Longevity and Bird Use of Hardwood Snags Created by Herbicides

Herbicides are frequently used in pine stands to control competing hardwoods. We investigated the longevity of 4 species of hardwood snags (mockernut hickory [Carya tomentosa], sweetgum [Liquidambar styraciflua], southern red oak [Quercus falcata], and post oak [Q. stellata]) after treatment with 2,4-D herbicide. In addition, we observed evidence of foraging activity and cavity excavation by cavity-nesting birds. Hickory and sweetgum were the least durable; by the fifth year only 16% of sweetgum and 47% of mockernut hickory snags remained standing, and only 11% of the original snags of each species was standing the sixth year post treatment. The oaks were somewhat more durable with 44% of southern red oak snags and 65% of post oak snags remaining by the sixth year. However, by the eighth year only one-fourth of these original snags remained. Bird foraging activity began the first year for sweetgum, the second year for post oak and the third year for southern red oak and hickory. Foraging activity was present at all heights once begun and continued until the snag fell. Ten bird cavities (9 woodpecker and 1 brown-headed nuthatch (Sitta pusilla)) and 2 mammal cavities were observed in the 76 snags over the course of the 16-year study.

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