreation demand of visitors is needed, particularly about the rhythms of the visitor flow. A scientific project in Stuttgart, a town in South-Germay, provides for an example. The central objective of this paper is to detect periodicities in a time series of frequencies of certain groups of visitors, observed by a fix video camera over one year (March 1999-March 2000) (n=1421 measurements). A not widespreaded statistical method, the spectral analysis, will be applied on the data. Certain periodicities can be found, especially a day-cycle, week-cycles and year-cycles for the various groups of visitors. Impacts of weather (sunny, cloudy, rainy) and weekday (weekend or not) have significant influence on the visitor flow. A simulation illustrates the shape of the cycles, which are detected.