The forest effect: Biosphere 87Sr/86Sr shifts due to changing land use and the implications for migration studies

Abstract

This study documents a transect of 87Sr/86Sr values from a variety of plant, soil and rock samples across the ancient woodland of the Sherwood Forest National Nature Reserve (SFNNR) and into adjoining farmland in Britain. All samples were collected from the Triassic Sherwood Sandstone Group. A shift of +0.0037 in 87Sr/86Sr values is observed between the average plant from the biosphere of the ancient forest and that of the farmland. This shift is caused by the leaf litter accumulation in the forest, through time, leading to soil acidity that leaches out the carbonate component of the soil. This results in the forest floor soil reflecting only the silicate minerals from the original Sandstone rock formation. We have named this process “the forest effect”. Rock samples from boreholes of the Sherwood Sandstone Group, as well as water samples from aquifers and mineral waters from previous studies, further indicate that the change in biosphere 87Sr/86Sr is a result of the wooded environment rather than the anthropological addition of lime to farmland.The extent of the forest effect will vary with differing lithologies with the most susceptible terrains being those with mixed carbonate-silicate composition, and it may be sufficient to impact the interpretation of animal and human 87Sr/86Sr in studies of mobility and migration. The model provides an opportunity to understand and assess food procurement strategies and animal management practices in the past, as well as the interaction of humans with their natural environment.