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  • Why are sandstone outcrops home to acid-loving plants?

    Question

    If silica is pH neutral, why are silicate sandstone stone outcrops like Thompson Ledges populated with acid loving plants like chestnut oaks, low bush blueberry and wintergreen?

    Naturalist's Response

    Soil pH is the result of numerous factors. Composition of the bedrock is one factor. In this case, the silica which is a component of sandstone actually does create slightly acidic soil.

    Another factor creating acidic soil is the leaching out of the soil of nutrients and minerals by rainfall, which itself is moderately acidic.

    A third factor in soil acidification is decomposition of organic material such as leaves. Since the sandstone outcropping creates sandy soil, it drains more easily and therefore leaches out more quickly.

    All of these factors together create the acidic soil seen at Thompson Ledges, and therefore you will find acid-loving plants there.

    Thanks for your question!

    -Naturalist Denise Wolfe