Date of Award

2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Natural Resources

First Advisor

E. Carol Adair

Abstract

Elevated atmospheric CO2 levels pose a threat the global climate stability but large amounts of carbon can be held within soils worldwide. Forests function to capture carbon and eventually, through litter inputs and decomposition, add this carbon to soil systems. This process is driven by climate, landscape conditions, forest and soil characteristics, that have complex interactions with one another across spatial scales. In this dissertation, I examine drivers of carbon contributions to the mineral soil, via litter decomposition and forest floor carbon pools, and how these contributions vary with forest composition and soil conditions. First, using data from a 10-year litterbag decomposition experiment, I determined that variance in leaf and root litter decomposition rates have no link to soil carbon stocks in 27 sites across North America. Soil carbon instead has a positive correlation to the amount of litterbag materials remaining when decomposition ceases, but only when litter materials are decomposed in ecosystems similar to their origin. Next, I examined how controls on soil carbon stocks vary in strength with increasing soil depth in the diverse forests of Vermont. I found that soil carbon in surface soils was driven by forest characteristics, climate conditions and soil enzyme activity. Subsoil carbon stocks responded only to the abundance of iron- and aluminum-oxides, and all significant driving variables in our study had correlations with site elevation, suggesting complex interactions between variables in these forests. Finally, I used national forest inventory data from the USDA Forest Service Inventory and Analysis program and structural equation modeling to examine the link between forest floor and mineral soil carbon pools in the northeastern temperate forests. I discovered that there is no link between the size of these two carbon pools and that each has a distinct set of drivers, although for both carbon pools. tree species identity effects were more important that species diversity effects. Collectively, this body of research sheds new light on environmental drivers of soil carbon that have been overlooked and suggests new foci for landowners and forest management organizations seeking to manage landscapes with carbon sequestration objectives to combat climate change.

Language

en

Number of Pages

173 p.

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