SEASONAL TRENDS IN LIGHT REFLECTANCE
FROM TREE FOLIAGE 1 )
by Charles E. Olson, Jr.
University of Illinois - U.S.A.
Abstract During the 1960 and 1961 growing seasons, weekly measurements of light re
flectance from tree foliage were made with a General Electric recording spectrophotometer
in the wavelength range from 400 to 700 millimicrons. Distinct patterns of seasonal change
seemed apparent in the 1960 data. During 1961, an attempt was made to define and confirm
these trends. This paper summarizes the results of the 1960 and 1961 sampling programs.
Résumé Pendant les saisons de croissance en 1960 et 1961, on a fait des mesures chaque
semaine pour déterminer le coefficient de réflexion de la lumière sur le feuillage d’arbres. On
a utilisé un spectrophotomètre General Electric mesurant la longueur d’onde entre 400 et 700
millimicrons. On a distingué dans les résultats obtenus en 1960 des variations du coefficient de
réflexion dans le courant d’une même saison de croissance. En 1961, on a essayé de confirmer
ces tendances. L’auteur presente ici un sommaire des résultats obtenus en 1960 et 1961.
Zusammenfassung Während der Wachstumssaisonen in 1960 und 1961, hat man den
Lichtreflexionskoeffizient von Baumblätter mit einem General Electric Spektrophotometer
(Wellenlänge von 400 bis 700 Millimikronen) wöchentlich gemessen. Man hat bestimmte
jahrzeitliche Veränderungen bemerkt. In 1961 versuchte man solche Veränderungen zu
definieren und zu konfirmieren. Hier gibt der Autor eine Zusammenfassung der Resultate
der Jahre 1960 und 1961
Spectral reflectance studies of forest vegetation were begun at the University
of Illinois in 1959. During 1960 and 1961, light reflectance from foliage of
several tree species was measured at weekly intervals from May through
October. Data collected in 1960 seemed to exhibit distinct patterns of seasonal
change [Olson and Good, 1962], and in the 1961 study an attempt was made
to clarify and confirm these patterns. This report summarizes part of the 1961
data.
Methods
During 1961 samples were taken from four broadleaved and two coniferous
species. These were cottonwood (Populus deltoides, Bartr.), silver maple (Acer
saccharinum, L.), sycamore (Platanus occidentalis, L.), yellow poplar (Lirioden-
dron tulipifera, L.), red pine (Pinus resinosa, Ait.), and Scots pine (Pinus sylvestris,
L.). Sample trees were located in 10- and 11-year-old forest plantations near
Urbana, Illinois. Tree height ranged from 15 feet in Scots pine to 40 feet in
cottonwood but was nearly constant for any one species. Once each week two
leaves were picked from the south side of the upper quarter of the crown of
9 Prepared under the support of the Office of Naval Research, U.S. Navy, as a con
tribution of Project No. NR 387-025.
