Neighborhood-scale analyses of non-additive species effects on cation concentrations in forest soils

Trees affect soil chemistry and nutrient availability via a broad range of processes. Effects can vary dramatically among species, whose distinctive spatial “footprints” can vary for different nutrients. Potentially overlapping effects of neighboring trees in mixed-species stands make footprint shape and interspecific interactions important: If interactions are non-additive, then not only abundance but also spatial configuration influence tree species’ effects on ecosystem properties. We used spatially explicit neighborhood-scale data on tree distributions to fit maximum likelihood models of exchangeable calcium, magnesium, and potassium in surface soils of four sites in northern hardwood forests in northwestern Connecticut, USA. The models incorporated parent material, site, and tree species or functional group configuration to predict availability of the three cations. Site had a stronger effect than species for all cations (there was no species effect for potassium), even after accou...