Two-year Growth and Mortality of Sub-Canopy Baldcypress (Taxodium distichum [L.] Rich.) in Artificial Canopy Gaps in a North Carolina Swamp

Baldcypress (Taxodium distichum, [L.] Rich.) -tupelo (Nyssa spp.) swamp forests are a major component of the total area of southeastern U.S. forested wetlands which provide valuable ecosystem services related to water quality, stormwater catchment, and wildlife habitat. Historically, baldcypress has also been an important source of wood products, and clearcutting the principal method of harvesting and regenerating the species. However, anthropogenic alterations to flows of many rivers and the associated flood patterns of alluvial wetlands have prevented the establishment of new baldcypress cohorts in many swamps. Regular, extended growing season flooding could prevent germination and/or establishment of baldcypress seedlings if clearcutting were to occur. Where advanced baldcypress regeneration does occur, its ability to respond to release via overstory cutting or removal remains unknown, especially for long-suppressed saplings. In this study, I tested sub-canopy baldcypress sapling response to release in twelve 456 m2 artificial canopy gaps created through girdling and injection of all canopy trees in a water tupelo-dominated `backswamp\u27 of the lower Roanoke River floodplain, eastern North Carolina. Leaf area index and diffuse non-interceptance were measured for all treated and untreated plots, and diameter growth, basal area growth, and mortality of clustered saplings ranging from \u3c1 - 24 cm dbh were recorded over two post-treatment years. Additionally, a subset of saplings were cut and slabs removed for aging. Saplings ranged in age from 12 - 38 years and most likely established during short periods of minimal growing-season flooding. Sub-canopy light levels averaged 1.3+/- .4% in untreated plots and 16.9 +/- 6.5% in treated plots. Saplings responded to treatment with strong radial growth, adding nearly eight times as much basal area and diameter growth as saplings beneath intact canopy over two years. Mortality levels in both groups were quite high (9-11%) in the first post-treatment year, but by year two death in treated plots had dropped to 2.5%. Mortality was inversely related to plot initial quadratic mean diameter of plots. The study confirms the ability of sub-canopy baldcypress to respond well to release, and provides justification of a useful tool for the management of the species in uneven-aged stands