Southern California Vegetation, Wildfire, and Erosion Had Nonlinear Responses to Climatic Forcing During Marine Isotope Stages 5–2 (120–15 ka)

Abstract

A multiproxy record from Baldwin Lake, San Bernardino Mountains, allowed us to examine variation and relationships between erosion, wildfire, vegetation, and climate in subalpine Southern California from 120 to 15 ka. Bulk organics, biogenic silica, and molar C:N data were generally antiphased with magnetic and trace element data and displayed long‐term (105 year) shifts between autochthonous and allocthonous deposition. This was most pronounced during Marine Isotope Stage (MIS) 5, and we hypothesize that local summer insolation was the primary driver for Baldwin Lake's productive and unproductive lake state alternations. Wildfire history was inferred from charcoal concentrations and vegetation change from pollen. Relationships between these ecological processes, basin deposition, and summer insolation were often nonlinear. Sagebrush expansion, wildfire, and weak basin weathering characterized MIS 4, while during MIS 2, the basin was highly erosive, rarely burned, and the forest was impacted by shifts in Southern Californian hydroclimate. Despite coniferous forest cover throughout MIS 3, submillennial oscillations in charcoal, pollen, and bulk organic content occurred, consistent with pollen records from Eurasia's Mediterranean biome that span multiple glacial‐interglacial cycles. Highly resolved global CO2 records and sea surface temperatures in key regions of the Pacific show no apparent relationship to these landscape conditions, and we suggest submillennial hydroclimatic variability as a potential driver. Highly resolved long pollen records from Southern California are an urgent research need to better understand the finer‐scale (≤103 year) interactions between past vegetation, wildfire, and erosion, given the current natural disaster risks that 21st century climate change poses to both human and ecological communities.

Genetic structure and historic demography of endangered unarmoured threespine stickleback at southern latitudes signals a potential new management approach

“…However, we interpret these relative population size estimates in the earliest part of the IICR curves with scepticism (see Caveats to the MSMC below). Wetter and cooler conditions within the SCB were prevalent from ~65 ka up to ~14 ka (Faribanks & Carey, 1910 ; Glover et al, 2017 , 2020 ; Heusser et al, 2015 ; Kirby et al, 2013 ; Owen et al, 2003 ; Sharp et al, 1959 ) and probably provided more expansive freshwater habitat that could have sustained larger and more interconnected populations of G. aculeatus in inland areas. In fact, habitat supporting unarmoured G. aculeatus extended well into the Los Angeles Basin as recently as the mid‐20th century (Culver & Hubbs, 1917 ; Mendenhall, 1908 ; Swift et al, 1993 ).…”

Terrestrial ecosystem transformations in response to rapid climate change during the last deglaciation around Mono Lake, California, USA

“…Despite the extensive paleoecological work conducted in the Sierra Nevada and the Great Basin, very few pollen studies have had the sampling resolution necessary to detect more rapid events (<250 years per sample, after Anderson et al, 2022). Instead, most ecological interpretations in the region have centered on responses to gradual, orbitally forced climate change (e.g., Davis et al, 1985; Anderson, 1990a; Anderson and Smith, 1994), rather than more rapid and nonlinear events (e.g., Heusser et al, 2015; Glover et al, 2020; Zimmerman and Wahl, 2020). More recent investigations (Mensing, 2001; MacDonald et al, 2008; Oster et al, 2009; 2015; Heusser et al, 2015; Ali, 2018) have shown hydroclimatic sensitivity to rapid change, but the ecological response remains poorly understood, particularly east of the Sierra Crest (Anderson et al, 2022; Fig.…”