What is the importance of the Preserve in the novel, Fablehaven?

The Preserve is the extensive property surrounding Grandma and Grandpa's house. The property is home to an array of magical beings, such as naiads, trolls, fairies, a golem, a magic cow, and more. The yard around the main house is protected by magic so that access is limited to only a few kinds of creatures, including fairies. The Preserve is one of a series of similar properties around the world, but it is one of five that are secret from other magical caretakers. Grandma reveals to Kendra and Seth that the Preserve is one of five that has a secret artifact hidden on the property, which sets them apart.