U. S. Forest Serv ice

Research Note

PSW-166

ABSTRACT: Soil moisture was measuredaround an isolated mature sugar pinetree (Pinus lambertiana Dougl.) in t h emixed c o n i f e r f o r e s t t y p e o f t h enorth centra l S ierra Nevada, Califor-n ia , f rom November 1965 to October1966. From a sequence of measure-m e n t s , h o r i z o n t a l a n d v e r t i c a l s o i lmoisture p r o f i l e s w e r e d e v e l o p e d .Estimated soil moisture depletion fromt h e 6 1 - f o o t radius p lot for the 1966summer depletion season was 22.57 inches.

RETRIEVAL TERMS: soi 1 moisture de- p l e t i o n ; vegetat ive water use ; evap-o t r a n s p i r a t l o n ; f o r e s t i n f l u e n c e s ;watershed management; Pinus lambert-iana; C a l i f o r n i a .

OXFORD: 116 .254 :111 .73 :174 .7 Pinus1ambertiana (794).

Soil Moisture Depletion Patterns

Around Scattered Trees

ROBERT R. ZIEMER

Ever-growing demands for fresh water inthe West have, for some time, resulted in anemphasis on new sources of supply. The majorefforts to date have been devoted to import-ing water from areas of relative abundanceto areas of deficit. Alternative means toaugment local water supplies may be possiblein many areas by treating the vegetativecover so as to reduce the amount of waterused by plants.

Streamflow and soil moisture storage inforested watersheds are affected by the na-ture of logging and by the resultant spacingof the residual vegetation. If the landmanager is to decide rationally what effectland treatment will have on water yield, heneeds to know how vegetation is related tothe soil moisture regime. He may wish totreat the vegetative cover so as to reducethe amount of water used by plants.

Effects of vegetation on soil moisturehave been studied for some time. As earlyas 1889, Wyssotzky1l reported the effect oflogging on soil moisture depletion in Ger-many. Since then, the volume of literaturehas grown and some of the findings appearcontradictory. The contradictions are rela-ted to soil, vegetative, and climatic varia-bles, as well as to sampling technique.Since the introduction of the neutron meth-od of soil moisture measurement in the1950's, the researcher has a much more re-liable tool with which to study soil mois-ture depletion. As a result, the samplingproblem is closer to solution.

To get an idea of how much and at whatrate isolated trees deplete soil moisture, Isampled soil moisture around a single maturesugar pine (Pinus lambertiana). One year ofsampling provided a profile of soil moisture

\C A L I F O R N I A

Figure 1. - -A study plot was set up onthe Challenge Experimental Forest, Cali- fornia, to measure soil moisture aroundan isolated mature sugar pine tree.

C H A L L E N G EE X P E R I M E N T A L F O R E S T I _

Yuba County, California ,Figure 2. -- Soil moisture was sampledwith a neutron meter at six distancesranging from 2 feet to 60 feet awayfrom the study tree.

LEGEND

+ Neutron meteraccess tube

0 Study tree

Other trees:d.b.h.-inches

. <I

0 1 -4.50 4.5 - 12

0 1 2 - 2 40 > 24 0

00800

CFD8

.

tO0 feet

depletion. Nearby vegetation couldbe affecting the amount of soil mois-ture use. Therefore,, we plan to re-measure this moisture use after we cutthe surrounding vegetation within 120feet of the study tree.

CHALLENGE EXPERIMENTAL FOREST

The study was made on the Chal-lenge Experimental Forest, in YubaCounty, California (fig. 1). TheExperimental Forest lies between theSouth fork of the Feather River andthe North fork of the Yuba River.The Forest is representative of morethan 1 million acres of highly pro-ductive timberland of the Sierra Ne-vada mixed-conifer forest type.

Precipitation averages 68 inchesa year --most of i t falling in thewinter months and in the form ofrain. Less than l /2- inch of precip-itation per month falls during June toSeptember- - chief ly from high intensityconvectional thunderstorms. The tem-peratures are mild, with a mean annualmaximum of 69 degrees F. and a meanannual minimum of 42 degrees F.

The soils within the ExperimentalForest are principally of the Aikensoi l ser ies . The soil is of a uniformclay loam texture. Bedrock is estima-ted to be at a depth of 50 to 100 feet.

THE S T U D Y S I T E

A study plot was set up in a cut-over area at 2,900 feet elevation. Thearea was originally logged in the early1870’s. In 1962, 88 percent of thetrees larger than 3.5 inches d.b.h.was removed from the study site. Thelogging slash was left on the ground.

Before cutting, the stand had a basalarea of 230 sq . f t . /acre . The predom-inate species were, in order of frequen-cy: ponderosa pine (Pinus ponderosaLaws. ) , sugar pine (P. lambertianaDougl.), tanoak (Lithocarpus densiflorusRehd.), madrone (Arbutus menziesiiPursh), Douglas-fir (Pseudotsuga men-ziesii Franco), incense-cedar (Libo-cedrus decurrens Torr.), and white fir

(Abies concolor Lindl.) (table 1).

After logging, trees of only twospecies --ponderosa pine and sugar pine--were larger than 12 inches d.b.h. Thebasal area for all species was reducedfrom 230 sq.ft . /acre to 27.5 sq. ft . /acre.

STUDY METHODS

During the summer 1963, I insertedthree aluminum access tubes in thesoil to a depth of 21 feet. To deter-mine soil moisture we took readingswith a neutron meter at l-foot inter-vals in each access tube. In late sum-mer 1964, a ground water observationwell was drilled to a depth of 43 feetand lined with a 2-inch diameter per-forated plastic pipe. At no time sincethe well was installed have we seenthe water table within the 43-footdepth.

Climatological data was obtainedfrom recording rain gages, hygrother-mographs, and maximum and minimum ther-mometers.

Analysis of soil moisture data from1963 and 1964 showed the plot to bewell drained, with no evidence of sur-face ponding, and the soil to be deepand uniform in texture. In 1965, 20additional access tubes were insertedto depths varying from 16 to 21 feet.The tubes were placed in specific quad-rants on concentric circles at sixdistances from a 27.7-inch diametersugar pine. The distances were 2, 5 ,10, 20, 40, and 60 feet (fig. 2).

All vegetation within 120 feet ofthe study tree was measured (fig. 2).There were several large trees 80 to90 feet from the study tree, and agroup of smaller trees about 10 feetsoutheast of the study tree. Scatter-ed throughout the ptanoak and madronewithin 60 feet of t

less than 12 inches

lot weresprouts.he study

d .b .h . ,than 4.

hat thee f f e c t

p l o t .

clumps ofAll trees

tree werewith the

5 inchesresidualon moisture

great majority lessd.b.h. I assumed tvegetation had somedepletion from the

Table 1. --Stand conditions in the study plot before and after logging, Challenge ExperimentalForest , Yuba County, California

Diameterclass(inches)

3 a 12 0, or 0.3 4>1 2.5 37 <#9 44?912 - 24 37.8 4.5 0. 20.7 2-4 403 690724 + 48.~ 7 66s 0. 0. 0. 0 1153

Ponderosa White Incense pine

Sugarpine fir

Douglas fir cedar Hardwood Total

S q . f t . / a c r e

Total I 86s 71.0 .3 24c8 4”9 42u2 229 9

3 - 1212 2424 +

Total

3 - 12

12 = 24

24 +

Total

0. 0. 0. 0.0. l-9 8 .v 3 10 30, 0. 0. 0. O> 0, 0.

8*9 8.4 0, 0. O? 0 II 17,2

8-9 804 0% 0. L9 8-3 27 > 5

Percent o f ini tial stocking

__ _- 0 . 0. 75*9 22”O 22*90, 0. -- 0, 0 .l 0, 0,

18,2 12..6 -m . _ _> -1 11 L4d9

10.2 11-8 0. 0, 38-8 19,8 1250

Table 2. --Daily precipitation 1 Challenge Ranger Station, Challenge Experimental Forest, YubaCounty, California, October 1965-September 1966

Day

123456789

10111213141516171819202122232425262728293031

Monthlytotals

I

0-d Nov Dee Jan Jbr May Jun 3 1u Aw SePInches

Pm

AL

I LI

0102

- -c _e_

_WLa_

_ e>-44

_ _L .m_I-__. ---.- I_I..I___-c _Mb_I__- *.

me __

-_ “I

__ a Q_

Y -1 I_

.I L -0

__ a __

&3 ::II 2-s

II _u

-:19 01851.64 - -

2.74 _-*35 A-_ 05 -’ =’

1.35 -42L 87

<,93 1,,02 _I’

. _ -.A

-:45 :J1.75 * 19

s 78 3,79.26 c-1 17

_L -101-_ 2067l.. l 79a- 1.20

-m _

ii,24.94

5.351.01

-:073 03

.m L

::04l 11

-_- -

ii173

-:42.63l 58

-w_..LUI_

- -_ -.

-:80.42

- -

-137e 32o 27064

- -muB_-___

0.07_BU”

-11611

:31W

.o5,97*Of

-:65I”*s

925-_

-154__

0<46 13023 9.50 10.37 5.18 3.10 3.68 0% 45 0.10 0.09 0.05 0,OO

‘Total2Trace

annual precipitation 46.21 inches (28 year normal precipitation 67.83 inches).

-4-

Table 3. --Monthly air temperature and precipitation, Challenge Ranger Station, Challenge Ex-perimental Forest, Yuba County, California, October 1965 - September 1966

Month

Air temperature IAverages Extremes . P rec ip i tat ion

Max. Min I MeanOF. OF. OF.

H i g h e s t . Date Lowest DateOF. OF.

cktNovDeC

ansebMarAPrMayJuneJuly

79 46 6358 39 4952 29 4151 29 4052 30 4159 36 4872 43 5876 48 6281 51 6686 50 68

92827063637986889996

k 91 56 74 100Sept 84 51 68 101

Total

Average- . . _ - 46 21 -21 6270 42 57 4 _ ,

8 34 151 29 26, 284 19 207 23 21

22 23 1331 20 3

3 31 204, 19 39 31

15 30 223 41 8 , 10,

14 157 40 31

30 38 14

Xnches Inches

0 461323

g45010 37

53183& 103 . 6 8

4510

I 09

* 05(20

Departurefrom l

normal.

1 3 52+ 6-01

22882 386287

_ 6801,742 32

52+ 06

05- 61

1Normal precipitation based upon 28 years of record.2Trace

THE 1965-1966 RECHARGE SEASON P R E C I P I T A T I O N

The Sierra Nevada characteristical-ly has cool wet winters followed byhot dry summers. Precipitation issporadic and soil moisture rechargeinsignificant during summer. For pur-poses of this report, the year wasdivided into two hydrologic periods:the recharge season and the depletionseason.

The recharge season begins in lateOctober or early November, after thefirst major storm with 2 to 3 inchesof precipitation. Vegetative growthhas slowed, and the trees are becomingdormant. The recharge season continuesuntil the heavy spring rains have endedand the soil has drained to field ca-pacity. SOIL MOISTURE

The first significant precipitationthat ended the 1965 summer depletionperiod fell on November 8, 1965 (tables2, 3). Intermittent precipitation forabout 20 days followed. The result wasmore than 13 inches of rainfall--abouttwice the 28-year normal precipitationfor November. Winter rainfall was sub-stantially below normal. By May 1, thetotal precipitation since October 1amounted to only 45.52 inches--or 18.18inches below normal for that period.But even with the low precipitation,the soil was probably fully rechargedto at least a depth of 20 feet beforethe 1966 depletion season began, inMay.

The depletion season extends from Soil moisture was measured at l -late spring to early winter when the foot depth intervals in the plot’s 23soil water is depleted from field neutron meter access tubes at variouscapacity to its driest state. During times through the recharge season.this time nearly all vegetative growth From the data, we developed a patternand a major portion of the transpira- of total soil moisture held in the sur-tion occurs. face 15 feet of soil (figs. 3-6). The

January 17, 1966

COWOUR 1WTERVAt

* Study tree= Access tube

0.2 feet of water pert5 feet of sOi1

February 11, 1966

4

CONTOUR INTERVAL

0.2 feet of wateris feet of soti

= acctu t u b e

CONTOUR INTERVAL

0.03 feet of waterp e r foot of Soil

bstance from tree (feet) I

~

O&once from tree (feet)2 0 4 0

CONTOUR INTERVAL

0.03 feet of waterfoot of Soil

F i g u r e 3 .--Patterns of total soil moisture in the surface 15 feet of soil,left; and of distribution of soil moisture as related to depth and distance

from the study tree, right; on dates shown.

-6-

May 6, 196

CONTOUR INTERVAL

L1 Cl.2 feet of w a t e r p e r

a Study t r e ex Access t u b e

I.

I5 feet of 5011

Scale0 I5 30 ft

I

May 19, 196

x Access tube

Distance from tree (feet)

Dtstance from tree (feet)

C O NT O U R tNTERVAL

June 9, 1966

CONTOUR INTERVAL

a Study t r e ex A c c e s s tube-

,0.2 feet of water per15 feet of soil

Scale0~ 3ytI5L

Distance from tree (feet)

0.03 feet of waterper foot of soil I

F i g u r e 4 --Patterns of total soil. moisture in the surface 15 feet of soilleft; and of distribution of soil moisture as related to depth and distance from the study tree, right; on dates shown.

-7-

June

Study treeAccess tube

0 2 feet of waterN per1

1 0 15feetofsoll Scale i5 30 ft

D~stoncc from tree tfcctl

CONTOUR rNTERVAL

e Study treeI Access tube /

N, 0.2 feet of water per15 feet of so11 CONTOUR LNTERVAL

0.03 feet of woterper foot of soil

CONTOUR INTERVAL

August 12, 1966

44 Dtstonce from tree (feet)

COFiTOUR INTERVAL

* Access tube - Scalet. . ,0 I5 3 0 ft per per foot of Soil

Figure 5. - -Patterns of total soil moisture in the surface 15 feet of s o i l ,left; and of distribution of soil moisture as related to depth and distancefrom the study tree, right; on dates shown.

-8-

diagrams were drawn by interpolatingthe position of iso-moisture linesaround the plotted location of the 23access tubes and the measured mois-ture content at those points. Theyrepresent "best guess" patterns ofthe total soil moisture around thetree and of the mean soil moistureof each l-foot depth measurementpoint at each of the six distancesfrom the study tree. They provide areasonable estimate of the verticaland horizontal distribution of soilmoisture in the plot.

On November 30, 1965, after heavyrainfall, soil moisture was low nearthe study tree, showing the same gen-eral pattern as that observed a monthearl ier ( f ig . 3) . The vertical pro-file revealed that a wetting fronthad penetrated about 8 feet deep nearthe tree and to about 10 to 12 feetdeep away from the tree. At depthsgreater than 10 feet under the tree,the soil moisture remained unchanged,and--in some cases--it was slightlylower than in the October 19 measure-ment. A pocket of low soil moistureat the 11-foot depth noted earlierwas still in evidence.

By January 17, 1966, when an addi-tional 17.14 inches of precipitationhad fallen, the soil moisture contentin the plot had approached a nearlyuniform condition (fig. 3). The mois-ture content near the study tree re-mained slightly less than that awayfrom the tree, but the differenceshad become less obvious. The verti-cal profile indicated that the wet-ting front had moved below the meas-urement depth and that the entireprofile was being recharged.

Another soil moisture measurementwas made on February 11, 1966 (fig.3). Since the previous measurement,5.09 inches of rain had fallen. Thesoil moisture profile was approachinggreater uniformity. Very slight d i f -

The first soil moisture measure-ment of the 1966 season was taken onMay 6 (fig. 4). The soil moistureprofiles were fairly uniform, withmoisture content generally increasingas distance from the tree increased.Soil moisture 10 feet from the studytree was lower than it was closer orfarther away. And it was lowest tothe southeast, where several 6- to10-inch diameter trees grew. Anotherarea of low moisture was about 60feet north of the study tree andwithin 25 feet of a 31.2-inch diam-eter ponderosa pine. The verticalprofile on May 6, 1966 showed thegreatest change in moisture contentoccurring in the surface 3 f e e t . Thevegetation was then just breakingwinter dormancy, and the largestcause of moisture loss was probablysurface evaporation.

Throughout the depletion period wemade repeated soil moisture measure-ments --May 19 (fig. 4), June 9 (fig.4), June 30 (fig. 5), July 15 (fig.5), August 12 (fig. 5), August 28(fig. 6), September 9, and October 25(f ig . 6) . As the season progressed,the point of the lowest total moisturecontent remained about 10 feet fromthe study tree. The difference be-tween the moisture content near the

ferences existed between soil moisture tree and that at greater distancescontents near the tree and away from from it became more pronounced laterthe tree. in the summer. The large ponderosa

THE 1966 DEPLETION SEASON

CLIMATE

Only two significant storm periodsoccurred after March 19, 1966: April10-13, when 3.65 inches of rain wererecorded, and May 9-11, when 0.45 inchof rain fell (table 2). The remainderof the spring and summer was unusuallydry. Temperatures were higher andhumidities lower than normal, particu-larly in late spring (table 3). Thesummer depletion season began in mid-April and continued until the firstfall rain, on November 6, 1966.

SOIL MOISTURE

pine north of the plot had a continu-ing effect on moisture content. Thevertical pattern of soil moisture in-dicated a zone of low soil moisture ata depth of 8 to 13 feet extending fromthe tree to about 10 feet away. Anarea of high moisture content centered3 feet under the tree may have been dueto the presence of large non-absorbingroots used by the tree for support.The primary zone of soil moisture deple-tion extended outward to a distance ofslightly over 20 feet from the treeand somewhat deeper than 15 feet underthe tree.

By October 25, 1966, when the lastmeasurement of the depletion seasonwas made, the low moisture contentnear the tree was quite evident (fig.6). Again, the moisture content 10feet from the tree was lower than thatnext to the tree; the moisture content40 to 60 feet from the tree had changedlittle from previous measurements. Thevertical profile showed an expandedzone of low moisture content centeredat a depth of 8 to 11 feet under thetree and extending a distance of about15 feet away. The high moisture pocketat the 3-foot depth was still evident.And the moisture content 60 feet fromthe tree was lower than that 40 feetfrom the tree. These differences wereprobably due to the large trees outsidethe plot.

DISCUSSION AND CONCLUSIONS

The depletion patterns reported inthis note are only indicative of thedepletion within the zone of influenceof a tree surrounded by soil moisturesampling points.

To obtain a better idea of the mois-ture distribution in the plot on anareal basis, I computed the area betweenthe iso-moisture lines which lie withineach distance class. In this manner,we obtained weighted mean moisture con-tents representative of conditions inthe area between the study tree and 2feet from the tree, from 2 feet to5 feet from the tree, 5 to 10 feet from

the tree, 10 t o 2 0 feet, 20 to 40 feetand 40 to 60 feet from the tree (fig.

As the depletion season progresseddifferences between the moisture con-tent of those areas near the tree andthose further away became greater.

If the entire plot were completelybare of vegetation, the depletion ofsoil moisture would be due to evapora-tion and to subsurface drainage andlateral water movement. We could thenhypothesize that depletion from thesetwo causes was the same at each accesstube and, in addition, that moisturecontent at each tube was equal. Ifthe hypothesis were true and if a treewere then situated so that moisturedepletion from it was negligible atsome distance from the tree, we couldthen estimate the amount of water used.

The estimate could be made by meas-uring the difference in moisture con-tent at sampling points not under theinfluence of the tree and those closerto i t . If each series of samplingpoints were considered to be represen-tative of the plot, the volume of thewater use by the tree could be estima-ted by subtracting the moisture con-tent near the tree from that outsideits influence and multiplying by therepresentative area.

We cannot be sure that these assumptions are valid because we did not havea completely isolated tree, Severalsmall trees within the plot contributedto moisture depletion near the testtree. And several large trees outsidethe plot probably affected moisture deplet ion. Therefore, we had no areaoutside the influence of vegetation.

Some initial estimates of the volu-metric soil moisture differences be-tween the area farthest from the testtree and that closer to the tree maybe useful. In addition, it may bepossible to make some preliminaryestimates of the volumetric moistureuse by the test tree.

-10-

August 28, 1966

I!5 feet of so11CONTOUR INTERVAL

0.03 feet of waterper foot of soil

Figure 6. - -Patterns of total s o i l moisture in the surface 15 feet of soilleft; and of distribution of soil moisture as related to depth and distance from the study tree, right; on dates shown.

The quantity of soil moisture deple- tance class, the difference can beted by the small residual vegetationwithin the plot is probably smallerthan that depleted by the study tree.In addition, the moisture depletionwithin the farthest distance class isundoubtedly affected to some extentby large trees outside the plot. Themoisture depletion measured in the40- to 60-foot distance class is prob-ably greater than that which would befound after these trees are removed.Consequently, if the moisture contentof the area close to the tree is sub-tracted from that of the outer dis-

considered an estimate of the moistureuse by the study tree plus the smallvegetation in the plot--provided theforegoing assumptions are correct.

I multiplied the area of each ofthe six distance classes by the dif-ference between the weighted mean soilmoisture content in each distanceclass and that in the 40- to 60-footdistance class, and totaled these dif-ferences (table 4). The result is avolumetric difference, in cubic feet,of water. By early February 1966,

- l l -

Table 4. --Soil moisture measurements at six distances from the study tree and their differences from that at the 40- to 60-footdistance class , Challenge Experimental Forest , Yuba County, California, 1965-1966.

MEAN SOIL MOISTURE

Distance fromstudy tree

( f e e t )

0 - 22 - 55 -10

10 -2020 -4040 -60

Weightedmean

0 - 2I

2 - 5n 5 -10iu 10 -20I 20 -40

40 -60

Winter recharge season Summer depletion seasonT

11/30/65 l/17/66 2/H/66 S/6/66 S/20/66 6/8/66 6/3 Q/66 7/15/66 8,‘12/66 9/6/66 10/25/661Ft, w a t e r / l 5 f t . s o i l

5 .89 7 . 0 8 7 . 3 0 6 . 9 0 6 . 7 0 5.866.01

6 . 3 0 5 . 6 5 SJO 4.167.04

4.687.28 6.87 6967 6.23 5.77 5.56

6.125.06 4.68 4*17

7.02 7.16 6.75 6‘59 6.17 5.74 5.506.29

Sl9 4.76 4.197.03 7.12 6.66

6-726,62 6.28 5.95 5.77 5~46 S-06 4.43

7.18 7025 60837*00

6.75 6.47 6.25 6,ll 5.867.37

5.52 5.337.32 7.00 6095 6:63 6343 6.27 6e 11 S88 5.66

6.81 7.27 7.28 6.91 6184 6S3 6:31 6,lS S94 5.65 5.39

DIFFERENCES IN MEAN SOIL MOISTURE FROM THAT IN 40- TO 60-FT DISTANCE CLASS1

Ft .. l

SOI1wa teril5 f t .

ill .29 902 10*99

2s * 33 .s7 .62 1.01 1.20 1.50-33 * 04 113 :

.8828 .40 966 .71 LOS 1.20 1.49

l 3s 16: .07 20

l 2s:28 71

.36 .46 .69 .77 -92 1.12 1.47l l 34 19 .34 .17 -33 03s .48 l 50 .6S .82 1.23

.20 m 16 . 18 I 16 .2s .36 .33-a I_ _I _c L_ .._ Y-. __ _I I __ II

VOLUME DIFFERENCES IN MEAN SOIL MOISTURE FROM THAT IN 40- to 60-FT. DISTANCE CLASS2

0 - 22 - 55 -10

10 -2020 -4040 -60

Total 2,177.74 l222.18 524.71 lO93.19 1,248.26 lJS2.20 1,455.33 1,425.04 2,012.45 2,689.14 3,117*86

Inches Inches Inches Inches Inches Inches Inches Inches Inches Inches Inches

4491 2 . 7 6 1118 2.47 2.82 2.60 3.28 3.21 4.54 6.06 7.03

1Computed by subtracting mean soil moisture in 40- to 60- ft . distance class from that in each of the other distance classes foreach date.

2Computed by multiplying the difference in soil moisture from that in the 40- to 60-ft. distance class by the area of each dis-tance class.

Cubic f t .

34.41 8099 .62 3.1087.12 7.75 10.23 17.6729‘04 19.22 31.31 37.20 46.50239.36

3‘ 52 11.4424.64 35.20 58‘089s. 20 62.48 92,40 105.60 131.12

720.6543.52 68.00

97,9234S 10 125.12 187.68 209 a 44 250.24 399 l 84203.00 304 o 641,096.20

345‘ 10743.85 334.9s 355 < 2s 487.20 507.50 659.75274: OS 832.30665.55 l248.45783.00 626.40 704.70 626 40

o 978.75 l409.40 1,291.95

7

6

zL.

5

1 II I 1 I 1S O I L M O I S T U R E

-

I - 40-60 i I I I II I4I i 1

P R E C I P I T A T I O N -

-T

1 h_.d 1 Aug TI S e p 1 Ott

Figure 7. --Soil moisture recorded in the six distance classes from the study tree. Measure- ments were taken from November 1965 to October 1966.

after substantial recharge, the volu-metric difference of soil moisture be-tween the area from 0 to 40 feet fromthe tree and the area from 40 to 60feet from the tree amounted to about525 cubic feet. This difference isequivalent to 1.18 inches of waterover the 41.15-foot radius area. Byearly September, the areas showed avolumetric difference of 2,689 cubicfeet . And by the end of October 1966,it had increased to 3,118 cubic feetor about 7.03 inches of water.

February 11 it was 7.28 feet or 87.36inches. We could assume these valuesto be reasonable approximations offield capacity for the study plot. Thedifference between the moisture con-tent on October 25, 1966--5.39 feet or64.73 inches --and that of the Februarymeasurement amounted to 22.57 inchesof soil moisture depletion for thesummer.

The total water content of the 1 5 - +vyssotzky G. N. Vim. Boden feuch ti gkei tsun ter-

foot profile on January 17, 1966 was suchungen' in Waldbes t&den der Ukrainiselen

7.27 feet or 87.24 inches, and onSteppen und Wa1ds t e p p e n z o n e . Tharandter Forst-liches Jarhbuch 83521-534. 1932.

The Author

R. ROBERT R. ZIEMER heads the Station’s researchon flood and sediment reduction in the coni-fer forest zone, with headquarters in Berkeley,Calif . He earned B.S. (1959) and M.S. (1963)degrees in forestry at the University of C a l i -fornia, Berkeley, and has been with the Sta-t ion’s research staff since 1959.

-13-