FESSEL, KEITH E.* AND BETH A. MIDDLETON. Biology Department, Grand Valley State University, Allendale, MI 49401 and Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901. - Survivorship of woody plant seeds in bald cypress swamps in southern Illinois.
Woody plant species in bald cypress swamps are recruitment limited.
Seeds of most wetland plants will not germinate under water and so
must survive until draw down. Therefore, seed survivorship is a
crucial component for natural regeneration of these forests. A field
study was conducted to examine seed survivorship of four woody plant
species common in bald cypress swamps in southern Illinois. Seeds of
bald cypress (Taxodium distichum), water tupelo (Nyssa
aquatica), water locust (Gleditsia aquatica) and buttonbush
(Cephalanthus occidentalis) were placed under flooded
conditions in situ over 18 months. Considerable variation was observed
in initial seed viability among the four species. There were
significant declines in seed viability of all four species. Rates and
patterns of seed survivorship differed among the four species. Bald
cypress had the fastest decline in seed survivorship with only one
half of seeds surviving 1.4 months, followed by water locust (14
months). One half of water tupelo and buttonbush seeds were predicted
to survive 20 and 39 months, respectively. Bald cypress seeds had an
exponential decline in viability over time, where as water tupelo and
water locust seeds declined according to a second order regression
line and seeds of buttonbush declined linearly over the duration of
the study. Estimated maximum age of seeds was similar between water
tupelo (30 months), bald cypress (25 months) and water locust (23
months). Buttonbush had the longest estimated seed longevity (150
months). These differences in seed survivorship may have significant
effects on community structure by all but eliminating bald cypress
seedling establishment following drawdown while favoring the
establishment of buttonbush. Infrequent drawdown events are also
likely to greatly favor the establishment of buttonbush over other
species due to seed longevity.
Key words: Cephalanthus occidentalis, Gleditsia aquatica, Nyssa aquatica , Seed survivorship, Taxodium distichum