Long-term changes in forest structure and species composition of an upland oak forest in Arkansas

Describing long-term dynamics in oak stands is hindered by a lack of archival data. In this study, archival data from the 1934 inventory of a 673ha area within the Sylamore Experimental Forest were compared to a recent 2002 inventory to quantify changes in forest structure and species composition of this upland oak forest in the Ozark Mountains of Arkansas. When established in 1934, the Sylamore Experimental Forest was typical of the unharvested forests of the region that had a long history of frequent fires. Some improvement cutting was conducted after establishment and a fire prevention program was implemented, but little management occurred after 1960. From 1934 to 2002, total tree density increased from 364 to 1032 trees/ha and basal area from 10 to 23 m/ha. Increases occurred among understory, midstory, and overstory trees for most species. However, declines were observed for Ozark chinkapin (Castanea ozarkensis Ashe.) and black oak (Quercus velutina Lam.). Chestnut blight (Cryphonectria parasitica (Murrill) Barr.) is the most probable cause of the decline in chinkapin, but the decreases in black oak are less understood. In both inventories, oaks and shortleaf pine (Pinus echinata Mill.) dominated the overstory and midstory. Species composition changes primarily occurred in the understory. Among these smaller trees, fire-intolerant and shade-tolerant species were more important in 2002 than in 1934, while most oaks and shortleaf pine decreased in importance over time. We attribute the changes in forest structure and species composition primarily to changes in the disturbance regime. Before the 1920s, the study area burned repeatedly for at least 100 years. Frequent fires reduced tree establishment and recruitment and resulted in the relatively understocked conditions observed in 1934. In contrast, effective fire suppression beginning in the 1920s facilitated tree establishment and recruitment, increased the importance of fire-intolerant species, and resulted in the overstocked conditions observed in 2002. # 2006 Elsevier B.V. All rights reserved.