Forest soil Ca depletion through leaching and vegetation uptake may threate
n long-term sustainability of forest productivity in the southeastern USA.
This study was conducted to assess Ca pools and fluxes in a representative
southern Piedmont forest to determine the soil Ca depletion rate. Soil Ca s
torage, Ca inputs in atmospheric deposition, and outputs in soil leaching a
nd vegetation uptake were investigated at the Panola Mountain Research Wate
rshed (PMRW) near Atlanta, GA. Average annual outputs of 12.3 kg ha(-1) yr(
-1) in uptake into merchantable wood and 2.71 kg ha(-1) yr(-1) soil leachin
g exceeded inputs in atmospheric deposition of 2.23 kg ha(-1) yr(-1). The a
nnual rate of Ca uptake into merchantable wood exceeds soil leaching losses
by a factor of more than five. The potential for primary mineral weatherin
g to pro,ide a substantial amount of Ca inputs is low. Estimates of Ca repl
enishment through mineral weathering in the surface 1 m of soil and saproli
te was estimated to be 0.12 kg ha(-1) yr(-1). The weathering rate in saprol
ite and partially weathered bedrock below the surface 1 m is similarly quit
e low because mineral Ca is largely depleted. The soil Ca depletion rate at
PMRW is estimated to be 12.7 kg ha(-1) yr(-1). At PMRW and similar hardwoo
d-dominate forests in the Piedmont physiographic province, Ca depletion wil
l probably reduce soil reserves to less than the requirement for a merchant
able forest stand in approximate to 80 yr. This assessment and comparable a
nalyses at other southeastern USA forest sites suggests that there is a str
ong potential for a regional problem in forest nutrition in the long term.