Westward Expansion by Juniperus virginiana of the Eastern United States and Intersection with Western Juniperus Species in a Novel Assemblage

Abstract

Eastern redcedar (Juniperus virginiana L.) is increasing in density in the eastern United States and expanding in range to the west, while western Juniperus species also are increasing and expanding, creating the potential for a novel assemblage. I estimated range expansion and intersection by comparing recent USDA Forest Service Forest Inventory and Analysis surveys (mean year = 2009) to the oldest available surveys (mean year = 1981), with adjustments for sampling changes, and predicted climate envelopes during the following year ranges: 1500–1599, 1800–1849, 1850–1899, 1900–1949, and 1960–1989. During approximately 28 years, eastern redcedar range expanded by about 54 million ha (based on ≥0.5% of total stems ≥12.7 cm in diameter in ecological subsections). Combined range of western species of juniper did not expand. Range intersection of eastern redcedar and western Juniperus species totaled 200,000 km2 and increased by 31,600 km2 over time, representing a novel assemblage of eastern and western species. Predicted ranges during the other time intervals were 94% to 98% of predicted area during 1960–1989, suggesting major climate conditions have been suitable for centuries. The southern western Juniperus species and Rocky Mountain juniper (Juniperus scopulorum Sarg.) have the greatest potential for intersection with eastern redcedar, whereas eastern redcedar may have concluded westward expansion.