WSP09221

• File Number: 7630.425
• Description: Wild and Scenic - Piedra River
• State: CO
• Basin: Western Slope
• Water Division: 7
• Date: 1/1/1991
• Author: Julie Stromberg Dunc
• Title: Instream Flow Requirements for Cottonwoods at Bishop Creek - Inyo County - California
• Water Supply Pro - Doc Type: Report/Study

000078

ror, the large range of the classes mini-
mizes the error rate.

commonality in
reaches.
Univariate re~
to explore telat
ring width from
lowing variablt"!
during the wa
growing season
year flow volur
and during the
cipitation durinl
ing season, (4) a
ature during t
during indivirll.;
year ring width.
sian analysis .....
reach-specific IT
nual ring width
the most approF
ring width was
cause it servE'S a~
or-year environ I
berg and Patten
flow was selectee
able over paran
taneous minima
riparian trees ca
of droughl. Flo
measured disch
plant 6, whereas
reaches were es
tions on inputs
runoff and othel
nearest stream;
saciates 1990).
The instream
5 WE're calibrate
oped from rane
trees and verifie
sample (n = 14 ;
son correlations
actual ring widt:
within-reach VI
Cook and Jacob:
4 cottonwoods
small sample si:
verified beo..'eel
correlation COl
widths for a gi'

TABLE 1
Location. age. al/d $I::.e (dbhJ of $!udy trres at Bishop Creekil

Distance to Height above
slreambank streambt'd Ag. EIl'valion
Reach Site Species " (m) (ml (years) dbh (em) (m)
2 POTR II 11.1 !; 8.2 1.3!; 0.5 57 !; 17 25 ~ i 2.024
2 POTR 12 8.6!; 5.9 1.7 = 1.3 62 = 20 29 ~ 9 2.020
3 POTR . 7.0 = 3.5 1.3 = 0.3 47=12 29 = 7 2,015
. I POFR . 3.91:0.7 I.l .:!: 0.3 6-11:12 361:11 1.508
2 POIR 5 16.2 = 1.2 1.1 = 0.1 29 = 7 21=4 104M.
3 POTR 5 7.2 = 3.0 1.7.:!: 0.4 21 .:!: 4 19:!:6 10465
5 I POFR 5 1.8 = 1.1 0.6 = 0.4 39=19 42:!: 17 1,390
2 rOFR 5 6.0 = 49 0.6 = 0.4 34 ::t 18 45 1: 22 1,387
3 POFR 5 0.7:!: 1.3 0.1 = 0.1 38:!: 2 50:!: 7 1,385
6 I POFR . 6.2 =:21 l.l :!: 0.-1 09.:!: 15 71 ::t 19 1,380
. Values shown are means followt'd by standard dt'viation. POTR - Populus trichocarpa. POFR - P.
trrmllllln.

~1ETHODS

The gent"Tal methodology consisted of
field sampling in fall 1989 to colll'ct incre-
ment cores and assess tree vigor,laboratory
.....ork to prepare the cores and measure
.....idth of tree rings, and data analysis.

Field Sampling

Three sites \\-'ere sampled in each of the
divt"Tted reaches, and one site was sampled
in the supplemented-flow reach. immedi-
ately belo..... power plant 6. Sites were not
randomh' located. Thev were selected in
those se~tions of the ;eaches supporting
cottonwood populations. The response of
the study populations thus may not accu-
rately represent the reaches as a whole.
particularly for reaches 4 and 5. Trees .....ere
selected randomly within sites. after ex-
cluding trees < 15 em diameter at brea~t
height (dbh). Trees were distributed from
o to 30 m from the streambank, and 0 to 5
m above the thalweg (Table 1).
Increment cores (t\o.'o per tree) were col-
lected from 4 to 12 cottonwoods (black or
Fremont) per site. Vigor of the cored trees,
and of additional trees at each site, was
assessed by assigning each tree a canopy
vigor class based on subjective determi-
nation of the fullness of the canopy. The
classes were as follows: class 5 trees had
81-100% of potential canopy; class 4, 61-
80%; class 3, 41-60%; class 2, 21-40%; class
1. <21%; and 0 trees were dead. Although
subjective and thus subject to sampling er-

Increment Core Analysis

Increment cores were mounted and
sanded following standard methods (Fritts
1976). After cross-dating between speci-
mens. the ring widths were measured to
Ihe nearest 0.01 mm using an automated
measurement system. Ring-width chro-
nologies were generated for each tree by
laking the mean value for the two repli-
cates. Chronologies for individual trees
were then standardized to a value of I 10
remove the variance in growth due to age
(Fritts 1976). This involved fitling a curve
or straight line to each chronology and di-
viding the actual annual ring width by the
values generated from the curve. Reach
chronologies were gent:'rated by averaging
the standardized chronologies for all ma-
ture (>20 years) trees.

Statistical Analysis

Mean sensitivity of the ring chronolo-
gies (a measure of the year-to--year varia-
tion in growth; Fritts 1976) was calculated
for each reach. Correlation coefficients be-
tween ring chronologies were determined
among all trees within each reach as a mea-
sure of the between-tree commonalitv in
annual growth pattern. Correlation coef-
ficients .....ere also determined betv.'een
reach chronologies as a measure of the

Instream Flow-l
DlVerud Reaches
three diverted re

I.... ·
..~-

January 1991

I J. c. Strom bel

RiveN' Volume 2, Number 1