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New Mexico State University (2021)

Connectivity and Seed Availability in Drylands : Interactions of Vegetation and Seed Movement at Multiple Scales

Turk, Tyler G

Titre : Connectivity and Seed Availability in Drylands : Interactions of Vegetation and Seed Movement at Multiple Scales

Auteur : Turk, Tyler G

Université de soutenance : New Mexico State University

Grade : Master of Science (MS) Range Science 2021

Résumé
Drylands globally make up 41% of the terrestrial land surface area. These systems are highly vulnerable to degradation due to a variety of interacting factors including climatic events and land use. Woody plant encroachment into arid grasslands is one widespread phenomenon that is often associated with dryland degradation. This encroachment leads to structural and functional changes in the system which facilitate positive feedback loops that further reinforce the shrubland state. For instance, shrub encroached areas are characterized by large, bare plant-interspaces where wind and water erosion occur, redistributing resources including sediment, seeds and litter. This results in greater nutrient availability and infiltration under shrub canopies as well as deficient interspaces where the ability of herbaceous plants to establish is greatly restricted. As encroachment worsens and presence of bare ground increases, the interspaces become connected pathways through which abiotic transport occurs. Sediment deposition, in turn, occurs at increasingly coarser scales, further separating deposited resources from the source. An emerging framework to understand dryland dynamics describes dry-landscapes with many large bare plant-interspaces, and associated movement of materials at large extents, as having a high degree of connectivity. Restoration in drylands has often incorporated methods to reduce the length of connectivity pathways to mitigate erosion and retain resources locally which promote herbaceous plant growth. This can be achieved in areas with high aeolian transport using structures known as connectivity modifiers (ConMods), which have been found to increase recruitment of desirable species. Seeds are an important resource captured by ConMods : quantifying the seeds captured in ConMods will allow us to gain insight into seed movement on the landscape, and has implications for the resilience of the system. For this research I quantified the amount of sediment and number of germinable seeds captured in ConMods at two long term research sites with variable grass and shrub cover at the Jornada Experimental Range in the Northern Chihuahuan desert by performing a seedling emergence study on the materials collected over one growing season. I also conducted a seed predation study to determine whether removal by granivores was contributing to patterns of seed availability. I found that seed movement was occurring broadly across the landscape, and that perennial grass species made up a large portion of the total seeds collected. However, sediment and seed movement did not have similar relationships to coarse scale connectivity metrics and patches with altered connectivity. My research suggests that successful use of ConMods as restoration tools necessitates consideration of current and past vegetation, and that increased seed removal by rodent granivores in shrublands may be further reducing seed availability.

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Page publiée le 5 décembre 2021