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Abstract
Deadwood supports a highly diverse fauna of “saproxylic” (i.e., deadwood-dependent) species. Most forest cover in the southeastern United States is relatively young second-growth that has regrown after historic logging or agriculture, and may not be suitable for saproxylic species. I conducted a series of studies to understand these impacts on saproxylic beetle (Coleoptera) biodiversity and to gain insight on their conservation in the region. In a study comparing saproxylic beetle communities in old (mature in 1938) and young (regrown after 1938) forests located along a landscape forest cover (LFC) gradient in the Piedmont, local and regional species richness was higher in old forests and no support was found for a dispersal limitation hypothesis. However, distinct community composition between forest ages suggests both contribute to regional biodiversity. In a follow-up study investigating how morphological traits are filtered in this same system, body length influenced species responses to forest age and LFC, and communities in old forests and with high LFC had larger mean and dispersion of body length. In a study comparing species occurrence among forest disturbance histories in the southern Appalachian Mountains, Phellopsis obcordata (Kirby) (Zopheridae) was restricted inside or near to old-growth forests due to dispersal limitation, whereas Megalodacne heros (Say) (Erotylidae) was distributed in all disturbance categories. I additionally found that P. obcordata populations show low connectivity and short-range endemism of mitochondrial lineages, although occasional contact during the Pleistocene is supported. Future habitat suitability for this high-elevation species is predicted to decline under warming climates. Finally, I reviewed the deadwood associations for the tumbling flower beetles (Mordellidae) in North America. Although saproxylic lifestyles appear widespread among genera in this family, precise ecological information is lacking for most species. In conclusion, older (and especially old-growth) forests are disproportionately important for saproxylic beetle biodiversity in the southeastern United States. Although dispersal limitation is not widespread in the highly forested region, it remains an important factor determining old forest dependency for low-mobility species. Targeted conservation approaches are optimal, but action is precluded by our limited or lacking knowledge of most species’ biology and habitat requirements.