Soil chemical properties in forest patches across multiple spatiotemporal scales in mid-Atlantic U.S. metropolitan areas

Abstract

Temperate deciduous forests in the United States are in the most densely populated states across the northern and mid-Atlantic east coast. Land development and associated human activities have resulted in small forests that are susceptible to various anthropogenic influences across multiple spatiotemporal scales. The objective of this study was to assess soil chemistry in forest patches of various sizes embedded within an urban development gradient. We established 36 forest sites along the U.S. east coast in northern Delaware and southeastern Pennsylvania, and assessed soil chemical properties across metro (city size), landscape (surrounding urban density), patch (forest patch size/shape, non-native plant invasion), and temporal (time since forest canopy closure) scales. At the metro and landscape scale, we found significantly greater soil Cu, Zn, and S concentrations in forest patches with greater surrounding urban density. At the forest patch scale, soil pH and Ca increased with greater abundance of non-native invasive plants within the forest, whereas soil organic matter decreased with plant invasion. However, increased soil pH and Ca with decreasing SOM may also be a result of land use legacies since we found younger forests had significantly more plant invasion. Forest patch size and shape were primarily related to urban density, where smaller forests with greater edge to interior ratios had greater soil Cu and Zn concentrations. These findings support the importance of considering forest patch structure (size and shape), site legacies, proximity to urban land uses, and duration of intact canopy in understanding patterns and processes in forest soils.