Effects of watershed liming on a food web in an Adirondack forest

Background/Question/Methods Loss of calcium and other changes in soil chemistry that result from acidic deposition can cause changes in the abundance and diversity of terrestrial fauna.  We conducted a watershed liming study in the Adirondack Mountain Region, an area that is affected by acidic deposition.  Liming replaces calcium and increases buffering capacity of the soil.  Two 1590-m² circular plots were selected, such that one was on each side of a stream, in each of four watersheds in forests of Herkimer County, New York.  One plot within each pair was limed over three applications during 2005 and 2006 to effect a rate of 10 metric tons ha^-1.  During 2006-2008 we sampled green and fallen leaves, herbaceous plants, and forest floor fauna using a variety of methods.  Samples were used to estimate elemental calcium concentration in this food web, as well as relative abundance, diversity, and composition of forest-floor animals.  We expected that liming would cause an increase in calcium availability in leaf litter, the nutritional base for this food web, and that this change would be reflected in increased calcium concentration or abundance of many animals at the forest floor.

Results/Conclusions Calcium concentration was greater in leaves at limed than unlimed plots during the two years following liming.  Among the three most common tree species – red maple, yellow birch, and American beech – yellow birch demonstrated the strongest increase in calcium concentration in leaves following liming.  Millipedes were the most common large detritivores at our plots and demonstrated greater whole-body calcium concentration, but not greater abundance, at limed plots.  Snails were markedly more abundant at limed than unlimed plots.  This was expected given that snails have high calcium needs and have demonstrated increased abundance at other limed forests.  Both of the two earthworm species that we found at our plots are known acidophiles and did not apparently respond to liming.  We detected a decrease in abundance of shrews, which are mammalian insectivores and represent high-order predators in this system, at limed plots.  Changes in abundance of certain foods or physical changes at the forest floor may have negatively affected shrew survival or reproduction.  Overall, we found that liming mitigation can be used to amend calcium in forest food webs affected by acidic deposition.  However, effects of liming might be complicated by the acidophilic nature of communities at Adirondack and other acid-impacted forests.