Effects of complex spatial patterns on bark beetle-caused tree mortality in northern Arizona

Landis, Gia K. (2023) Effects of complex spatial patterns on bark beetle-caused tree mortality in northern Arizona. Masters thesis, Northern Arizona University.

Text Landis_2023_effects_complex_spatial_patterns_on_bark_beetle-caused_tre.pdf - Published Version Download (2MB)

Abstract

Bark beetles are native forest insects that cause low levels of tree mortality at endemic population levels and have the potential to cause widespread mortality when populations increase. High stand densities increase competition between trees, increasing tree stress and susceptibility to mortality from bark beetles. Recent silvicultural treatments in northern Arizona create complex spatial patterns, leading to variable individual tree competition within treated stands. However, the effect of variable individual tree competition on mortality from bark beetles is understudied. We examined the effects of tree competition on bark beetle-caused tree mortality in paired treated and untreated stands using randomly located stand-scale plots and paired individual tree-scale plots. Biotic and abiotic data were collected. We asked the following questions: 1. Is there less inter-tree competition around a bark beetle-killed tree compared with a similarly sized live tree? 2. Is there less competition around a bark beetle-killed tree compared with the overall stand-scale competition? 3. Is tree size influencing bark beetle-caused tree mortality? 4. Is site productivity an influencing factor in tree competition and overall bark beetle-caused tree mortality? We calculated differences between treated and untreated stands, individual tree-scale plots, and individual tree- and stand-scale means then analyzed the data using weighted t-tests, and paired and unpaired t-tests. Although few significant differences were found between the paired individual tree-scale plots, between individual tree-scale and stand-scale competition (inferred from stand density index, basal area, and trees per acre), or between treated and untreated stands, there was a notable amount of variation (assessed from the coefficient of variation) in the data and differences within individual stands, which may indicate that reducing stand density does not always reduce susceptibility to bark beetle-caused tree mortality in northern Arizona. Furthermore, they could influence the perception of the relationship between bark beetles and tree competition because our results deviate from historical trends (high densities = susceptibility to bark beetles). This study highlights the importance and need for monitoring, even of well-studied disturbances.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	bark beetles; competition; silviculture; southwest; spatial patterns;forest density
Subjects:	S Agriculture > SD Forestry
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > School of Forestry
Date Deposited:	19 May 2025 16:57
Last Modified:	19 May 2025 16:57
URI:	https://openknowledge.nau.edu/id/eprint/6151

Actions (login required)

IR Staff Record View

Downloads