Influence of flooding, gap size, and surrounding forest characteristics on the fate of UMRS floodplain forest canopy gaps

Abstract

A natural loss of forest canopy creates gaps that can serve as locations for the growth of new cohorts of seedlings. However, adverse environmental conditions (e.g. change in flood regime, invasive species) may inhibit typical successional patterns and prevent gap closure. This project aims to improve our understanding of factors that determine the fate of canopy gaps in the Upper Mississippi River System floodplain forests. Collaborators identified forest gaps with GIS data and LiDAR imagery. We surveyed a subset of 20 gaps across a range of sizes and flood conditions in Pools 8 and 9 of the Mississippi River in summer 2019. Across all surveyed gaps, the presence of tree seedlings < 50 cm tall declined as the presence of reed canarygrass increased. Tree saplings > 50 cm in height were only recorded within 45% of sites, suggesting a lack of natural regeneration. Statistical modeling suggests that multiple environmental factors may interact to influence the vegetation that grows within canopy gap sites, including gap size, flood period, and forest buffer percentage. This insight may be used to select project areas that are suitable for forest management and for the design of management plans to most effectively conserve our forests.