From the text...'Preservation of rare species and communities is a noble conservation goal, but it has two unfortunate drawbacks: it promotes a piecemeal approach to preservation, and it frequently results in species or communities being ignored until they become endangered. The Herculean efforts made to protect these rarities sometimes involve the purchase of either exorbitantly expensive and unmanageable remnants or sites where the species* natural habitat no longer exists. Impossible to burn, subject to exotic species invasions, and isolated from associated systems, they are likely transitory and of little global significance. Although decline toward endangerment and extinction is progressive, the imperiled species and communities of tomorrow are seldom identified beforehand. In the long run, large units of the natural landscape probably capture more biological diversity than do small units containing species or communities that are currently sparse. The biological importance of Lake Wales Ridge scrub and the Dade County pine rocklands was recognized decades ago. Fortunately, a significant portion of the latter was included in Everglades National Park. In the case of scrub, the opportunity for an intact natural landscape no longer exists, and the future of the few protected pieces is uncertain. Although small conservation units do serve the important function of preserving biological curiosities for education and scientific study, an ecosystem-level approach contributes to achieving our primary goal: sustaining the biosphere.'