Browsing by Author "McWethy, David B."

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Broad-Scale Surface and Atmospheric Conditions during Large Fires in South-Central Chile
(2021-05) McWethy, David B.; Garreaud, Rene D.; Holz, Andres; Pederson, Gregory T.
The unprecedented size of the 2017 wildfires that burned nearly 600,000 hectares of central Chile highlight a need to better understand the climatic conditions under which large fires develop. Here we evaluate synoptic atmospheric conditions at the surface and free troposphere associated with anomalously high (active) versus low (inactive) months of area burned in south-central Chile (ca. 32–41° S) from the Chilean Forest Service (CONAF) record of area burned from 1984–2018. Active fire months are correlated with warm surface temperatures, dry conditions, and the presence of a circumpolar assemblage of high-pressure systems located ca. 40°–60° S. Additionally, warm surface temperatures associated with active fire months are linked to reduced strength of cool, onshore westerly winds and an increase in warm, downslope Andean Cordillera easterly winds. Episodic warm downslope winds and easterly wind anomalies superimposed on long-term warming and drying trends will continue to create conditions that promote large fires in south-central Chile. Identifying the mechanisms responsible for easterly wind anomalies and determining whether this trend is strengthening due to synoptic-scale climatic changes such as the poleward shift in Southern Hemisphere westerly winds will be critical for anticipating future large fire activity in south-central Chile.
Drivelines, hunting blinds, effigies and intercept hunting strategies in the Greater Yellowstone Ecosystem, USA
(Liverpool University Press, 2022) Lee, Craig M; Neeley, Michael; Horton, Elizabeth; McWethy, David B.
This paper shares a description of cairn lines and hunting blinds in association with an ice patch in the Greater Yellowstone Ecosystem. Until now no definitive stone features, including drivelines and hunting blinds, have been reported in association with Greater Yellowstone Ecosystem ice patches; however, such features are known from ice patches in northern North America, eg Yukon Territory. In the system reported here, the ice patch is presumed to be an animal attractant with the drivelines and blinds positioned to serve as intercepts. The paper also shares a brief report of a stone effigy of a probable bighorn sheep that appears to be associated with an ice patch. Such features are emblematic of spiritual provisioning in the alpine.
A High-Resolution Chronology of Rapid Forest Transitions following Polynesian Arrival in New Zealand
(Public Library of Science, 2014-11) McWethy, David B.; Whitlock, Cathy; Wilmshurst, Janet; Wood, Jamie; McGlone, Matt
Human-caused forest transitions are documented worldwide, especially during periods when land use by dense agriculturally-based populations intensified. However, the rate at which prehistoric human activities led to permanent deforestation is poorly resolved. In the South Island, New Zealand, the arrival of Polynesians c. 750 years ago resulted in dramatic forest loss and conversion of nearly half of native forests to open vegetation. This transformation, termed the Initial Burning Period, is documented in pollen and charcoal records, but its speed has been poorly constrained. High-resolution chronologies developed with a series of AMS radiocarbon dates from two lake sediment cores suggest the shift from forest to shrubland occurred within decades rather than centuries at drier sites. We examine two sites representing extreme examples of the magnitude of human impacts: a drier site that was inherently more vulnerable to human-set fires and a wetter, less burnable site. The astonishing rate of deforestation at the hands of small transient populations resulted from the intrinsic vulnerability of the native flora to fire and from positive feedbacks in post-fire vegetation recovery that increased landscape flammability. Spatially targeting burning in highly-flammable seral vegetation in forests rarely experiencing fire was sufficient to create an alternate fire-prone stable state. The New Zealand example illustrates how seemingly stable forest ecosystems can experience rapid and permanent conversions. Forest loss in New Zealand is among the fastest ecological transitions documented in the Holocene; yet equally rapid transitions can be expected in present-day regions wherever positive feedbacks support alternate fire-inhibiting, fire-prone stable states.
Increased whitebark pine (Pinus albicaulis) growth and defense under a warmer and regionally drier climate
(Frontiers Media SA, 2023-03) Kichas, Nickolas E.; Pederson, Gregory T.; Hood, Sharon M.; Everett, Richard G.; McWethy, David B.
Introduction: Tree defense characteristics play a crucial role in modulating conifer bark beetle interactions, and there is a growing body of literature investigating factors mediating tree growth and resin-based defenses in conifers. A subset of studies have looked at relationships between tree growth, resin duct morphology and climate; however, these studies are almost exclusively from lower elevation, moisture-limited systems. The relationship between resin ducts and climate in higher-elevation, energy-limited ecosystems is currently poorly understood. Methods: In this study, we: (1) evaluated the relationship between biological trends in tree growth, resin duct anatomy, and climatic variability and (2) determined if tree growth and resin duct morphology of whitebark pine, a high-elevation conifer of management concern, is constrained by climate and/or regional drought conditions. Results: We found that high-elevation whitebark pine trees growing in an energy-limited system experienced increased growth and defense under warmer and regionally drier conditions, with climate variables explaining a substantive proportion of variation (∼20–31%) in tree diameter growth and resin duct anatomy. Discussion: Our results suggest that whitebark pine growth and defense was historically limited by short growing seasons in high elevation environments; however, this relationship may change in the future with prolonged warming conditions.
Integrating Subjective and Objective Dimensions of Resilience in Fire-Prone Landscapes
(2019-05) Higuera, Philip E.; Metcalf, Alexander L.; Miller, Carol; Buma, Brian; McWethy, David B.; Metcalf, Elizabeth C.; Ratajczak, Zak; Nelson, Cara R.; Chaffin, Brian C.; Stedman, Richard C.; McCaffrey, Sarah; Schoennagel, Tania; Harvey, Brian J.; Hood, Sharon M.; Schultz, Courtney A.; Black, Anne E.; Campbell, David; Haggerty, Julia Hobson; Keane, Robert E.; Krawchuk, Meg A.; Kulig, Judith C.; Rafferty, Rebekah; Virapongse, Arika
Resilience has become a common goal for science-based natural resource management, particularly in the context of changing climate and disturbance regimes. Integrating varying perspectives and definitions of resilience is a complex and often unrecognized challenge to applying resilience concepts to social–ecological systems (SESs) management. Using wildfire as an example, we develop a framework to expose and separate two important dimensions of resilience: the inherent properties that maintain structure, function, or states of an SES and the human perceptions of desirable or valued components of an SES. In doing so, the framework distinguishes between value-free and human-derived, value-explicit dimensions of resilience. Four archetypal scenarios highlight that ecological resilience and human values do not always align and that recognizing and anticipating potential misalignment is critical for developing effective management goals. Our framework clarifies existing resilience theory, connects literature across disciplines, and facilitates use of the resilience concept in research and land-management applications.
Pinus contorta invasions increase wildfire fuel loads and may create a positive feedback with fire
(2017-03) Taylor, Kimberley T.; Maxwell, Bruce D.; McWethy, David B.; Pauchard, Anibal; Nunez, Martin A.; Whitlock, Cathy
Invasive plant species that have the potential to alter fire regimes have significant impacts on native ecosystems. Concern that pine invasions in the Southern Hemisphere will increase fire activity and severity and subsequently promote further pine invasion prompted us to examine the potential for feedbacks between Pinus contorta invasions and fire in Patagonia and New Zealand. We determined how fuel loads and fire effects were altered by P. contorta invasion. We also examined post-fire plant communities across invasion gradients at a subset of sites to assess how invasion alters the post-fire vegetation trajectory. We found that fuel loads and soil heating during simulated fire increase with increasing P. contorta invasion age or density at all sites. However, P. contorta density did not always increase post-fire. In the largest fire, P. contorta density only increased significantly post-fire where the pre-fire P. contorta density was above an invasion threshold. Below this threshold, P. contorta did not dominate after fire and plant communities responded to fire in a similar manner as uninvaded communities. The positive feedback observed at high densities is caused by the accumulation of fuel that in turn results in greater soil heating during fires and high P. contorta density post-fire. Therefore, a positive feedback may form between P. contorta invasions and fire, but only above an invasion density threshold. These results suggest that management of pine invasions before they reach the invasion density threshold is important for reducing fire risk and preventing a transition to an alternate ecosystem state dominated by pines and novel understory plant communities.
Returning Fire to the Land: Celebrating Traditional Knowledge and Fire
(2017-09) Lake, Frank K.; Wright, Vita; Morgan, Penelope; McFadzen, Mary; McWethy, David B.; Stevens-Rumann, Camille
North American tribes have traditional knowledge about fire effects on ecosystems, habitats, and resources. For millennia, tribes have used fire to promote valued resources. Sharing our collective understanding of fire, derived from traditional and western knowledge systems, can benefit landscapes and people. We organized two workshops to investigate how traditional and western knowledge can be used to enhance wildland fire and fuels management and research. We engaged tribal members, managers, and researchers to formulate solutions regarding the main topics identified as important to tribal and other land managers: cross-jurisdictional work, fuels reduction strategies, and wildland fire management and research involving traditional knowledge. A key conclusion from the workshops is that successful management of wildland fire and fuels requires collaborative partnerships that share traditional and western fire knowledge through culturally sensitive consultation, coordination, and communication for building trust. We present a framework for developing these partnerships based on workshop discussions.