Change in oak abundance in the eastern United States from 1980 to 2008

Although oaks (Quercus spp.) have historically dominated much of the forest land in eastern North America, a great deal of fragmentary and sometimes anecdotal evidence suggests that they have been yielding dominance in recent decades to other, typically more shade-tolerant species. Using FIA data, our work formally quantifies the change in oak abundance in the eastern U.S. during the period of 1980-2008. The results indicate that most areas in the eastern U.S. experienced some decline in oak abundance, but the decrease was not universal either geographically or among species. Declines were especially marked in the Central Hardwood Region, which lost oak abundance on 81% its forested area as measured by importance value (IV). Areas with a high oak abundance were more likely to see a reduction in abundance. Among all 25 species analyzed, eight species decreased significantly in IV while two increased. Both the top two most prevalent white oak species (white oak (Quercus alba) and post oak (Quercus stellata)) and red oak species (northern red oak (Quercus rubra) and black oak (Quercus velutina)) had significant decreases in density and IV. Water oak (Quercus nigra) is one of the red oak species that had a near universal increase of its abundance throughout its native range (83% of area). This study provided a comprehensive quantification of the dynamic of oak species in a regional-wide geographic context, which will provoke forest researchers and managers to revisit the oak decline problem by using knowledge from other regions and other species.