Baldcypress (Taxodium distichum (L.) Rich.) restoration in southeast Louisiana: The relative effects of herbivory, flooding, competition, and macronutrients

Abstract

In the early 1900s, old-growth baldcypress (Taxodium distichum) was completely logged out of what is now the Manchac Wildlife Management Area, located in the Lake Pontchartrain Basin, Louisiana. Natural regeneration of swamp did not occur; the area is currently dominated by bulltongue (Sagittaria lancifolia) marsh. This study was conducted to isolate the major factors prohibiting cypress restoration. Specifically, four hundred baldcypress seedlings were planted in a three-way factorial treatment arrangement that included nutrient augmentation (fertilized vs. unfertilized), management of entangling vegetation (managed vs. unmanaged), herbivore protection (Tubex tree shelters, PVC sleeves, Tanglefoot), and elevation (included as a covariable). Highly significant differences in diameter growth were found for all main effects. For the herbivore protection treatment, relatively inexpensive PVC sleeves were as effective as Tubex Tree Shelters; unprotected trees experienced 100% mortality. Seedlings that received Osmocote 18-6-12 fertilizer showed nearly a two-fold increase in diameter growth. Similarly, seedlings that were managed grew nearly two times greater in diameter than unmanaged seedlings. However, seedlings that wereunmanaged grew nearly two times greater in height than managed seedlings. This study indicates that biotic factors are primarily responsible for the lack of cypress regeneration in southeastern Louisiana, not the prevalent, but largely untested, hypothesis of salt-water intrusion. Moreover, it is likely that, with a combination of management techniques, it is possible to restore swamp habitat in this area. Though labor intensive in the short run (i.e., first few years), once established, these trees may survive for hundreds of years.