CURRENT STATUS, STRUCTURE, AND PLANT SPECIES COMPOSITION OF THE RIPARIAN VEGETATION OF THE TRUCKEE RIVER, CALIFORNIA AND NEVADA

14 Pages·1998·8.3 MB·English

by  Steven L Caicco

Madrono, Vol. 45, No. 1, pp. 17-30, 1998
CURRENT STATUS, STRUCTURE, AND PLANT SPECIES COMPOSITION
OF THE RIPARIAN VEGETATION OF THE TRUCKEE RIVER, CALIFORNIA
AND NEVADA
Steven L. Caicco
U.S. Fish and Wildlife Service, Sacramento Field Office1 3310 El Camino
CA ,
Avenue, Sacramento, 95825
Abstract
Although riparian areas are a critical component ofbiodiversity in arid lands, our knowledge ofmany
major rivers ofthe western United Startes remains limited. The Truckee River ofCalifornia and Nevada
is typical, with a general lack of published data on its riparian vegetation. Cover type mapping ofeight
reaches shows that the relative proportions between natural vegetation and cultural land-use types vary.
Despite impacts from logging, railroad and highway construction, and water resource development, ri-
parian vegetation along the upper three reaches is currently dominated by native riparian species. In the
remaining reaches large proportions of the floodplain have been converted to urban and industrial or
agricultural uses, or have been disturbed and are dominated by introduced weeds. Downstream reaches
have also been more affectedby flow regulation, waterdiversions, and related impacts. The lowerreaches
also, however, offer the greatest opportunities for restoration and enhancement of the riparian corridor.
Data is also presented on the current plant species composition and structureofnatural riparian vegetation
which, inconjunction withhydrologicaldata,can helplandmanagersandbiologiststoformulatestrategies
for wildlife habitat enhancement.
Riparian areas are a critical component of bio- Truckee River drainage began in the 1860's with
diversity within the arid lands ofthe westernUnited extensive logging to provide timber to the nearby
States and their importance is amplified by the mi- mining boomtown, Virginia City, and for railroad
nor proportion of the overall area which they oc- ties and snowsheds along the route of the Central
cupy (Carothers 1977). Despite an increasing em- Pacific Railroad (California Department of Water
phasis on the ecology and management of western Resources 1991). Much of the Lake Tahoe Basin
riparian ecosystems over the past two decades (e.g., and the surrounding area was stripped of trees and
Johnson and Jones 1977; Warner and Hendrix the logs were transported by flumes along the river,
1984; Johnson et al. 1985; Knopfet al. 1988; Abell as well as down the river channel itself.
1989; Clary et al. 1992), there remains a striking Prior to the turn of the century, numerous dams
lack of published basic ecological data on many had been built at the outlets oflakes, including one
major western rivers. The Truckee River, one of at the outlet ofLake Tahoe constructed in the early
three large rivers which drain eastward from the 1870's (California Department of Water Resources
SierraNevadato sinks in westernNevadais typical, 1991). Subsequent to the passage of the Reclama-
with refereed publications infrequent and ofnarrow tion Act of 1902, the U.S. Bureau of Reclamation
focus. Papers have appeared regarding food pref- became the major developer of water projects on
erences and demographics of beaver (Hall 1960; the Truckee River. Derby Dam, downstream of
Busheret al. 1983), local flora (Savage 1973; Smith Reno, was this agency's first construction project
1984), historical avifaunal changes along the lower (Fig. 1). Completed in 1905 as partofthe Newlands
Truckee River (Klebenow and Oakleaf 1984), and Project, the dam and its conveyance canal were de-
seed germination in Salix (Martens and Young signed to transfer water from the Truckee River to
1992). arable land with little rainfall in the adjacent Carson
The Truckee River drains a 3100 km2 basin in River drainage. Irrigation water supplied by the
the Sierra Nevada into Pyramid Lake (elevation project continues to be the single largest use of
1160 m), Nevada (Fig. 1). From Lake Tahoe (ele- Truckee River water.
vation 1899 m), the river flows 174 km through As a result of this water diversion, a steep de-
steep mountain canyons and narrow valleys, passes cline in the water surface elevation of Pyramid
highly urbanized areas near the city of Reno, and Lake began in about 1910. The lake elevation
continues through high desert canyons and irrigated reached a low point in the late 1960's at about 23
agricultural land in broader valleys to its terminus. m below its pre-Derby Dam diversion level. In re-
Significant development of natural resources in the sponse, the lower eight km of the river channel
widened and incised into its floodplain, stranding
the adjacent river terraces (Born 1972; Water En-
&
1 Current Address: Portland Eastside Federal Complex, gineering Technology, Inc. 1991). Channeliza-
911 N.E. 11th Avenue, Portland, OR 97232-4181. tion of the river during the 1960's led to further
MADRONO
18 [Vol. 45
incision downstream of Wadsworth (Glancy et al. 1960). Evidence of beaver activity, primarily
1972). Since about 1990, the lake elevation has gnawed trunks, is present throughout the river cor-
been about 15 m below the pre-Derby Dam level. ridor although serious impacts seem highly local-
Federal reservoirs for water storage and flood ized.
control in the Truckee River watershed and their This study was restricted to the riparian corridor
construction dates include Boca (1937), Prosser along the 174 river kilometers of the mainstem of
Creek (1962), and Stampede Reservoir (1970), all the Truckee River from Lake Tahoe Dam to Marble
owned by the Bureau of Reclamation, and Martis BluffDam. In this paper, I present baseline data on
Creek (1971), owned by the U.S. Army Corps of the vascular plant species composition, structure,
Engineers. These reservoirs combined provide and areal extent of the existing riparian vegetation
about 317,000 acre-feet of usable storage. Numer- of this area in order to provide a framework for
ous smaller non-Federal reservoirs and diversions future ecological research.
are located in the Truckee River watershed.
Methods
In an attempt to reduce water loss due to evapo-
transpiration, beaver (Castor canadensis) were in- Terminology. Throughout this paper, the terms
troduced to the drainage in the late 1940's (Hall "riparian" and "riparian corridor" are used in the
i
1998] CAICCO: TRUCKEE RIVER RIPARIAN VEGETATION
functional sense of a "three-dimensional zone of £ 6
u Q
interaction between terrestrial and aquatic ecosys- P <+-
tems" (Gregory et al. 1991). As such, the riparian H06 <=+H
zone includes, at a minimum, the low-flow and ac- OH DMQ
tive river channels and the inferred historic flood-
plain. Because ofthe vertical component ofthe def- S|
inition, the riparian zone upstream of State Line & &.
may also include, as a minor component, lower hil- P
U, On
Islopes supportingconiferous forests. It is important XH 00
to note that "riparian" as used in this paper is not
synonymous with "wetland" in a jurisdictional
sense. In most areas downstream of Reno, and es- « £
pecially downstream of Derby Dam, flow regula- > E
tion and water diversion have altered the natural (2 c3 7o3 O_ E
hgryodurnodgwraatpehry otfabtlheesrwiivtehraandcocnosnetqruiebnuttedshtioftltoowwearredd <H«06!£O 'UoE 2- 6-« ^Ontto—nic<Nn—m<-—^irm^
a less hydrophytic vegetation. As noted earlier, this <U
effect has been most profound in the lower eight
km of the river upstream of Pyramid Lake.
Cover type mapping. The 174 km river corridor 9 J
was subdivided into eight reaches based on mor-
o ^OOONrnOOt^(N O
phological, geological, and hydrological character- O '|JJ3 -h ri m in ^ id tJ- r»
istics. The reaches vary in length, stream gradient, < Q,
floodplain area, and the ratio between floodplain
w 9c3
ainrdeiacaatnodr rofeacthhelleoncgatlh c(oTnasbtlreain1t)s. Tihmeposlaetdteronistahne HQ TO3
channel and valley floor by geomorphic features
and, by extension, the width ofthe riparian corridor < ° OO oo h ^ ri \C mh (N
(Gregory et al. 1991). Natural vegetation and land <i - cn on rJ r- tj- vo <—
use types within the riparian zone were mapped on a
acetate overlays of enlarged black-and-white aerial
photography at a scale of 1:1200. Source photos for
these enlargements were flown on November 4, w8^^5
1991; the scale ofthe original photos was 1:12,000.
CTwohavseemartilnteyiapsmetusmpioxmlatyrpgepoenissn(gaswcerdrieetfeirnmieoadnnubfaoerlllofywo)redsientleiadnnetaytaperede.sa I06f> so«> °0<£3u CC Orr(fvjjO4N0r—<04no—^cooDoi oo0on0o^(OoNNmvt»qmJr—<-ini(o<-Ndnh qor(rN-n
of 0.2 ha. The overlays were scanned into AUTO- it
bCyApDolayngdona.reAarsewaseraedjcaaclecnutlattoe,dafnodreenarcohutceovteor, ftiyepled QW 2™
sample sites were field checked for boundary and o s
cclaaussseifiocfatiionntearcprceutraatciyonanddiffriecvuilstieeds,acscoormdeingnloyn.-fBoer-- > 8 43 rOoOmjmOrc^n—hHoT^frN^ oooq
ested areas outside of the historic floodplain may
have been incorrectly included. These inaccuracies O <D
are believed to have resulted in only minor over- <> W«Ds
estimates of the extent of the riparian zone down- 3 1
stream of Reno.
tioDnatanadcoalbluenctdiaonn.ceDawteareoncoplllaencttesdpeocnileysfcroommponsait-- az< -o0a3
uarlaolngve3g1etatrtainosnecttyspeast, e11xcseipttesi.ngSimtaersswheerseacnhdopsoenndst,o UXH £' ' JCOS X
be representative of general conditions with the a cI/3 £ O
study reaches and to isolate, to the extent possible, " u< ™ o3 cd d
river hydrology as a controlling variable for vege- 06 UJ
tation from other hydrological influences (e.g., ir- * Q
rgiagtaitoendcpaansatlusr,esspraibnogvse, csheawnangeelebfafnlkuse,nturnulnionfefd, iarnrid- ^. OB0 e. c —
tsiiognnailficcaonntstrgariandtinwgasanrdelafitlilveplparcoexmiemnitt)y. tAonstardedaim- H 2 iO«—jSI C0OQ3 51 c33 Heg
MADRONO
20 [Vol. 45
gages so that channel hydraulics could be calculat- also reflected in the river gradient which generally
ed in order to relate flow rates to topographic in- decreases from Lake Tahoe to PyramidLake. There
undation. Areas with extensive recent activity by is a corresponding general increase in the width of
beavers were avoided, as were areas of recent log- the riparian corridor. Exceptions to this trend occur
ging or fuelwood cuttings. The transects were ori- in the State Line-Vista and Dead Ox-Numana Dam
ented perpendicular to the river channel and varied reaches, where theriverpasses throughnarrowbed-
in length according to the width of the riparian rock canyons.
zone. A total length of 3380 m was sampled. Data
were collected by structural layer according to the Cover type mapping. Four major categories of
following def—initions and procedures: aquatic ecosystem, natural vegetation, and cultural
Tree layer. Single- or multiple-stemmed woody types were mapped (Fig. 2). These include: 1) the
plants > 6 m in height and >10 cm diameter-at- active channel of the river including the low-flow
breast height (dbh). Data were collected on dbh and wetted channel; 2) riparian forest andriparian shrub
density within 15 m of the transect (i.e., a 30 m communities on the floodplain; 3) cultural types on
belt transect). Standcanopy coveragewasestimated the floodplain; and, 4) upland forest and upland
by species at random locations along the transect shrub communities. The boundaries ofthe low-flow
using a spherical densiometer. Average stand can- wetted channel were based on the area covered by
opy height was e—stimated using a clinometer. water on the November 4th date of the aerial pho-
Shrub layer(s). All woody plant species < 6 m tographs. Also occurring within the active channel
in height or < 10 cm dbh. Canopy coverage was were sparsely-vegetated cobble bars and patches of
estimated visually along each transect using the graminoids and herbs, here referred to as the veg-
line-intercept method (Mueller-Dombois and Ellen- etated streambed. There is a dynamic relationship
berg 1974). Data were collected in three height among these three elements of the active channel.
classes: tall shrubs (>3 m), medium shrubs (>1 m The boundaries ofthe low-flow wetted channel ex-
and <3 m), and low—shrubs (<1 m). pand and contract in response to annual climatic
Herbaceous layer. Non-woody species includ- variation, and water regulation or diversion. Chan-
ing herbs, grasses, and graminoids. Canopy cover- nel scour during high flows leads to an increase in
age visually estimated by species using the line- the amount ofcobble bars. Conversely, the absence
intercept method. — of scouring flows results in an increase in the total
Ground surface. Ground surface data on brush- area of vegetated streambed. Because this study
piles, litter, and bare ground was tallied using the was conducted during the sixth consecutive year of
line-intercept method. Bare ground was further re- drought, the ratio ofvegetated streambed within the
corded as clay, sand, gravel, cobbles, or boulders. active channel was greater than normal, when com-
Other information collected included site eleva- pared to either the cobble bars or the low-flow wet-
tion (taken from topographic maps), transect ori- ted channel. Overall, the active channel comprises
entation (measured from aerial photos), currentland about 25% of the riparian corridor, although in the
use, and evidence ofrecent disturbance (e.g., graz- steep, narrow canyons which characterize the Lake
ing, beaver activity). The taxonomic reference for Tahoe-Boca and Dead Ox Wash-Numana Dam
all plant scientific names is Hickman (1993). reaches, this value increases to 51% and 38%, re-
spectively (Fig. 2).
Data analysis. The areal coverage of individual Riparian forest and riparian shrub communities
vegetation and land use types was calculated by
occur on the floodplain ofthe riverin most reaches.
reach. Vegetation datafrom the transects were sum- Deciduous riparian forests comprise between 2%
marized for transect segments stratified by physi- and 20% ofthe riparian corridor upstream ofReno,
ognomic type (forest, shrub, herbaceous). Each seg- with the lowest percentage occurring above Boca
tmyepnet. wTahse ttroetaaltedofas17a8ssaammpplleesofwietrsephsyusbijoecgtneodmitco (Fig. 2). Downstream ofReno, the range is narrow-
TSPwAoN-)w,aya hiIenrdairccahtiocral cSlpaescsiifeiscatAinonalpyrsoicsedu(rTeW(IHNil-l einr t(h6e%Dteoad18O%x),-NaulmthaonuaghDnaomrirpeaarcihan(Ffiogrse.st2,oc3)c.urAs
1979; Gauch and Whittaker 1981); theTWINSPAN similar pattern is seen in the riparian shrub com-
munities. Upstream of Reno, riparian shrub com-
output was further refined based on the field ex- munities comprise 22% to 28% of the riparian cor-
perience and professional judgement of the inves-
ridor (Fig. 2). Downstream of Reno, riparian shrub
tigator. communities comprise 5% to 14% of the riparian
Results corridor (Figs. 2, 3).
Cultural types were defined to include agricul-
Physical characteristics. Physical characteristics tural fields and facilities, urban and industrial areas,
of each of the eight reaches are provided in Table sites dominated by the noxious weed Lepidium la-
1. The disparity in reach lengths is due to the va- tifolium, and other disturbed areas. The proportions
riety of geologic and topographic settings through of the riparian corridor occupied by these habitats
which the Truckee River passes along its course is low to moderate (7%-29%) in the upper three
from the Sierra Nevada to Pyramid Lake. This is reaches, high (45-60%) in the middle threereaches,
1998] CAICCO: TRUCKEE RIVER RIPARIAN VEGETATION 21
Lake Tahoe to Boca Boca to State Line
(37km/166 ha) (21 km/207 ha)
Low-FlowChannel 39% Low-FlowChannel 23%
VegetatedStreambed 6% Vegetated Streambed/ Ider-WillowShrub 22%
Cobble Bars 6% Cobble Bars 1%
Disturbed 3%
Urban/Industrial 4% Marshes 1% Agricultural 16%
Upland Shrub 10%
Mixed Pine 9%
Upland Shrub Alder-WillowShrub 28% Disturbed 9% Mixed Pine 4%
Black Cottonwood 2%
Black Cottonwood 16%
State Line to Vista Vista to Derby Dam
(37 km/394ha) (27km/538 ha)
FremontCottonwood 6%
Vegetated Streambed/Cobble Bars Peppergrass 23%
Low-FlowChannel 23%
Agriculture 16%
Upland Shrub 10%
Disturbed 11%
Urban/Industrial 7% WillowShrub 6%
WillowShrub 23% Cobble Bars 2% Urban/Industrial 7%
Disturbed 6%
Low-FlowChannel 14%
VegetatedStreambeds 3% Agriculture 18%
FremontCottonwood 8% Mixed Pine/UplandShrub
Black Cottonwood 12%
Fig. 2. Percentages of vegetation, aquatic, and land-use types for the upper four study reaches along the Truckee
River. The length and area ofriparian corridor is provided for each reach in parentheses.
and moderate (29-33%) in the lower two reaches Populus trichocarpa ssp. balsamifera, with 80%
(Figs. 2, 3). canopy coverage, is the dominant tree species in
Mixed pine communities occur on lower hillslopes deciduous riparian forests along the upper three
adjacent to the floodplain only along the upper reaches (Table 2). A tall shrub layer with 15% cov-
three reaches where they comprise 2% to 9% ofthe er, dominated by Salix lutea, is present. The only
riparian corridor (Fig. 2). Upland shrub communi- other riparian shrubs present are S. exigua and sap-
ties occur on the floodplain in all reaches where lings of P. trichocarpa ssp. balsamifera, each with
they account for 2% to 10% ofthe riparian corridor, only a few percent cover. Minor amounts ofupland
except along the lower two reaches where they shrubs also occur in this type. The understory is
comprise 18% and 28% of the corridor (Fig. 3). dominated by Elymus trachycaulus and Poa pra-
Marshes and ponds occur in several reaches, but tensis with 19% and 14% coverage, respectively.
they never account for more than 1% in any reach Conium maculatum and Urtica dioica are the dom-
in which they occur (Figs. 2, 3). inant herbaceous species.
Species composition and abundance. The results Both Populus trichocarpa ssp. balsamifera and
of the TWINSPAN analysis supported distinctions P. fremontii ssp. fremontii (Fremont cottonwood)
between groups of samples of riparian forest, ri- dominate individual deciduous riparian forest
parian shrub, vegetated streambed and cobble bar patches in the State Line-Vista reach, although no
communities based on their occurrence upstream or mixed stands of these species as canopy dominants
downstream of Reno (Tables 2, 3). Upstream of were observed. Downstream of this reach, P. fre-
Reno samples correspond roughly to the upper montii, with 70% canopy coverage, is the sole dom-
three study reaches, while samples downstream of inant tree in the riparian forests (Table 3). There is
Reno correspond to the lower five study reaches. a conspicuous dearth ofriparian shrubs in these for-
Upland shrub communities showed no such dis- ests, where tall shrubs of P.fremontii provide only
tinction, perhaps due to the infrequent occurrence about 8% cover. Artemisia tridentata ssp. tridentata
of this type along transects upstream of Reno. Up- is present in small amounts, and there is a sparse
land mixed pine forests occur only along the upper understory of Elymus trachycaulus and Lepidium
three reaches. latifolium.
MADRONO
22 [Vol. 45
Derby Dam to Wadsworth Wadsworth to Dead Ox Wash
(18 km/403 ha) (6.2km/505 ha)
Vegetated Streambeds/Cobble Bars Vegetated Streambeds/Cobble Bars
13%
Agriculture 42%
Low-FlowChannel 10% LoMwa-rFslhoews/CPhoanndnsel16%%
Agriculture 28%
WillowShrub 11% WillowShrub 14%
Urban/IndDuissttruiralbed1%9% UplandShrub 8% Disturbed 2% Upland Shrub 9%
Peppergrass 8% Peppergrass 15%
Fremont Cottonwood 11%
Fremont Cottonwood 12%
Dead Ox Wash to Numana Dam Numana Dam to Marble Bluff Dam
(11 km/73 ha) (11 km/422ha)
Vegetated Streambeds 3% Vegetated Streambeds/Cobble Bars
Cobble Bars 8% Low-FlowChannel 27% 17%
Low-FlowChannel 6%
Agriculture 28% Marshes/Ponds 1%
WillowShrub 5%
Peppergrass 29% WillowShrub 18%
Upland Shrub 28% P„eDpipsetrugrrbaesds32%s/
Upland Shrub 18%
FremontCottonwood 8%
Fig. 3. Percentages of vegetation, aquatic, and land-use types for the lower four study reaches along the Truckee
River. The length and area ofriparian corridor is provided for each reach in parentheses.
A shift occurs in the dominant species of the ri- alba are the most abundant associated species. Cob-
parian shrub communities which corresponds to ble bars are only sparsely vegetated in all reaches,
that seen in the riparian forest, although the tran- but still differ distinctly in species composition.
sition is more gradual. Upstream of Reno, tall and Upstream of Reno, Carex utriculata and Glyceria
medium height shrubs of Alnus incana ssp. tenui- striata are the most abundant species (Table 2).
folia dominate this community, although numerous Downstream ofReno, the most abundant species on
o2)t.heAr rwiipdaeriavnarisehtryubosftgyrpaiscsaelsl,ygorcacmuirnowiidtsh,iatn(dTahbelre- cobUbplleanbdarfsoriessLtsepaildoinugmthleatuipfpoleirumth(rTeeabslteud3)y.reach-
baceous plants make this the most diverse ofall the es are generally comprised of mixtures of Abies
hmaubcithatlsesisnvceostmimgaotned.doAwlnnsutsrienacmanoafsRsepn.ot,enwuhieforleiathies concolor, Pinusjeffreyi, and P. contorta ssp. mur-
rayana, although pure stands of the latter species
dominant species in the riparian shrub community can be found. Populus balsamifera ssp. trichocarpa
ilsowPopsutlatuusrefre(mToanbtliei 3s)s.p.Nfuremmeornotiuisofotmheerdiruimparainadn loacncdursshirnufbrseqcuoemnptlryisien atbhoesuet f2o6re%stsco(vTearbalgee,2).whUipl-e
shrubs are associated with this type, and there is a
grasses and graminoids dominate the understory.
well-developed grass, graminoid and herbaceous
layerdominated by Lepidium latifolium with 21.8% Upland shrub communities are the predominant
coverage. vegetation adjacent to the riparian corridor along
Vegetated streambed communities in the upper the five lower reaches, where they occasionally ex-
three reaches were dominated by Poapratensis and tend onto the floodplain. Artemisia tridentata ssp.
Elymus trachycaulus, with 10.7% and 9.4% cov- tridentata is the dominant species in this commu-
erage, respectively (Table 2). Carex aquatilis and nity (Table 3). The most abundant associated shrub
C. utriculata are common associates. Downstream species are Chrysothamnus viscidiflorus and Shep-
of Reno, vegetated streambed communities are herdia argentea. Associated grasses include Ley-
dominated by Eleocharis acicularis and Lepidium mus cinereus and Bromus tectorum. Because this
latifolium with 29.4% and 29.8% coverage, respec- study was conducted during the sixth consecutive
tively (Table 3). Scirpus americanus and Melilotus year ofdrought, the abundance ofthe latter species
1998] CAICCO: TRUCKEE RIVER RIPARIAN VEGETATION 23
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1998] CAICCO: TRUCKEE RIVER RIPARIAN VEGETATION 25
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