Calcium depletion in a southeastern United States forest ecosystem

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.