Age structure and radial growth in xeric pine-oak forests in western Great Smoky Mountains National Park

In the 19(th) and early 20(th) centuries, xeric upper slopes and ridges in western Great Smoky Mountains National Park burned frequently, largely as a result of anthropogenic ignitions. Fire frequency dropped dramatically following the removal of human settlements in the 1920s and 1930s and the implementation of effective fire control measures circa 1940. To evaluate the effects of this change in fire regime on forest composition and structure, we measured tree ages, diameters, and radial growth rates in four xeric Pinus-Quercus stands. Most trees in the present canopy (stems greater than or equal to 10 cm dbh) established between 1920 and 1959. Although canopy individuals of fire resistant, light-demanding Pinus and Quercus species established throughout the 19(th) and early 20(th) centuries, few have established since 1945. In addition, shade-intolerant Pinus species are absent from the sapling stratum (stems greater than or equal to 1.37 m high, > 10 cm dbh), and Quercus species are poorly represented. The oldest extant individuals of Pinus strobus, Acer rubrum, and Oxydendrum arboreum established circa 1920. The abundance of fire-sensitive species in the canopy has increased steadily over the past 50 years, and these species are currently well-represented as saplings. Recent patterns of recruitment and decreases in rates of radial growth are consistent with the hypothesis that changes in fire regime have caused xeric sites to develop from open-canopy woodlands dominated by fire-resistant, light-demanding Pinus and Quercus species to closed-canopy forests increasingly dominated by more fire-sensitive, shade-tolerant taxa.