RANGELAND SOIL SEED BANK DYNAMICS: SOIL PROPERTY RELATIONSHIPS, PATTERNS ACROSS A DEGRADATION GRADIENT, AND RESPONSES TO SHRUB MANAGEMENT

Author

Ryan Willis Richard Schroeder

Year of Award

2024

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Systems Ecology

Department or School/College

W.A. Franke College of Forestry

Committee Chair

Akasha Faist

Commitee Members

Ben Colman, Cory Cleveland, Dean Pearson, Erik Lehnhoff

Keywords

dryland, regenerative potential, restoration ecology, shrub encroachment, soil-seed-plant interactions, state transition

Abstract

Rangeland ecosystems are globally important for their ecosystem service delivery, however, they are experiencing several threats pushing systems across ecological states. Thus, creative science-based management is imperative to maintain ecosystem sustainability and improve ecosystem service delivery. Soil seed banks – the living seeds in the soil profile and on the soil surface – and their soil-seed-plant interactions are one area of inquiry that could help guide science-based management efforts when it comes to rangeland community assembly and ecological restoration.

In this dissertation, I investigated rangeland soil-seed-plant interactions in New Mexico, USA. In Chapter 1, I worked with an expert group to identify soil physical, chemical, and climate properties that influence a soil’s suitability to store and maintain viable rangeland plant seeds over time. Here, I developed a model and tool to predict the soil seed bank (SSB) suitability of soil map units within the Web Soil Survey (WSS) framework. The model and tool developed in Chapter 1 is publicly available via the USDA’s WSS platform (https://websoilsurvey.sc.egov.usda.gov/app/). The tool is intended to help identify potential promoting or limiting factors influencing seed storage, maintenance, and carry-over in surficial mineral soil and provide a suitability interpretation rating to aid in rangeland seeding, restoration, and conservation planning efforts. Chapters 2 and 3 were conducted in the northern Chihuahuan Desert, USA to understand soil-seed-plant interactions along a shrub encroachment degradation gradient (Chapter 2) and the potential direct and indirect effects of synthetic auxin herbicide application on the SSB across the gradient (Chapter 3). A Before-After-Control-Impact-Paired-Series experiment was established along a black grama (Bouteloua eriopoda) grassland to honey mesquite (Prosopis glandulosa) shrubland gradient and aboveground vegetation data, SSB samples, and soil property samples from shrub and interspace microsites were collected over three years (2020, 2021, and 2022). Soil seed bank samples were quantified using greenhouse emergence trials to express the readily germinable SSB. In Chapter 2, I found that soil resource depletion from interspaces and concentration underneath shrubs during grassland degradation are an amplifying feedback and may be a mechanism through which alternate shrubland states are maintained, likely posing a barrier to grassland restoration. Lastly, in Chapter 3, I found herbicide application had a significant negative direct impact on the SSB species richness in interspaces immediately post-treatment, primarily impacting forb species in Asteraceae. However, this management method may be unlikely to pose a major unintended restoration barrier of shrub-invaded grasslands and can indirectly increase SSB expression and its regenerative potential.

Although the SSB and aboveground vegetation are decoupled, the SSB provides resilience and resistance to change and can influence the success or failure of both active and passive restoration actions. Ecological resilience is increasingly important to consider and implement in a changing environment. The SSB is a core facet of how ecosystems buffer change and respond to perturbations. By incorporating SSB storage and maintenance strategies and leveraging compositional dynamics – both the in situ SSB and when actively modifying the SSB – rangeland ecological restoration may better meet the challenges faced to improve and maintain the delivery of important ecosystem goods and services across spatial and temporal scales.

Recommended Citation

Schroeder, Ryan Willis Richard, "RANGELAND SOIL SEED BANK DYNAMICS: SOIL PROPERTY RELATIONSHIPS, PATTERNS ACROSS A DEGRADATION GRADIENT, AND RESPONSES TO SHRUB MANAGEMENT" (2024). Graduate Student Theses, Dissertations, & Professional Papers. 12421.
https://scholarworks.umt.edu/etd/12421