Dendrographic records for four tropical rainforest trees, collected by Drs K. Yoda and H. Sato at the Pasoh Forest Reserve in June 1971, suggested the rhythmic diurnal changes in trunk radii. The Fourier transform (FT) was applied to the radius oscillations of the four sample trees for understanding the trunk behavior in frequency domains. The maximum FT amplitude occurred at a specific frequency (f^*) of 0.0469 h^-1 in all trees and suggested consistent diurnal changes in trunk radii, although f^* = 0.0469 ^-1 does not correspond to the ideal period of 24 h. The phase angle at a given frequency (f), or θ_i(f), for an individual tree with identification number (i) was not significantly correlated with θ_i(f) for another individual with the identification number j (i≠j, p> 0.05). Autocorrelation coefficients between θ_i(f) and θ_i(f + Δf), designated with f and the lag frequency Δf, were not significant for most Δf, suggesting a lack of order in θ_i(f) with respect to f. The frequency distribution of θ_i(f) followed a uniform distribution within the range of ±π(± 12 h d^-1), where π is the circular constant. These traits of θ_i(f) associated with trunk radii corresponded well with the traits of a different θ_i(f) calculated from sap flow sequences of conifers, implying temporal partitioning of soil-water resources among trees. The ecological significance of temporal resource partitioning on an hourly basis within small land areas is discussed with reference to hydraulic architecture and hydraulic lift (or redistribution), which are known to be important mechanisms facilitating the coexistence of competing plant species or individuals within a forest stand.