Response of Willow (Salixcaroliniana Michx.) in a Floodplain Marsh to a Growing Season Prescribed Fire
Mary Ann B. Lee
Kimberli J. Ponzio
Steven J. Miller
In marshes, fire is considered vital in restricting woody invasion and maintaining herbaceous dominance. However, many shrub species are not killed by fire and respond to this disturbance by resprouting. We assessed the response of coastal plain willow (Salixcaroliniana Michx.), a common shrub in southeastern wetlands, to a growing season prescribed fire using three metrics: stem density, stem basal area, and cover. We sampled burned and unburned sites before the fire and annually for four years thereafter. Cover of understory species were sampled before the fire and annually for two years after the fire.
The initial response of willow was prolific resprouting. However, stem density returned to pre-fire levels by the second year. Basal area and canopy level (>1.5 m) cover decreased after the fire and remained lower throughout the duration of the study. Basal area and canopy cover declined significantly in the unburned site, but the cause of these declines could not be identified. Despite these declines, basal area and canopy cover in the burned sites were lower than in the unburned sites for each of the four years after the fire, although differences were not always significant at the p<.05. Cover of dominant understory species, sawgrass (Cladiumjamaicense Crantz) and cattail (Typhadomingensis Pers.) declined after the fire and did not recover to pre-fire levels within two years after the fire. Understory species richness increased after the fire.
The Seed Ecology of Iliamna longisepala (Torr.) Wiggins, an East Cascade Endemic
Richy J. Harrod
Charles B. Halpern
We examined the seed ecology of Iliamna longisepala as an aid to developing a conservation strategy for this rare endemic forb of northcentral Washington. We conducted field, greenhouse, and laboratory studies to quantify: (1) densities of buried viable seed among sites with different histories of burning, (2) post-fire spatial distributions of germinants relative to reproductive plants and burn severity, (3) seed production and its annual variation, and (4) germination requirements. Density of seed in the soil was not significantly related to history of burning, but sites that experienced fire 10 years before sampling averaged 10 times as many seeds as sites that burned recently and four times as many seeds as sites that had not burned within 50 years. Density of viable seeds in the soil did not correlate with density of reproductive plants. In a field experiment, germinants appeared after fall burning, but not after spring burning. Germinants were most abundant within 10 m of reproductive plants and were concentrated in areas of high burn severity. Seed production per plant was significantly correlated to crown diameter, but production varied dramatically from year to year. Experimental germination trials were largely unsuccessful due to low (8%) viability of seeds collected from mature plants. However, field studies illustrate that fire is sufficient to break the dormancy of seeds that have accumulated in the soil. Long-term exclusion of fire may lead to local extinction of populations as the longevity of reproductive plants and seeds are exceeded. However, burning more frequently than every 10 years could deplete local seed reserves.