Effects of flooding on the forest community in a greentree reservoir 18 years after flood cessation

Abstract

Greentree reservoir (GTR) management is a common waterfowl habitat management technique used in both the northeastern and southeastern United States. However, this management technique is controversial because greentree reservoir management can cause changes in forest composition and structure. We studied the effects of GTR management at the Montezuma National Wildlife Refuge in central New York by comparing vegetation in permanent plots in two GTRs and a natural forest wetland over 30-year period (preflood and 2 years and 18 years after flood cessation). We detected long-term effects of GTR management on vegetation composition and structure. Red maple and green ash remained the dominant overstory species, but density of green ash saplings was higher (P=0.026) in a natural forested wetland (300 trees/ha) compared to the two GTRs (30–90 trees/ha). Age determinations of several green ash saplings suggest these changes were likely caused by reduced regeneration in the GTRs. Mortality of green ash seedlings in 1996 was greatest in a GTR flooded for 1 year (60%) versus an unflooded GTR (12%) and a natural forested wetland (27%). Overall, shrub density was similar 18 years post-flooding and preflooding, but several species had lower densities (P=0.001–0.031) than a natural forested wetland. Shannon-Weiner diversity index (1.8–2.0) and richness (29–31) of herbaceous species were similar among all sites 18 years after flood cessation. However, two species of fern remained at lower densities (P=0.0001–0.026), while three herbaceous species remained at higher densities (P=0.0001–0.015) 18 years after flood cessation as compared to preflood densities and densities in a natural forested wetland. It is unknown after which year of flooding these changes occurred, but 12 years of GTR management did cause long-term effects on the forest community.