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REMOTE SENSING OF CHANGES IN MORPHOLOGY AND
PHYSIOLOGY OF TREES UNDER STRESS
Charles E. Olson, Jr,
Jennifer M. Ward
School of Natural Resources
University of Michigan
Annual Progress Report
30 September, 1968
A report of research performed under the auspices of the
FORESTRY REMOTE SENSING LABORATORY^^^^M
BERKELEY, CALIFORNIA—
A Coordination Facility Administered By
The School of Forestry and Conservation,-
University of California in Cooperation with the
Forest Service, U.S. Department of Agriculture
EARTH RESOURCES SURVEY PROGRAM ■'"{i' '
OFFICE OF SPACE SCIENCES AND APPLICATIONS
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
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REMOTE SENSING APPLICATIONS
IN FORESTRY
REMOTE SENSING OF CHANGES IN MORPHOLOGY AND
PHYSIOLOGY OF TREES UNDER STRESS
By
Charles E. Olson, Jr.
Jennifer M. Ward
School of Natural Resources
University of Michigan
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Annual Progress Report
30 September, 1968
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A report of research performed under the auspices of the
FORESTRY REMOTE SENSING LABORATORY,
BERKELEY, CALIFORNIA—
A Coordination Facility Administered By
The School of Forestry and Conservation,
University of California in Cooperation with the
Forest Service, U.S. Department of Agriculture
For
EARTH RESOURCES SURVEY PROGRAM
OFFICE OF SPACE SCIENCES AND APPLICATIONS
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
412616
TABLE OF CONTENTS
ABSTRACT i
ACKNOWLEDGMENTS iii
INTRODUCTION 1
OBJECTIVES 2
STUDY I: INVESTIGATION OF CHANGES IN FOLIAR REFLECTANCE 2
AND EMITTANCE OF TREE SEEDLINGS EXPOSED TO
VARYING SALINE TREATMENTS
Pilot Study 3
The Current Study 7
Results 10
Discussion 20
Work in Progress 23
STUDY II: PRELIMINARY FLIGHT TESTS FOR REMOTE SENSING 23
OF MOISTURE STRESS IN FOREST TREES
Objectives 24
Description of the Study Site 24
Flight Parameters 25
Field Procedures 26
Resul ts 2 7
Discussion 28
Work in Progress 32
STUDY III: INVESTIGATION OF DIFFERENCES IN FOLIAR REFLECT- 33
ANCE CHARACTERISTICS OF SEEDLINGS OF RING-POROUS
AND DIFFUSE-POROUS TREE SPECIES SUBJECTED TO
MOISTURE STRESS
Work Completed 33
Work in Progress 34
LITERATURE CITED
35
ABSTRACT
This is the second annual progress report describing results of
continuing studies of forest trees subjected to varying types of stress.
Greenhouse work with tree seedlings exposed to varying concentrations
of NaCl and CaCl^ indicates that the oak species tested were more
resistant to salt injury than aspen, tulip poplar, maple, or willow;
and that salt tolerance of these species decreased in the order listed.
No consistent differences in foliar reflectance or moisture
tension between salt-treated and control plants were observed until
leaf mortality occurred. Radiometric temperatures for seedlings sub¬
jected to heavy salt concentrations were between 0.5 and 1 .0°C higher
than for control plants.
Drought conditions in sugar maple seedlings, created by varying
the frequency of watering, were accompanied by increasing foliar re¬
flectance of the stressed plants at all wavelengths from 0.5 to 2.5
micrometers. Radiometric temperatures for stressed plants averaged
nearly 2°C higher than for control plants. During this study, it was
observed that leaves began to wilt when foliar moisture tensions exceed¬
ed 200 lb./sq.in., and leaf margins became dry and brittle after mois¬
ture tension exceeded 350 lb./sq.in.
Previsual detection of drought or salt-stress was not achieved
using color or infrared-color photography in the laboratory.
Field tests of infrared scanning systems for detecting moisture
stress in mature trees were also begun during this reporting period.
Girdled oaks were successfully detected in daytime imagery obtained
from altitudes up to 4,000 feet above mean terrain. The girdled trees
showed clearly in aerial photographs on panchromatic, i nf rared-aerographic ,
i
normal color, and infrared-color films; and on infrared imagery in the
8-14 micrometer wavelength band obtained in mid-afternoon. Detection
was unsuccessful from any altitude when the infrared imagery was ob¬
tained at night.
ACKNOWLEDGMENTS
The research described in this report is being conducted as part
of the Earth Resources Survey Program in Agriculture/Forestry spon¬
sored by, and with financial assistance from, the National Aeronautics
and Space Administration (Contract No. R-09-038-022) . The work is a
cooperative undertaking of the Forest Service, U. S. Department of
Agriculture, and the University of Michigan School of Natural Resources.
Part of the salaries of professional employees are contributions of
the University of Michigan and the Forest Service.
The generous support of Dr. Warren H. Wagner, Jr., Director of
the University of Michigan Botanical Gardens, and the entire staff of
the Botanical Gardens, is gratefully acknowledged.
Special thanks must also be extended to Messrs. Wayne G. Rohde,
Kaew Nualchawee, Robert Wadsworth, William E. Butler, Jr., and Robert
C. Beall for their assistance in collecting the laboratory and field
data .
1 i i
REMOTE SENSING OF CHANGES IN MORPHOLOGY AND
PHYSIOLOGY OF TREES UNDER STRESS
by
Charles E. Olson, Jr.
Jennifer M. Ward
School of Natural Resources
University of Michigan
INTRODUCTION
Early detection of insect and disease attacks is one of the keys
to preventing epidemic conditions, but is difficult to achieve over
large areas using ground methods. Recent advances in aerial recon¬
naissance techniques appear to provide improved detection capabi 1 i t ies.
Many insect and disease attacks cause disruption of the water
metabolism of host trees by plugging or severing the water and solute
conduction tissues. Trees subjected to such attacks become less
vigorous and their foliage develops higher moisture tensions than un¬
affected trees. Reduced vigor and increasing moisture stress are
found in trees subjected to drought as well as in trees attacked by
organisms, however. Careful analysis of the pattern in which symptoms
occur may permit inferrential determination of their probable cause.
Several workers have shown that the reflectance and emi ttance
characteristics of tree foliage vary dynamically during the growing
season. These variations result in equally pronounced variations in
the appearance of the trees on imagery obtained from any of the electro¬
magnetic remote sensors. Despite this, there is increasing evidence
that differences in moisture stress can be detected in natural and
planted vegetation (Weber, 1965; Olson, 1967b; Weaver, Butler and Olson,
1968).
Carefully controlled studies of changes in reflectance and emittance
characteristics of foliage on trees subjected to different levels of
moisture stress were begun at the University of Michigan in 1965. Re¬
sults of work completed through the 1967 growing season were described
by Weber and Olson (1967). The present report summarizes additional
work performed through September 1968.
OBJECTIVES
Three primary objectives governed the work done during the year end¬
ing on 30 September, 1968. These were:
1. To enlarge the laboratory work to include investigations of the
specific effects of nutrient imbalance and some common disease organisms.
2. To prepare for field tests of those remote sensing systems
which the laboratory data indicate offer most promise of successful
early detection of tree vigor decline.
3. To investigate possible differences between ring-porous and
diffuse-porous species in their response to moisture stress.
\
To meet these objectives it was necessary to design three relative¬
ly discrete, but related studies. The objectives, procedures, results
and conclusions reached to date will be described for each study in turn.
STUDY I: INVESTIGATION OF CHANGES IN FOLIAR REFLECTANCE AND EMITTANCE
OF TREE SEEDLINGS EXPOSED TO VARYING SALINE TREATMENTS
Trees growing in many areas are exposed to organic and inorganic
wastes of man. In the northeast, and in the Lake States, frequent use
2
of salt for removing winter ice from roads and streets exposes roots of
adjacent trees to high levels of salinity. Significant increases in
injury to, and mortality of, such trees have been observed in recent
years. This study was begun in an attempt to determine whether remote
sensing techniques offer a rapid means of assessing the extent of such
injury before the damage becomes severe.
The current work was designed to provide information bearing on the
following questions:
1. Does salt accumulation alter the reflectance properties of
f ol i age?
2. If salt accumulation does affect reflectance properties, are
the changes continuously progressive and is there a threshold level at
which changes first become noticeable?
3. If changes in reflectance properties are observed, do these
changes result from increased moisture stress similar to drought,
osmotic action, or blockage of vessels in the xylem tissues?
4. Does exposure to high salinity increase susceptibility to
Vert i ci 1 1 i urn wi 1 t infection?
Pilot Study
Preliminary studies of the salt tolerance of several tree species
to CaC^ and NaCl were conducted to aid in design of more detailed
studies. One to three year old seedlings of quaking aspen (Popul us
tremul oi des Michx.) , tul ip poplar (L i r i odend ron tul i p i f e ra L.) , red
oak (Quercus rubra DuRoi ) , bl ack oak (Q. vel ut i ni a Lam) , willow (Sal i x sp . ) ,
and sugar maple (Acer saccharum Marsh.) were used. All sugar maple
3
seedlings were collected from natural reproduction in the Ottawa Nation¬
al Forest in Iron County, Michigan. All other seedlings were grown in
the University of Michigan greenhouses for other studies completed
previously. Early in January, 1968, all plants were placed in four inch
pots containing a soil mixture consisting of one part sand, one part
screened peat, and two parts loam. Mean oven-dry weight for the soil
in the past was 477.38 grams, plus or minus 20 grams.
After potting, the seedlings were kept in the greenhouse under
artificial lighting and air temperatures of approximately 25°C to bring
them out of dormancy and maintain growth. Measured amounts of salt
were applied to the surface of the soil in the pots to give concentra¬
tions of 100, 1,000, 10,000 and 100,000 parts of salt per million parts
of soil. The salt was carried into the soil by downward percolation of
distilled water applied regularly to the soil/salt surface. A summary
of the salt treatments is shown in Table I.
Initial salt applications were made on January 12, 1968. By Janu¬
ary 17, foliage on plants treated with 100,000 parts per million was
severely wilted, discolored and quite brittle, but there was little
evidence of marginal burning. Tulip poplar receiving the 10,000 parts
per million treatment showed some discoloration in the vein areas and
the leaves had begun to wilt. The 10,000 parts per million treatment
of aspen produced less yellowing and the leaves were not wilted, al¬
though marginal burning was evident.
On March 4, 1968, a second application of CaC^ was made to the oak,
willow and maple seedlings using the same concentrations as in the first
application, except that the 100,000 parts per million treatment was
4
Salt Used
CaCl 2
CaCl 2
CaCl 2
CaCl 2
CaCl ^
NaCl
Species
Tulip
pop.
Aspen
Oak
Willow
Maple
Maple
Date Treated
Jan 1 2
Jan 1 2
Mar 4
Mar 4
Mar 4
Mar 4
None
X
X
X
X
X
X
100 ppm
X
X
X
X
X
X
1 ,000 ppm
X
X
X
X
X
X
10 ,000 ppm
X
X
X
X
X
X
100 ,000 ppm
X
X
Table I. Summary of the species, type and concentrations of salt used during
a pilot study on the effect of salt uptake on light reflectance properties of
tree foliage conducted in 1968.
5
omitted. An additional group of maple was treated with NaCl in the
same concentrations as with CaC^- The first spectral reflectance
curves were obtained on March 15 and additional curves obtained at
weekly intervals through March 29, 1968. In all cases reflectance
measurements were made without removing the leaves from the seedlings.
After a reflectance curve had been obtained, the leaf was removed and
placed in a fixing solution preparatory to microscopic examination of
the leaf tissues. Leaves picked for microscopic examination were placed
in a fixing solution made up of 75% Chromic Acid-1%, 5% Glacial Acetic
Acid, and 20% Formal dehyde-A0% Aqueous. Leaves were placed in individ¬
ual screw top vials just large enough to accommodate single leaves,
covered with fixing solution and sealed with masking tape. Microscopic
examinations of these materials have not yet been completed. By March
29, all trees treated with 10,000 parts of salt per million parts of
soil showed severe burning, discoloration and wilting of the foliage.
Of those treated with 1,000 parts per million, the oak appeared least
affected with slight burning of the spines and tips of lobes, while
willow was least tolerant and there was discoloration over entire
leaves. The maple foliage was also damaged extensively; however, damage
did not appear as severe as in willow. Comparison of the sugar maple
seedlings treated with NaCl and Ca Cl^ indicated no difference in visual
appearance or in the reflectance curves, suggesting that under present
test conditions there is no significant difference in toxicity of the
salts to the seedlings. Based on data now available, oak appears to
be more resistant to the chloride salts than all other species tested.
Aspen, tulip poplar, maple and willow showed decreasing tolerance to
6
the salt, in that order.
The Current Study
Following the pilot study, two hundred sugar maple seedlings (9 to
15 inches tall) were purchased from the Forest Nursery Company of McMinn¬
ville, Tennessee. These seedlings were placed in six inch pots contain¬
ing uniform volumes of the soil mixture previously described. The total
number of trees was divided into two groups, one for subjection to drought
conditions by withholding water and the second for salt treatment.
A. Drought
The group of trees selected for the drought treatment was divided
into two sections. In one section the young trees had leafed out during
the previous week, while in the other they leafed out shortly after the
treatment began. In each section half the trees were watered twice
weekly with 150 ml of distilled water, and the other half received 150 ml
of distilled water once a week. Twice weekly, photographic impressions
of selected leaves were made for leaf area determination, and the lengths
of the lamina and petiole on newly formed and expanding leaves were mea¬
sured. The rate of stem extension on the new season's growth also was
measured. A control group of plants was watered adequately every day with
distilled water. Measurements of leaf area and lamina length, and petiole
and stem extension were made twice weekly on these plants.
Light reflectance measurements (0.5 to 2.6 micrometers) were
made at intervals on each tree. Repeated reflectance measurements were
made on each plant over a period of two months or until the tree died.
7
At the end of this period these leaves were removed from the seedlings,
their moisture tension determined in a Scholander pressure cell, and
the leaves prepared for microscopic examination of selected cross sec¬
tions. A Barnes IT-3 radiometer was used in obtaining radiometric
temperature data from leaves near the top, and leaves near the middle,
of the crown of each seedling.
B . Sal i n? ty
Trees assigned to the salinity test were randomly divided into
twenty groups of seven trees each. Ten groups were treated with NaCl
and ten groups with CaC^- In each group trees were randomly assigned
to one of seven salt concentration treatments. Concentrations of 0.0,
0.05, 0.10, 0.25, 0.50, 1.0 and 2.0 percent salt (by weight) in distilled
water were used. During the initial salt application, each plant was
watered to excess with the appropriate solution and allowed to drain.
Each pot was placed on a plastic saucer, and any further liquid that
drained out was discarded. Thereafter, each pot was watered regularly
with a sufficient amount of distilled water to allow a little to drain
out into the saucer. This liquid was placed back in the pot a few hours
later. It is believed that this procedure kept the concentration of
salt in the soil solution nearly constant. Since each pot was maintained
at field capacity, any moisture tension developing in the leaves should
not be the result of insufficient water.
Measurements of petiole and lamina extension were made during the
first month after treatment began. Ten of the twenty seedling groups
were randomly chosen for these measurements; five treated with Ca Cl 2
8
and five treated with NaCl . Throughout the first six weeks after treat¬
ment began, four groups were chosen randomly each day and reflectance
measurements obtained from selected leaves on each plant. Each selected
leaf was tagged for identification so that subsequent reflectance mea¬
surements could be made on the same leaves. Since four groups out of
twenty were randomly chosen each day, the interval between consecutive
reflectance measurements on any one group of seedlings varied from group
to group.
Additional reflectance measurements were made at hourly intervals
on 3 July for four plants treated with 0.0, 0.1, 0.5 and 1.0 percent NaCl .
Daily reflectance measurements were obtained for four groups of seedlings
from 5 to 15 August. Two groups were treated with CaCl^* and two with
NaCl, and all four groups were maintained at field capacity during this
period .
Reflectance measurements were obtained at intervals from two
leaves from selected plants and the leaves detached from the seedling
and prepared for microscopic examination. One leaf in each pair was
one of the tagged leaves from which repeated reflectance measurements
had been obtained, and moisture tension was determined for that leaf
before it was prepared for sectioning.
Radiometric temperatures of individual leaves near the top, and
near the base, of the crown of each seedling were determined with a
Barnes IT-3 radiometer on 1 , 3 and 5 July.
Photographs of all, or part, of each seedling in eleven groups
were obtained on 11 July and 22 August. Kodachrome II and Aerial Ekta-
chrome IR (Type 8443) films were used on both occasions.
9
The soil in the pots of all surviving plants is being maintained
at field capacity at the same salt concentration as during the study.
These trees will be repotted in soil infected with the Vert ici Ilium
wilt fungus, to determine whether the salt treatments increased the
susceptibility of the seedlings to attack by this organism.
Resul ts
Since data collection continued through August 1968, data reduc¬
tion and analyses are incomplete. However, a preliminary analyses of
the data provide clues as to the probable nature of the results.
A. Drought Treatment
1. Leaf extension. Measurements of lamina and petiole extension
under different frequencies of watering indicate that leaf size increased
as watering frequency increased (Table II).
Watering
Frequency
Number of
PI ants
Number of
Leaves Measured
Ave rage
Leaf Length
Once weekly
10
62
7 .0 cm
Twice weekly
10
67
8 .6 cm
Daily
10
57
10.7 cm
Table II. Average length of lamina plus petiole for sugar maple
leaves developing under varying frequencies of water
appl ication.
Leaf area data have not yet been reduced to reportable form.
2. Moisture tension. All plants undergoing drought treatment
developed moisture tension in excess of 200 lb./sq. in. before leaf
10
I
/
wilting occurred. As drought was prolonged the effects became more severe
and leaves began to dry around the edges, but not until moisture tension
exceeded 350 lb./sq. in. (the limit of the pressure gauges on the Scholan-
der Pressure Cell used). Moisture tensions remained low throughout the
period and active oozing of sap from the cut end of the leaf petiole was
common, for the control plants. Occasional leaves cut from plants watered
twice weekly had moist petiole surfaces, but in most cases pressure was
required before moisture appeared. Freshly cut ends of Teaf petioles
were dry for all leaves from plants watered only once weekly.
3. Reflectance . All leaves showed generally increasing reflectance
over time at all wavelengths from 0.5 to 2.5 micrometers (Figures 1, 2 and
3). Reflectance increases were greater at long, than at short wavelengths;
with greatest increases observed near 2.2 micrometers. The magnitude of
these increases is indicated in Table III.
Water i ng
Frequency
Wavelength
Reflectance
Increase^/
Plant Condition
At End of Period
Once Weekl y
1 .0
5 .6%
Dead
Twice Weekl y
1 .0
5.5%
Living
Daily
1 .0
4.2%
Living
Once Weekl y
2.2
9.5%
Dead
Twice Weekl y
2.2
5 .0%
Living
Daily
2.2
3.6%
Living
1/ % Reflectance
at end mi nus /
! o reflectance at
start .
Table III. Typical data for reflectance increases at 1.0 and 2.2
micrometers for sugar maple foliage from seedlings
watered at varying intervals.
1 1
50
40
30
20
10
0
20
10
0
F
"I
“T - T~
» I . 'T~
1
8 r
—r™
r
1.00 pm
— — — *
- — —
— —
__ _ — — «
-
1.62 jim
- - —
— — —
_ — •
-
2.20pm
-
— — —
- —
1.93 m
-
-----
—
_
- — —
-
s
1 1
1 1 1
1 l
l i
1
i l i
i
0
10
20
30
40
50
60
70
1
' 1
1 | I
S J
1 1
"T"
1 | 1
1
0.53pm
-
-
*
0.64pm
s
I s
i i .
I .
i i
1
j i .
1
0
10
20
30
40
50
60
70
TIME (IN DAYS)
re 1. Apparent change in reflectance over time at six wavelengths
a typical leaf on a wel 1 -wate red sugar maple seedling (leaf C05A) .
12
50
40
30
20
to
0
20
10
0
Fig
for
b ; » i i a * . n — r
J _ I _ I _ L
,.L- .1
1 _ L
10
20 30 40
T~T
r » ■ ? . 1 r
LOO pm
1.62 pm
2.20 pm
1 .93 pm
E » _ S _ i _ L_
50 60 70
n — ' — i — i — n
0.53 pm
0.64 pm
J - 1 _ L _ i _ I _ i _ l _ i _ I _ i _ I _ i _ I _ L
0 10 20 30 40 50 60
_j _ l
70
TIME (IN DAYS)
2 e Apparent change in reflectance over time at six wavelengths
typical leaf on a sugar maple seedling watered twice weekly
DI07B).
13
50
40
30
20
10
0
20
10
0
T - 1 - 1 - 1 - 1 - l - I - 1 — 1 — i I i I ■ T
_ -♦ 100
jjm
ym
__ 2.20 Jim
1.93 Jim
i i _ I _ i _ I _ i _ I _ i _ I _ c _ I _ i _ 1 _ i i
0 10 20 30 40 50 60 70
t - r — t - i - 1 - i - I - r - 1 - '' I t r- i s
JL
0
__ ^0 0.53 jjm
^ 0.64 pm
J _ i _ I _ i _ I
40 50 60
■ i '
70
TIME (IN DAYS)
jure
)1 A)
3. Apparent change in reflectance over time at six wavelengths
typical leaf on a sugar maple seedling watered once weekly (leaf
14
Increasing reflectance at wavelengths shorter than 1.2 micrometers
for trees under stress is contrary to results published by several authors
including Colwell (1956), but in agreement with a more recent report by
Olson (1967a). Differences in species may be a factor and the fact that
earlier authors had worked with picked foliage may also be important.
4. Radiometric temperatures. In all treatments, apparent tem¬
peratures determined with the Barnes radiometer were nearly the same for
leaves from the upper and lower parts of the crown. The control plants,
watered daily, gave apparent temperatures with averages approximately
2°C lower than the treated plants. Differences between plants watered
once, or twice weekly were less than 0.5°C.
B . Salinity Treatment
The first visible effect of the salt treatments was usually a
slight yellowing of the leaf near the margin, particularly at the tips
of the lobes. As the yellowing increased, the tips died and turned a
light yellow-brown, or fawn color. The area of dead, fawn-colored,
material per leaf increased as the study progressed. Color, and false
color, photographs of typical plants are shown in Figures 4, 5 and 6.
Visible effects began to appear in plants subjected to the highest
salinity (2.0%) on the sixth day after treatment began. All of the high
salinity treatment plants showed visible symptoms after 34 days. Most
plants receiving the second highest salinity treatment (1.0%) showed
definite symptoms after 23 days, but half of the trees treated with the
0.5% salt solution showed no visible symptoms, and weaker salt treat¬
ments had produced no visible symptoms, after 77 days. No differences
15
Kodachrome Il/no filter
Ektach rome- IR/Wratten 1 2 filter
Figure 4. Normal color (top) and infrared color (bottom) photographs of
a single, full-sized leaf on a suqar maple seedlinq from the control qroup
(leaf 1 8C74B) .
16
Upper Photographs Taken on 11 July 1 968
Kodachrome II/No filter
Ektachrome IR/Wratten 12 filter
Lower Photographs Taken on 22 August 1 968
Figure 5. Normal color and infrared color photographs taken on two dates
of the foliage on a sugar maple seedling watered regularly with a 1.0 per¬
cent solution of CaCl ^ in distilled water (plant 08 C 16).
17
Upper Photographs Taken on 11 July 1968
Lower Photographs Taken on 22 August 1968
Figure 6. Normal color and infrared color photographs taken on two dates
of the foliage on a sugar maple seedling watered regularly with a 2.0 per¬
cent solution of CaCl2 in distilled water (plant 08C27) .
18
in symptoms were observed between plants treated with the two salts used.
1. Leaf extension. Most of the leaves formed in a single flush
of growth at the time the seedlings were placed in individual pots. Leaf
expansion was completed before salt treatment began. Since sugar maple
is one of the few diffuse-porous species that do not flush continuously
during the growing season, measurement of leaf extension was not prac¬
ticable during the study.
2. Moisture tension. Measurements obtained with the Scholander
pressure cell for plants treated with salt seldom exceeded 100 lb./sq.in.,
even in plants exhibiting visible damage symptoms. No correlation is
apparent between moisture tension and the salt concentrations used.
3. Reflectance . Data for foliar reflectance showed no obvious
differences between leaves from control plants and leaves from plants
subjected to any treatment until leaf mortality occurred. However, all
reflectance measurements were made at a point near leaf center, the last
area to be affected by the yellowing, and then fawn coloration, as salt
effects become more severe. Short term variations in reflectance mea¬
sured at hourly intervals were greatest in a control plant, but did not
exceed 2 percent at any wavelength. Of those plants for which reflec¬
tance data were obtained at daily intervals near the end of the study
period, reflectance changes were greatest in two of the trees treated
with the highest salinity (2.0%), but results were sufficiently variable
that no obvious trend is evident from our preliminary analysis of the
data .
4. Radiometric temperatures. Apparent temperatures measured with
the Barnes radiometer indicate an average temperature of leaves in the
19
upper part of the crown that Is approximately 0.5°C higher than for
leaves lower down. The plants receiving the two highest concentrations
of either salt gave apparent temperatures between 0.5 and 1°C higher
than the control plants.
DISCUSSION
The work undertaken proved overly ambitious for the personnel
and equipment available. Breakdown of the DK-2a spectrophotometer, and
erratic performance of the digital readout components prevented sam¬
pling as often as desired. The defects in the digital readout have also
increased the time needed to reduce the reflectance data.
Our preliminary analyses of the data are inconclusive but seem to
indicate that high salinity does not produce the sane physiologic effects
as drought. This tentative conclusion is based on the moisture tension
measurements made with a Scholander pressure cell. While this is a re¬
liable means of determining moisture tension, some abnormalities were
observed with the sugar maple leaves.
When using a Scholander pressure cell a leaf is cut from the plant
and immediately placed in a thick-walled, sealed container with only the
cut end of the petiole protruding through an air tight gasket. Inert
nitrogen gas is bled from a high-pressure tank into the cell until the
pressure in the cell is just high enough to force water out of the cut
end of the petiole. The pressure inside the cell at this instant, and
the pressure at which the water film on the cut end of the petiole
disappears as the pressure inside the cell is slowly reduced, are av¬
eraged to give a measure of the moisture tension inside the leaf.
20
When sugar maple leaves were subjected to pressure in this manner,
the initial oxygenation of water was obscured by the formation of a foam,
or froth, which solidified in air and could not be sucked back into the
leaf by reducing the pressure in the cell. This was observed in almost
all cases when pressures over 100 Ib./sq.in. were required. In such cases,
the pressure at the time foam first appeared was recorded as the leaf
moisture tension. When a water film appeared at lower pressures, it was
sometimes, but not always, accompanied by foam formation. It was not
clear whether the foam formed from the contents of the xylem or phloem
but the foam may result from the sugary sap characteristic of sugar maple.
It was mentioned above that control plants for the drought treat¬
ments actively oozed water from the cut end of the petioles on many
occasions. This occurred both when leaves were held in the hand and when
they were laid gently on the bench. The appearance of water without
application of pressure indicates negligible moisture tension, or possible
positive pressure inside the leaf. Oozing of moisture from cut petioles
was also observed with 69 of 84 plants in the salinity test, and was
noticed for leaves from all concentrations of either salt. The possi¬
bility that the sugary sap of the maple lessened the osmotic gradient
between internal water and external salt solutions may be a factor in
our inability to detect high moisture stresses in the plants subjected
to saline conditions. On the other hand, salinities of 2 percent or
less in the soil solution may not be sufficient to creat an osmotic
gradient that will bring about physiologic drought in sugar maple.
It was interesting to observe the differences in visible stress
symptoms between plants subjected to drought and salt treatments. The
21
sequences for the two groups can be summarized as follows.
Drought treatment. The first visible symptoms of drought were
wilting of the leaves and progressive distal bending of the leaf petioles.
This was followed by drying of the leaves and withering of the petioles.
Finally, the leaves turned fawn-colored and abscission occurred.
Sait treatment. Visible symptoms were more numerous and pro¬
longed in salt treated plants, but usually occurred in the following
orde r :
1. Midribs of unfolding leaves bent distally.
2. Tips of unfolding leaves turned black.
3. Tips of full expanded leaves turned fawn-colored, but remained
f 1 ex i bl e .
4. Interlobate areas turned fawn-colored, but the central portion
of the leaf remained a normal green.
5. Entire leaf border turned fawn-colored. Fawn-colored border
sometimes dry and brittle, but green center remained turgid.
6. Whole leaf eventually turned fawn-colored and leaf petioles
bent d i stal 1 y .
7. Green mold began to form on those fawn-colored leaves that had
not dried.
8. Fawn-colored leaves dried and abscission occurred.
It appeared that leaves on plants subjected to drought died because
of insufficient water, but that leaves on plants subjected to salt treat¬
ments died from other causes. If moisture stress was not significant in
plants receiving salt treatments, the lack of observable changes in infra¬
red reflectance from leaves on such plants may not be incongrous.
Microscopic examination of cross-sections through leaves from
plants subjected to various levels of salinity has revealed little
22
difference in structure that can be attributed to the treatment, except
in cases where the cross-section included part of the leaf which was
dead and dry when sectioned. The absence of observable intermediate
conditions in leaf anatomy is probably due to the fact that the leaves
were already fully expanded when the treatments began.
Work Currently in Progress
Detailed analyses of the data are underway, and sectioning and
microscopic analyses of leaf tissues from various treatments are con¬
tinuing. In addition, preparations are being made to inoculate surviving
trees from each salt treatment with the Vert i ci 1 1 i urn wilt fungus, and to
study the effect of the fungus on reflectance and emittance character¬
istics of foliage from infected trees. This will also provide an oppor¬
tunity to determine if the salt treatments increase the susceptibility
of the treated plants to this organism.
STUDY II: PRELIMINARY FLIGHT TESTS FOR REMOTE SENSING OF MOISTURE STRESS
IN FOREST TREES
Previous work (Olson, et al , 1964; Olson, 1967a; Weber and Olson,
1967) indicates that changes in reflectance and emittance characteristics
of forest trees are closely related to moisture stress. The differences
noted in laboratory studies appear great enough to permit detection by
airborne remote sansors. Long range plans call for field testing of the
laboratory results during calendar year 1969. Preliminary field testing
to gain calibration data for the test site, and to insure that at least
major changes in moisture stress can be detected from the air was ac-
compl i shed i n 1 968 .
23
Early in the year, the Michigan Conservation Department's Game
Research Division proposed a cooperative test of infrared sensors for
mapping wetland areas suitable for ducks. By combining our preliminary
field testing with the flight program proposed by the State of Michigan,
significant cost savings were realized. This required use of a different
test area than originally planned.
OBJECTIVES
The cooperative test program was designed to provide data concern¬
ing:
1. The accuracy of wetland mapping from infrared imagery obtained
in early-May and mid- July, and the accuracy with which swamp dry-up
between these dates can be determined from the infrared data.
2. The ability of infrared and photographic sensors to detect
gross differences in moisture stress in forest stands.
3. The adequacy of planned ground truth collection to document
the important environmental conditions affecting the remote sensor
i magery .
Description of the Study Site
The Rose Lake Wildlife Research Center is located twelve miles
northeast of Lansing, Michigan, in rolling morainal topography along the
Cl i nton-Sh i awassee County line. Small marshes and swampy pot-holes are
scattered among sandy ridges and extensive areas of active cultivation
are interspersed among the natural vegetation. Pine plantations supple¬
ment the native hardwoods in the forest areas. Oak (Quercus sp.) and
hickory (Carya sp.) are the most common trees in the upland stands and
24
elm (Ulmus sp.) and red maple (Acer rubrum L.) dominate the lowland forest
types. Patches of quaking aspen (Popul us tremuloi des Michx) and balsam
poplar (Popul us balsamifera DuRoi) are conrenon.
Flight Parameters
Cost and the large size of the Rose Lake Center, precluded complete
aerial coverage of the research area. Instead, two flight lines were
chosen that crossed some of the most diverse cover conditions in the
area .
Day and night flights were scheduled on both 6 May and 17 July.
The University of Michigan C-47 was the primary aricraft and all flights
were completed on schedule. During the afternoon of 17 July, an aircraft
from Bendix Aerospace also made data runs over the Rose Lake test site.
The University of Michigan aircraft carried an infrared line
scanner with a mercury-doped germanium detector having an instantaneous
f i el d-of-vi ew of 6 milliradians on all flights. The detector was filtered
to the 8 to 1 4 micrometer wavelength band on both daytime flights, but
was not filtered at night. During the afternoon flight on 17 July, this
aircraft also carried four 70mm, P-2 cameras. One camera was equipped
with Panchromatic film and a Wratten 22 filter, another with Infrared
Aerographic film and a Wratten S9B filter, a third with Aerial Ektachrome
film, and the fourth with Aerial Ektachrome IR (type 8443) film and a
Wratten 12 filter.
The Bendix Aerospace aircraft carried a Bendix Thermal Mapper
filtered to the 3.5 to 5.5 micrometer band.
During both day and night flights in May, and again in July,
25
infrared imagery was obtained over the test area from altitudes of approxi¬
mately 1,000, 2,500 and 4,000 feet above mean terrain. Both direct
record and tape record systems were used. During the afternoon flight
in July, aerial photography was obtained with all four cameras during
the runs at 2,500 and 4,000 feet.
Field Procedures
A preliminary site reconnaissance on 1 May 1 968 revealed that
most tree species had not leafed out and would be essentially leafless
at the time of the over-flights scheduled for 6 May. Three upland stands
suitable for creating gross differences in moisture stress later in the
year were selected and approved by State Game Division personnel. All
three of these stands were located near the centerline of the planned
f 1 i ght track.
On the afternoon of 1 May, a one acre patch of balsam poplar was
the only stand available with nearly full foliage. Approximately half
of this stand was girdled with a chain saw and severe moisture stress
was expected by 6 May. Two charcoal fires, each approximately one
square foot in area, were located so that the area of girdled poplars
was mid-way between these two hot, point targets.
Field data collection began at noon on 6 May, approximately two
hours before the first overflight. A recording hygrothermograph was
set up, and apparent and actual temperatures of several background con¬
ditions were determined using Stoll-Hardy HF-2 radiometers, a Barnes IT-3
radiometer, and an Alnor Contact Pyrometer. A small, hand-held anemometer
of unknown manufacture was used to gather surface wind information. Data
26
was gathered with each instrument before, during and after the mid-after¬
noon and night flights. In addition to this data, State Game Division
personnel prepared field maps showing the status of wetland habitats
along the flight lines.
On 9 and 10 July three additional plots were girdled to produce
severe moisture stress. Two plots were located in nearly pure upland
stands of oak, and the other in a mixed stand of oak and red maple. Each
plot was approximately one-half acre in size and nearly circular. One
large tree was left ungirdled near the center of one of the upland oak
plots (PI ot No. 2) .
Ground instrumentation was the same as in May except that an
additional hygrothermograph was used, and a pair of black and white
panels, three by five feet in size, was placed in the area for addition¬
al cal i brat i on .
Ground data collection was begun at 0900 on 17 July and continued
through 2300. Data were collected at one hour intervals for a designated
series of test objects. The recording hygrothe rmographs provided con¬
tinuous data on air temperature and relative humidity one foot above
ground in a low brushy area, and four feet above ground in one of the
upland oak plots.
Resul ts
Preliminary results of the wetlands mapping phase of the study
indicate that areas suitable for ducks can be mapped readily from thermal
infrared imagery obtained in early May, but obscuration by tree foliage
reduces accuracy when the imagery is obtained in mid- July. Image en¬
hancement techniques using the tape recorded signals may facilitate
27
wetland mapping in both cases. While interpreting the imagery for this
phase of the study, much greater tone differences between vegetation types
in swampy acres were observed in the night imagery than in imagery obtained
during daylight hours. The reverse was true in upland areas.
The balsam poplar stand girdled on 1 May was not visibly different
from the ungirdled portion of the same stand at the time of the 6 May
flight. The leaves had not wilted, and the foliage on most trees was
still green on 17 July. The girdled trees appeared no different than
the ungirdled trees on the infrared imagery obtained on any flight, nor
was this plot detectably different on any of the aerial photographs ob-
tai ned on 1 7 Jul y .
The two upland oak plots girdled on 9 and 10 July were readily
apparent on all four sets of aerial photography, and in both the 8 to
14 micrometer imagery obtained by the University of Michigan aircraft
and the 3.5 to 5.5 micrometer imagery obtained by Bendix during the day¬
time (Figures 7 and 8). Both plots were detected at all altitudes used
during the test and the plot with the ungirdled tree near the center
resembled a small donut in the imagery. Although both of these plots
were readily apparent, the oak-red maple plot on lower ground would not
have been detectable if its exact location had not been known.
Only one of the plots was detectable on any of the infrared imagery
obtained at night (Figure 9). However, this plot would not have been
detected if its exact location had not been known in advance.
DISCUSSION
Imagery from the two flights conducted during this study indicate
28
Figure 7. Panchromatic (top)
portion of the Rose Lake test
plots of girdled trees. Both
eously at mid-afternoon on 17
and infrared (bottom) photo-mosaics of a
site showing the locations of the four
sets of photographs were obtained simultan-
Jul y 1 9^8 .
29
1
I
I
Altitude Above Ground, Approximately 1,000 Feet
Altitude Above Ground, Approximately 4,000 Feet
Figure 8. Infrared imagery in the 8 to 14 micrometer wavelength band of
a portion of the Rose Lake test site obtained in mid-afternoon on 17 July
1968. Girdled trees in plots 2 and 4 are clearly visible in the original
imagery from both altitudes.
30
I
I
I
R
R
Altitude Above Ground, Approximately 1,000 Feet
Altitude Above Ground, Approximately 4,000 Feet
Figure 9. Infrared imagery in the 0.7 to 14 micrometer wavelength band of
a portion of the Rose Lake test site obtained at 11 :00 p.m. on 17 July 1968.
None of the girdled trees in any plot are detectable without prior know¬
ledge of their location.
31
that gross differences in moisture stress can be detected in photographic
or line-scan imagery in any of several wavelength bands, at least in
some circumstances. Detection of girdled trees was greatest in upland
areas with trees having a ring-porous wood structure. Bottomland areas
where many trees have diffuse-porous wood structure produced poor results;
possibly because the girdles were not deep enough to completely sever the
wider band of water conducting tissues usually present in diffuse-porous
species as compared with ring-porous species. The results of this test
are considered good enough to justify continued field testing to determine
the threshold level at which increasing moisture stress first becomes
detectable in trees of different species.
Confirmation of the hypothesis that differences between plant
species are most readily detected on infrared imagery obtained in the
daytime in upland areas, but at night for swampy areas, was not an ob¬
jective of this study (Weaver, Butler and Olson, 1968). The imagery
obtained supports the hypothesis, however.
Work in Progress
Plans are actively underway for continuation of field trials for
remote sensing of moisture stress in forest trees. Expansion of the
study to include loss of vigor due to root-rotting fungi will be accom¬
plished by including an area of pine plantations infected with Fomes
annosus in the test site. A request for formal designation of our test
area as a NASA test site has been submitted.
32
STUDY III: INVESTIGATION OF DIFFERENCES IN FOLIAR REFLECTANCE CHARACTER¬
ISTICS OF SEEDLINGS OF RING-POROUS AND DIFFUSE-POROUS TREE
SPECIES SUBJECTED TO MOISTURE STRESS
Data for tulip poplar (Li riodendron tulipifera L.) seedlings under
moisture stress indicate that leaves unfolding under high stress are less
reflective than leaves on seedlings with little stress, but that little
difference in reflectance characteristics is observed if the leaves un¬
fold and attain full size before the plants are subjected to the stress
(Weber and Olson, 1967). If this is also true of ring-porous species,
such as the oaks (Quercus sp.), then moisture stress symptoms should be
harder to detect in ring-porous than in diffuse-porous species. This
hypothesis is based on the fact that ring-porous species usually have
only one flush of growth in the spring — while most diffuse-porous species
flush continuously during the growing season. Moisture stresses are
usually low in the spring but increase later in the growing season. When
this is the case, leaves on ring-porous trees would already have attained
full size when high stress developed and little change in reflectance
would occur. The outer (newer) leaves on the continuously flushing,
diffuse-porous trees would be unfolding under increasingly high moisture
stress, and this should made the affected trees appear darker than un¬
affected trees when viewed from above.
Work Completed
Lack of suitable seedlings delayed work on this study. Moisture
stress treatments should not be started until the plants to be treated
have had sufficient time to recover from any transplanting shock, and
33
have developed effective root systems. Funding limits prevented acquisi¬
tion of the needed seedlings until April 1968. At that time, sixteen
seedlings between 15 and 2k inches in height, and of each of three species
were obtained from the Forest Tree Nursery, McMinnville, Tennessee. The
species are: red oak (Quercus rubra DuRoi), white ash (Fraxi nus ame r i -
cana L.) and sugar maple (Acer saccharum Marsh.). Oak and ash are ring-
porous, and sugar maple is a diffuse-porous species. All seedlings were
planted in individual four-gallon containers kept well watered and ex¬
posed in full sunshine throughout the 1 968 growing season.
Work in Progress
Following bud set in early winter of 1968, the plants will be moved
indoors and induced to break dormancy under varying degrees of moisture
stress. Measurements of light reflectance and radiant emittance will be
determined for foliage on each plant at regular intervals as this foliage
develops. Methods will be essentially the same as those described by
Weber and Olson (1967).
34
LITERATURE CITED
Colwell, R. N. 1956. Determining the prevalence of cereal crop disease
by aerial photography. Hilgardia 26:223-68.
Olson, C. E., Jr. 1967a. Optical sensing of the moisture content in
fine forest fuels. University of Michigan 1ST Report No. 8036-
1-F. 21 pp.
Olson, C. E., Jr. 1967b. Accuracy of land-use interpretations from
infrared imagery in the 4.5 to 5.5 micron band. Annals of the
American Assoc, of Geographers. 57:382-8.
Olson, C. E., Jr., R. E. Good, C. A. Budelsky, R. L. Liston and D. D.
Munter. 1964. An analysis of measurements of light reflectance
from tree foliage made during 1 960 and 1 96 1 . Univ. of Ill.,
Agric. Exp. Sta. Report on ONR Proj . No. NR- 387-025, Contract
1834(31) , 222p .
Weaver, D. K., W. Butler and C. E. Olson, Jr. 1968. Observations on
interpretation of vegetation from infrared imagery. In Proceed¬
ings of the AIBS Symposium on Remote Sensing in Ecology (to be
published by the University of Georgia Press).
Weber, F. P. 1965. Exploration of changes in reflected and emitted
radiation properties for early remote detection of tree vigor
decline. Unpublished M. F. thesis, Univ. of Mich., 101 pp.
Weber, F. P., C. E. Olson, Jr. 1967. Remote sensing implications of
changes in physiologic structureand function of tree seedlings
under moisture stress. Ann. Prog. Report. Forestry Remote
Sensing Laboratory for Natural Resource Program, NASA, by the
Pacific SW Forest and Range Exp. Sta. 60pp.
35
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