The Holocene

Evidence for the presence and pre-European use of maize on the lower Saginaw River drainage, southern Michigan, Great Lakes, USA, is presented and evaluated. An integrated multiproxy approach is employed, including macro-botanical data from feature contexts and micro-botanical data from adhered carbonized residues, δ13C isotope information derived from carbonized food residues, and dental disease data from a local mid-eighteenth-century indigenous burial population. Results of absolute dating and ceramic stylistic analysis reveal an early micro-botanical presence of maize ca. 1900 BP, with macro-botanical evidence lagging until 1000 years later. Absolute dates, both direct and associated, reveal macro-botanical evidence through the 18th century, when local populations display dental pathologies consistent with a high maize consumption diet. Of interest is the presence of an inverse spatial and altitude relationship between micro-botanical evidence of maize from carbonized food residues on ceramic vessels, and the presence of macro-botanical remains, suggesting a behavioral partitioning of maize-related activities.

The Eastern European Alps boasts highly biodiverse ecosystems and a rich archaeological history. However, there is limited research on the enduring impacts of historical climate change and human activities on plant biodiversity in this region. Using sedimentary ancient DNA, we reconstructed plant and animal dynamics from 8500 years before present (ka BP) around Großer Winterleitensee (Zirbitzkogel, Austria). Variable intensities of human activities since the Middle Bronze Age (~3.5 ka BP) facilitated the persistence of biodiverse Alpine meadow communities and lowered timberlines below their natural limit. Since the end of the Bronze Age (~2.8 ka BP), human activities, particularly pasturing, and increasing temperatures, emerged as significant drivers of plant community dynamics. The introduction of sheep (Ovis aries) did not reduce wild mammal presence, including red deer (Cervus elaphus), hare (Lepus), European mole (Talpa europaea), bank vole (Myodes glareolus), and short-tailed field vole (Microtus agrestis). During the High & Late Mediaeval Period, (~1150–450 BP), cattle (Bos taurus) and horses (Equus caballus) became the dominant domesticates, while all wild mammals except the short-tailed field vole and Eurasian water shrew (Neomys fodiens) declined or even disappeared. These changes are also accompanied by a significant transformation of plant community structure. The ability to determine both plant responses and animal drivers from the same palaeolimnological sequence vastly improves our ability to partition causes of vegetation change over the Holocene. Here, we reveal that plant biodiversity is maintained or increased by moderate cattle grazing. Therefore, non-intensive domesticated stock grazing is essential for maintaining diverse Alpine meadows.

Historical archives for the Roman Monarchic and Republican periods (753–29 BCE) offer a highly resolved series of observations of environmental and climatic phenomena in Central Italy. This paper presents a new collection of these historical archives, gathering 319 observations across the period. We introduce the historical character of these archives and point out aspects affecting their analysis and interpretation for reconstruction of past environmental and climatic conditions in Italy in the latter half of the first millenium BCE. Archival information is seen to be generally reliable from the fifth century BCE onward, providing a valuable source about regional past climate. The historical archives’ anecdotal nature along with complexities of their formation and transmission encourage cautious and closely contextualized interpretation, and we advocate the use of this information most of all to understand Romans’ changing experience of environment and climate. We offer comparison of this data to current understanding of regional climate conditions based on scientific proxies, especially speleothems and marine cores. These records show some convergence with the historical archives, and we discuss the possibility that this may reflect a relatively warm, wet climate period (Roman Warm Period) in Italy coterminous with Rome’s initial phase of imperial expansion.

This study examines the sedimentation rates (SR) during the last 20 kyr in the Niger Delta using selected biostratigraphic datum levels. Three gravity cores (GCs) collected at −40 m below sea level from the shallow offshore Niger Delta (GC1 = Western, GC2 = Central, and GC3 = Eastern) were analysed for their calcareous nannoplankton species (Emiliania huxleyi, Gephyrocapsa oceanica, Helicophaera sellii and Reticulofenestra asanoi). Successive datums were established mainly from the informal biozones and ranges of Gephyrocapsa oceanica and Emiliania huxleyi marker species due to their abundance. By correlating the First Occurrence (FOC) and Last Occurrence (LOC) datums of the marker species in the cored sequences (GCs), SRs were reconstructed. Based on the constructions, the FOC of Gephyrocapsa oceanica (20 kyr) reflects a position towards the bottom of the GCs, the FOC of Emiliania huxleyi (11–8.5 kyr) delineates the middle of the GCs, and the LOC of Emiliania huxleyi (6.5 kyr) marks the uppermost part of the GCs. The sediment load by average calculated from each location in the Western, Central, and Eastern Niger Delta shows sequences of sedimentation rates of ~36.7 cm/kyr for the late Pleistocene, ~174 cm/kyr for the early Holocene, and ~18.6 cm/kyr for mid-Holocene time periods. Consequently, on average, ~229.3 cm/kyr of sediment were deposited at −40 m water level over the last 20 kyr, with the early Holocene experiencing the highest sedimentation rates (~174 cm/kyr) across the three locations. Additionally, this study provides evidence that the Niger Delta sink deposits responded to the West African Monsoon (WAM) driven sedimentation rates during the late Quaternary (20–6.5 kyr). Furthermore, this sediment deposit facilitated the development of a high-resolution age-depth and sedimentation rate model linked to the regional sea level of the Eastern Equatorial Atlantic that succinctly delineates the late Pleistocene and early Holocene boundary of the Niger Delta. The outputs of this study bridged the research gap and knowledge on the impact of coastal accretion and depositional processes on sedimentation rates in the shallow offshore Niger Delta.

The Holocene history of vegetation and fire in the northern Great Basin (USA) is poorly understood, especially concerning forest-steppe ecotones. Dog Lake is a rare perennial freshwater landslide-dammed lake located near the lower elevation of conifer forests. The lake has a maximum water depth of 8 m which often lowers by several meters during late summer. A 13 m, 9600-yr sediment core revealed periods of increased aridity from indicators of lake levels (aquatic macrophytes, elemental analysis of carbon and nitrogen, and sediment composition), vegetation change (pollen assemblages) and fire (macroscopic charcoal). From 9200 to 8700 cal yr BP, 122 cm of dense Chara matting indicates that lake levels were periodically lower than ca. 3 m. From 8700 to 8200 cal yr BP, high detrital silt input and lower C:N suggests high levels of regional dust and/or erosion, consistent with increased drought, reduced terrestrial plant cover, and dust-fertilized aquatic productivity. Fire activity was also low between 8700 and 8200 cal yr BP, consistent with limited herbaceous fuel availability. Following 8200 cal yr BP, silt levels declined, and pollen assemblages show vegetation trending toward mesic conditions. Deposition of 12 cm of Mazama tephra had no discernable effect on vegetation or fire. Fires increased during the mid-Holocene between 6000 and 4000 cal yr BP during higher grass cover, consistent with cooler conditions relaxing fuel limitation on the fire regime. Vegetation changed little during the late Holocene, with Cupressaceae increasing at 5400 cal yr BP through to current day, and Pinus fluctuating, peaking at 800 cal yr BP and declining through to current day. Our findings matched other regional paleodrought studies and reveals the millennial-scale pattern of climate and fuel limitation on the fire regime at lower treeline.

Modern pollen-rain analysis was carried out for the first time across central, western and eastern regions of Mizoram, encompassing different regional climatic zones. The vegetation experiences massive ecological pressure as a consequence of environmental factors, including the monsoon winds from the Bay of Bengal, high temperature, precipitation conditions, and varied topography. Additionally, intense human activities in the state of Mizoram impact the forest landscape in the remote northeastern part of India. These include agricultural activities such as shifting cultivation (Jhum), commercial crop plantations such as banana, rubber, oil palm, tea, etc., pastoral activities and others. We collected moss cushion samples across transects in the central, western and eastern regions of Mizoram, to comprehend the impact of natural and anthropogenic factors on the modern vegetation and resultant pollen taxa on the surface deposits. The modern pollen data were analyzed statistically, including constrained redundancy analysis (RDA). The RDA analysis revealed the impact of bioclimatic variables on the pollen record, such as isothermality, precipitation in the warmest quarter and annual precipitation. The most significant variable was isothermality (bio_3) which indicated the dominance of anthropogenically impacted sites on the species distribution. Here, we identified that an interplay of climate- and anthropogenic-driven forcing were primarily controlling the modern vegetation and pollen-rain across Mizoram. The anthropogenic indicator pollen, such Poaceae (>50 µm), Caryophylaceae, Asteroideae, Cannabaceae, and Palmae at various sites reveal the impact of anthropogenic activities on the modern vegetation. The results reveal the impact of climatic zones, altitude gradients, anthropogenic activities and vegetation distribution on the pollen yield from the surface deposits.

Fluctuations in timber/treeline have largely been subjected to past climatic changes; but throughout the Holocene humans became one of the leading drivers of these changes. By understanding the reasons for timber/treeline changes, we retraced past climate variability and/or anthropogenic impact on the alpine environment. This study focussed on the sedimentary sequence of the Lake ‘Jezero v Ledvicah’ (Julian Alps, Slovenia), which is currently located at the treeline and covers the last ca. 6200 years. We used mineralogical and geochemical analyses to understand sedimentary changes in the lake and its catchment area. By combining this dataset with palynological data we tracked the causes of vegetation changes with a focus on human impact. Geological analyses indicate slow continuous and undisturbed sedimentation with a combined biogenic and detrital calcite input throughout the Holocene. High percentage of clay minerals indicate that they were eroded from the catchment bedrock and/or were brought to the catchment indirectly by wind. The palynological results indicate that area around the lake was forested around 6200–4300 cal. BP, with predominant occurrence of coniferous taxa. Infrequent but fairly continuous grazing indicators during this period suggest a human presence in the highlands. By 4300–1100 cal. BP, the human influence in the area increased, resulting in a gradual decrease in tree taxa. Since 1000 cal. BP relatively open landscape developed with increased grazing indicators suggesting a continuous use of highlands.

The Central Highlands region of Madagascar is currently dominated by open and mosaic ecosystems, and the region is targeted for afforestation projects. At present, little is known about the origin of these ecosystems and whether or not they are ancient or anthropogenically derived mosaics. This paper provides new insights into the environmental history and drivers of change in the Central Highlands of Madagascar during the last 6300 years through palaeoecological records from Lake Dangovavy. Our results suggested that open and mosaic ecosystems have been present in the landscape for at least 6000 years that is, 4 cal. ka BP before human settlement (2 cal. ka BP). Between 6.3 and 2 cal. ka BP landscapes were characterized by a mosaic ecosystem dominated by a matrix of open montane grassland and ericoid shrubland with extent forest patches, associated with seasonal variation of rainfall, and fire. A matrix of ericoid shrubland remained abundant in the landscape despite an increase of fire regime and herbivory activities between 2 and 1.1 cal. ka BP. Major changes in the vegetation were recorded during the last millennium with a shift towards a more open C₄-dominated grassland associated with high fire frequency and herbivory activities, most likely linked to human influence. Our findings support the notion of the natural presence of open ecosystems on the islands. These shed light on the landscape history which should be considered when setting conservation goals with a particular focus on areas targeted for tree plantations and fire bans like the Central highlands of Madagascar.

The morphometry of sedimentary charcoal particles illuminates the source fuel types. This study explores the variation in morphometry (specifically, the length-to-width (L/W) ratio) of charcoal particles of different sizes, using charcoal collected from Miscanthus sinensis (Japanese pampas grass) fields following controlled burning. We also investigated the impact of pretreatment processes on sedimentary microcharcoals. The results indicate a general decrease in the L/W ratio with decreasing particle size, with the microcharcoal exhibiting a substantial decrease. The mean L/W ratios for size categories of 250 µm–1 mm, 125–250 µm, 63–125 µm, and <63 μm in size are 6.42, 5.54, 4.94, and 3.45, respectively. Furthermore, pretreatment processes for microcharcoal decrease the L/W ratio. Consequently, the L/W ratio of grass microcharcoal (<125 μm) likely falls within 50–80% of the ratios observed in grass macrocharcoal (>125 μm), necessitating caution in interpreting microcharcoal data. Our findings emphasize the importance of considering particle size and pretreatment effects when interpreting paleofire records and highlight the need for further research to establish robust cutoff values for fuel type inference based on charcoal morphometry, particularly for microcharcoal.