Abstract: “Matching site with trees” is a fundamental principle in silviculture. It refers to finding the right tree species for a given site, or finding the right site for a given tree species for a maximum tree growth. This matching of tree species with site was conventionally achieved through correlation analyses between tree growth(typically tree height)and empirically chosen site physicochemical variables(including topographical, soil and climatic parameters)with subsequent site quality classification for high, medium, fare and poor tree-growth sites. Noticeably, physicochemical variables used for evaluating site quality vary with evaluators, locations and tree species, thus the approach for site quality evaluation is unreplicatable and unscientific. Here we propose using site calcium supply potentials as an unified site quality index. A site is suited for a tree species, or a tree species grows well in a site, when a tree’s calcium demand for a maximum growth coincides with the site calcium supply potential. Based on this principle, we calculated the calcium supply potentials for Liaoning Province of China. Using leaf tissue calcium concentration we estimated the growth index of cross section area at DBH for Liaodong oak(Quercus liaotungensis Koidz). This index correlated notably well with the forestry inventory data in permanent plots spaced at 4 km×8 km across Liaoning Province. Our analyses demonstrated that calcium supply potential can reflect site quality for silvicultural practices, and the principal foci for “matching site with trees” is “matching calcium with trees”.