First Advisor

Andrés Holz

Term of Graduation

Summer 2024

Date of Publication

8-9-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.) in Earth, Environment, & Society

Department

Earth, Environment, & Society

Language

English

Physical Description

1 online resource (xvi, 271 pages)

Abstract

Altered fire regimes, combined with a warmer and drier climate, have been eroding the resilience of temperate rainforests and peatlands worldwide and leading to alternative post-fire vegetation communities. I used a social-ecological systems framework informed by theories of non-linear ecosystem dynamics on the one hand and political ecology and 'politics of scale' scholarship on the other to investigate, 1) the underlying causes of a shift in vegetation dominance from forests dominated by the conifer, Pilgerodendron uviferum, to peat-generating ecosystems dominated by the peat moss, Sphagnum magellanicum; and 2) what this means for the futures of local people's livelihoods in the forest-peatland ecotone of western Patagonia.

First, I compared present-day environmental conditions and vegetation structure and composition across a reburned and unburned ecotone using ordinations and hierarchical Bayesian regression models to examine mechanisms through which forests may recover following fire or become locked into alternative development pathways. I found evidence for a water table depth-sun exposure-Sphagnum feedback that limits post-fire tree establishment by placing seedlings in direct competition with Sphagnum mosses and reducing the availability of microsites that are protected from both seasonal inundation and seasonal drought, thus reinforcing a non-forested state of structure and composition.

Next, I expanded the spatiotemporal scale of my investigation using proxy data derived from lake sediment cores to examine climate-fire-vegetation dynamics at decadal to centennial intervals over the past ca. 1000 years. Post-fire vegetation recovery appeared to be driven more by the responses of individual taxa to climatic conditions and competition than by generalized post-fire regeneration traits. I found tradeoffs in overstory dominance by either angiosperms or conifers, but no evidence for transitions between forested and nonforested vegetation communities over the past millennium.

Finally, I synthesized emergent themes from semi-structured interviews and participant observation and compared these, via qualitative content analysis, to a key document to identify and characterize the socio-political scales of stakeholders, explore their understandings and values of forest-peatland sites, and examine the content and quality of information and knowledge exchange within and across socio-political scales. Differences in the perspectives, needs and power (i.e., capacities to realize their interests) of distinct groups of stakeholders created issues of legitimacy and trust that impacted the quality of their interactions and likelihood of reciprocally exchanging information and knowledge. I also found that higher power stakeholders like regional government personnel asserted interests in forest-peatland sites that were not shared by local land managers, landowners or resource users. In addition, local land managers were striving to work across forestry and agricultural jurisdictions to form more holistic management recommendations, but felt unsupported by their agencies' regional offices. Another important takeaway was that neither higher nor lower power stakeholders tended to recognize that the latter held meaningful ecological knowledge or that they should be empowered to participate in efforts to understand, monitor and/or manage forest-peatland sites.

Ultimately, the results from this dissertation contribute to our understanding of the ecology of the world's southernmost conifer, which is endemic to southern South America and considered threatened on a global scale. They also suggest common drivers, mechanisms and types of shifts between forested and nonforested ecosystem states on edaphically wet sites in temperate forest biomes around the world, but especially those in the Southern Hemisphere. Importantly, this research highlights the roles of climate and fire in driving a shift from temperate forests to moss-dominated ecosystems, which contrasts with the better-documented shift between temperate forests and shrub-dominated ecosystems. This dissertation also reveals that not all actors understand or appreciate the dynamics of forest-peatland ecosystems in the same way. I learned that direct stakeholders (including science practitioners) and members of the scientific research community at large held different understandings of post-fire or 'anthropogenic' ecosystems, including appreciation of their most salient features (e.g., their functioning as wetlands or the role of past disturbance in determining present-day plant community composition). This suggests that as a society we need to expend more effort to share knowledge and experience across sometimes vast differences in socio-political and geographic scales to ensure that, under ongoing changes to climate and disturbance regimes, social-ecological system trajectories most closely match those needed and desired by the most vulnerable people.

Rights

© 2024 Kyla Sara Zaret

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

Comments

Research funding for this project was provided by the National Science Foundation (NSF awards 1806037 and 1832483), and the Ryoichi Sasakawa Young Leaders Fellowship Fund.

Persistent Identifier

https://archives.pdx.edu/ds/psu/42535

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