Evaluating critiques of evidence of historically heterogeneous structure and mixed-severity fires across dry-forest landscapes of the western USA

The structure and role of fire in historical dry forests, ponderosa pine (Pinus ponderosa) and dry mixed-conifer forests, of the western USA, have been debated for 25 years, leaving two theories. The first, that these forests were relatively uniform, low in tree density and dominated by low- to moderate-severity fires was recently reviewed, including a critique of opposing evidence. The second, that these forests historically had heterogeneous structure and a mixture of fire severities, has had several published reviews. Here, as authors in part of the second theory, we critically examined evidence in the first theory’s new review, which presented 37 critiques of the second theory. We examined evidence for and against each critique, including evidence presented or omitted. We found that a large body of published evidence against the first theory and supporting the second theory, presented in 10 published rebuttals and 25 other published papers, by us and other scientists, was omitted and not reviewed. We reviewed omitted evidence here. Omitted evidence was extensive, and included direct observations by early scientists, maps in early forest atlases, early newspaper accounts and photographs, early aerial photographs, seven paleo-charcoal reconstructions, ≥18 tree-ring reconstructions, eight land-survey reconstructions, and an analysis of forest-inventory age data. This large body of omitted published research provides compelling evidence supporting the second theory, that historical dry forests were heterogeneous in structure and had a mixture of fire severities, including high-severity fire. The first theory is rejected by this large body of omitted evidence.

Supplemental Material: Emergence of wet conditions in the Mono Basin of the Western USA coincident with inception of the Last Glaciation

Assessment of Ash 19 age data; Figure S1: Measured section at the Tufa Site of Lower Wilson Creek (38.02986°N, 119.12459°W; ~1987 m); Figure S2: Our measured section of IV D of Bridgeport Creek (38.08968°N, 119.04885°W; ~2006 m); Figure S3: Measured section at the Between Site of Bridgeport Creek (38.09056°N, 119.04985°W; ~2010 m).

Supplemental Material: Emergence of wet conditions in the Mono Basin of the Western USA coincident with inception of the Last Glaciation

Assessment of Ash 19 age data; Figure S1: Measured section at the Tufa Site of Lower Wilson Creek (38.02986°N, 119.12459°W; ~1987 m); Figure S2: Our measured section of IV D of Bridgeport Creek (38.08968°N, 119.04885°W; ~2006 m); Figure S3: Measured section at the Between Site of Bridgeport Creek (38.09056°N, 119.04985°W; ~2010 m).

Supplemental Material: Emergence of wet conditions in the Mono Basin of the Western USA coincident with inception of the Last Glaciation

Assessment of Ash 19 age data; Figure S1: Measured section at the Tufa Site of Lower Wilson Creek (38.02986°N, 119.12459°W; ~1987 m); Figure S2: Our measured section of IV D of Bridgeport Creek (38.08968°N, 119.04885°W; ~2006 m); Figure S3: Measured section at the Between Site of Bridgeport Creek (38.09056°N, 119.04985°W; ~2010 m).

THE OLENEKIAN-ANISIAN/EARLY-MIDDLE TRIASSIC BOUNDARY, AND ASSESSMENT OF THE POTENTIAL OF CONODONTS FOR CHRONOSTRATIGRAPHIC CALIBRATION OF THE TRIASSIC TIMESCALE

The conodont Chiosella timorensis (Nogami, 1968) has for a long time been considered to be a suitable biotic proxy for the Olenekian-Anisian/Early-Middle Triassic boundary. The recently acquired ammonoid record around that boundary clearly shows that the FAD of this conodont is located well below the boundary, i.e., in the late Spathian. In the present paper, it is underlined that the conodont Chiosella timorensis was promoted as a proxy for the nominated boundary in the early 1980s when the ammonoid record around the boundary was not yet well established. On the other side, until the mid 1990s the taxonomic definition and the lineage of the conodont Chiosella timorensis were not well stated, and even now there are still controversial interpretations of the taxonomic content of this conodont species. The new data achieved from the ammonoid/conodont record around the nominated boundary, especially in the western USA, and also in the Deşli Caira section in Romania, firmly demonstrate that the conodont Chiosella timorensis is a defunct proxy for the Olenekian-Anisian/Early-Middle Triassic boundary. As a consequence, the present data on the ammonoid-documented Olenekian-Anisian/Early-Middle Triassic boundary requires the recalibration of all physical events that have been tied to the FAD of the conodont Chiosella timorensis. The case of the Albanian Kçira-section, for which the chronostratigraphic interpretation of the ammonoid record is proved incorrect, definitely makes the conodont Chiosella timorensis a defunct proxy for the nominated boundary. Also, the case of the two Chinese sections recently proposed as being “exceptional” GSSP candidates for the Early-Middle Triassic boundary, which is based on an inconsistent ammonoid/conodont biochronology, fully strengthens this conclusion. The history of the controversial usage of the conodont species Chiosella timorensis in defining the Olenekian-Anisian boundary justifies a discussion about the usefulness of conodonts in the chronostratigraphic calibration of the standard Triassic timescale. One may conclude that the conodonts are not qualified, and have not a reasonable potential, to be used to define or to redefine the boundaries of chronostratigraphic units in the standard Triassic timescale, which have been basically defined on ammonoid biochronology.

Fire-weather interaction fed the 2020 western USA gigafire

Wildfires threaten human lives, destroy infrastructure, disrupt economic activity, and damage ecosystem services. A record-breaking gigafire event ravaged the western United States (USA) in mid-September 2020, burning 1.2 million acres (4,900 km2) in Oregon and California, and resulting in severe smoke pollution with daily fine particulate matter (PM2.5) concentrations over 300 µg/m3 for multiple days in many cities. Although previous studies have shown that regional warming escalates wildfire in the western USA, such an unprecedented fire cannot be explained by climate variability alone. Here we show that the synoptic-scale feedback between the wildfires and weather played an unexpectedly important role in accelerating the spread of this fire and also trapped pollutants in the shallow boundary layer over valley cities. Specifically, we find that aerosol-radiation interaction of the smoke plumes over the Cascade Mountains enhanced the downslope winds and weakened the moisture transport, thereby forming a positive feedback loop that amplified the fires and contributed to ~54% of estimated air-pollution related deaths. Our study underscores the complexity of the Earth system and the importance of understanding fundamental mechanisms to effectively mitigate disaster risks in a changing climate.