Browsing by Author "Friedman, Jonathan, committee member"

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Open Access
Environmental predictors of annual incremental Populus deltoides growth, and riparian forest structure of the South Platte River in northeastern Colorado
(Colorado State University. Libraries, 2020) Christensen, Cetan, author; Norton, Andrew, advisor; Katz, Gabrielle, advisor; Friedman, Jonathan, committee member; Redmond, Miranda, committee member
Riparian forests are biologically diverse systems that provide essential ecological services, such as flood attenuation, bank stabilization, habitat, nutrient cycling, temperature regulation, etc., for the landscapes they occupy. The present-day South Platte River riparian forest is dominated by native phreatophytes (Populus and Salix species) which require hydrologic disturbance to reproduce. However, with changing water-use patterns and hydrology in the South Platte basin of Colorado, the future riparian forest status is unknown. This study describes the contemporary forest composition and age structure. Data was collected along transects from seven randomly selected sites within three randomly positioned 30-km river sections between Kersey and Julesburg, Colorado on the South Platte River. A ring width chronology was developed using cores from 237 Populus deltoides (plains cottonwood) trees and was used in linear mixed modeling to describe relationships between climate, hydrology, and site attributes that affect annual biomass production (Basal Area Increment). Populus deltoides dominate the riparian forest overstory, while later successional species (Ulmus pumila and Fraxinus pennsylvanica) are present at low densities. Though the timing of recruitment has varied among sites, overall recruitment of P. deltoides is abundant, reflecting the ongoing flow-related channel change occurring in this system. Summer mean flows, as well as November and March mean flows, and climate factors (Palmer Drought Severity Index) during the growing season were responsible for variations in P. deltoides annual tree growth, as were tree age, site, and attributes of the individual trees. Our findings contrast with previously hypothesized successional trajectories for this system, which predicted the replacement of the Populus-Salix overstory by later successional species (Ulmus pumila and Fraxinus pennsylvanica). The linear mixed model results highlight the importance of not only summer season flows and climate, but also the potential effects of off-season flow variables in a changing system.
Open Access
Linking riparian vegetation to precipitation using NDVI at Yuma Proving Ground, Arizona
(Colorado State University. Libraries, 2015) Birtwistle, Amy N., author; Laituri, Melinda, advisor; Bledsoe, Brian, committee member; Friedman, Jonathan, committee member
Measuring precipitation in semi-arid landscapes is important for understanding the processes related to rainfall and run-off. However, rain gauges are sparsely distributed. Linear regressions comparing rain gauge and RADAR precipitation estimates revealed that RADAR data is often misleading especially for monsoon type storms. This study investigates an alternative way to map the spatial and temporal variation of precipitation inputs along ephemeral stream channels using NDVI derived from Landsat TM imagery. NDVI was derived on 26 pre- and post-monsoon season Landsat images across Yuma Proving Ground (YPG) in southwestern Arizona. The mean NDVI values along ephemeral stream channels explained 73% of the variance in precipitation totals from a nearby rain gauge for 25 monsoon seasons. A 0.0006 increase in NDVI per day between pre- and post-monsoon season imagery was found to indicate high precipitation inputs and possibly indicate flow events. A second set of Landsat TM imagery were used to relate gains in NDVI during seven winter seasons to precipitation recorded from a nearby NEXRAD radar station. The NEXRAD Stage IV radar data were found to be more accurate during winter precipitation events when associated with rain gauge stations (adjusted R2: 0.81 & 0.84). High correlations were found between NDVI and precipitation at the 32, 48, 64 and 96d time intervals, though each season varied. The number of precipitation events with >5mm at the 96d interval showed significant correlation (0.63 & 0.77) while the number of events with >10mm had less correlation. Moreover, the combination and analysis of these two NDVI datasets revealed that wet winters may influence the vegetation for more than four years into the future.
Open Access
Process linkages in large watersheds: connecting tributary erosion to downstream channel change and floodplain forest establishment in the Yampa and Green River Basin
(Colorado State University. Libraries, 2022) Kemper, John Trusal, author; Rathburn, Sara, advisor; Friedman, Jonathan, committee member; Wohl, Ellen, committee member; Leisz, Stephen, committee member; Redmond, Miranda, committee member
It is well-understood that the physical state of a river is a combination and culmination of present processes and past trajectories. Similarly, conceptualizations of fluvial connection hold that various aspects of a given river reach – ecologic, geomorphic, hydrologic – do not operate in isolation, but rather as components within a linked system, both influencing and influenced by upstream and downstream conditions. To expand understanding of the river system as an intrinsically linked network of both process and form, here I establish connections between the processes of historical tributary erosion and distal downstream channel migration and floodplain forest establishment in the Yampa and Green River Basin. I then additionally summarize the extensive body of literature concerning the geomorphic response to sediment supply increases in low-gradient, alluvial rivers to further emphasize that the translation of sediment through the landscape can catalyze myriad responses that manifest across a continuum of scales. Concentrating initially on the investigation of historical erosion, examination of historical documents and aerial photos suggests that three key sediment contributing tributaries of the Yampa River – Sand Creek, Muddy Creek, and Sand Wash – underwent substantial historical erosion from 1880-1940. Using field investigation to determine historical channel location and field surveys of present-day dimensions, I then calculate that historical arroyo incision within the latter two tributary watersheds injected 30 x 106 tons of sediment into the mainstem Little Snake and Yampa Rivers during this time. Taking present-day annual sediment loads as an approximate background for the pre-erosion sediment regime, this represented a sizable increase in the sediment load of the Yampa River during the period of historical erosion. Moving downstream, results of dendrochronologic analysis of tree cores from three separate forest locations – Deerlodge Park on the Yampa River, Island Park and Tuxedo Bottom on the Green River – indicate that major portions of these forests established during the same time period of elevated historical erosion. Moreover, channel change analysis suggests that the channel at this time was relatively more dynamic than it has been since, and the area of forest dating to the historical period is much greater than can be explained by high flows alone. Viewed collectively, these findings suggest tributary erosion played a vital role in successful downstream forest establishment. Additional sediment fingerprinting analysis further supports this process link between geomorphic and ecologic process. Using sediment samples taken at the rooting surface of the cottonwood forest in Deerlodge Park, geochemical analysis indicates that the majority of this sediment was sourced from those tributaries – Muddy Creek and Sand Wash – that were undergoing enhanced erosion via arroyo incision during the historical period. Overall, the temporal overlap between the timing of historical tributary erosion and the establishment of substantial portions of downstream floodplain forest, in conjunction with the fact that floodplain sediment is dominantly sourced from watersheds that experienced enhanced historical erosion, together indicates a demonstrable link between the geomorphic process of historical erosion and the ecologic process of downstream floodplain forest establishment. From a summary of existing studies concerning the geomorphic adjustment of low-gradient, alluvial rivers to increased sediment supply, it is additionally clear that tributary erosion that injects substantial amounts of sediment into a river system can result in the requisite channel change necessary for successful forest establishment. The fluvial system is thus best understood as not just a physically coupled network, but a collectively connected web of processes that together regulate and are regulated by one another. Such an understanding emphasizes that management of large watersheds must be holistic and undertaken at the basin scale in order to ensure that vital riverine ecosystems endure.
Open Access
Seeing the river through the trees: using cottonwood dendrochronology to reconstruct river dynamics in the Upper Missouri River Basin
(Colorado State University. Libraries, 2017) Schook, Derek Michael, author; Rathburn, Sara, advisor; Friedman, Jonathan, committee member; Wohl, Ellen, committee member; Covino, Tim, committee member; Denning, Scott, committee member
Understanding the past is critical to preparing for the future, especially regarding rivers where extreme events and gradual changes underlie modern forms and processes. Both biological and human communities rely on the abundant resources provided by rivers and floodplains, particularly in dry regions of the western U.S. where water limits growth. To expand temporal perspectives on river processes, I reconstructed flow, channel migration, and riparian forest growth patterns in the Upper Missouri River Basin. Flow reconstructions typically use tree rings from montane conifers. However, I used riparian plains cottonwoods (Populus deltoides ssp. monilifera) directly connected to the alluvial water table to reconstruct flow on the Yellowstone (n = 389 tree cores), Powder (n = 408), and Little Missouri Rivers (n = 643). A two-curve Regional Curve Standardization approach was used to remove age-related growth trends from tree rings at each site. The flow reconstructions explained 57-58% of the variance in historical discharge and extended back to 1742, 1729, and 1643, respectively. Low-frequency flow patterns revealed wet conditions from 1870 to 1980, a period that includes the majority of the historical record. Two 19th century droughts (1816-1823 and 1861-1865) and one pluvial (1826-1829) were more severe than any recorded, revealing that risks are underestimated when using the instrumental period alone. These are the first flow reconstructions for the Lower Yellowstone and Powder Rivers, and they are the farthest downstream among Rocky Mountain rivers east of the Continental Divide. Cottonwood-based flow reconstructions were possible because the trees used river-connected groundwater, and tree ring width strongly correlated with March-June flow magnitude at the Yellowstone River (r = 0.69). Beyond the site-level growth patterns typically used to reconstruct flow, I found that biological and spatial characteristics affected how individual trees responded to flow and climate. Older trees contained stronger signals of non-growing season flow, precipitation, and temperature, which challenges the common dendrochronological assumption of stable tree ring-climate relationships through time. Although trees both near and far from the channel were better correlated to spring flow than precipitation, more distant trees had a stronger relative connection to precipitation, suggesting that greater distance decreases the ability of river water to fulfill transpirative demands. Like annual growth, cottonwood establishment is related to river flows, and tree age indicated fluvial processes including channel migration. I quantified nearly two centuries of channel migration on the Powder River by integrating measured channel cross-sections (1975-2014), air photos (1939-2013), and transects of aged cottonwoods (1830-2014). The combined data revealed that channel migration rates were lower (0.81 m/yr) in the recent and intensively studied cross-section period compared to the longer air photo (1.52 m/yr) and cottonwood (1.62 m/yr) periods. On the Powder River, extreme floods such as those in 1923 and 1978 increase subsequent channel migration rates and initiate decades of channel morphological adjustments. Across the study rivers, data indicate that fundamental fluvial processes have responded to climatic and watershed pressures. By identifying and quantifying past events, diverse research approaches improve understanding of the river, floodplain, and riparian forest processes that are essential to the persistence of these valuable ecosystems.
Open Access
The ecology and evolution of plant-insect interactions among hybrid populations of the invasive plant, tamarisk (Tamarix sp.), in the western United States
(Colorado State University. Libraries, 2012) Williams, Wyatt I., author; Norton, Andrew, advisor; Friedman, Jonathan, committee member; Hufbauer, Ruth, committee member; Nissen, Scott, committee member; Bauerle, William, committee member
Tamarisk is one of the most abundant invasive tree species in the western United States. Several species belonging to the genus Tamarix were imported intentionally to the U.S. in the mid-nineteenth century. Currently, most U.S. populations are comprised of a hybrid swarm between T. ramosissima and T. chinensis and other species. Negative consequences of hybrid tamarisk invasion include alteration of ecosystem functioning and decreases in native biodiversity. Very few natural enemies attack this invasive plant, contributing to its success on the landscape. In an attempt to provide top-down population control, a specialized herbivore that coevolved with tamarisk in its native range was intentionally released in the introduced range (i.e. biological control). I investigated interactions between tamarisk hybrids and herbivores in order to better understand the dynamics that contribute to the control of this exotic weed. In Chapter 1, which was published in Volume 57 of The Southwestern Naturalist, I describe how a native stem-boring beetle was found attacking tamarisk populations in eastern Colorado, western Kansas, and southwest Nebraska. This is an important discovery because very few native insects have been reported to consume this plant and never at the levels of the stem-borer. The beetle may reduce tamarisk growth and fecundity on the Great Plains, providing evidence for the biotic resistance hypothesis. In Chapter 2, I investigate the interaction between drought and herbivory by the biological control agent, Diorhabda carinulata. Under which environmental conditions or geographical locations can biological control be maximized? Finally, in Chapter 3, I speculate whether hybrid tamarisk individuals or populations differ in plant performance and herbivore defense traits. Since the biological control agent coevolved with one parent species, T. ramosissima, I hypothesized that some hybrids may be more or less susceptible to attack by this herbivore. Success of biological control may hinge upon the level of species introgression, and if hybridization occurs predictably across the landscape, managers can exploit this information for tamarisk control. My research not only attempts to improve control strategies, but also addresses fundamental questions in plant-insect ecology and evolution.
Open Access
The influence of chilling requirement on the southern distribution limit of exotic Russian olive (Elaeagnus angustifolia) in western North America
(Colorado State University. Libraries, 2011) Guilbault, Kimberly Rose, author; Brown, Cynthia S., advisor; Friedman, Jonathan, committee member; Shafroth, Patrick B., committee member; Angert, Amy L., committee member
Russian olive (Elaeagnus angustifolia L.), a Eurasian tree, is now a dominant species along rivers in western North America. The southern boundary of Russian olive distribution in western North America runs through southern California, Arizona, New Mexico and Texas. I related the distributional pattern of Russian olive to temperature regime and investigated potential temperature-dependent mechanisms that might explain this distributional limit. Specifically, I investigated whether lack of cold temperatures at the southern limit may prevent the accumulation of sufficient chilling and inhibit dormancy loss of seeds and buds, potentially constraining Russian olive's southern distribution boundary. First, I used field observations to thoroughly define the southern limit of Russian olive across western USA and related this distribution to temperature variables. I found that Russian olive occurrence was more strongly associated with low winter temperatures than with excessive summer heat. I then carried out controlled seed germination and vegetative bud-break experiments and a field survey of fruit production and seed viability. Next, I cold stratified Russian olive seeds in growth chambers with temperature regimes simulating six locations along a latitudinal gradient from Socorro, New Mexico (33.8°N latitude) to Presidio, Texas (29.56°N latitude). Both germination proportion and germination times were highest under temperature regimes simulating locations near the southern range limit and declined for temperature regimes simulating locations north and south of the range limit. This pattern only weakly supports the hypothesis that germination would decrease south of the southern range limit. I then conducted an additional controlled germination experiment containing treatments with varying levels of cold stratification, the results of which suggest that the chilling requirement for germination is partly responsible for the southern range limit. Both seed germination proportion and germination time decreased when the amount of cold stratification dropped below values typical of the southern range limit. I also carried out a preliminary bud-break experiment where Russian olive cuttings that were pre-exposed to natural chilling were subjected to various levels of additional chilling in a refrigerator. The results of this experiment suggest that a high percentage of buds burst with chilling values less than those typical of the southern limit. I then conducted a controlled bud-break experiment with cuttings that accumulated varying levels of chilling naturally. Percent bud break decreased when chilling dropped below values typical of the southern range limit, suggesting that the chilling requirement for bud-break is partly responsible for the southern range limit. In 17-65% of the years from 1980-2000, the chilling accumulated at a site near the southern range limit (El Paso, Texas) would lead to a 10% or more decrease in bud-break. The potential decline in growth could have large fitness consequences for Russian olive trees. Finally, I collected fruit production and seed viability data. While fruit production did not decline towards the southern range limit, seed viability declined with decreasing latitude. If climate change follows a warming trend, it is very likely that the chilling requirement for bud-break of Russian olive trees will not be met in some years and this combined with decreased seed viability at lower latitudes may cause its southern range limit to retreat northward. The retreat of a widespread non-native species, such as Russian olive, may present land managers and ecologists with a unique restoration opportunity.
Open Access
Vegetation and lithologic influences on channel morphology in the southwestern U.S.
(Colorado State University. Libraries, 2024) Wieting, Celeste, author; Rathburn, Sara, advisor; Wohl, Ellen, committee member; McGrath, Dan, committee member; Morrison, Ryan, committee member; Friedman, Jonathan, committee member
Vegetation and lithology play critical roles in shaping landscapes, creating diverse river and gully morphologies. Vegetation stabilizes banks and alters flow dynamics. In the Southwestern United States, non-native, invasive plant species contributed to regional trends of river channel narrowing and simplification and degraded diverse riparian habitats throughout the 20th century. More recently, efforts to remove invasive riparian vegetation (IRV) have been widespread, especially since 1990. Restoration practitioners who perform IRV treatments often focus on wildlife or vegetation response; however, geomorphic processes should be considered in restoration planning because they drive flow, sediment transport, and aquatic habitat and vegetation dynamics, and because of the potential for damage to downstream people and infrastructure. Depending on the restoration goal, management practices can be used to enhance or minimize the increase in channel dynamism caused by IRV removal. At the river reach scale, I investigated biogeomorphic feedbacks at one of the 15 previously analyzed study sites, the Rio Grande in Texas. Along the Rio Grande in Big Bend National Park (BIBE), restoration goals to remove invasive giant cane (Arundo donax) include decreasing channel narrowing and increasing water and sediment conveyance. Recent work has indicated that removal of giant cane has successfully reduced its extent, but the geomorphic effects of giant cane treatment and subsequent revegetation are still not well understood. A general lack of reach-scale studies of riparian plant pronation during flow inundation and the biogeomorphic feedbacks between plants, flow, and sediment transport contribute to this knowledge gap. I quantified morphological-effect plant traits for three common riparian plant species: invasive giant cane, native baccharis (Baccharis salicifolia), and native phragmites (Phragmites australis). I collected data at the plant, plot, and reach scales and created upright and flexible frontal area and vegetation roughness curves using photographs of plants and stem counts of plots. Then, I used these data in a reach-scale 2D hydraulic model to simulate species-specific effects and the effects of giant cane removal on channel hydraulics. Results indicate that the mean vegetation roughness is similar for all three species at the plant scale, but at the plot scale, vegetation roughness is higher for giant cane and phragmites due to higher stem densities. Hydraulic modeling results suggest that vegetation increased velocities in the center of the channel and decreased velocities on the channel margins. When all the vegetation was represented as giant cane, reach-scale water surface elevations were the highest and reach-scale velocities the lowest. Removing giant cane decreased water surface elevations, indicating increased conveyance. To determine the effects of IRV removal on a regional scale across the Southwest U.S., treated and untreated reaches at 15 sites along 13 rivers were compared before and after IRV treatment using repeat aerial imagery to assess long-term (~10 year) channel change. Resolving observations of channel change into separate measures of floodplain destruction and formation provided more information on underlying processes than simple measurements of channel width and centerline migration rate. IRV treatment significantly increased channel width and floodplain destruction. Treated reaches had higher floodplain destruction than untreated reaches at 14 of 15 sites, and IRV treatment increased floodplain destruction by a median factor of 1.9. The effect of treatment increased with the stream power of the largest flow over the study period. From the results, I suggest that restoration managers consider the system's susceptibility to change, downstream threats, and desired process changes when defining their geomorphic restoration goal because treatment of a dominant species over a large area can be expected to have major fluvial geomorphic consequences. In addition to vegetation, the lithology and surficial sediment properties influence hydrological processes, sediment transport, and gully and channel morphology. In semi-arid environments where vegetation is lacking, and precipitation is sufficient to drive erosion, sediment yields tend to be greatest. Increased landscape erosion is predicted as more extreme weather causes frequent or intense rainfall, and flooding. In Wupatki National Monument (WUPA), heavy rainstorms over the past decade, lack of vegetation, and presence of unconsolidated volcanic-derived cinders expose archaeological sites to erosion, a concern to cultural resource managers. To identify archaeological sites of highest vulnerability to erosion, I analyzed gully morphologic change over a 5-year period. I found that 35 measured gullies are actively eroding, with statistically significant changes in gully depth from 2016 to 2021. Up to 0.5 m of incision was documented over a five-year period. A structure-from-motion analysis at the hillslope scale confirmed gully morphological changes and supports the applicability of conducting similar analyses on a larger scale. More erosion occurred in gullies with catchments predominantly covered with cinders because of cinder mobility. A weak relationship was noted between gully catchment area and gully head slope, likely related to runoff processes from outcrops of resistant sedimentary rocks forming cliffs and characteristics of cinders that maximize infiltration and transport. Based on assessment of gully morphologic change and substrate characteristics, 22 archaeological sites along Wupatki Wash were identified as having a high vulnerability to erosion.