Ginkgo Biloba Depletion

I have been taking Ginkgo Biloba for 6 years or so. It really seems to help with my memory and mental alertness. My wife is interested in taking but she is afraid that we are depleting the supply of Ginkgo trees. Doesn't the herb come from the seeds and/or leaves that are dropped by the tree?

The part of the plant used in medicine is the leaf. Unlike other medicinal trees harvested for the roots or bark or the wood, taking the leaves from the trees does not kill the Ginkgo tree – in fact Ginkgo trees will go on to produce harvests for many years.
Your wife's concern may stem from the fact that Ginkgo is not found in the wild. The species has persisted to the present day only because man finds the plant appealing enough to collect the seeds and plant them to increase the species. But that doesn't mean that the species is in any danger of depletion because there are farms devoted to the production of Ginkgo leaves for the medicinal herbs market.