Arctic shrub growth responses to environmental drivers and implications for tundra community decomposition

Tall deciduous shrubs are expanding into graminoid-dominated landscapes by measures of both range and abundance throughout the Arctic. This expansion has the potential to reduce ecosystem diversity and function as well as carbon pools in the tundra. Shrub growth is known to respond to climatic patterns over long temporal scales, and shrubs are expected to alter local patterns of litter decomposition by changing litter quality inputs and localized abiotic and biotic conditions. However, the relative importance of determinants of shrub growth and shrub expansion on litter decomposition remains unclear at the regional scale. I addressed these knowledge gaps by conducting two studies across five sites spanning a 160 km latitudinal gradient in northern Alaska. First, I used dendroecological methods to measure and characterize growth responses in Alnus viridis ssp. fruticosa and Betula nana stems collected from all five sites, and I associated these measurements with climate data and previously collected plant traits and microclimate characteristics from corresponding shrub plots. I used linear mixed-effects models (LMMs) and structural equation models (SEMs) to analyze the direct and indirect effect pathways of climate, microclimate, and plant traits on shrub growth. Second, to address shrub-related effects on litter decomposition, I employed a one-year litter bag experiment to decompose leaf and root litter in situ from three expanding shrub genera (Alnus, Betula, and Salix) and a dominant graminoid sedge (Eriophorum vaginatum). I used LMMs to characterize the relationships and establish the relative importance of litter quality, vegetation effects, and macro- and microclimate driving root and leaf litter decomposition around tall deciduous shrubs. In addition to strong climatic effects, I found that plant traits, including plant height, leaf nitrogen (N), and root tissue density can predict shrub growth across the lifetime of the individual. However, I did not find evidence of significant indirect effect pathways on shrub growth. Additionally, Alnus growth was more accurately described by these effects in comparison to Betula. Regarding litter decomposition, I found that macroclimate served as the primary control on E. vaginatum leaf and root mass loss as well as leaf N release across all vegetation types. In comparison, shrub litter decomposition was mainly driven by litter quality differences between genera. Shrub root litter decomposed more quickly than sedge root litter, and this pattern varied among the three shrub genera for leaf litter. These findings demonstrate that plant traits, as well as climate variables, can be used to predict shrub growth in the Arctic, and therefore demographic processes that drive shrub expansion. Additionally, shrub expansion in the Arctic can generate variation among leaf and root litter decomposition at the regional scale and diminish root litter carbon stocks by altering litter inputs and accelerating root litter decomposition. Including plant traits and shrub-related processes in demographic and Earth system models will therefore improve the community’s capacity to accurately predict shrub expansion and regional-scale litter decomposition and its effects on carbon and nutrient cycling in a warming Arctic.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Natural Res & Env Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Vozzo, Justin Timothy

Contributors dc:contributor

• Fraterrigo, Jennifer

• Arctic Tundra
• Ecosystems
• Deciduous Shrubs
• Litter Decomposition

Statement dc:rights

• Copyright 2024 Justin Vozzo

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/124694

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F124694