A beech bark disease induced change in tree species composition influences forest floor acid–base chemistry

Beech bark disease (BBD) has demonstrable ecosystem consequences for eastern US forests stemming from American beech (Fagus grandifolia Ehrh.) mortality, often leading to increased dominance by its competitor, sugar maple (Acer saccharum Marsh.). We hypothesized that this BBD-induced shift in tree species composition leads to changes in soil acid–base chemistry, mediated through differences in leaf litter chemistry of the two species. Using a sequence of plots representing the progression of the disease in the Catskill Mountains, NY, USA, we examined the influence of tree species composition shift on soil chemistry. The BBD impact on tree species composition was confounded by variability in substrate (or nonexchangeable soil) calcium (Ca). While substrate Ca explained much of the variation in acid–base chemistry, increasing BBD was associated with increasing forest floor exchangeable Ca, sum of base cations, base saturation, cation-exchange capacity, and decreasing hydrogen. An apparent threshold effect of substrate Ca on sugar maple litter Ca concentration suggests that underlying soil Ca availability may contribute to the spatial extent and timeframe of BBD-induced shifts in species composition. The species compositional shift is a mechanism contributing to a vegetation effect on soil acid–base status and may partially counteract soil acidification in this acid deposition impacted region.