There are currently 4,506 trees on the site that Apple bought from Hewlett-Packard. Some of those will be boxed up and preserved for re-planting, probably stored elsewhere on the site.
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Not only must [the Apple Campus 2 Arborist] ensure that the old trees remain healthy, he's also been traveling extensively in recent months to find and identify trees in other nurseries that are appropriate for the Apple campus. Some of these trees have been harvested from other developments and some have been grown from seedlings. In many cases, the trees will have be stored for several years at the nurseries, then transported to the Apple campus and planted.