Tree-of-heaven, Ailanthus altissima (P. Mill. [Swingle]), and its effects on vegetation and soils of southern Ohio mixed-oak forests

Background/Question/Methods

Ailanthus altissima (TOH) is the most widespread invasive tree in the eastern US. Prevailing thought has generally relegated TOH to disturbed, urban plant communities; but, recent investigations have shown TOH’s ability to colonize interior hardwood forests. The 42,097 ha Ironton District of the Wayne National Forest, a third-growth mixed-oak forest in southern Ohio, provides an excellent opportunity to analyze patterns of TOH colonization and broader vegetation effects. The Ironton District is interspersed with many private landholdings, experiences regular anthropogenic and natural disturbance, and was most recently heavily damaged by an ice storm in 2004. These factors have led to TOH colonization and proliferation within the forest. Twenty-five sets of paired 10 x 25 m Whittaker plots were established in spring of 2007 to analyze vegetation differences between infested and adjacent, uninfested control sites. Each pair was sited in similar forest vegetation of similar age, composition, slope, aspect and elevation to minimize variation. Vegetation data for trees, saplings, woody shrubs, seedlings, and forest herbs was collected in mid-summer of 2007. At the same time, soils within each plot were sampled assess pH, total N, C, N mineralization, bulk density, and available base cations. Light estimates were also taken using hemispherical photography.

Results/Conclusions

While the TOH-infested plots on average are similar in number of trees (535 stems/ ha v. 565 stems/ ha), they have almost five times more saplings (1010 stems/ ha v. 236.66 stems/ ha) than their adjacent, un-infested counterparts. But, most of these saplings were all TOH (78.9% of total infested-plot saplings), and this is to be expected given TOH’s clonal growth habit and prolific seed production. Mean shrub coverage was slightly higher within infested plots (16.44%) than within uninfested counterparts (10.82%). It also appears there is a negative correlation between forest herb density and density and basal area of TOH.