Browsing by Author "Rhoades, Charles C., committee member"

Now showing 1 - 5 of 5

Open Access
An investigation of nitrogen fixation by Russet buffaloberry in Colorado conifer forests
(Colorado State University. Libraries, 2011) Miller, Zoe May, author; Paschke, Mark W., advisor; Binkley, Daniel E., committee member; Rhoades, Charles C., committee member; Stromberger, Mary E., committee member
Russet buffaloberry (Shepherdia Canadensis (L.) Nutt.) is an actinorhizal shrub capable of forming a symbiotic relationship with the N2-fixing soil actinomycetes Frankia. Actinorhizal shrubs are important species as they are able to fix an ecologically significant amount of N and can inhabit disturbed sites with infertile soils. Buffaloberry is commonly found as a dominant understory species in lodgepole pine (Pinus contorta Douglas ex Louden) communities and is a common post-fire disturbance species. There is a lack of information regarding buffaloberry's ability to fix atmospheric N2 in Colorado forests. This study used the 15N natural abundance method in a survey of buffaloberry in north central Colorado to determine the percent of foliar N that buffaloberry derives from fixation (%Ndfa) and how fixation may be affected by local environmental factors. The mountain pine beetle (Dendroctonus ponderosae) epidemic is currently responsible for large losses in lodgepole pine forests. As the overstory canopies of lodge pole pine communities die off, there is an increase in available light in the understory. I investigated buffaloberry's response to light availability because with more photosynthetic activity, buffaloberry could potentially have more energy to expend in the energy intensive N2-fixation process. 59 plots (0.1-ha) were sampled in July 2009 and were distributed among Larimer, Jackson, and Grand counties in Colorado. Buffaloberry (15N: ‒0.63 /, N: 3.48%) had a 15N abundance closer to the atmospheric standard with high foliar %N content as compared to non-N2-fixing reference species (15N: ‒.29- ‒4.81 / N: 1.11-3.20%), indicating biological N2-fixation. I estimate a probable range of foliar %N derived from biological fixation as 60-100%. Buffaloberry (2.65%) also had higher % foliar N as compared to the reference species (1.50%) in the autumn, just before leaf abscission. There were no significant correlations between light availability and N2-fixation by buffaloberry suggesting that N2-fixation in buffaloberry may not benefit from an increase in light availability.
Open Access
Evaluating soil productivity and climate change benefits of woody biochar soil amendments for the US Interior West
(Colorado State University. Libraries, 2018) Ramlow, Matthew Alan, author; Cotrufo, M. Francesca, advisor; Ogle, Stephen, committee member; Rhoades, Charles C., committee member; von Fischer, Joseph, committee member
Managing our lands to provide for today and the future requires sustainable land management practices that enhance productivity while reducing climate impacts. Proponents claim biochar soil amendments offer a comprehensive solution to enhance soil capacity to deliver water and nutrients to plants while decreasing climate impacts through reduced nitrous oxide (N2O) emissions from fertilizer use and carbon (C) sequestration. This dissertation evaluates such claims for woody biochar applications within the US Interior West; to enhance crop production and reduce N2O emissions in deficit irrigation agricultural systems, and to support forest road restoration efforts. It also employs laboratory incubations and soil biogeochemical modeling to predict and to better understand the controls on biochar's greenhouse gas mitigation potential. The field studies demonstrate that this woody biochar improved soil moisture content but its enhanced capacity to retain water did not alleviate plant water stress when water inputs were low. Similarly, in forest soils, this woody biochar amendment improved plant available N but at levels that did not impact productivity. In lab incubations this woody biochar reduced N2O emissions. While this reduction could not be explained by bulk soil mineral N transformations, the soil moisture regime did affect biochar's ability to reduce N2O emissions. Despite the observed biochar N2O emission reductions in incubated soils, under field conditions biochar effects on N2O emissions were inconclusive. When evaluating biochar's C sequestration potential, soil biogeochemical modeling revealed that 59 percent of the biochar C applied will be sequestered in soils after 100 years. Losses from biochar fragmentation and leaching may constitute a considerable proportion of the C losses. Of the applications considered, C sequestration remains the most promising use for biochar soil amendments within the US Interior West.
Open Access
Forest regeneration and future stand trajectories following mountain pine beetle-caused lodgepole pine mortality
(Colorado State University. Libraries, 2014) Pelz, Kristen A., author; Smith, Frederick W., advisor; Dickinson, Yvette L., committee member; Martin, Patrick H., committee member; Rhoades, Charles C., committee member
A mountain pine beetle (MPB) (Dendroctonus ponderosae) outbreak that began in the late 1990s has killed lodgepole pine (Pinus contorta var. latifolia) on up to 10 million hectares in western North America. Over one million hectares have been affected in northern Colorado and southern Wyoming. The large footprint of this disturbance has prompted widespread concern about the composition, structure, and function of forests as they develop following MPB. In this dissertation, I ask how variation in species composition and mortality level will affect the future forest in the Southern Rockies. I used forest growth models to predict forest structure and fuel loads during the century after MPB outbreak. I compared three lodgepole pine-dominated forest types (all > 80 % lodgepole by basal area) and the simulated effects of no-action and fuel reduction treatments. Forest with Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa var. lasiocarpa) became much more dominated by these species, resulting in highly hazardous canopy fuels. In contrast, stands of lodgepole and aspen (Populus tremuloides) did not shift composition and did not show a marked increase in fire hazard. The effects of management were also differed: hazardous fuels were best mitigated in the forest types with spruce and fir, but treatment had few positive effects in the stands of only lodgepole and aspen due to their lower hazard without treatment. The results show management of lodgepole-dominated forests must consider even subtle variation in composition to be effective. I also examined post-outbreak regeneration in these forests. In mixed lodgepole pine and aspen stands, I asked if regeneration is sufficient to reforest areas affected by MPB. Both species excel in high light environments that are created by overstory mortality, but lodgepole pine is thought to require ground disturbance to regenerate. Aspen regeneration can be prevented by browsing. I found lodgepole regeneration is occurring in 85% of stands, and all stands had aspen sucker density above 1000 stems ha-1. Many suckers are damaged by browsing, but my results suggest that sufficient quantities of down lodgepole pine may protect suckers and allow them to recruit to the overstory. Overall, I conclude aspen and lodgepole forests are regenerating successfully and that these areas will remain mixed forests of both species in the future. Finally, I measured the effects of mortality level on regeneration. I compared regeneration density and growth of lodgepole, spruce, and fir in high (85% of basal area) and moderate (40% of basal area) mortality forest. Lodgepole pine regeneration density and growth was high where outbreak was most severe, though all species grew faster in high mortality than moderate mortality. All three species will likely be important to future forest in areas with high mortality, and lodgepole pine will play a substantial role. In contrast, in moderate mortality areas lodgepole pine regeneration is nearly absent and spruce and fir are growing fastest. Here the forest understory will be made up of shade tolerant species, and the forest will become progressively more dominated by these species as this stratum develops.
Embargo
Lodgepole pine resilience in Troublesome times: the influence of stand-level characteristics on regeneration following bark beetle mortality and wildfire
(Colorado State University. Libraries, 2025) Horn, Mattie, author; Rocca, Monique, advisor; Stevens-Rumann, Camille, committee member; Rhoades, Charles C., committee member
Climate-driven increases in disturbance activity from bark beetle outbreaks and wildfire have prompted concerns for potential declines in tree regeneration. In forests of the Southern Rocky Mountains, widespread tree mortality from bark beetles over the last few decades has resulted in forest conditions that may drive alternate patterns of recovery following subsequent wildfire. As such, the extreme fire season of 2020 presents a unique opportunity to examine the patterns of forest recovery following two disturbances that are unprecedented in their severity and extent. In this study, I collected field data on lodgepole pine seedling recruitment following the East Troublesome fire, which burned through beetle-killed lodgepole pine stands (11-19 years post outbreak), to 1) assess the potential for natural forest recovery and 2) determine the primary stand-level factors that influence the abundance of post-fire lodgepole pine seedlings. In the summer of 2022, I sampled 116 plots across gradients of beetle severity, fire severity, and stand age in Rocky Mountain National Park, Colorado. In each plot, I measured variables capturing fire effects, forest structure, topography, and post-fire regeneration. General linear mixed models were used to determine the relative influence of fire effects, seed source, stand characteristics, and topography on post-fire lodgepole pine seedling density. I found that 97% of the study area had lodgepole pine seedlings established at 2 years post-fire, and 70% of the study area had seedling densities exceeding 370 t ha -1, however, seedling densities were highly variable across the landscape. The abundance of lodgepole pine seedlings at the plot-level was strongly associated with the density of cone-bearing trees, elevation, and tree consumption. These results highlight the mechanisms by which pre-fire forest structure and canopy consumption alter post-fire seed availability to influence post-fire lodgepole pine recruitment. My findings help inform predictions of future forest trajectories following sequential disturbance by bark beetle outbreaks and wildfire and underscore the need for tailored forest management approaches that consider both the legacy of bark beetle outbreaks as well as the variable nature of fire effects.
Open Access
Weathering and soil properties on catenary sequences in forest and alpine ecosystems of the central Rocky Mountains
(Colorado State University. Libraries, 2017) Bergstrom, Robert Mark, author; Kelly, Eugene F., advisor; Rhoades, Charles C., committee member; Borch, Thomas, committee member; Melzer, Suellen, committee member; Martin, Patrick H., committee member
The evolution of soil landscapes can be evaluated by studying soil properties along catenary sequences—soil sequences that are hydrologically and topographically connected along hillslopes from higher elevation to lower elevation. Using the catena model, I investigated the manifestation of soil forming factors in conditioning weathering and soil development in the Mountain Ecosystems of the Fraser Experimental Forest (FEF), Colorado. The research outlined and presented in this dissertation is preceded by a short narrative on soil forming properties, hillslope models, and assessing weathering in soils. The work presented in this dissertation is a result of a multidisciplinary framework for pedological research, derived from the integration of and consideration of pedology, geomorphology, and hydrology. The future of pedological research will involve the assimilation of multidisciplinary approaches and thinking. This dissertation elucidates on (1) the distribution of soil properties along soil catenas and their implication for hydrologic and biogeochemical linkages across landscapes, (2) the evaluation of chemical alteration thru modeling soil strain along soil catenas, (3) the quantification and distribution of soil elemental fluxes along soil catenas, and (4) the determination of the contributions of weathering and atmospheric inputs to landscapes at FEF. My field sites were located in FEF, a model site of the alpine and forested environments of the central Rocky Mountains. The FEF is an ideal setting to study the interaction of soil forming factors in complex mountain terrain. A combination of traditional and more modern methods to explore the linkages between soil properties along mountain catenas were employed in order to gain insight into soil landscape evolution in complex mountain terrain. I established eight catenas along relatively steep mountain hillslopes while constraining the lithologic differences along the soil landscapes. Vegetative changes along these catenas could not be ignored; rather, the differences provided insight into the influence of vegetative cover on soil properties. Soils were sampled along the catenas, beginning in the mountaintop landscapes (crests or summit) and ending in the mountainbase landscapes, where wetlands along riparian corridors dominate. Soil morphology and soil chemistry along the catenas provided understanding into the evolution of soil landscapes at FEF and their connectedness to the hydrologic flowpaths along these hillslopes. Results suggested that these soil landscapes are in various states of evolution, marked by the relative development of illuvial and elluvial horizons, and that the landscapes are dominated by subsurface lateral flow. The data also suggested that atmospheric deposition may be an important contributor to pedogenesis in these landscapes and that there are expected hot-spots of nutrient accumulations in the mountainbase landscapes, where upland soils have transported and deposited dissolved ions and fine soil particles into wetland soils along riparian corridors. The next question became: does the distribution of elements along soil landscapes reflect what was expected from the aforementioned analyses and is the fate of elements controlled by the landscape positions? What is the balance between the atmospheric contributions to weathering and internal cycling of cations? Subsequently, the analysis for soils along the catenas was extended to model soil strain within the soil landscapes, quantify mass fluxes and distribution of elements within the soil landscapes, and quantify the atmospheric contributions to weathering in these systems. Results indicated that dilation in upper soil horizons reflect the textural patterns in the same horizons across all landscapes—supporting the notion that the soils along theses catenas have been strongly influenced by additions via atmospheric deposition, and this influence is detectable across entire hillslopes. Also, modeled soil strain indicated that great pedogenic additions have occurred in the mountainbase landscapes—supporting the notion that dissolved ions and fine soil material have been transported and deposited downslope via subsurface lateral flow. Calculated elemental flux values indicated that soil nutrients originating the upland landscape positions are transferred to lower landscapes through the mountainflanks, and are deposited in the mountainbase landscapes, where the soils were found to be enriched in the following major elements—Ca, Na, K, Al, Fe, and Mg. In turn, the impact of atmospheric contributions to soil landscapes along a catena was revealed. The data suggested that surface soil horizons are more strongly influenced by atmospheric contributions than subsurface horizons. Likewise, subsurface horizons are increasingly more influenced by the weathering of parent material moving from higher soil landscapes to lower soil landscapes. Lastly, results suggest that the isotopic signature within mountaintop soil landscapes is coupled to vegetative cover and snowfall and snowmelt hydrology dynamics. The soil catena model endures as a framework for providing insight into the relationships of soil forming factors across gradients of variation.