More Like this

1. A Holocene history of climate, fire, landscape evolution, and human activity in northeastern Iceland

   https://doi.org/10.5194/cp-20-1087-2024  

   Ardenghi, Nicolò; Harning, David J.; Raberg, Jonathan H.; Holman, Brooke R.; Thordarson, Thorvaldur; Geirsdóttir, Áslaug; Miller, Gifford H.; Sepúlveda, Julio (January 2024, Climate of the Past)

   Abstract. Paleoclimate reconstructions across Iceland provide a template for past changes in climate across the northern North Atlantic, a crucial region due to its position relative to the global northward heat transport system and its vulnerability to climate change. The roles of orbitally driven summer cooling, volcanism, and human impact as triggers of local environmental changes in the Holocene of Iceland remain debated. While there are indications that human impact may have reduced environmental resilience during late Holocene summer cooling, it is still difficult to resolve to what extent human and natural factors affected Iceland's late Holocene landscape instability. Here, we present a continuous Holocene fire record of northeastern Iceland from proxies archived in Stóra Viðarvatn sediment. We use pyrogenic polycyclic aromatic hydrocarbons (pyroPAHs) to trace shifts in fire regimes, paired with continuous biomarker and bulk geochemical records of soil erosion, lake productivity, and human presence. The molecular composition of pyroPAHs and a wind pattern reconstruction indicate a naturally driven fire signal that is mostly regional. Generally low fire frequency during most of the Holocene significantly increased at 3 ka and again after 1.5 ka BP before known human settlement in Iceland. We propose that shifts in vegetation type caused by cooling summers over the past 3 kyr, in addition to changes in atmospheric circulation, such as shifts in North Atlantic Oscillation (NAO) regime, led to increased aridity and biomass flammability. Our results show no evidence of faecal biomarkers associated with human activity during or after human colonisation in the 9th century CE. Instead, faecal biomarkers follow the pattern described by erosional proxies, pointing toward a negligible human presence and/or a diluted signal in the lake's catchment. However, low post-colonisation levels of pyroPAHs, in contrast to an increasing flux of erosional bulk proxies, suggest that farming and animal husbandry may have suppressed fire frequency by reducing the spread and flammability of fire-prone vegetation (e.g. heathlands). Overall, our results describe a fire frequency heavily influenced by long-term changes in climate through the Holocene. They also suggest that human colonisation had contrasting effects on the local environment by lowering its resilience to soil erosion while increasing its resilience to fire. 

   more » « less
2. Assessing changes in global fire regimes

   https://doi.org/10.1186/s42408-023-00237-9  

   Sayedi, Sayedeh_Sara; Abbott, Benjamin_W; Vannière, Boris; Leys, Bérangère; Colombaroli, Daniele; Romera, Graciela_Gil; Słowiński, Michał; Aleman, Julie_C; Blarquez, Olivier; Feurdean, Angelica; et al (February 2024, Fire Ecology)

   Abstract BackgroundThe global human footprint has fundamentally altered wildfire regimes, creating serious consequences for human health, biodiversity, and climate. However, it remains difficult to project how long-term interactions among land use, management, and climate change will affect fire behavior, representing a key knowledge gap for sustainable management. We used expert assessment to combine opinions about past and future fire regimes from 99 wildfire researchers. We asked for quantitative and qualitative assessments of the frequency, type, and implications of fire regime change from the beginning of the Holocene through the year 2300. ResultsRespondents indicated some direct human influence on wildfire since at least ~ 12,000 years BP, though natural climate variability remained the dominant driver of fire regime change until around 5,000 years BP, for most study regions. Responses suggested a ten-fold increase in the frequency of fire regime change during the last 250 years compared with the rest of the Holocene, corresponding first with the intensification and extensification of land use and later with anthropogenic climate change. Looking to the future, fire regimes were predicted to intensify, with increases in frequency, severity, and size in all biomes except grassland ecosystems. Fire regimes showed different climate sensitivities across biomes, but the likelihood of fire regime change increased with higher warming scenarios for all biomes. Biodiversity, carbon storage, and other ecosystem services were predicted to decrease for most biomes under higher emission scenarios. We present recommendations for adaptation and mitigation under emerging fire regimes, while recognizing that management options are constrained under higher emission scenarios. ConclusionThe influence of humans on wildfire regimes has increased over the last two centuries. The perspective gained from past fires should be considered in land and fire management strategies, but novel fire behavior is likely given the unprecedented human disruption of plant communities, climate, and other factors. Future fire regimes are likely to degrade key ecosystem services, unless climate change is aggressively mitigated. Expert assessment complements empirical data and modeling, providing a broader perspective of fire science to inform decision making and future research priorities. 

   more » « less
3. Leaving home: Technological and landscape knowledge as resilience at pre-Holocene Kharaneh IV, Azraq Basin, Jordan

   https://doi.org/10.1177/09596836221121784  

   Macdonald, Danielle_A; Maher, Lisa_A (September 2022, The Holocene)

   Humanity’s relationship with the environment during the Holocene, and into the Anthropocene, is structured around our dependance on agricultural production, which has resulted in risk mitigation strategies that include intensive landscape modifications, among other tactics. However, to understand broader patterns of human resilience and the shifts in human/environment relationships, we need to look further back in time. Through this paper, we explore cultural strategies of risk management and resilience in pre-Holocene communities and how these practices allowed hunter-gatherer communities to adapt to a changing environment. For over 1000 years, the Epipalaeolithic site of Kharaneh IV was a focal point on the landscape for hunter-gatherer groups, acting as an aggregation site for Early and Middle Epipalaeolithic peoples. Located in the eastern desert of Jordan, at the time of occupation the site was a lush wetland surrounded by a rich grassland environment, providing abundant food and other resources for the site’s occupants. However, over time the wetland began to dry up and by 18,600 cal BP Kharaneh IV was abandoned. In this paper, we discuss the final occupation of Kharaneh IV, linking the site’s abandonment to the increasing aridification of eastern Jordan. Environmental change led to the eventual abandonment of Kharaneh IV and other nearby sites, as people relocated within the Azraq Basin in search of new water resources during the Holocene. Flexible technological strategies and knowledge of the landscape created resilient cultural practices that allowed these communities to use population movement as a risk management strategy. 

   more » « less
4. Arctic and boreal paleofire records reveal drivers of fire activity and departures from Holocene variability

   https://doi.org/10.1002/ecy.3096  

   Hoecker, Tyler J.; Higuera, Philip E.; Kelly, Ryan; Hu, Feng Sheng (June 2020, Ecology)

   Abstract Boreal forest and tundra biomes are key components of the Earth system because the mobilization of large carbon stocks and changes in energy balance could act as positive feedbacks to ongoing climate change. In Alaska, wildfire is a primary driver of ecosystem structure and function, and a key mechanism coupling high‐latitude ecosystems to global climate. Paleoecological records reveal sensitivity of fire regimes to climatic and vegetation change over centennial–millennial time scales, highlighting increased burning concurrent with warming or elevated landscape flammability. To quantify spatiotemporal patterns in fire‐regime variability, we synthesized 27 published sediment‐charcoal records from four Alaskan ecoregions, and compared patterns to paleoclimate and paleovegetation records. Biomass burning and fire frequency increased significantly in boreal forest ecoregions with the expansion of black spruce, ca. 6,000–4,000 years before present (yr BP). Biomass burning also increased during warm periods, particularly in the Yukon Flats ecoregion from ca. 1,000 to 500 yr BP. Increases in biomass burning concurrent with constant fire return intervals suggest increases in average fire severity (i.e., more biomass burning per fire) during warm periods. Results also indicate increases in biomass burning over the last century across much of Alaska that exceed Holocene maxima, providing important context for ongoing change. Our analysis documents the sensitivity of fire activity to broad‐scale environmental change, including climate warming and biome‐scale shifts in vegetation. The lack of widespread, prolonged fire synchrony suggests regional heterogeneity limited simultaneous fire‐regime change across our study areas during the Holocene. This finding implies broad‐scale resilience of the boreal forest to extensive fire activity, but does not preclude novel responses to 21st‐century changes. If projected increases in fire activity over the 21st century are realized, they would be unprecedented in the context of the last 8,000 yr or more. 

   more » « less
5. A Holocene history of monkey puzzle tree (pehuén) in northernmost Patagonia

   https://doi.org/10.1111/jbi.14041  

   Nanavati, William; Whitlock, Cathy; Outes, Valeria; Villarosa, Gustavo (December 2020, Journal of Biogeography)

   Abstract AimAlthough it is established that climate and fire have greatly influenced the long‐term ecosystem dynamics of Patagonia south of 40°S, the environmental history from northernmost Patagonia (37–40°S), where endemic and endangered monkey puzzle tree (Araucaria araucana) occurs, is poorly known. Here we ask: (a) What is the Holocene vegetation and fire history at the north‐eastern extent ofA. araucanaforest? (b) How have climate and humans influenced the past distribution ofA. araucana? LocationNorthernmost Patagonia, Argentina and Chile (37–40°S). TaxaAraucaria araucana,Nothofagus, Poaceae. MethodsSedimentary pollen and charcoal from Laguna Portezuelo (37.9°S, 71.0°W; 1,730 m; 11,100 BP) were evaluated using statistical methods and compared with other palaeoecological, independent palaeoclimate, and historical records to assess how changes in climate and land use influenced local‐to‐regional environmental history. ResultsAn open forest‐steppe landscape persisted at L. Portezuelo throughout the Holocene with generally low‐to‐moderate fire activity. IncreasedNothofaguspollen after ~6,590 BP suggests increases in shrubland and moisture in association with cooler conditions and greater seasonality and ENSO activity.Araucariapollen appeared at L. Portezuelo at ~6,380 BP, but was low in abundance until ~370 BP, when it rose with charcoal levels. This increase inAraucariaand fire coincided with a regional influx of Mapuche American Indians.Nothofagusdeforestation andPinussilviculture marked Euro‐American settlement beginning in the 19–20th century. Main conclusions(a) Rapid postglacial warming and drying limited the distribution ofAraucariain the central valley of Chile. In the middle and late Holocene, decreased temperatures and greater seasonality and ENSO activity increased precipitation variability allowingAraucariaexpansion at its north‐eastern limit. (b) Greater abundance ofAraucariaand heightened fire activity at L. Portezuelo after 370 BP coincided with increased Mapuche‐Pehuenche American Indian land use, suggesting thatAraucariamay have been managed in a human‐altered landscape. 

   more » « less