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Browsing by Author "Rhoades, Chuck, advisor"

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    Evaluating post-fire woody mulch effects on soil and stream nitrogen
    (Colorado State University. Libraries, 2024) Richardson, Mikaela, author; Kampf, Stephanie, advisor; Rhoades, Chuck, advisor; Ross, Matt, committee member; Wilkins, Mike, committee member
    Severe wildfires often increase nitrogen (N) loss from burned watersheds, impacting downstream water quality, water treatability, and aquatic habitat. Woody mulch is commonly applied to mitigate soil erosion and enhance revegetation post-fire, but it also provides a source of labile carbon (C) that may stimulate microbial immobilization and limit N release from soils. The objective of our study was to evaluate whether mulch application influenced turnover and loss of soil C and N in laboratory leaching trials and hillslope field settings, and then compared post-fire C and N in streams draining mulched and unmulched catchments. In the laboratory, we quantified C and N inputs and leaching outputs from mulched and unmulched soil columns. Within the Cameron Peak fire burn scar in northern Colorado, we compared soil N availability and potential leaching losses between mulched and unmulched hillslope plots. We also measured C, N, and other chemical constituents in streams draining three mulched and three unmulched catchments. In the laboratory leaching studies, mulch added high concentrations of dissolved organic carbon (> 500 mg L-1) and decreased nitrate leaching from soil columns by 27% during repeated simulated rainfall events. In hillslope plots, mulching also reduced soil nitrate, with greater impacts following spring snowmelt when N losses from soils to streams was highest. However, the effect of mulching was not measurable at the catchment scale due to low application rates and mulch extent, paired with high topographic and geomorphic variability amongst the catchments. Our findings show that C inputs from woody mulch can influence soil N retention in burned watersheds when applied at a minimum rate of 5 Mg ha-1; however practical constraints on aerial application may make it challenging to apply enough mulch for any downstream response to be detectable. Coupled with physical erosion protection, the biogeochemical impacts of mulching may facilitate soil and vegetation recovery following severe wildfire and reduce post-fire N losses to streams if sufficiently applied. Therefore, further post-fire rehabilitation efforts should optimize mulch operations by prioritizing sensitive watersheds and treating them with adequate mulch.
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    Soil seed bank composition and implications for ecological restoration in degraded Colorado shrublands
    (Colorado State University. Libraries, 2020) Schroeder, Ryan W. R., author; Paschke, Mark, advisor; Rhoades, Chuck, advisor; Meiman, Paul, committee member; Grant-Hoffman, M. Nikki, committee member; Melzer, Suellen, committee member
    Soil seed banks of shrub-dominated ecosystems in western North America are poorly understood. The potential of the soil seed bank – the species composition and abundance of seeds – to impact ecological restoration has rarely been considered in ecological restoration of shrublands and could influence management decisions. I analyzed the germinable soil seed bank composition and distribution in two high-conservation priority ecosystems in Colorado. Studies were carried out to characterize seed bank composition and relationship to aboveground vegetation in "undesirable" and "desirable" plant communities; determine if "shrub islands" influence seed bank distribution; and assess the landscape and vertical distribution of the seed bank in a Bromus tectorum L. (cheatgrass) invaded rangeland. For all seed bank studies, soil seed bank samples were collected to a depth of 5 cm and grown in greenhouse conditions to determine the species composition and abundance of germinable seeds. I found that seed bank species richness and Shannon-Wiener diversity (H) did not differ in either shrubland between undesirable sites dominated by non-native vegetation and desirable sites dominated by native vegetation. Total seed abundance in a montane sagebrush shrubland was significantly greater in desirable sites (1401 ± 165 seeds m-2) compared to undesirable sites (588 ± 190 seed m-2). In a salt desert shrubland of the Colorado Plateau, total seed abundance did not differ, but on average non-native species seeds made up more than 60% of the total seed bank in undesirable sites, compared to 40% in desirable sites. In a separate study, shrub islands across Colorado were not associated with increased seed bank species richness or seed abundance compared to adjacent shrub-less interspaces. Differences in seed bank Shannon Wiener diversity (H) varied between shrublands, with salt desert shrublands having significantly greater (p-value < 0.05) seed bank diversity inside of shrub islands compared to shrub-less interspaces. Another study was conducted in a Bromus tectorum L. (cheatgrass) invaded rangeland of the Colorado Plateau to determine the seed bank horizontal and vertical distribution. The germinable soil seed bank had a greater abundance and lower spatial variability of native species seeds (3390 seeds m-2, CV = 75%) than non-native species seeds (1880 seeds m-2, CV: 124%) across the sampled landscape. Non-native species (primarily Bromus tectorum L.) seed were concentrated in the upper 2 cm soil (1294 ± 155, p-value <0.0001), but were found in substantive abundance in the 2 – 5 cm seed bank layer (585 ± 91). In addition to seed bank studies, in the fall of 2018, I established a study in a montane shrubland to test the effectiveness of seeding a high diversity native seed mix (39 species, 1496 PLS m-2) and treatments to increase site heterogeneity to increase native plant species diversity. One growing season following plot establishment, I found that plots that received a high diversity seed mix and those that received heterogeneity treatments had greater seeded species diversity (H) and richness than control plots.