Advancing the Fundamental Sciences
Proceedings of the Forest Service
National Earth Sciences Conference,
San Diego, CA, 18-22 October 2004
In October 2004, the Forest Service
convened a national conference for
earth scientists in San Diego, CA.
The conference was attended by
nearly 450 Forest Service earth
scientists representing hydrology,
soil science, geology, and air. In
addition to active members of the
earth science professions, many
retired scientists participated in the
conference. The various technical
and scientific talks presented at the
conference reflects the collective
knowledge, experience, and future
potential of earth scientists in the
Forest Service.
The publication, Advancing the
Fundamental Sciences:
Proceedings of the Forest Service
National Earth Sciences
Conference, San Diego, CA, 18-22
October 2004, is a lasting product of
the conference and reflects the work
of various authors, reviewers, and
editors (figure 1). It captures an
invaluable week of technical and
scientific presentations, keynote
addresses, and short courses and
demonstrates the depth and breadth
of earth science expertise that exists
in the Forest Service. The contents of
the proceedings represent a unique
blend of various physical science
disciplines and showcase the work of
multiple generations of Forest
Service scientists; from retirees to
young scientists just beginning their
careers.
This two-volume publication
includes 60 peer-reviewed technical
papers and 81 abstracts of posters
presented at the conference. The 60
papers are organized into five major
themes or sections:
1) A p p l i e d S c i e n c e a n d
Technology.
2) Experimental and Research
Watersheds.
3) Watershed Protection and
Restoration.
4) Valuing the Earth Sciences.
5) Partnership and Collaboration.
Each section includes numerous case
studies conducted by various earth
scientists working on national
forests, providing a range of
perspectives and approaches to
addressing land-management issues
and advancing our understanding of
physical processes.
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Fort Collins, Colorado.
STREAM is a unit of the Watershed,
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CONTRIBUTIONS are voluntary
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IN THIS ISSUE
• Proceedings of the
2004 Forest Service
National Earth
Sciences Conference
• Homogenization of
Regional River
Dynamics by Dams
and Global
Biodiversity
Implications
Section 1, Applied Science and Technology,
contains 21 papers that discuss the application of
various earth science disciplines to address issues
related to fire and smoke, watershed management,
and surface water and groundwater. Section 2,
Experimental and Research Watersheds, contains
six papers that discuss the importance of
experimental and research watersheds on national
forests to better understand fundamental hydrologic
and biogeochemical processes and their linkages
with geology, soil, vegetation, climate, and landmanagement practices. Section 3, Watershed
Protection and Restoration, contains 12 papers that
demonstrate how resource specialists are
implementing and monitoring best management
practices for different land-management activities
and restoring impaired streams and watersheds.
Section 4, Valuing the Earth Sciences, consists of
14 papers documenting various studies of soil,
Figure 1B. Cover of Volume 2 of the Proceedings. Photos counterclockwise from the upper left
corner are: (1) The Rio Chama, Santa Fe National Forest, NM. (2) Salmon River, Mount Hood
National Forest, OR. (3) Pawnee Buttes, Pawnee
National Grassland, CO. (4) Kayakers on the
Cossatot River, just outside the Ouachita National Forest, AR. (5) Refuge Lake in the southern High Sierra, CA.
geology, air, and water occurring on the diverse
landscapes of the national forests. Section 5,
Partnership and Collaboration, contains seven
papers showing the importance of developing
partnerships, building relationships, and
collaborating with communities and organizations
to help the Forest Service manage and protect
national forest resources.
Figure 1A. Cover of Volume 1 of the Proceedings.
Photos counterclockwise from the upper left corner are: (1) Fridley Run, George Washington and
Jefferson National Forest, VA. (2) Dolores River,
Uncompahgre-Gunnison National Forests, CO.
(3) Quartz Creek, Clearwater National Forest, ID.
(4) Hubbard Glacier terminus, Tongass National
Forest, AK. (5) Island Lake and Fremont Peak,
Bridger-Teton National Forest, WY.
Included with the two-volume proceeding is a
multimedia CD containing many of the plenary
talks and two of the short courses given at the
conference (figure 2). For those attending the
conference, the keynote speaker talks provided a
historical perspective of the Forest Service,
presented thought-provoking new ideas and
concepts for managing national forest resources,
and discussed the continued need for proper
Figure 2. The introductory screen to access the electronic presentations of many of the plenary talks given
and two of the technical workshops conducted during the conference. The CD also contains digital reprints
of the 60 papers and 81 abstracts of posters presented at the conference and contained in the two-volume
proceedings.
stewardship and management
of the unique
physical resources on Forest Service lands. For
those who could not attend the conference, the
electronic presentations allow them to watch the
plenary talks and short courses and learn about the
concepts, ideas, and recommendations presented by
the various speakers.
The format of the CD provides for interactive
access: individual plenary talks or short courses can
be watched from start to finish or just parts of the
presentation of interest can be viewed. A help
screen is available from the home page to assist
with navigating the presentations. The CD also
contains digital reprints of papers and abstracts
presented in the two-volume proceedings. The CD
runs on computers using Windows or Macintosh
operating systems. The contents of the CD can also
b e
v i e w e d
o n l i n e
a t
http://www.stream.fs.fed.us/afsc. The multimedia
CD was produced by Mike Furniss, Pacific
Northwest and Southwest Research Stations, and
Jeff Guntle, Pacific Northwest Research Station.
Hardcopies and companion CD of Advancing the
Fundamental Sciences: Proceedings of the Forest
Service National Earth Sciences Conference, San
Diego, CA, 18-22 October 2004 can be obtained by
placing an order to the Pacific Northwest Research
Station by telephone (503-808-2138), facsimile
(503-808-2130),
or
e-mail
(pnw_pnwpubs@fs.fed.us). An electronic copy of
proceedings can also be downloaded online at
http://www.fs.fed.us/pnw/publications/pnw_gtr689.
The citation for this publication is: Furniss, M.;
Clifton, C.; Ronnenberg, K. eds. 2007. Advancing
the Fundamental Sciences: Proceedings of the
Forest Service National Earth Sciences Conference,
San Diego, CA, 18-22 October 2004. Gen. Tech.
Rep. PNW-GTR-689. Portland, OR: U.S. Forest
Service, Pacific Northwest Research Station. 577 p.
Homogenization of Regional River Dynamics by
Dams and Global Biodiversity Implications
by N. LeRoy Poff, Julian D. Olden, David M. Merritt, and David M. Pepin
The construction and operation of more than
45,000 large dams (heights greater than 15 m)
worldwide during the 20th century (World
Commission on Dams, 2000) has severely altered
the global flux of water and sediment throughout
the world’s river basins (Syvitski et al., 2005).
From an ecological perspective, the fragmentation
of river corridors by dams (Nilsson et al., 2005)
and the associated modification of fluvial processes
and streamflow dynamics pose significant threats
to native river biodiversity (Power et al., 1996; Poff
et al., 1997; Bunn and Arthington, 2002; Postel and
Richter, 2003). The numerous negative effects of
individual dams on individual river ecosystems are
well documented (Collier et al., 1996; Magilligan
and Nislow, 2005; Graf, 2006); however, an
important, unresolved question is whether the
cumulative effects of dams are diminishing
regional-scale variation that helps maintain broader
patterns of native biodiversity (Pringle et al., 2000).
This question can be addressed quantitatively for
the United States (U.S.) because long-term,
spatially extensive, and high quality daily
streamflow records exist that allow natural
disturbance regimes to be characterized in an
ecologically meaningful manner.
regional precipitation and river runoff that have
occurred over the 20th century (Lins and Slack,
1999; McCabe and Wolock, 2002).
A broad consensus has emerged over the last 10
years among ecologists that the function of riverine
ecosystems, and the evolutionary adaptations of
resident biota, are often dictated by the dynamic
nature of a river’s natural disturbance regime. By
strongly modifying natural flow regimes, dams
have the potential to reduce these natural regional
differences and thus impose environmental
homogeneity across broad geographic scales.
Many techniques have been developed to
characterize the statistical properties of a river’s
flow regime for ecological study (Richter et al.,
1996; Olden and Poff, 2003). Likewise, ongoing
monitoring of free-flowing rivers allows the effects
of river regulation on regional disturbance regimes
to be distinguished from the natural range of
variation associated with climate-driven changes in
In this article, we focus on third- through seventhorder rivers, which comprise over a quarter of the
total stream channel kilometers in the U.S. Using
river disturbance theory (Poff et al., 1997; Resh et
al., 1988), we defined flow regimes in terms of
magnitude, frequency, duration, and timing of
ecologically relevant flows, expressed both as longterm averages and interannual variation. For 16 a
priori defined ‘‘hydroregions’’ across the
continental U.S., we used a total of 186 long-term,
daily streamflow gauges to calculate each region’s
predam, unregulated flow regime, and postdam
regulated flow regime (figure 1). In these same
regions, we used 317 undammed reference gauges
to quantitatively compare the magnitude of changes
in regional flow regimes caused by dams versus
climatic variation over the same time period.
Study Approach
We quantitatively tested the hypothesis that dams
have homogenized regionally distinct river flow
regimes across the continental U.S., independently
of climatic variation. Over the course of the 20th
century, more than 75,000 structures with heights
greater than 2 m were constructed on stream and
river channels in the U.S. These ubiquitous dams
occur on average about every 70 km on the
approximate 5.2 million km of river channels
ranging from first-order small streams to 10thorder large rivers. The effects of these dams
extend both upstream by inundating approximately
10 percent of the total stream and river channel
length (Echeverria et al., 1989) and downstream by
modifying flow regimes and other environmental
factors for tens to hundreds of km (Collier et al.,
1996; Richter et al., 1998). Indeed, unregulated,
free-flowing rivers are now rare in the U.S., with
only 42 rivers with lengths greater than 200 being
free from the influence of dams (Benke, 1990).
Results and Discussion
Regional-scale differences in natural flow regimes
that existed in the first half of the 20th century in
the United States have been significantly reduced
in regulated rivers, but not in free-flowing rivers.
Overall, 15 of the 16 regions show evidence of
flow homogenization (figure 1).
Different characteristics of the flow regime
(depicted by the 16 flow metrics) have been
affected by dams, and thus differentially contribute
to observed levels of flow homogenization among
regions (figure 2). Broadly speaking, operations of
the dams examined tend to homogenize regional
flow variability by modifying the magnitude and
timing components of high and low flows, with
lesser contributions from changes in flow duration
and frequency. Across almost all regions, average
maximum flow consistently declined, as did
interannual variation in daily maxima. Minimum
flow magnitudes generally increased, whereas
interannual variation in minimum flows generally
declined. Timing of maximum flows exhibited a
geographic pattern, with more eastern, rainfalldominated regions showing earlier timing of peak
flows [e.g., Eastern Broadleaf Forest–Oceanic
(EOF), Eastern Broadleaf Forest–Continental
(ECF), and Southeastern Mixed Forest (SMF)]
Figure 1. Hydroregion map and dam locations (dots) used in analysis for the continental U.S. Shading of
the individual regions refers to degree of regional homogenization in flow regimes in the post-dam period.
White regions were excluded because of inadequate dam-gauge pairs. Higher values indicate a higher
degree of homogenization.
Hydroregion abbreviations: Eastern Broadleaf Forest–Oceanic (EOF), Eastern Broadleaf Forest–
Continental (ECF), Southeastern Mixed Forest (SMF), California Dry Steppe (CDS), Cascade Mixed Forest-Coniferous Forest-Alpine Meadow (CMF), Middle Rocky Mountain Steppe-Coniferous Forest-Alpine
Meadow (MRM), Great Plains Steppe and Shrub (ISD), Intermountain Semidesert (GSS), California
Coastal Range Open Woodland-Shrub-Coniferous Forest-Meadow (CCR), Outer Coastal Plain Mixed Forest (OCP), Intermountain Semidesert (ISD), Adirondack-New England Mixed Forest-Coniferous ForestAlpine Meadow (NMF), Colorado Plateau Semidesert (CSD), Great Plains Steppe (GPS), Nevada-Utah
Mountains-SemiDesert-Coniferous Forest-Alpine Meadow (NUM), Prairie Parkland–Temperate (PPT),
Southern Rocky Mountain Steppe-Open Woodland-Coniferous Forest-Alpine Meadow (SRM).
Our findings have broad-scale ecological
implications that are directly applicable to
management and conservation of aquatic and
riparian ecosystems. Dam-induced flow changes
alone are known to alter ecological diversity and
function on individual rivers (Poff et al., 1997;
Bunn and Arthington, 2002), where they often act
synergistically with other dam-induced alterations,
including disruption of sediment flux (Collier et al.,
1996), geomorphic simplification (Graf, 2006),
floodplain disconnection (Poff et al., 1997;
Magilligan and Nislow, 2005), thermal regime
alteration (Collier et al., 1996), and extensive
longitudinal and lateral fragmentation of river
corridors (Nilsson et al., 2005).
Figure 2. Relative contributions of 16 hydrologic
metrics to flow homogenization for dammed rivers
in 16 hydroregions. Metrics include magnitude, duration, frequency, and timing for average high flows
and low flows and their interannual coefficient of
variation (CV). For each region, the size of the circle represents the percent change in the relative
importance of the metric for describing interregional
flow difference from pre-dam to post-dam periods.
Filled symbols indicate an increase in the magnitude of the metric from predam to postdam period
for each region, and unfilled symbols indicate a
decrease. Regions are ordered from left to right
according to the increasing degree of homogenization. Refer to figure 1 for hydroregion abbreviations.
compared with delayed peak flows in more
snowmelt-dominated western regions [e.g.,
California Dry Steppe (CDS), Cascade Mixed
Forest-Coniferous Forest-Alpine Meadow (CMF),
and Middle Rocky Mountain Steppe-Coniferous
Forest-Alpine Meadow (MRM)]. Trends in the
timing of minimum flows were more variable. The
interannual variation in timing for both maximum
and minimum flows generally increased across
regions irrespective of geography and climate.
Based on our analysis, we argue that dams are
homogenizing natural flow regimes for entire
regions across the U.S., even though data
availability restricted our analysis to 186 regulated
river hydrographs. We estimate that there is, on
average, one dam every 48 km of third- to seventhorder river channel in the U.S. The downstream
effects of individual dams on river hydrology
typically extend for tens to hundreds of kilometers
(Postel and Richter, 2003; Collier et al., 1996;
Richter et al., 1998).
The ecological consequences of regional
hydrologic alteration are poorly understood, but
important (Pringle et al., 2000). Indeed, biotic
homogenization of freshwater fish faunas in the
U.S. (Rahel, 2000) has been hypothesized to be
facilitated by broad-scale river regulation, which
presumably simplifies regionally unique
disturbance dynamics and allows establishment of
nonnative and otherwise poorly adapted species
(Olden et al., 2006). As humans continue to face
the dilemma of attaining ecosystem sustainability
in the face of global change (Millenium Ecosystem
Assessment, 2005), there is growing need for
preservation of remaining intact systems and
deliberate and strategic design of resilient
ecosystems. Setting clear targets for flow
restoration will help to sustain key components of
riverine ecosystems and may be used to restore
rivers as well.
Conclusion
Maintaining dynamic elements of regional
distinctiveness in key environmental drivers of
ecosystem function and native biodiversity should
be a conservation priority for rivers and other
ecosystems, as this will contribute landscape-scale
ecosystem resilience in the face of global change
(Millenium Ecosystem Assessment, 2005).
Opportunities such as dam re-regulation to provide
formative flows having some semblance to the
historical regime should be exploited (Stanford et
al., 1996; Poff et al., 2003; Richter et al., 2003), as
should the conservation potential of relatively freeflowing rivers that can serve as cornerstones of
‘‘dynamic reserves’’ (Bengtsson et al., 2003;
Saunders et al., 2002)
homogenized world.
in
an
increasingly
Additional Information
For additional information and references, please
refer to the following publication: Poff, N.L.; J.D.
Olden; Merritt, D.M.; Pepin, D.M. 2007.
Homogenization of regional river dynamics by
dams and global biodiversity implications.
Proceedings of the National Academcy of Sciences.
104:5732-5737. Copies are available online from
the STREAM website:
h t t p : / / ww w. s t r e a m. f s . f e d . u s / p u b l i c a t i o n s /
documentsStream.html
References
Bengtsson, J.; Angelstram, P.; Elmqvist, T.; Emanuelsson, U.;
Folke, C.; Ihse, M.; Moberg, F.; Nyström, M. 2003.
Reserves, Resilience and Dynamic Landscapes. Ambio.
32:389–396.
Benke, A.C. 1990. A perspective on America’s vanishing
streams. Journal of the North American Benthological
Society. 9:77–88.
Bunn, S.E.; Arthington, A.H. 2002. Basic principles and
ecological consequences of altered flow regimes for aquatic
biodiversity. Environmental Management. 30:492–507.
Collier, M.; Webb, R.H.; Schmidt, J.C. 1996. Dams and
Rivers: A Primer on the Downstream Effects of Dams. U.S.
Geological Survey Circular 1126. Reston, VA.
Echeverria, J.D.; Barrow, P.; Roos-Collins, R. 1989. Rivers at
Risk: The Concerned Citizen’s Guide to Hydropower. Island
Press. Washington, DC.
Graf, W.L. 2006. Downstream hydrologic and geomorphic
effects of large dams on American rivers. Geomorphology.
79:336–360.
Lins, H.F.; Slack, J.R. 1999. Streamflow trends in the United
States. Geophysicial Research Letters. 25:227–230.
Magilligan, F.J.; Nislow, K.H. 2005. Changes in hydrologic
regimes by dams. Geomorphology. 71:61–78.
McCabe, G.J.; Wolock, D.M. 2002. A step increase in
streamflow in the conterminous United States. Geophysical
Research Letters. 29:2185.
Millennium Ecosystem Assessment. 2005. Ecosystems and
Human Well-being: Biodiversity Synthesis. World
Resources Institute. Washington D.C.
Nilsson, C.; Reidy, C.A.; Dynesius, M.; Revenga, C. 2005.
Fragmentation and flow regulation of the world's large river
systems. Science. 308:405–408.
Olden, J.D.; Poff, N.L. 2003. Redundancy and the choice of
hydrologic indices for characterizing streamflow regimes.
River Research and Applications. 19:101–121.
Olden, J.D.; Poff, N.L.; Bestgen, K.R. 2006. Life-history
strategies predict fish invasions and extirpations in the
Colorado River basin. Ecological Monographs. 76:25–40.
Poff, N.L.; Allan, J.D., Bain, M.B.; Karr, J.R.; Prestegaard,
K.L.; Richter, B.D.; Sparks, R.; Stromberg, J. 1997. The
natural flow regime: A new paradigm for riverine
conservation and restoration. BioScience. 47:769–784.
Poff, N.L.; Allan, J.D., Palmer, M.A.; Hart, D.D.; Richter,
B.D.; Arthington, A.H.; Meyer, J.L.; Stanford, J.A.; Rogers,
K.H. 2003. River flows and water wars: Emerging science
for environmental decision making. Frontiers in Ecology
and the Environment. 1:298–306.
Postel, S.; Richter, B. 2003. Rivers for Life: Managing Water
for People and Nature. Island Press. Washington, DC.
Power, M.E.; Dietrich, W.E.; Finlay, J.C. 1996. Dams and
downstream aquatic biodiversity: Potential food web
consequences of hydrologic and geomorphic change.
Environmental Management. 20:887–895.
Pringle, C.M.; Freeman, M.C.; Freeman, B.J. 2000. Regional
Effects of hydrologic alterations on riverine macrobiota in
the new world: Tropical–Temperate comparisons.
BioScience. 50:807–823.
Rahel, F.J. 2000. Homogenization of fish faunas across the
United States. Science. 288:854–856.
Resh, V.H.; Brown, A.V.; Covich, A.P.; Gurtz, M.E.; Li,
H.W.; Minshall, G.W.; Reice, S.R.; Sheldon, A.L.; Wallace,
J.B.; Wissmar, R. 1988. The role of disturbance in stream
ecology. Journal of the North American Benthological
Society. 7:433–455.
Richter, B.D.; Baumgartner, J.V.; Powell, J.; Braun, D.P.
1996. A method for assessing hydrologic alteration within
ecosystems. Conservation Biology. 10:1163–1174.
Richter, B.R.; Baumgartner, J.V.; Braun, D.P.; Powell, J. 1998.
A spatial assessment of hydrologic alteration within a river
network. Regulated River Research Management. 14:329–
340.
Richter, B.D.; Mathews, R.; Harrison, D.L.; Wigington, R.
2003. Ecological sustainable water management: managing
river flows for ecological integrity. Ecological Applications.
13:206–224.
Saunders, D.L.; Meeuwig, J.J.; Vincent, A.C. 2002. Freshwater
protected areas: Strategies for conservation. Conservation
Biology. 16:30–41.
Stanford, J.A.; Ward, J.V.; Liss, W.J.; Frissell, C.A.; Williams,
R.N.; Lichatowich, J.A.; Coutant, C.C. 1996. A general
protocol for restoration of regulated rivers. Regulated
Rivers: Research and Management. 12:391–413.
Syvitski, J.P.M.; Vörösmarty, C.J.; Kettner, A.J.; Green, P.
2005. Impact of Humans on the Flux of Terrestrial Sediment
to the Global Coastal Ocean. Science. 308: 376-380.
World Commission on Dams. 2000. Dams and Development:
A New Framework for Decision-Making. Earthscan
Publications. London.
N. LeRoy Poff is a professor; Colorado State University, Dept. of Biology, Fort Collins, CO 80523; 970491-2079; poff@lamar.colostate.edu.
Julian D. Olden is a professor; University of Washington; School of Aquatic and Fishery Sciences; Seattle, WA 98195; 206-616-3112;
olden@u.washington.edu.
David M. Merritt is a Riparian Ecologist, USDA
Forest Service, Stream Systems Technology Center;
Fort Collins, Colorado 80526; 970-295-5987;
dmmerritt@fs.fed.us.
David M. Pepin is a Graduate Student; Colorado
State University, Dept. of Biology, Fort Collins, CO
80523; 970-491-2414; dpepin@lamar.colostate.edu.
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IN THIS ISSUE
• Proceedings of the
2004 Forest Service
National Earth
Sciences Conference
• Homogenization of
Regional River
Dynamics by Dams
and Global
Biodiversity
Implications
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