Modeling Historic Rangeland Management and Grazing Pressures in Landscapes of Settlement

Defining historic grazing pressures and rangeland management is vital if early landscape threshold crossing and long–term trajectories of landscape change are to be properly understood. In this paper we use a new environmental simulation model, Búmodel, to assess two contrasting historical grazing landscapes in Mývatnssveit Iceland for two key periods—the colonization period (ca. Landnám, A.D. 872–1000) and the early eighteenth century A.D. Results suggest that there were spatial and temporal variations in productivity and grazing pressure within and between historic grazing areas and indicate that land degradation was not an inevitable consequence of the livestock grazing introduced with settlement. The results also demonstrate the significance of grazing and livestock management strategies in preventing overgrazing, particularly under cooler climatic conditions. The model enables detailed consideration of historic grazing management scenarios and their associated landscape pressures

Islands of change vs. islands of disaster: Managing pigs and birds in the Anthropocene of the North Atlantic

The offshore islands of the North Atlantic were among some of the last settled places on earth, with humans reaching the Faroes and Iceland in the late Iron Age and Viking period. While older accounts emphasizing deforestation and soil erosion have presented this story of island colonization as yet another social–ecological disaster, recent archaeological and paleoenvironmental research combined with environmental history, environmental humanities, and bioscience is providing a more complex understanding of long-term human ecodynamics in these northern islands. An ongoing interdisciplinary investigation of the management of domestic pigs and wild bird populations in Faroes and Iceland is presented as an example of sustained resource management using local and traditional knowledge to create structures for successful wild fowl management on the millennial scale

Temporal and Spatial Variations in Freshwater \u3csup\u3e14\u3c/sup\u3eC Reservoir Effects: Lake Mývatn, Northern Iceland

Lake Mývatn is an interior highland lake in northern Iceland that forms a unique ecosystem of international scientific importance and is surrounded by a landscape rich in archaeological and paleoenvironmental sites. A significant freshwater reservoir effect (FRE) has been identified in carbon from the lake at some Viking (about AD 870–1000) archaeological sites in the wider region (Mývatnssveit). Previous accelerator mass spectrometry (AMS) measurements indicated this FRE was about 1500–1900 14C yr. Here, we present the results of a study using stable isotope and 14C measurements to quantify the Mývatn FRE for both the Viking and modern periods. This work has identified a temporally variable FRE that is greatly in excess of previous assessments. New, paired samples of contemporaneous bone from terrestrial herbivores and omnivores (including humans) from Viking sites demonstrate at least some omnivore diets incorporated sufficient freshwater resources to result in a herbivore-omnivore age offset of up to 400 14C yr. Modern samples of benthic detritus, aquatic plants, zooplankton, invertebrates, and freshwater fish indicate an FRE in excess of 5000 14C yr in some species. Likely geothermal mechanisms for this large FRE are discussed, along with implications for both chronological reconstruction and integrated investigation of stable and radioactive isotopes

Radiocarbon reservoir effects in human bone collagen from northern Iceland

Human bone collagen from a series of Icelandic human pagan graves was radiocarbon (14C) dated to aid understanding of early settlement (landnám) chronologies in northern Iceland. These individuals potentially consumed marine protein. The 14C age of samples containing marine carbon requires a correction for the marine 14C reservoir effect. The proportion of nonterrestrial sample carbon was quantified via measurement of carbon stable isotopes (δ13C) using a simple mixing model, based on δ13C measurements of archaeofaunal samples. Nonterrestrial carbon was also quantified in six pig bones from the archaeofaunal dataset. Assuming all non-terrestrial carbon in human and pig bone collagen was marine-derived, calibrated age ranges calculated using a mixed IntCal09/Marine09 calibration curve were consistent with an early settlement date close to landnám, but several samples returned prelandnám age ranges. Measurements of nitrogen stable isotopes (δ15N) strongly suggest that many of the human bone collagen samples contain freshwater diet-derived carbon. Icelandic freshwater systems frequently display large freshwater 14C reservoir effects, of the order of 10,000 14C years, and we suggest that the presence of freshwater carbon is responsible for the anomalously early ages within our dataset. In pig samples, the majority of non-terrestrial carbon is freshwater in origin, but in human samples the proportion of freshwater carbon is within the error of the marine component (± 10%). This presents a major obstacle to assessing temporal patterns in the ages of human remains from sampled graves, although the majority of grave ages are within the same, broad, calibrated range

Reservoirs and radiocarbon: 14C dating problems in Mývatnssveit, northern Iceland

This paper examines two potential sources of the 14C offset between human and terrestrial mammal (horse) bones recovered from Norse (c.870-1000 AD) pagan graves in Mývatnssveit, North Iceland. These are the marine and freshwater 14C reservoir effects that may be incorporated into human bones from dietary sources. The size of the marine reservoir 14C effect (MRE) during the Norse period was investigated by measurement of multiple paired samples (terrestrial mammal and marine mollusc shell) at two archaeological sites in Mývatnssveit and one on the North Icelandic coast. These produced three new ΔR values for the North coast of Iceland, indicating a ΔR of +106 ± 1014C yr at 868-985 AD, and of +144 ± 2814C yr at 1280-1400 AD. These values are statistically comparable and give an overall weighted mean ΔR of +111 ± 1014C yr. The freshwater reservoir effect was similarly quantified using freshwater fish bones from a site in Mývatnssveit. These show an offset of between 1285 and 1830 14C yr, where the fish are depleted in 14C relative to the terrestrial mammals. This is attributed to the input of geothermally derived CO2 into the groundwater and subsequently into Lake Mývatn. We conclude that: i.) some of the Norse inhabitants of Mývatnssveit incorporated non-terrestrial resources into their diet that may be identified from the stable isotope composition of their bone collagen, ii.) the MRE off the North Icelandic coast during the Norse period fits a spatial gradient of wider North Atlantic MRE values with increasing values to the northwest, and iii.) it is important to consider the effect that geothermal activity could have on the 14C activity of samples influenced by groundwater at Icelandic archaeological sites

Temporal and spatial variations in freshwater 14C reservoir effects: Lake Mývatn, northern Iceland

Lake Mývatn is an interior highland lake in northern Iceland that forms a unique ecosystem of international scientific importance and is surrounded by a landscape rich in archaeological and palaeoenvironmental sites. A significant Freshwater 14C Reservoir Effect (FRE) has been identified in carbon from the lake at some Norse (c.870-1000 AD) archaeological sites in the wider region (Mývatnssveit). Previous AMS measurements indicated this FRE was ~1500-1900 14C years. Here we present the results of a study using stable isotope and 14C measurements to quantify the Mývatn FRE for both the Norse and modern periods. This work has identified a temporally variable FRE that is greatly in excess of previous assessments. New, paired samples of contemporaneous bone from terrestrial herbivores and omnivores (including humans) from Norse sites demonstrate at least some omnivore diets incorporated sufficient freshwater resources to result in a herbivore-omnivore age offset of up to 400 14C yrs. Modern samples of benthic detritus, aquatic plants, zooplankton, invertebrates and freshwater fish indicate an FRE in excess of 5000 14C yrs in some species. Likely geothermal mechanisms for this large FRE are discussed, along with implications for both chronological reconstruction and integrated investigation of stable and radioactive isotopes

A grazing model for simulating the impact of historical land management decisions in sensitive landscapes: Model design and validation

This paper reports the construction and testing of a historical environmental simulation model, Búmodel (bú: Icelandic – farm estate or enterprise). The model permits the investigation of historical grazing management under variable environmental conditions in Iceland through the prediction of spatial and temporal patterns of vegetation biomass and utilisation. Input parameters of the model are environmental, livestock and management variables from historical and archaeological sources. Process sub-models were constructed using contemporary Icelandic data. Validation of the model was based on an independent, published grazing experiment and demonstrated that Búmodel-predicted utilisable biomass values and biomass intake values fall within ±1 standard deviation of observed values. Búmodel provides a validated representation of linkages between environmental and management elements in a historical grazing system. It incorporates key issues of spatial and temporal scale, data quality, model validation and the inherent stochasticity of landscape change over historical periods. In doing so, it enables researchers interested in past landscapes to investigate the flexibility of the historical Icelandic grazing systems within the constraints of climate and vegetation cover, and provides a framework and methodology that can be applied to other historical extensive livestock-based agricultural systems