Soil seed bank composition and implications for ecological restoration in degraded Colorado shrublands
Date
2020
Authors
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
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Abstract
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.
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Subject
public land
salt desert
ecological restoration
soil seed bank
sagebrush