Baldcypress and water tupelo sapling response to multiple stress agents and reforestation implications for Louisiana swamps

Abstract Forested wetlands in Louisiana are hydrologically isolated from the Mississippi river, impacted by saltwater intrusion, and are sinking, resulting in more frequent flooding for longer periods; and these problems are exacerbated in some areas by impoundment from manmade structures. Additionally, defoliation of the two dominant trees, baldcypress and water tupelo, occurs frequently during spring. In Louisiana, the baldcypress leafroller, BCLR, ( Archips goyerana Kruse) and the forest tent caterpillar, FTC, ( Malacosoma disstria Hubner) defoliate up to 120,000 ha of baldcypress-tupelo swamps annually. In combination, these factors have led to severely degraded forested wetlands with reduced basal area, dieback, and tree mortality over extensive, formerly productive, swamplands. Restoration plans call for creating diversions to reintroduce Mississippi river water to increase sediment elevation, promote natural regeneration, and enhance primary and secondary productivity. In this study, insect-tree-health relationships were evaluated in a multifactor, greenhouse experiment incorporating these environmental stressors as well as nutrient enhancements under simulated diversion conditions. The combination of nutrient deprivation and flooding led to “poor” sapling growth, while nutrient enhancement under flood conditions led to significantly higher growth and saplings grew as well as, or better than those that were non-flooded and unfertilized. Importantly, nutrient deprived saplings had growth similar to salt-stressed (3 ppt) saplings. Defoliated saplings had significantly lower growth, with the largest differences seen in the fresh, nutrient-rich treatments, while salinity and the combined effects of nutrient deprivation and flooding still remained the most important factors contributing to sapling growth. Taken collectively, these experiments demonstrated that river diversions may be a viable management tool for improving health and productivity of declining forested wetlands. Findings from this study are meaningful for post-harvest management in existing forests because they describe a variety of local environmental conditions that predict which areas may be successfully regenerated.