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1. Pre-Columbian agriculture, fire, and Spanish contact: A 4200-year record from Laguna Los Mangos, Costa Rica

   https://doi.org/10.1177/0959683619862032  

   Johanson, Erik N ; Horn, Sally P ; Lane, Chad S ( July 2019 , The Holocene)

   We present a lake-sediment record of pre-Columbian agriculture and fire history from the lowlands of southern Pacific Costa Rica that captures the arrival of maize agriculture at ca. 3360 cal yr BP in the Diquís subregion of the Gran Chiriquí archeological region. Our 4200-year record from Laguna Los Mangos begins 1000 to 2000 years earlier than other lake records from the region and provides the first microfossil and geochemical evidence of vegetation and fire prior to the establishment of maize agriculture. This early portion of the record shows evidence of fire events associated with land clearance or field preparation and maintenance for subsistence activities. Alternatively, these were wildfires ignited unintentionally by people or naturally by lightning or volcanism. Evidence of early maize by ca. 3200 cal yr BP was found at Laguna Zoncho in the southeastern section of the Diquís subregion. Our discovery of early maize agriculture at ca. 3360 cal yr BP in the Laguna Los Mangos watershed in the northwestern portion of the Diquís subregion indicates a rapid adoption of maize agriculture in the region after initial introduction. Pre-Columbian agriculture and fire activity at Los Mangos is nearly continual until historic times, but with a decline after ca. 1170 cal yr BP, coincident with the early Terminal Classic Drought (TCD). We infer a pronounced drying of the lowland environment at Laguna Los Mangos based on a depositional hiatus in the record at ca. 950 during late TCD. Agricultural proxies indicate reduced watershed activity during the ‘Little Ice Age’ following Spanish contact in southern Central America until the 20th century. 

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2. Response of diatom communities to climate and human disturbance: A 4200-year record from Costa Rica

   https://doi.org/10.1177/09596836231197775  

   Bitting, Madeleine ; Johanson, Erik N ; Haberyan, Kurt A ; Horn, Sally P ( December 2023 , The Holocene)

   This study integrates diatom analysis with existing records of pollen, charcoal, elemental composition, and stable light isotopes to expand upon the 4200-year history of human activity and climate change from Laguna Los Mangos in southern Pacific Costa Rica. We counted diatoms in peroxide-treated samples and analyzed community composition using cluster analysis, revealing four distinct assemblage zones with diatom variability most closely correlated with phosphorus, titanium, and organic content. The earliest assemblage (Zone D, 4150–3430 cal yr BP) was dominated by Encyonema silesiacum and Nitzschia incognita and aligned with a period of deforestation, erosion, and abundant macrophytes. Gomphonema affine proliferated in Zone C (3430–2450 cal yr BP), reflecting increased pH and productivity likely caused by agriculture-induced nutrient loading. We attributed the preservation gap from 3290 to 2970 cal yr BP in Zone C to silica depletion and erosional deposition that induced decline in diatom abundance by diluting valve concentrations in lake sediments. Nitzschia incognita and G. affine became the dominant taxa in Zone B (2450–1400 cal yr BP), likely reflecting eutrophy, increasing conductivity, and drying climate. Dominance of Diadesmis confervacea indicated reduced lake level in Zone A (1400 cal yr BP–modern) at the onset of the Terminal Classic Drought (TCD). A hiatus in the record indicates lake desiccation from 950 to 450 cal yr BP. During the Little Ice Age (LIA), diatoms reflect conditions similar to Zone B indicating increased lake level, circumneutral pH, and eutrophy. Refilling of the lake indicates increased precipitation during the LIA despite evidence of severe regional drought reported at other sites. Variable precipitation during this period likely resulted from the combined effects of Spanish contact, agricultural collapse, forest recovery, and shifts in Atlantic and Pacific climate forcing mechanisms. Overall, the Los Mangos diatom record reflects shallow, slightly alkaline, eutrophic conditions influenced by nutrient enrichment, erosion, and deforestation associated with maize agriculture.

    

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3. Human disturbance amplifies Amazonian El Niño–Southern Oscillation signal

   https://doi.org/10.1111/gcb.13608  

   Bush, Mark B. ; Correa‐Metrio, Alexander ; van Woesik, Robert ; Shadik, Courtney R. ; McMichael, Crystal N. H. ( March 2017 , Global Change Biology)

   The long‐term interaction between human activity and climate is subject to increasing scrutiny. Humans homogenize landscapes through deforestation, agriculture, and burning and thereby might reduce the capacity of landscapes to provide archives of climate change. Alternatively, land‐use change might overwhelm natural buffering and amplify latent climate signals, rendering them detectable. Here we examine a sub‐annually resolved sedimentary record from Lake Sauce in the western Amazonian lowlands that spans 6900 years. Finely‐laminated sediments were deposited from ca. 5000 years ago until the present, and human activity in the watershed was revealed through the presence of charcoal and maize agriculture. The laminations, analyzed for color content and bandwidth, showed distinctive changes that were coupled to more frequent occurrence of fossil maize pollen. As agricultural activity intensified ca. 2200 cal.BP, the 2‐ to 8‐year periodicity characteristic of El Niño–Southern Oscillation became evident in the record. These agricultural activities appeared to have amplified an existing, but subtle climatic signal that was previously absorbed by natural vegetation. When agricultural activity slowed, or land use around Lake Sauce changed at ca. 800 cal.BP, the signal of El Niño–Southern Oscillation (ENSO) activity became erratic.

    

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4. Long‐term ecological legacies in western Amazonia

   https://doi.org/10.1111/1365-2745.13501  

   Åkesson, Christine M. ; McMichael, Crystal N. H. ; Raczka, Marco F. ; Huisman, Seringe N. ; Palmeira, Mona ; Vogel, Johnny ; Neill, David ; Veizaj, Jason ; Bush, Mark B. ; de Lafontaine, ed., Guillaume ( October 2020 , Journal of Ecology)

   Modifications of Amazonian forests by pre‐Columbian peoples are thought to have left ecological legacies that have persisted to the modern day. Most Amazonian palaeoecological records do not, however, provide the required temporal resolution to document the nuanced changes of pre‐Columbian disturbance or post‐disturbance succession and recovery, making it difficult to detect any direct, or indirect, ecological legacies on tree species.

   Here, we investigate the fossil pollen, phytolith and charcoal history of Lake Kumpak^a, Ecuador, during the last 2,415 years inc. 3–50 year time intervals to assess ecological legacies resulting from pre‐Columbian forest modification, disturbance, cultivation and fire usage.

   Two cycles of pre‐Columbian cultivation (one including slash‐and‐burn cultivation, the other including slash‐and‐mulch cultivation) were documented in the record around 2150–1430 cal. year BP and 1250–680 cal. year BP, with following post‐disturbance succession dynamics. Modern disturbance was documented afterc. 10 cal. year BP. The modern disturbance produced a plant composition unlike those of the two past disturbances, as fire frequencies reached their peak in the 2,415‐year record. The disturbance periods varied in intensity and duration, while the overturn of taxa following a disturbance lasted for hundreds of years. The recovery periods following pre‐Columbian disturbance shared some similar patterns of early succession, but the longer‐term recovery patterns differed.

   Synthesis. The trajectories of change after a cessation of cultivation can be anticipated to differ depending on the intensity, scale, duration and manner of the past disturbance. In the Kumpak^arecord, no evidence of persistent enrichment or depletion of intentionally altered taxa (i.e. direct legacy effects) was found but indirect legacy effects, however, were documented and have persisted to the modern day. These findings highlight the strengths of using empirical data to reconstruct past change rather than relying solely on modern plant populations to infer past human management and ecological legacies, and challenge some of the current hypotheses involving the persistence of pre‐Columbian legacies on modern plant populations.

    

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5. Precipitation variability, vegetation turnover, and anthropogenic disturbance over the last millennium in the Atacama highlands of northern Chile (19°S)

   https://doi.org/10.1177/09596836231151834  

   Domic, Alejandra I ; de Porras, María Eugenia ; Capriles, José M ; Zamora-Allendes, Andrés ; Ivory, Sarah J ; Maldonado, Antonio ( May 2023 , The Holocene)

   The Late-Holocene history of hydroclimatic variability in the Atacama Desert offers insights into the effects of precipitation and humans on ecosystems in one of the most extremely arid regions of the world. However, understanding the effects of regional precipitation variability in relation to local ecological stressors remains to be fully resolved. Here, we present a pollen-based qualitative precipitation reconstruction derived from fossil rodent middens recovered from two sites near Laguna Roja (LRO; n = 25) and Isluga (ISL; n = 15) in the Atacama highlands (19°S) of northern Chile. At LRO, the fossil pollen record shows multi-centennial hydroclimatic anomalies during the last millennium, with wetter than present phases at 1155–1130, 865–670, and 215–80 cal yrs BP, and similar to present conditions between 1005 and 880 cal yrs BP. In contrast, the ISL record shows a wet phase during 1115–840 cal yrs BP, suggesting that meso-ecological processes were as important in vegetation turnover as regional hydroclimate anomalies. Wetter conditions derived from LRO partially overlap with the Medieval Climate Anomaly (865–670 cal yrs BP) and with the latest part of the Little Ice Age (215–80 cal yrs BP). Furthermore, no strong anthropogenic signal was identified possibly related to the remote location of the records. Palynological diversity analyses evidence increasing diversification of plant communities during wet events at both sites. In correlation to existing regional hydroclimatic records from the Western Andes, our precipitation reconstruction verifies that centennial-scale changes in the strength of the South American Summer Monsoon (SASM) and partial influence of El Niño-like (ENSO) conditions drove vegetation turnover in the Atacama Desert during the last millennium. 

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