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

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rom J to 5), annual
It annual variation

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th Mean
St'nsilivity

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5 38!; 18
9 34 !; 18
B 34 :! 7
3 491:.29
6 36:! 8
3 47 =: 9
~ 29 !; 6
r 49 =- 10
) 35::!: 8
3 39 ... 15

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:r 2.50"1
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FIGURE 3. Ring-width chronologirsofPop.
UlU5 frt'montii (PH ~nd P. trichourp.. 1FT)..'
divtrtrd rt'..ches fA' ..nd,J supplemrntt'd-flow
rneh (H} on Bishop Crt't"k.

ith volume of flow
In explaining most
40% for the influ-
% (or the two cot-
ffluent reach). An-
(plained as much
; season flow, be-
I during the grow-
nodels for reach 2
reach 4 Fremont
d on three vari-
Jwing season, pri-
lverage maximum
growing season.
n 4 black cotton-
\ont cottonwoods

were based, respectively. on two variables:
growing season flow and average maJo:.i-
mum May temperature, and growing sea-
son flow and prior.year ring width. Models
based exclusively on abiotic variables (i.e.,
excluding prior.year ring width as a vari.
able) explained a smaller amount of the
variance in growth (51-70%). but had high
significance (P < 0.001).
Although instream models differed
somewhat beno.'een reaches, between-reach
verification statistics had relatively high
significance (r values from 0.68 to 0.85. P
< 0.001). Within-reach verification statis-
tics also had high significance (r "" 0.87. P
< 0.001 for reach 2; r = 0.85. P < 0.001 for
reach 5). The predicted values closely
tracked actual values over most of the pe-
riod (Figure 5).

Supplementt'd-flou' Reach. Growth of cot-
tonwood trees at the supplemented-flow
reach fluctuated annuall\'. but showed low
correspondence to annual patterns for the
diverted reaches (Figure 3). The ring-width
chronology for the reach was generally not
highly correlated with ring.width chro-
nologies for the diverted reaches, and
chronologies were not significantl~' cor-
related between trees within the reach (Ta-

Qt Bishop Creek"

5 Reach 6
) (POFR)
0.33'
0,15
0.57<
0.29
-0.03
h.

January 1991

I J. C. Stromberg and D. T. Patten

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OISCHARGE(_J)
FIGURE 4. RegrHSion IinH rel~ting ~nnu~l
volume oE stre~mnow in the 8rowing se~son
to 5t~nd~rdized ring widths oE Populus fre-
montH IPf} ~nd r. trichourp. IPT} ., thru
di"'uted re~(hes on Bishop Creek. fqu~tions
~re: y - 0.90 + 1.45 x 10..... R' - 0.70, P <
0.001, PT-f"('~(h 4; '" - 0.59 + 224 x 10...., R'
... 0.-17, P < 0.001, 'pF-re~(h 4; y - 0.74 + 0.99
. 10 't, R' - 0.40, P < O.OOZ. PF-re~ch 5.

.
00"
o

ble 3). Average chronology for the reach
shows gro.....th peaking in some .....et years
(e.g.. }978, 1986) but not in others (e.g..
1969). A few trees showed reduced growth
in \-'ery wet years (e.g., 1969). A significant
model predicting annual tree growth could
not be developed for the supplemented-
!low reach because annual growth was not
significantly related to streamflow (RZ =
0.04) or other variables (e.g.. temperature).

Growth-Vigor Relationships

Canopy vigor sho.....ed a significant cur-
vilinear relationship with gro.....th rate over
the last 10 or 20 years or the life span of
the tree in all diverted reaches (Figure 6).
A significant positive relationship also was
evident between site canopy vigor (CV)
and site ring width (RW) for Bishop Creek
as a .....hole (CV = 0.034 + 1.547(RW]
-0.130[RW~); R: = 0.85). The percentage of
dead trees on site (,\1") increased with
stand age (A) and decreased with age-ad-
Justed ring width (M "" 5.114 ... 0.789[A)
-6.273[R~"""]; R~ = 0.64). Trees with
"healthy" (class 5) canopies generally had
>4 mm annual ring width at lo.....er ele-
vations (reaches" and 5) and >3 mm ring
.....idth at higher elevations (reach 2). Sev-
eral trees in influent reach 5 had class 5
canopies and high growth rates. but many
had lo.....er values and growth for the reach
as a whole was <4 mm/vear. Few trees in
reaches 2 or 4 had high- values for either
growth or canopy vigor (Figure 6), and an-

7 II~_