Completing the Land Resource Hierarchy.

The Land Resource Hierarchy of the NRCS is a hierarchal landscape classification consisting of resource areas which represent both conceptual and spatially discrete landscape units stratifying agency programs and practices. The Land Resource Hierarchy (LRH) scales from discrete points (soil pedon and vegetation patch) up to broad continental climate zones (Land Resource Regions).  Inclusion of Ecological Sites into the LRH has renewed interest in strengthening the concepts behind the NRCS’s landscape classification system which ultimately will lead to revisions of Agriculture Handbook #296 and updates to Major Land Resource Areas. In this paper we identify knowledge gaps and provide recommendations to complete the Land Resource Hierarchy and the subsequent landscape classification mapping updates. For example, one major inconsistency of the LRH occurs at the mid-scales of the hierarchy, specifically the Ecological Site Groups, Land Resource Units, and Major Land Resource Areas. These middle category scales in the hierarchy currently lack strong guidance and policy required for a consistent national and scientifically defensible product. To strengthen the hierarchical model of the LRH, we recommend that respective scales in the hierarchy be defined by ecosystem components at spatial and temporal scales which reflect relevant ecological dynamics. Furthermore, each focal level in the hierarchy should be constrained by only the immediate up-scale resource area (which provides context, significance, and boundary conditions) and subsequently tested by only the immediate down-scale resource area (which gives specificity, explains, and provides mechanisms delineating the resource area). Adopting a combined top-down and bottom-up approach limited to the focal scale of interest is important as ecosystem processes operate at different temporal and spatial scales and often demonstrate cross-scale interactions that a limited scaled-up or scaled-down only system fails to identify.