Abstract
Pollen records contain a wide range of information about past land cover, but translation from the pollen diagram to other formats remains a challenge. In this paper, we present LandPolFlow, a software package enabling Multiple Scenario Approach (MSA) based land cover reconstruction from pollen records for specific landscapes. It has two components: a basic Geographic Information System which takes grids of landscape constraints (e.g. topography, geology) and generates possible 'scenarios' of past land cover using a combination of probabilistic and deterministic placement rules to distribute defined plant communities within the landscape, and a pollen dispersal and deposition model which simulates pollen loading at specified points within each scenario and compares that statistically with actual pollen assemblages from the same location. Goodness of fit statistics from multiple pollen site locations are used to identify which scenarios are likely reconstructions of past land cover. We apply this approach to two case studies of Neolithisation in Britain, the first from the Somerset Levels and the second from Mainland, Orkney. Both landscapes contain significant evidence of Neolithic activity, but present contrasting contexts. In Somerset, wet-preserved Neolithic remains such as trackways are abundant, but little dry land settlement archaeology is known, and the pre-Neolithic landscape was extensively wooded. In Orkney, the Neolithic archaeology includes domestic and monumental stone-built structures forming a UNESCO World Heritage Site, and the pre-Neolithic landscape was largely treeless. Existing pollen records were collated from both landscapes and correlated within a new age model framework (presented elsewhere). This allowed pollen data to be grouped into 200 year periods, or “timeslices”, for reconstruction of land cover through time using the MSA. Reconstruction suggests that subtle but clear and persistent impacts of Neolithisation on land cover occurred in both landscapes, with no reduction in impact during periods when archaeological records suggest lower activity levels. By applying the methodology to specific landscapes, we critically evaluate the strengths and weaknesses and identify potential remedies, which we then expand into consideration of how simulation can be incorporated into palynological research practice. We argue that the MSA deserves a place within the palynologist’s standard tool kit.
Highlights
Land cover is an important component of the earth system, through the habitats it provides for living things and through its interactions with the other major components, for example with the hydrosphere via modification of water flow and water quality, and with the atmosphere and climate system through albedo and evapotranspiration
As more sets of pollen dispersal and deposition parameters are published for different taxa and geographic areas, and as increasing processor speed reduces the time and computational resource needed to run LandPolFlow, we believe that modelling approaches should become a routine part of the pollen analysts’ tool kit, as zonation using a constrained clustering approach such as CONISS rather than merely visual inspection has become routine since its introduction (Grimm, 1987). Modelling approaches such as the Multiple Scenario Approach (MSA) offer a clear route to getting more information from existing published pollen records, which represent a huge investment of time and money
This paper presents two case studies of the MSA in use at a landscape level, filling the gap between the regional land cover reconstructions offered by REVEALS (Sugita, 2007a; 100 × 100 km squares in e.g., Trondman et al, 2015) and the single-site reconstruction of distanceweighted plant abundance made possible by LOVE (Sugita, FIGURE 8 | Recommended workflow for reconstruction of past land cover using the Multiple Scenario Approach (MSA)
Summary
Land cover is an important component of the earth system, through the habitats it provides for living things and through its interactions with the other major components, for example with the hydrosphere via modification of water flow and water quality, and with the atmosphere and climate system through albedo and evapotranspiration. Land cover is variable in both space and time, and reconstructing past land cover is an important contribution to understanding the longer-term dynamics of the earth system (for example for testing regional climate models or framing the context of archaeological records of human activity), as well as for ecological studies of ecosystem processes and dynamics and archaeological investigation of the controls on and environmental impacts of past human activity. Various methodologies have been explored, such as biomisation (e.g., Prentice et al, 1996), modern analog comparison methods (e.g., Overpeck et al, 1985), and the use of models of the relationship between pollen and vegetation or the process of pollen dispersal and deposition
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