Ecological Modelling, 4 (1978) 313--326 313 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands SPECTRAL ANALYSIS OF FOREST MODEL TIME SERIES * W.R. EMANUEL, D.C. WEST and H.H. SHUGART Jr. Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tenn. 37830 (U.S.A.) Publication No. 1059, Environmental Sciences Division, ORNL (Received 24 January 1977; revised 24 June 1977) ABSTRACT Emanuel, W.R., West, D.C. and Shugart Jr., H.H., 1978. Spectral analysis of forest model time series. Ecol. Modelling, 4: 313--326. The use of spectral analysis to elucidate the cyclic behavior in time series generated by a forest stand growth simulation model is discussed. A stand-level simulator, FORET, for an Appalachian deciduous forest is described. An estimate of the power spectral density of the total biomass time series is calculated, The power spectral density estimate indicates a dominant cyclic behavior with a period of about 200 years. In addition the spectral density is approximately bandlimited. This characteristic makes possible the application of the sampling theorem for analysis of sampling rates. INTRODUCTION Several modeling approaches to the analysis of forest stand dynamics and succession have recently been suggested (Botkin et al., 1972; Shugart et al., 1973; Horn, 1975). The stochastic stand growth simulation models of the type proposed by Botkin have provided insight into forest dynamics for mixed stands. This type of model represents a synthesis of knowledge about the forest ecosystem under consideration and provides a set of random time series for the variables of interest. Conclusions concerning stand dynamics are drawn, based on detailed examination of these time series. Additional analyt- ical techniques are often required. In this paper the use of spectral analysis as a technique for elucidating cyclic behavior in the growth simulation time series of stochastic stand growth models is considered. Much attention has been given to the inventory of the nation's forest re- sources. To provide information for management and development of the forest resource, forest area, timber volume, growth, mortality, timber cut, potential productivity and forest ownership are sampled on a periodic basis * Research sponsored by the Energy Research and Development Administration under contract with Union Carbide Corporation.