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M. L. Scott

Publications and source records attributed to M. L. Scott.

At least 19 recordsLinked to original sources
USGS2012

Long-term change along the Colorado River in Grand Canyon National Park (1889-2011)

The Colorado River and its riverine resources have undergone profound changes since completion of Glen Canyon Dam in 1963, as every river runner with any history in Grand Canyon will attest. Long-term monitoring data are difficult to obtain for high-value resource areas (Webb et al. 2009), particularly in remote parts of national parks, yet these data are important to determining appropriate actions for restoration of resources and (or) potential modifications of flow releases on regulated rivers. The river corridor through the bottom of Grand Canyon creates a challenging environment for change-detection monitoring techniques (Belnap et al. 2008).

Arizona↗
USGS2008

Assessing the extent and diversity of riparian ecosystems in Sonora, Mexico

Conservation of forested riparian ecosystems is of international concern. Relatively little is known of the structure, composition, diversity, and extent of riparian ecosystems in Mexico. We used high- and low-resolution satellite imagery from 2000 to 2006, and ground-based sampling in 2006, to assess the spatial pattern, extent, and woody plant composition of riparian forests across a range of spatial scales for the state of Sonora, Mexico. For all 3rd and higher order streams, river bottomlands with riparian forests occupied a total area of 2,301 km2. Where forested bottomlands remained, on average, 34% of the area had been converted to agriculture while 39% remained forested. We estimated that the total area of riparian forest along the principal streams was 897 km2. Including fencerow trees, the total forested riparian area was 944 km2, or 0.5% of the total land area of Sonora. Ground-based sampling of woody riparian vegetation consisted of 92, 50 m radius circular plots. About 79 woody plant species were noted. The most important tree species, based on cover and frequency, were willow species Salix spp. (primarily S. goodingii and S. bonplandiana), mesquite species Prosopis spp. (primarily P. velutina), and Fremont cottonwood Populus fremontii. Woody riparian taxa at the reach scale showed a trend of increasing diversity from north to south within Sonora. Species richness was greatest in the willow-bald cypress Taxodium distichum var. mexicanum-Mexican cottonwood P. mexicana subsp. dimorphia ecosystem. The non-native tamarisk Tamarix spp. was rare, occurring at just three study reaches. Relatively natural stream flow patterns and fluvial disturbance regimes likely limit its establishment and spread. ?? 2008 Springer Science + Business Media BV.

Biodiversity and Conservation↗
USGS2008

Planning riparian restoration in the context of tamarix control in Western North America

Throughout the world, the condition of many riparian ecosystems has declined due to numerous factors, including encroachment of non-native species. In the western United States, millions of dollars are spent annually to control invasions of Tamarix spp., introduced small trees or shrubs from Eurasia that have colonized bottomland ecosystems along many rivers. Resource managers seek to control Tamarix in attempts to meet various objectives, such as increasing water yield and improving wildlife habitat. Often, riparian restoration is an implicit goal, but there has been little emphasis on a process or principles to effectively plan restoration activities, and many Tamarix removal projects are unsuccessful at restoring native vegetation. We propose and summarize the key steps in a planning process aimed at developing effective restoration projects in Tamarix-dominated areas. We discuss in greater detail the biotic and abiotic factors central to the evaluation of potential restoration sites and summarize information about plant communities likely to replace Tamarix under various conditions. Although many projects begin with implementation, which includes the actual removal of Tamarix, we stress the importance of pre-project planning that includes: (1) clearly identifying project goals; (2) developing realistic project objectives based on a detailed evaluation of site conditions; (3) prioritizing and selecting Tamarix control sites with the best chance of ecological recovery; and (4) developing a detailed tactical plan before Tamarix is removed. After removal, monitoring and maintenance as part of an adaptive management approach are crucial for evaluating project success and determining the most effective methods for restoring these challenging sites. ?? 2008 Society for Ecological Restoration International.

Restoration Ecology↗
USGS2007

Early vegetation development on an exposed reservoir: Implications for dam removal

The 4-year drawdown of Horsetooth Reservoir, Colorado, for dam maintenance, provides a case study analog of vegetation response on sediment that might be exposed from removal of a tall dam. Early vegetation recovery on the exposed reservoir bottom was a combination of (1) vegetation colonization on bare, moist substrates typical of riparian zones and reservoir sediment of shallow dams and (2) a shift in moisture status from mesic to the xeric conditions associated with the pre-impoundment upland position of most of the drawdown zone. Plant communities changed rapidly during the first four years of exposure, but were still substantially different from the background upland plant community. Predictions from the recruitment box model about the locations of Populus deltoides subsp. monilifera (plains cottonwood) seedlings relative to the water surface were qualitatively confirmed with respect to optimum locations. However, the extreme vertical range of water surface elevations produced cottonwood seed regeneration well outside the predicted limits of drawdown rate and height above late summer stage. The establishment and survival of cottonwood at high elevations and the differences between the upland plant community and the community that had developed after four years of exposure suggest that vegetation recovery following tall dam removal will follow a trajectory very different from a simple reversal of the response to dam construction, involving not only long time scales of establishment and growth of upland vegetation, but also possibly decades of persistence of legacy vegetation established during the reservoir to upland transition. ?? 2007 Springer Science+Business Media, LLC.

Environmental Management↗
USGS2005

Use of individualistic streamflow-vegetation relations along the Fremont River, Utah, USA to assess impacts of flow alteration on wetland and riparian area

We analyzed the transverse pattern of vegetation along a reach of the Fremont River in Capitol Reef National Park, Utah, USA using models that support both delineation of wetland extent and projection of the changes in wetland area resulting from upstream hydrologic alteration. We linked stage-discharge relations developed by a hydraulic model to a flow-duration curve derived from the flow history in order to calculate the inundation duration of 361 plots (0.5 × 2 m). Logistic regression was used to relate plant species occurrence in plots to inundation duration. A weighted average of the wetland indicator values of species was used to characterize plots as Aquatic, Wetland, Transitional, or Upland. Finally, we assessed how alterations in the flow duration curve would change the relative widths of these four zones. The wetland indicator values of species and the wetland prevalence index scores of plots were strongly correlated with inundation duration. Our results support the concept that plants classified as wetland species typically occur on sites inundated at least two weeks every two years. The portion of the riparian zone along the high-gradient study reach of the Fremont River that satisfied the vegetation criterion for a regulatory wetland was narrow (2 m wide). Both the unvegetated Aquatic zone (7.8 m) and the Transitional zone (8 m) were substantially wider. The Transitional zone included the maxima of several species and was, therefore, not merely a combination of elements of the Wetland and Upland zones. Multiplicative increases or decreases in streamflow regime produced a wetter, or drier, bottomland vegetation, respectively. Systematic reductions in flow variability reduced the width of both the Wetland and Transitional zones and increased the width of the Upland zone. Our approach is widely applicable to inform water management decisions involving changes in flow regime.

Wetlands↗
USGS2003

Physiological and morphological response patterns of Populus deltoides to alluvial groundwater

We examined the physiological and morphological response patterns of plains cottonwood [ Populus deltoides subsp. monilifera (Aiton) Eck.] to acute water stress imposed by groundwater pumping. Between 3 and 27 July 1996, four large pumps were used to withdraw alluvial groundwater from a cottonwood forest along the South Platte River, near Denver, Colorado, USA. The study was designed as a stand-level, split-plot experiment with factorial treatments including two soil types (a gravel soil and a loam topsoil over gravel), two water table drawdown depths (∼0.5 m and >1.0 m), and one water table control (no drawdown) per soil type. Measurements of water table depth, soil water potential (Ψ s ), predawn and midday shoot water potential (Ψ pd and Ψ md ), and D/H (deuterium/hydrogen) ratios of different water sources were made in each of six 600-m 2 plots prior to, during, and immediately following pumping. Two additional plots were established and measured to examine the extent to which surface irrigation could be used to mitigate the effects of deep drawdown on P. deltoides for each soil type. Recovery of tree water status following pumping was evaluated by measuring stomatal conductance ( g s ) and xylem water potential (Ψ xp ) on approximately hourly time steps from before dawn to mid-afternoon on 11 August 1996 in watered and unwatered, deep-drawdown plots on gravel soils. P. deltoides responded to abrupt alluvial water table decline with decreased shoot water potential followed by leaf mortality. Ψ pd and percent leaf loss were significantly related to the magnitude of water table declines. The onset and course of these responses were influenced by short-term variability in surface and ground water levels, acting in concert with physiological and morphological adjustments. Decreases in Ψ pd corresponded with increases in Ψ md , suggesting shoot water status improved in response to stomatal closure and crown dieback. Crown dieback caused by xylem cavitation likely occurred when Ψ pd reached −0.4 to −0.8 MPa. The application of surface irrigation allowed trees to maintain favorable water status with little or no apparent cavitation, even in deep-drawdown plots. Two weeks after the partial canopy dieback and cessation of pumping, g s and Ψ xp measurements indicated that water stress persisted in unwatered P. deltoides in deep-drawdown plots.

Environmental Management↗
USGS2002

Potential responses of riparian vegetation to dam removal

Throughout the world, riparian habitats have been dramatically modified from their natural condition. Dams are one of the principal causes of these changes, because of their alteration of water and sediment regimes ( Nilsson and Berggren 2000 ). Because of the array of ecological goods and services provided by natural riparian ecosystems ( Naiman and Decamps 1997 ), their conservation and restoration have become the focus of many land and water managers. Efforts to restore riparian habitats and other riverine ecosystems have included the management of flow releases downstream of dams to more closely mimic natural flows ( Poff et al. 1997 ), but dam removal has received little attention as a possible approach to riparian restoration.

BioScience↗
USGS2000

Channel incision and patterns of cottonwood stress and mortality along the Mojave River, California

In 1995, mapping and classification of riparian vegetation along the Mojave River in southern California revealed an 8-km reach in which riparian cottonwoods ( Populus fremontii Wats.) were stressed or dying. We tested a set of predictions based on the inference that cottonwood decline was an indirect result of lowered water-table levels following flood-related channel incision. Comparisons of topographic cross-sections from 1963 and 1997, indicated a net change in channel elevation between −0·71 and −3·6 m within zones of cottonwood stress and mortality. Ages of young cottonwood and willow stems adjacent to the present channel and radial stem growth of surviving cottonwoods were consistent with the inference that channel incision, associated with sustained flooding in January and February of 1993, lowered channel elevations throughout the affected reach. Well records and soil redoximorphic features indicate that channel incision caused net water-table declines ⩾1·5 m on portions of the adjacent flood plain where cottonwood stand mortality ranged between 58 and 93%. In areas where water-table declines were estimated to be <1·0 m, stand mortality was 7–13%.

Journal of Arid Environments↗
USGS1998

Fluvial disturbance patches and cottonwood recruitment along the upper Missouri River, Montana

The disturbance patches most suitable for seedling establishment of pioneer riparian trees are also subject to future disturbances that produce high seedling mortality. We are monitoring plains cottonwood seedling establishment and mortality along the Wild and Scenic reach of the Missouri River upstream of Fort Peck Reservoir, Montana at four sites subject to livestock grazing and four paired, ungrazed enclosures. New seedlings at these sites were largely restricted to surfaces inundated by spring and summer flows. Winter ice drives and livestock grazing are important mortality factors along the study reach. Livestock grazing reduced seedling densities, although the position of these seedlings in normal flow years means it is unlikely that they will survive future disturbance. Average values of the maximum density parameter of a Gaussian curve of seedling distribution along a hydraulic gradient of inundating discharge were 30 and 114 seedlings/m 2 on ungrazed sites in 1996 and 1997, compared to 19 and 18 seedlings/m 2 for grazed sites. Water-surface elevations produced by ice drives and damming in the severe winter of 1995-1996 corresponded to inundating discharges of 1,670 to 4,580 m 3 /s. No existing trees at the study sites occurred at inundating discharges below 1,625 m 3 /s. Seedlings established as a result of maximum summer flows of 827 and 1,201 m 3 /s in 1996 and 1997 were all below the elevation of the 10-year return flow of 1,495 m 3/ s. Recruitment of plains cottonwood trees along this reach of the Missouri River is strongly dependent on infrequent high flows that position moist, bare disturbed patches high enough for seedlings to establish and survive subsequent flooding and ice scour, in contrast to other reaches and streams where hydrogeomorphic processes of channel meandering and narrowing produce different patterns of disturbance patches.

Montana↗
USGS1998

Downstream effects of dams on channel geometry and bottomland vegetation: Regional patterns in the Great Plains

The response of rivers and riparian forests to upstream dams shows a regional pattern related to physiographic and climatic factors that influence channel geometry. We carried out a spatial analysis of the response of channel geometry to 35 dams in the Great Plains and Central Lowlands, USA. The principal response of a braided channel to an upstream dam is channel-narrowing, and the principal response of a meandering channel is a reduction in channel migration rate. Prior to water management, braided channels were most common in the southwestern Plains where sand is abundant, whereas meandering channels were most common in the northern and eastern Plains. The dominant response to upstream dams has been channel-narrowing in the southwestern Plains (e.g., six of nine cases in the High Plains) and reduction in migration rate in the north and east (e.g., all of twelve cases in the Missouri Plateau and Western Lake Regions). Channel-narrowing is associated with a burst of establishment of native and exotic woody riparian pioneer species on the former channel bed. In contrast, reduction in channel migration rate is associated with a decrease in reproduction of woody riparian pioneers. Thus, riparian pioneer forests along large rivers in the southwestern Plains have temporarily increased following dam construction while such forests in the north and east have decreased. These patterns explain apparent contradictions in conclusions of studies that focused on single rivers or small regions and provide a framework for predicting effects of dams on large rivers in the Great Plains and elsewhere. These conclusions are valid only for large rivers. A spatial analysis of channel width along 286 streams ranging in mean annual discharge from 0.004 to 1370 cubic meters per second did not produce the same clear regional pattern, in part because the channel geometries of small and large streams are affected differently by a sandy watershed.

Great Plains↗
USGS1997

Constraints on establishment of plains cottonwood in an urban riparian preserve

Plot sampling and hydraulic modeling were combined to investigate establishment and survival of plains cottonwood along Boulder Creek, an urban stream on the Colorado Plains. We tested the hypothesis that establishment is limited to bare, moist surfaces produced by spring flooding in the current year. No cottonwood germination was observed in 1989 when peak flow was low. A moderate peak of 11.9 m 3 /s in 1990 resulted in cottonwood establishment on surfaces inundated by discharges less than 15 m 3 /s. Surviving sapling cottonwoods established before 1989 occurred on surfaces inundated by discharges of 15–31 m 3 /s and dated to years with peak flows over 15 m 3 /s. Since 1969, establishment of cottonwood has been limited to a floodplain 21 m wide. Flow regulation and channel stabilization upstream and downstream of the study area have reduced the channel movement and overbank flooding that otherwise would have created bare, moist sites suitable for cottonwood establishment across a wider area. GIS analysis of aerial photographs shows that between 1937 and 1992 the channel has not moved and forest has encroached upon formerly open areas near the channel. A terrace, 317 m wide, is now dominated by trees that can reproduce in the absence of disturbance, especially the exotic crack willow.

Colorado↗