Print PageLonicera maackii is an Asian shrub, known to be invasive in mesic, deciduous forests of North America. Both flooding and light conditions, and their interaction, are likely to influence the success of this invader in bottomland hardwood (e.g. wetland) forests, where this shrub has also been documented. In this study, survival and growth of Lonicera maackii seedlings were examined under different combinations of flood duration (3, 10 or 17 days), flood depth (inundated, saturated, moist, or upland control), and light (simulated canopy gap or simulated closed canopy). These treatments were applied in a split-split-plot outdoor mesocosm experiment (n=6), in a 41 day trial. A mixed model ANOVA was used to test for significant fixed effects of all explanatory variables on seedling growth rate, including all 2- and 3-way interaction terms. Logistic regression was used to test for significant effects of explanatory variables on seedling survival.
Results/Conclusions
Flood duration, depth, and depth*duration interaction significantly affected seedling growth rate. Compared to upland controls, moist conditions had somewhat beneficial effects when maintained for 3 or 10 days, but not 17 days. Growth rates of both inundated and saturated treatments were not significantly different from one another. Maintenance of these flooding depths for 10 and 17 days depressed seedling growth rates relative to 3 day flood durations. After 17 days of flooding, plant growth rates exhibited a monotonic response to flooding depth, with upland control and fully inundated treatments having the highest and lowest growth rates, respectively. Light and random effects (e.g. block, initial plant height) were non-significant.
Analysis of survival data revealed significant effects of flooding duration and depth on seedling survival probabilities. Inundated seedlings were less likely to survive than upland seedlings, and no seedlings survived inundation for 17 days. However, survival probabilities of saturated and moist seedlings did not significantly differ from upland. Light effects on survival were non-significant.
Regarding Lonicera maackii seedling growth rates, these results indicate that: 1) extended periods of soil inundation and saturation can have negative impacts, 2) brief flooding episodes may have beneficial effects, 3) flooding regimes may be more important than light availability, and 4) at 17 days of flooding, flooding depth becomes a primary determinant of seedling growth. Similar to growth rate trends, seedling survival was significantly affected by flooding duration and depth. However, despite their depressive effect on seedling growth rate, saturated treatments were rarely lethal to seedlings.
