The effects of submergence and light on two age classes of baldcypress (Taxodium distichum (L.) Richard) seedlings

In the early 1900s, baldcypress swamps were harvested en masse in coastal L ouisiana, USA. In many areas, natural regeneration did not occur; instead, these areas converted to marsh or open water. One of the factors that may h ave been responsible for the lack of regeneration was shading of newly-germ inated seedlings by herbaceous vegetation. Alternatively, prolonged floodin g or complete submergence may have suppressed germination or growth rates o f young seedlings and even caused mortality. This study investigated the ef fects of complete submergence and variable light regime on two age classes of baldcypress seedlings. Newly-germinated seedlings (under two weeks of ag e) subjected to complete submergence began to show clear signs of stress af ter approximately one month and substantial mortality following 45 days of submergence. In contrast, one-year-old seedlings submerged for as much as f ive months experienced up to 75% survival. In a four-way factorial experime nt, two age classes of baldcypress seedlings were subjected to five light t ransmissions (100%, 80%, 50%, 30%, 20%), five flood durations (0 days, 14 d ays, 25 days, 35 days, 45 days), and two nutrient regimes (fertilized vs. n ot fertilized). At 100% light transmission, the newly germinated seedlings suffered complete mortality after 35 days of submergence, whereas the one-y ear-old seedlings were largely unaffected by prolonged flooding or light re gime. Fertilized one-year-old seedlings that were submerged for an entire m onth had considerably greater growth in height and diameter than seedlings grown under mesic conditions without fertilizer. This is particularly impor tant in coastal Louisiana because several re-introductions (i.e., diversion s) of Mississippi River water into declining swamps are planned or underway , and these diversions will periodically increase nutrient and flood levels .