and mortality rates as functions of 

both grazing and stream flow. Since 

1996, we have observed seedling 

establishment, mortality, recruitment 

to sapling and pole stages, and sediment accretion and erosion through 

sequences of normal and dry years. 

To some extent, the positive recruitment response from a sequence 

of normal to dry years mirrors the 

response expected from a sequence 

of wet to normal years. However, 

survival through the next episodic 

ice scour (fig. 8) or flood is uncertain 

because along the laterally constrained 

Wild and Scenic reach of the upper 

Missouri River in the Missouri Breaks, 

most trees were established by flood 

flows that position them as seedlings 

high enough on the banks to survive 

mortality from subsequent floods and 

episodic ice scour (fig. 9).

Figure 9. Diagram of flood-dependent recruitment of cottonwood along constrained, ice-prone 

reach of the upper Missouri River. Major ice events are less frequent and trees at the higher 

elevations tend to grow large enough to withstand infrequent, major ice events. 

Figure 8. Ice on the Missouri 

River. Note flow from partially 

melted tributary entering 

still-frozen mainstem.

The moderate floods that have 

occurred recently may not have placed 

seedlings high enough above the ice 

zone, even if they do survive livestock 

grazing. 

References Cited

Auble, G.T., and Scott, M.L., 1998, 

Fluvial disturbance patches and cottonwood recruitment along the upper 

Missouri River, Montana: Wetlands, 

v. 18, p. 546–556.

Auble, G.T., Scott, M.L., Frazier, J., 

and Merigliano, M., 2001, Cottonwood seedling demography along the 

Wild and Scenic Reach of the Upper 

Missouri River: 22nd annual meeting 

of the Society of Wetland Scientists, 

Chicago, Illinois, May 29, 2001.

Bovee, K., and Scott, M.L., 2002, Implications of flood pulse restoration for 

Populus regeneration on the Upper 

Missouri River: River Research and 

Applications, v. 18, p. 287–298.

Coues, E., ed., 1893, The history of the 

Lewis and Clark Expedition: Volume 

I of IV, Francis P. Harper, New York, 

USA, Unabridged republication by 

Dover Publications, Inc., New York, 

NY, USA.

Lemke, R.W., Laird, W.M., Tipton, M.J., 

and Lindvall, R.M., 1965, Quaternary 

geology of the northern Great Plains, 

in Wright, Jr., H.E., and Frye, J.C., 

eds., The quaternary of the United 

States: Princeton University Press, 

Princeton, NJ, US, p. 15–27.

Scott, M.L., and Auble, G.T., 2002, Conservation and restoration of semi-arid 

riparian forests: a case study from the 

Upper Missouri River, Montana, USA, 

in Middleton, B., ed., Flood pulsing and wetland restoration in North 

America: John Wiley and Sons, Inc., 

p. 145–190.

Scott, M.L., Auble, G.T., and Friedman, 

J.M., 1997, Flood dependency of cottonwood establishment along the Missouri River, Montana, USA: Ecological 

Applications, v. 7, p. 677–690.

Scott, M.L., Friedman, J.M., and Auble, 

G.T., 1996, Fluvial process and the 

establishment of bottomland trees: 

Geomorphology, v. 14, p. 327–339.

Scott, M.L., Skagen, S.K., and Merigliano, M.F., 2003,Relating geomorphic 

change and grazing to avian communities in riparian forests: Conservation 

Biology, v. 7, p. 284–296.

Wayne, W.J., Aber, J.S., Agard, S.S., Bergantino, R.N., Bluemle, J.P., Coates, 

D.A., Cooley, M.E., Madole, R.F., 

Martin, J.E., Mears, Jr., B., Morrison, 

R.B., and Sutherland, W.M., 1991, 

Quaternary geology of the northern 

Great Plains, in Morrison, R.B., ed.: 

Geology of North America, Volume K2, The Geological Society of America, 

Boulder, CO, USA, p. 441–476.

Investigators

Gregor Auble and Michael Scott, 

U.S. Geological Survey

Joseph Frazier and Chad Krause, 

Bureau of Land Management

Michael Merigliano,

University of Montana
deposited or disturbed alluvium 

typically provides ideal substrate 

for germination and establishment, 

however young seedlings are also 

sensitive to mortality from flooding, 

burial, and scouring.

The conditions required for cottonwood recruitment can be summarized 

as bare, moist sites that are relatively 

safe from subsequent disturbance. 

These are restrictive requirements 

and are met most frequently and 

extensively by flow-induced channel 

change. Fluvial geomorphic processes 

like channel narrowing, meandering, 

as well as vertical accretion of alluvial 

surfaces by flood deposition produce 

the bare, moist substrates suitable for 

cottonwood regeneration and result in 

distinctive spatial and temporal 

patterns of cottonwood forest.

Missouri Breaks Cottonwood

The relative scarcity of cottonwood 

in the Missouri Breaks is partially 

explained by geologic setting. Before 

the Pleistocene, the Missouri River 

diverged from its modern course near 

Coal Banks Landing, flowing north 

Wild and Scenic reach occur in less 

constrained areas such as back 

channels and islands (fig. 4) and 

tributary junctions such as the mouth 

of the Judith River.

The Missouri River in Montana has 

a snowmelt-dominated hydrograph, 

with peak flows typically occurring 

in late May or early June and low 

flows occurring in fall and winter. 

Infrequently large floods occur when 

upslope orographic precipitation in 

May and June combines with snowmelt runoff. Stages produced by winter 

ice jams are frequently higher than 

Figure 3. Constrained reach of Missouri River, 

Montana, and the pre-glacial course redrawn 

from Lemke and others (1965) and Scott and 

others (1996). Quoted descriptions of riparian 

vegetation in 1805 are from Lewis and Clark 

journals (Coues, 1893). Photographs from 

nearby areas in the 1990s show little change in 

basic character of the forest.

and east into Hudson Bay (fig. 3, 

Lemke and others, 1965; Wayne and 

others, 1991). The channel in this 

geologically young reach has low 

sinuosity and is constrained within a 

narrow valley – in contrast to sections 

of the Missouri River in wider valleys 

where historically extensive meandering 

produced broad cottonwood forests. 

Local exceptions to the pattern of 

narrow, sparse cottonwood within the 

Figure 4. Mature stand of cottonwood on Cow Island viewed from side channel of Missouri River.

Marias River

Milk River

Ft. Benton

Coal Banks Landing

Virgelle gage

Landusky

gage Missouri River

"...timber increases in

quantity, the low grounds

become more level and

extensive... a handsome,

low cottonwood plain on

the south..."

"...timber increases in

quantity, the low grounds

become more level and

extensive... a handsome,

low cottonwood plain on

the south..."

"There is now no timber on

the hills, and only a few

scattering cottonwood,

ash, boxelder, and willows

along the water."

"There is, however, no

timber on either side of

the river, except for a few

pines on the hills." 

Pre-glacial course

Constrained reach

Descriptions from Lewis

and Clark in 1805

Photos of nearby

areas from 1990s.

gage

35 km
deposited or disturbed alluvium 

typically provides ideal substrate 

for germination and establishment, 

however young seedlings are also 

sensitive to mortality from flooding, 

burial, and scouring.

The conditions required for cottonwood recruitment can be summarized 

as bare, moist sites that are relatively 

safe from subsequent disturbance. 

These are restrictive requirements 

and are met most frequently and 

extensively by flow-induced channel 

change. Fluvial geomorphic processes 

like channel narrowing, meandering, 

as well as vertical accretion of alluvial 

surfaces by flood deposition produce 

the bare, moist substrates suitable for 

cottonwood regeneration and result in 

distinctive spatial and temporal 

patterns of cottonwood forest.

Missouri Breaks Cottonwood

The relative scarcity of cottonwood 

in the Missouri Breaks is partially 

explained by geologic setting. Before 

the Pleistocene, the Missouri River 

diverged from its modern course near 

Coal Banks Landing, flowing north 

Wild and Scenic reach occur in less 

constrained areas such as back 

channels and islands (fig. 4) and 

tributary junctions such as the mouth 

of the Judith River.

The Missouri River in Montana has 

a snowmelt-dominated hydrograph, 

with peak flows typically occurring 

in late May or early June and low 

flows occurring in fall and winter. 

Infrequently large floods occur when 

upslope orographic precipitation in 

May and June combines with snowmelt runoff. Stages produced by winter 

ice jams are frequently higher than 

Figure 3. Constrained reach of Missouri River, 

Montana, and the pre-glacial course redrawn 

from Lemke and others (1965) and Scott and 

others (1996). Quoted descriptions of riparian 

vegetation in 1805 are from Lewis and Clark 

journals (Coues, 1893). Photographs from 

nearby areas in the 1990s show little change in 

basic character of the forest.

and east into Hudson Bay (fig. 3, 

Lemke and others, 1965; Wayne and 

others, 1991). The channel in this 

geologically young reach has low 

sinuosity and is constrained within a 

narrow valley – in contrast to sections 

of the Missouri River in wider valleys 

where historically extensive meandering 

produced broad cottonwood forests. 

Local exceptions to the pattern of 

narrow, sparse cottonwood within the 

Figure 4. Mature stand of cottonwood on Cow Island viewed from side channel of Missouri River.

Marias River

Milk River

Ft. Benton

Coal Banks Landing

Virgelle gage

Landusky

gage Missouri River

"...timber increases in

quantity, the low grounds

become more level and

extensive... a handsome,

low cottonwood plain on

the south..."

"...timber increases in

quantity, the low grounds

become more level and

extensive... a handsome,

low cottonwood plain on

the south..."

"There is now no timber on

the hills, and only a few

scattering cottonwood,

ash, boxelder, and willows

along the water."

"There is, however, no

timber on either side of

the river, except for a few

pines on the hills." 

Pre-glacial course

Constrained reach

Descriptions from Lewis

and Clark in 1805

Photos of nearby

areas from 1990s.

gage

35 km
and mortality rates as functions of 

both grazing and stream flow. Since 

1996, we have observed seedling 

establishment, mortality, recruitment 

to sapling and pole stages, and sediment accretion and erosion through 

sequences of normal and dry years. 

To some extent, the positive recruitment response from a sequence 

of normal to dry years mirrors the 

response expected from a sequence 

of wet to normal years. However, 

survival through the next episodic 

ice scour (fig. 8) or flood is uncertain 

because along the laterally constrained 

Wild and Scenic reach of the upper 

Missouri River in the Missouri Breaks, 

most trees were established by flood 

flows that position them as seedlings 

high enough on the banks to survive 

mortality from subsequent floods and 

episodic ice scour (fig. 9).

Figure 9. Diagram of flood-dependent recruitment of cottonwood along constrained, ice-prone 

reach of the upper Missouri River. Major ice events are less frequent and trees at the higher 

elevations tend to grow large enough to withstand infrequent, major ice events. 

Figure 8. Ice on the Missouri 

River. Note flow from partially 

melted tributary entering 

still-frozen mainstem.

The moderate floods that have 

occurred recently may not have placed 

seedlings high enough above the ice 

zone, even if they do survive livestock 

grazing. 

References Cited

Auble, G.T., and Scott, M.L., 1998, 

Fluvial disturbance patches and cottonwood recruitment along the upper 

Missouri River, Montana: Wetlands, 

v. 18, p. 546–556.

Auble, G.T., Scott, M.L., Frazier, J., 

and Merigliano, M., 2001, Cottonwood seedling demography along the 

Wild and Scenic Reach of the Upper 

Missouri River: 22nd annual meeting 

of the Society of Wetland Scientists, 

Chicago, Illinois, May 29, 2001.

Bovee, K., and Scott, M.L., 2002, Implications of flood pulse restoration for 

Populus regeneration on the Upper 

Missouri River: River Research and 

Applications, v. 18, p. 287–298.

Coues, E., ed., 1893, The history of the 

Lewis and Clark Expedition: Volume 

I of IV, Francis P. Harper, New York, 

USA, Unabridged republication by 

Dover Publications, Inc., New York, 

NY, USA.

Lemke, R.W., Laird, W.M., Tipton, M.J., 

and Lindvall, R.M., 1965, Quaternary 

geology of the northern Great Plains, 

in Wright, Jr., H.E., and Frye, J.C., 

eds., The quaternary of the United 

States: Princeton University Press, 

Princeton, NJ, US, p. 15–27.

Scott, M.L., and Auble, G.T., 2002, Conservation and restoration of semi-arid 

riparian forests: a case study from the 

Upper Missouri River, Montana, USA, 

in Middleton, B., ed., Flood pulsing and wetland restoration in North 

America: John Wiley and Sons, Inc., 

p. 145–190.

Scott, M.L., Auble, G.T., and Friedman, 

J.M., 1997, Flood dependency of cottonwood establishment along the Missouri River, Montana, USA: Ecological 

Applications, v. 7, p. 677–690.

Scott, M.L., Friedman, J.M., and Auble, 

G.T., 1996, Fluvial process and the 

establishment of bottomland trees: 

Geomorphology, v. 14, p. 327–339.

Scott, M.L., Skagen, S.K., and Merigliano, M.F., 2003,Relating geomorphic 

change and grazing to avian communities in riparian forests: Conservation 

Biology, v. 7, p. 284–296.

Wayne, W.J., Aber, J.S., Agard, S.S., Bergantino, R.N., Bluemle, J.P., Coates, 

D.A., Cooley, M.E., Madole, R.F., 

Martin, J.E., Mears, Jr., B., Morrison, 

R.B., and Sutherland, W.M., 1991, 

Quaternary geology of the northern 

Great Plains, in Morrison, R.B., ed.: 

Geology of North America, Volume K2, The Geological Society of America, 

Boulder, CO, USA, p. 441–476.

Investigators

Gregor Auble and Michael Scott, 

U.S. Geological Survey

Joseph Frazier and Chad Krause, 

Bureau of Land Management

Michael Merigliano,

University of Montana