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A Method for Evaluating Streamflow DischargePlant Species Occurrence Patterns on Headwater Streams1
Richard R. Harris, Roland J. Risser and Carl A. Fox 2
Abstract.--On headwater streams proposed or developed
for hydroelectric projects, hydrologic simulation modeling
(Instream Flow Incremental Method) can be used in conjunction with vegetation sampling to assist in the evaluation of instream flow requirements for riparian plant
species. Field studies on the western and eastern slopes
of the Sierra Nevada have been undertaken to test the
method and have shown promising results.
INTRODUCTION
procure vegetation data for analysis, a sampling
method was devised for collecting information on
species' distributions along IFIM transects
(hereafter referred to as "belt transect
sampling"). Two streams in the Sierra Nevada
have been sampled to test the procedure.
The objective of this research was to
develop a procedure for sampling and analyzing
riparian vegetation occurrence along headwater
streams. Such a procedure is needed for
determining vegetation instream flow
requirements on streams proposed for or
developed as hydroelectric projects.
METHODS
Studies in other regions suggest that the
positions of plants on riverine floodplains are
related to the frequency, intensity, and
duration of flooding (Bell 1980; Hack and
Goodlet 1960; Hupp 1982). When natural flooding
characteristics are changed due to streamflow
diversions, species may be affected differently,
depending on their positions on stream
floodplains.
Study Site Location
Three reaches on the North Fork Kings River
(NFKR) located on the west slope of the Sierra
Nevada, California, were sampled during the
summer of 1984. Three additional reaches on
Bishop Creek on the east slope of the Sierra
Nevada were sampled during the fall 1984. The
NFKR is essentially an unregulated stream within
the reaches sampled and it experiences periodic
overbank flooding. Bishop Creek is regulated by
dams and hydroelectric diversions which
eliminate most flood peaks.
Fisheries biologists have recognized the
need for assessing the instream flow
requirements of resident fish life. The
Instream Flow Incremental Method (IFIM) (Trihey
and Wegner 1981) in conjunction with the IFG-4.
computer model (Mi1hous et a1. 1984), meets this
need and also provides the requisite physical
and hydrologic data for evaluating plant species
distributions in response to streamflow. To
Field Sampling
IFIM transects are placed in areas
representing "characteristic" fish habitat
conditions in a reach (Trihey and Wegner 1981).
Topography along each transect is measured at
small intervals « 1 meter) using an engineer's
transit and stadia rod. Streamflow measurements
are made along the transect during three flows;
usually the lowest and highest possible, and at
intermediate discharge levels. The objective is
to collect data for each transect to allow
computerized calculations of roughness,
velocity, and water surface elevations for
discharges of various magnitudes. Simulation
modeling establishes the elevation of the water
across each transect at various streamf10ws.
The method is further described in Trihey and
Wegner (1981) and Mi1hous et a1. (1984).
1Paper presented at the North American
Riparian Conference. [Tucson, Arizona, April
16-18 1985].
2Richard R. Harris is Assistant Professor
of Plant and Earth Sciences, University of
Wisconsin, River Falls, WI; Roland J. Risser is
Biologist, Pacific Gas and Electric Company,
San Ramon, CA; Carl A. Fox is Senior Research
Scientist, Southern California Edison Company,
Rosemead, CA.
87
Belt transect sampling over established
IFIM transects was performed after floodplain
topography had been surveyed. The rooted
location of all plants on the floodplain was
recorded within a belt 3 meters wide centered on
the IFIM transect line. Plant positions were
recorded as the cumulative distance from the
starting point of the transect to the nearest
0.1 meter. These data established the position
of each plant with respect to distance from the
stream, elevation above the stream, and
simulated discharge level.
On NFKR, only data on plant positions were
collected. The sampling procedure was modified
at Bishop Creek to collect auxiliary data on
light (percent canopy closure over plants),
rooting substrate, channel geometry and
groundwater influence.
2.
Species flooded at relatively low
discharge, frequently and/or for a
long duration. Juncus nevadensis,
Care x spp. and HeIeDIUm Bige10vii
represented this condition.
3.
Species flooded at intermediate
discharges or those whose bimodal
distribution causes them to be flooded
at both extremes. Six of the 12
species analyzed represented this
condition.
The work at NFKR indicated that each of
three different flooding environments had a
characteristic complement of plant species.
Within these environments, the effects of other
environmental conditions on plant occurrence
could not be evaluated because relevant data
were not available at time of the analysis.
Analysis Procedures
To analyze species' distributions across
all transects, the position of each plant was
calculated as the proportional horizontal
distance from the thalweg (lowest point of the
stream channel bottom) to the end of the ha1ftransect on which the plant occurs. Using
mUltiple analysis of variance, each species
distribution above and horizontally away from
the thalweg was compared to that of all other
species. The frequency distribution of each
species by simulated discharge class was also
evaluated.
Bishop Creek
A total of 60 IFIM transects were sampled
on Bishop Creek. Analysis of plant speciesdischarge relationships indicated no
differentiation of species by simulated
discharge class. This may be a consequence of
the fact that the modeled discharges were all
within the channel banks and that plants
dependent on streamflow were aggregated near the
banks. Plants rooted at greater distances could
not be directly affected by streamflow because
no overbank discharges were modeled and none
appeared to occur on this controlled stream.
Ko1mogrov-Smirnov two sample tests (Soka1
and Rohlf 1981) were used for the latter
analysis under the null hypothesis of no
significant differences between the species.
Differences were considered significant at
p 0.01. The procedure for statistical analysis
of environmental data from Bishop Creek (other
than streamflow) has not yet been defined.
Interested readers should contact the senior
author for further information.
These results led to an exploratory
analysis of the data to determine the effects of
other environmental factors on species'
occurrence patterns. Although this analysis has
not been completed, preliminary results indicate
that some species were associated with specific
environmental conditions. For example, Rosa
woodsii and Populus tremu10ides appear to De
associated with incised channels. Artemesia
tridentata, a dry land species, did not occur on
transects where groundwater influence was
evident. Other species appeared to be
associated with specific light or substrate
conditions.
RESULTS
NFKR.
Vegetation data were collected along
22 IFIM transects at NFKR. Occurrence patterns
of the 12 most frequently encountered riparian
species were analyzed. Statistical analysis
confirmed three types of riparian plant
distributions in relation to stream discharge on
NFKR:
1.
To fully evaluate species' responses to
environmental conditions at Bishop Creek, a
multivariate analysis will be undertaken in the
next phase of this research. For the present,
it is tentatively concluded that within a
specific zone of flooding effects or on
controlled streams, plant species may
differentiate along environmental gradients
other than those associated with flooding.
Species flooded infrequently, only at
high discharge, and with a short
duration. Rhododendron occidenta13 ,
Fraxinus 1atifo1ia and Alnus
rhombifo1ia represented this condition.
DISCUSSION
Alterations in instream flow often result
from hydroelectric development. The effects of
these alterations on riparian vegetation may be
manifested in terms of changes in the
distributions and characteristics of plant
3 Nomenclature follows Munz (1975)
88
species on the floodplain. A study of existing
diversions on headwater streams of the western
Sierra Nevada disclosed two different general
responses to diversion (Harris and Risser in
preparation). Some streams were observed to
have increased riparian species cover,
apparently due to reduced destructive effects of
flooding. Other streams were observed to have
decreased riparian species cover, presumably due
to induced soil moisture stress. Utilization of
IFIM data allows an analysis of the directional
response of plant species which may improve our
understanding of overall vegetation effects.
For impact assessment on streams proposed
for diversion, two levels of vegetation data are
required: 1) General habitat conditions need to
be described (e.g. vegetation characteristics,
subtrate, gradient). This type of data may be
obtained through extensive, rapid survey
techniques. 2) Plant distribution vis-a-vis
topography and discharge should be analyzed.
Belt transect sampling is suitable for
collection of this type of information.
An integrated instream resource inventory
method would include both techniques. Rapid
survey techniques could be used to generally
characterize the riparian vegetation on a
stream. Only vegetation data would be
collected. Collection of topographic data could
be reduced to classification of floodplain cross
sections to allow later correlation with IFIM
modeling results.
The distribution of riparian plants can be
interpreted as species' responses to ecological
conditions within the floodplain. If it is
assumed that flooding is the dominant
controlling variable on unregulated streams,
species most tolerant to flooding will be found
in relatively high abundance in lower discharge
classes. Areas closer to the thalweg are often
too disturbed by flooding for most plants to
survive in abundance (Menges and Waller in
press; Harris 1985). Since lower discharges
occur more frequently, these plants are flooded
more often and for a relatively greater
proportion of the year. These species may be
adversely affected if streamflow is reduced in
such a way that they are no longer flooded
according to existing conditions. Their
abundance may decline as a result of moisture
stress, reduced reproductive potential, or
invasion by more competitive species.
Belt transects should be situated to ensure
sampling of the range of vegetation conditions
found on streams. If properly located, the belt
transects are adequate for evaluating occurrence
patterns, density, and species diversity. The
results can be used to predict impacts for the
streamside vegetation as a whole.
ACKNOWLEDGMENTS
Dr. Robert F. Holland and Virginia Dains
collected the field data used for this study.
David Hanson, EA Engineering, Science, and
Technology, Inc. and Thomas Lambert, Pacific Gas
and Electric Company (PG&E) assisted in the
interpretation of IFIM hydrologic modeling.
Phillip Dunn, Jones & Stokes Associates,
provided information on IFIM field techniques.
Jordan Lang and JoAnne Sorenson (Jones & Stokes
Associates) and Michael Fry (PG&E) provided
helpful comments on drafts of the manuscript.
Some species are most frequently found in
locations where flooding occurs only at higher
discharges. These species appear the least
tolerant of flooding. If streamflow is reduced,
these species may increase in abundance by
occupying formerly unfavorable habitats.
Species which have indistinct distributions
in relation to discharge may be relatively
insensitive, or may have equal sensitivity to
flooding effects. Intermediate locations where
these plants are located are subject to greater
variability in both frequency and duration of
flooding then either adjacent zone. Within the
intermediate zone, rising and falling water
levels result in constantly changing conditions
for plant establishment. This may help explain
the fact that intermediate locations have a
greater number of plant species. Annually, as
flooding flows occur, conditions within a given
stream reach may change, creating optimal
conditions for a different complement of species.
This research was financially supported by
Pacific Gas and Electric Company and Southern
California Edison Company.
LITERATURE CITED
Bell, D. T. 1980. Gradient trends in the
streamside forest of central Illinois.
Bulletin Torrey Botanical Club 107:172-180.
Hack, J. T., and J. C. Goodlet. 1960.
Geomorphology and forest ecology of a
mountain region in the central
Appalachians. 66 p. U.S. Geological Survey
Professional Paper 347.
The effects of light, substrate, and root
stratification may affect these generalizations. On controlled streams or within a
specific zone of flooding effects, species may
differentiate on the basis of light, substrate
or other factors. Interactions among factors
and compensatory mechanisms may exist and may
affect responses of species to increases or
decreases in streamflow. In future testing of
this method these relationships will be studied
more fully.
Harris, R. R. 1985. Relationships between
fluvial geomorphology and vegetation on
Cottonwood Creek, Tehama and Shasta
Counties, California. Ph.D Dissertation.
329 p. Univeristy of California, Berkeley,
CA.
89
Information Paper 11. U.S. Fish and
Wildlife Service. FWS/OBS-8l/43 (Revised).
Harris, R. R. and R. J. Risser. In preparation.
Characteristics of riparian vegetation at
existing and proposed hydroelectric
diversions in the western Sierra Nevada,
California.
Munz, P. A., and D. D. Keck. 1975. A California
flora and supplement. University of
California Press, Berkeley, CA.
Hupp, C. F. 1982. Stream-grade variation and
riparian forest ecology along Passage
Creek, Virginia. Bulletin Torrey Botanical
Club 109:488-499.
Sokal, R. R., and F. J. Rohlf. 1981. Biometry.
Second Edition. 776 p. W. H. Freeman and
Company, New York,
N.Y.
Menges, E. S. and D. M. Waller. In press.
Plant strategies in relation to elevation
and light in floodplain herbs. American
Naturalist.
Trihey, E. W., D. L. Wegner. 1981. Field data
collection procedures for use with the
physical habitat simulation system of the
Instream Flow Group. U.S. Fish and
Wildlife Service, Cooperative Instream Flow
Service Group. 151 p. Fort Collins, CO
Milhous, R. T., D. L. Wegner, and T. Waddle.
1984. Users guide to the physical habitat
simulation system. Instream Flow
90