Region-wide characterization of structural diversity of the U.S. Outer Coastal Plain Mixed Forests Province

Abstract Forest structural diversity is related to stability, biodiversity, adaptability and resilience, as well as productivity of forest ecosystems. In this study, we characterized structural diversity of the diverse forest type groups in the southeastern Outer Coastal Plains Mixed Forest Province of the United States. We utilized data from 13,658 Forest Inventory and Analysis (FIA) plots across the region and classified them on the basis of forest type group (i.e., longleaf-slash pine, loblolly-shortleaf pine, oak-pine, oak-hickory, oak-gum-cypress, or other), disturbance type (disturbed by animal, fire, insect and disease, weather, other disturbances, or no disturbance), ownership (public or private and Native American), site condition (xeric, mesic, or hydric), stand origin (natural or planted), and age structure (one or two age classes). The structural diversity was estimated as Shannon index of tree size diversity. Our findings indicate a range of 0.00 to 2.40 for Shannon index values across the forest type groups and the ecoregion. All forest attributes (i.e., forest type groups, disturbance type, ownership, site condition, stand origin, and age structure) significantly affected structural diversity at α = 0.05. Oak-gum-cypress was structurally the most diverse forest type group. Overall, plots that were publicly owned, naturally regenerated, two-aged, and affected by weather disturbances exhibited higher structural diversity. We also created region-wide structural diversity distribution and hot spot maps. The maps identified southern Mississippi, northern and eastern Virginia, northern North Carolina, eastern South Carolina, and the border between the states of Texas and Louisiana as the structural diversity hot spots. The middle part of Outer Coastal Plain consisting of southcentral Georgia, northcentral Florida, and southwest Alabama exhibited the lowest structural diversity.