WORKING GROUP 4 
OLSON 
227 
each of six trees in each of the four broadleaved species. For the coniferous 
species, between one and two ounces of needles were picked from the same 
relative crown position. Foliage samples were picked between 10.00 and 
14.00 hours local sun time, but no samples were picked when foliage sur 
faces were wet. All samples were taken to the laboratory where reflectance 
measurements were completed within one hour of the time of picking. A 
General Electric recording spectrophotometer having a slit width of 10 milli 
microns and a wavelength range from 400 to 700 millimicrons was used. In 
cident energy was normal to the foliage surface, and the specular component 
was largely included in the measurements. 
In addition to the foliage sampling program, additional measurements were 
taken in each broadleaved plantation. A dial-gauge micro-dendrometer was 
used at weekly intervals to measure accumulated radial growth at breast 
height to the nearest 0.001 inch. Soil moisture was determined gravimetrically 
in each plantation at weekly intervals and was used to determine total avail 
able soil moisture in the upper 30 inches of the soil. Chemical analyses of the 
chlorophyll content of tree foliage were made at bi-weekly intervals for each 
broadleaved species. 
Partial weather data were collected for the study area. A continuous 
recording Bendix hygrothermograph and an Instruments, Inc. continuous 
recording pyrroheliometer were maintained in an open area which was 
within 300 yards of each of the six plantations. U.S. Weather Bureau standard 
and recording rain gauges were also installed at this location. 
Results 
Differences in foliage reflectance between the two pine species studied were 
insignificant at any one sampling period. Until early June, both pine species 
reflected less light at all wavelengths sampled than did the four broadleaved 
species. By mid-June, increased reflectance from pine due to the growth of new 
pine foliage, and decreasing reflectance from broadleaved foliage, essentially 
eliminated any difference in total reflectance between foliage types for the 
400- to 700-millimicron region. From mid-June to late October, reflectance 
from pine foliage remained nearly constant. 
Changes in light reflectance during the growing season were much greater 
with each broadleaved species than with pine. Average reflectance curves for 
four different dates during the growing season are shown in Fig. 1. Except in 
sycamore, reflectance at 680 millimicrons increases steadily during the growing 
season. 
The decreasing reflectance at 680 millimicrons noted in sycamore is believed 
to be associated with a disease commonly called Anthracnose, caused by the 
fungus, Gnomonia veneta (Sacc. & Speg.) Kleb. The growth records (fig. 2) 
for the four plantations suggest that the disease attack was severe. The relatively 
low growth rate of the silver maple may have been due to an attack by the 
same, or a similar, fungus. However, the silver maple was located on poorer