Understory Composition, Seedling Growth, and Snag Frequency Across a Water-Limited Forest Landscape

Global change is expected to increase drought intensity and make precipitation more uncertain. These changes can affect forest plant communities directly by altering demographic rates, and indirectly through interspecific interactions. Impacts can vary among forest strata. Here, I asked how different forest strata respond to topographic variation in soil moisture and other resources across a water-limited landscape. The objective of the second chapter was to compare responses of understory plant communities to soil moisture, nitrogen, and light, and to understand whether responses to soil moisture depend on the latter two. I measured functional traits (individual-level plant characteristics) of understory vascular plants and modeled the composition and diversity of understory plant communities as functions of soil moisture, nitrogen, and light availability. I found that understory plant communities on nitrogen-poor soils were more sensitive to soil moisture changes than communities on nitrogen-rich soil. The effect of soil moisture did not depend on light availability, however. In my third chapter, I conducted a competition removal experiment on white spruce seedlings to examine how competition intensity varies with both above and below-ground resource availability. I found that local competition and resource availability both affect the growth of white spruce seedlings, especially during a dry summer, when competition had an additive effect on seedling growth and mortality. The objective of my fourth chapter was to determine how snag (standing dead tree) distribution is affected by individual- and stand-level biotic and abiotic variables. I used an unmanned aerial vehicle to collect images of forest canopies and determine the position and characteristics of individual live and dead trees. I found that individual-level competition and stand-level biotic and abiotic factors affect three northern tree species in different ways, but that topographic variation in soil moisture had little direct effect on the frequency of snags. Resource availability affects every forest stratum. The intensity and direction of the effects depend on the biotic and abiotic environments, including soil conditions, individual plant traits, and competition from neighbours. Environmental variation in competition needs to be considered when predicting changes to plant communities under climate change.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Doctoral -- first

Discipline thesis:degree_discipline

Biology

Grantor dc:publisher

Faculty of Graduate Studies and Research, University of Regina

Year dc:date.issued

2020

Author dc:creator

• Shovon, Tanvir Ahmed

Advisors dc:contributor.advisor

• Vanderwel, Mark
• Gagnon, Daniel

Committee members dc:contributor.committeemember

• Sauchyn, David
• Gendron, Fidji
• Wilson, Scott

Language dc:language.iso

en

DOI

https://doi.org/10.82465/4254

OAI identifier oai:identifier

oai:uregina.scholaris.ca:10294/14346