Influence of Soil-Base Availability on Composition and Structure of Adirondack, NY, Sugar Maple-Beech Forests.

Decline of Acer saccharum (SM), an abundant and highly valued species in the northeastern U.S. and eastern Canada, has been linked to depletion of soil calcium by acidic deposition in numerous studies.   During the same period, beech bark disease (BBD) has been infecting Fagus grandifolia (AB), which co-exists with SM throughout its range.  Although BBD eventually kills all infected trees, mortality often does not occur in trees until they have reached the canopy and have been infected for more than a decade.  Infected canopy AB tend to regenerate aggressively through seeds and root sprouts, creating a dense understory of saplings.   The spread of BBD may benefit SM by providing gaps for regeneration, or be a detriment by expanding AB in areas where SM has declined from soil-calcium depletion.  Effects of decreased soil-calcium availability on SM-AB relations have received limited investigation, and have not been considered in light of recent indications of soil recovery from acidic deposition.

We present measurements of soils, canopy, subcanopy and seedlings from 20 watersheds in the Adirondack region of NY, where SM and AB were predominant.  Base saturation (BS) of the upper B horizon ranged among watersheds from 4.4% to 67%.  In contrast to SM, AB measurements were unrelated to the wide range of BS.   However, AB tended to occupy lower canopy positions than SM, and this difference increased with increasing BS.   At low BS, red maple was the dominant canopy species, but at high BS, SM dominated the upper canopy.   In an AB-dominated watershed where soil monitoring showed recovery from acidic deposition, SM total basal area and average DBH increased in each 5-year interval from 2000-2015, whereas for AB, total basal area increased from 2000-2010 , but didn’t change from 2010-2015, and average DBH showed no changes from 2000-2015.