7 research outputs found

    Exploration of large-scale vegetation transition in wet ecosystems: a comparison of conifer seedling abundance across burned vs. unburned forest-peatland ecotones in Western Patagonia

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    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. Chronic anthropogenic burning of temperate rainforests at the forest-peatland ecotone in western Patagonia appears to have shifted vegetation communities in poorly-drained sites from forests dominated by the threatened conifer, Pilgerodendron uviferum, to peat-accumulating wetlands covered by Sphagnum mosses. We collected and modeled post-reburn field data using ordinations and hierarchical Bayesian regressions to examine mechanisms through which P. uviferum forests may recover following fire or become locked into alternative development pathways by comparing biophysical factors of a reburned ecotone to those of an unburned (control) ecotone. We found that, (1) the significantly higher densities of P. uviferum trees and seedlings in the forested patches at both the reburned and control sites were associated with significantly lower seasonal water tables, lower cover of Sphagnum mosses and higher cover of other mosses (i.e., not in the Sphagnum or Dicranaloma genera); (2) despite abrupt boundaries in vegetation at both sites, successive fires homogenized the environment at the reburned site; and (3) the distinct life forms and individual species that characterized the understory plant communities across the ecotones affected seedling abundance by shaping microtopography and the substrates available for establishment. Together, our results suggest that fire can push edaphically wet P. uviferum-dominated sites towards a non-forested state by reducing the diversity of microsite structure and composition, thereby placing P. uviferum seedlings in direct competition with Sphagnum mosses and potentially limiting the availability of microsites that are protected from both seasonal inundation and seasonal drought. If wildfires continue under increasingly warmer and drier conditions, the forest-peatland ecotone of western Patagonia may be susceptible to large-scale transformation towards a non-forested state

    Altered Disturbance Regimes and Novel Ecosystems: Understanding and Managing Ecosystem State Change in the Forest-Peatland Ecotone of Western Patagonia

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    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 \u27politics of scale\u27 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\u27s 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\u27 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\u27s 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 \u27anthropogenic\u27 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

    Distribution, Use and Cultural Meanings of Ciprés de Las Guaitecas in the Vicinity of Caleta Tortel, Chile

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    This study examined the changing roles of ciprés de las Guaitecas (Pilgerodendron uviferum) in the lives and livelihoods of Tortel community members. A political ecology framework built on concepts of power, scale and social construction was used to problematize the availability of the tree as a resource by revealing the multiple, contrasting perspectives of different socio-political actors. National and international policy documents were analyzed in order to uncover the discourses that drive decision-making at those scales. Participant observation and semi-structured interviews were conducted to explore local people’s knowledge, perceptions and opinions regarding the difficulties they face in accessing and utilizing ciprés, as well as the significance of the tree species to their lives/livelihoods. Ultimately, an examination of people’s relationships to ciprés and their interests in the continuation of those relationships speaks to whether and how ciprés can or should remain an important part of their lives/livelihoods
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