Germination and Early Survival of Carolina Willow ( Salix caroliniana )

1. Experiment 1: Germination responses to soil moisture Experiment 2: Germination responses to types of soil and sites where seeds were collected Experiment 1: Effects of soil moisture Experiment 3: Effects of soil type and seed sources Experiment 2: Effects of soil types Experiment 2: Effects of seed source Germination and Early Survival of Carolina Willow(Salix caroliniana) Castro-Morales L. M. 1, Quintana-Ascencio P.F.1, and Fauth J. E.1 1 University of Central Florida, Orlando, 32816; e-mail: l-castro@knights.ucf.edu • OBJECTIVES • Understand how environmental conditions control the spread of Salix caroliniana along the St. Johns River, FL • Evaluate effects of water availability and soil texture on germination and early seedling survival of Salix caroliniana INTRODUCTION Carolina willow (Salix caroliniana Michx.) is a plant native to the southeastern US that has increased along the Upper St. Johns River, Florida. Its expansion transforms herbaceous marshes to willow swamps. METHODS We performed three experiments to assess the effects of environmental parameters on germination and seedling survival of S. caroliniana. Willow seeds were collected and placed into pots filled with commercial potting soil or sand. Seeds were assigned to six different moisture treatments: continuous flooding, soil kept continuously moist by capillarity (outside container filled with 2 cm of water), watered daily, and once every 3, 5 or 8 days. Samples were placed into a growth chamber under controlled temperature; data on germination and survival was recorded daily for 30 days (n = 36; 6 replicates x 6 treatments; 20 seeds per pot). Figure 5. Differences of germination among soils. Figure 6. Differences of germination among soils. Germination was >80% and most occurred during the first five days (Figure 5). Weibull analysis showed no significant differences in mortality among soil types (Figure 6). The results do not support an effect of soil type on seedling mortality. Herbaceous marsh with sawgrass. Carolina willow along an airboat trail. RESULTS An exponential model represented the germination schedule well because most germination occurred during the first five days. Germination was significantly higher in the capillarity treatment than in any other treatment (Figure 1). Mortality was significantly higher when seeds were watered every 8 days (Figure 2). No other treatments differed significantly. Arcsine (proportion) Arcsine (proportion) Willow seeds were planted on top of six soils differentiated by texture. Soils were collected at three different locations along the river basin: Blue Cypress Marsh (BC) and River Lakes (D) are peaty soils, and St. Johns (U) is a sandy soil. We created three more soils by mixing each pair in a 50:50 ratio. All pots were watered with the capillarity treatment (n = 24; 4 sites x 6 soil types; 30 seeds per pot). Figure 7. Germination as a function of days until watering and collecting sites: North (State Route 50) and South (SR 60). Box plots show the median (horizontal bar), 25th and 75th percentiles (boxes), 5th and 95th percentiles (whiskers) and outliers (circles). Figure 2. Differences of seedling survival due to water availability. Figure 1. Germination survivorship curve (Type II). Figure 8. Box plot of germination as a function of days until watering and temperature regime. Site Site Germination decreased when seeds were not watered for four or more days (Figure 7). There was no significant difference in germination between locations (Figure 7). Germination was higher in the colder, north temperature treatment during days four and eight (Figure 8). Germination also was greater during the middle flowering season (data not shown). Experiment 3: Germination responses to sites, season, temperature regime and days to watering Willow seeds were collected from northern and southern sites on the upper St. Johns River. Seeds were collected in early, middle, and late flowering seasons. Samples were placed into a growth chamber with a spring temperature regime similar to either Titusville, FL, (North) or Lake Wales, FL (South). Groups of 30 seeds were watered either the same day as collection, or 2, 4, 6, 8 or 10 days later (n=18 groups of seeds per site). We collected germination data for 16 days.  • CONCLUSIONS • Constant soil moisture promotes germination and survival of S. caroliniana, but too little water limits them. • Germination and early seedling survival did not differ among the soil types and seed sources that we evaluated. • Soil moisture may be more critical than soil texture for recruitment success of Carolina willow. • Willow has a very limited interval - about five days - for germination after seeds are released. • Germination decreases at higher temperatures. • This information is useful to manage Carolina willow and prevent it from spreading within the St. Johns River floodplain. Figure 3. Differences of germination among seed sources. Figure 4. Seedling survival among seed sources. North South Germination was >80% and occurred during the first five days (Figure 3). We used a Weibull analysis to compare germination and survival among treatments and did not find significant differences among seed sources (Figure 4). ACKNOWLEDGMENTS We are grateful to the St. Johns River Water Management District’s staff : Kimberli Ponzio, Dianne Hall, and Ken Snyder for supporting this research. Merari E. Ferrer, Beth Stephens, Lina M. Sanchez-Clavijo, Andres Ruiz, Daniel Atalaya, and the graduate students of the 2009 Restoration Ecology class: Camille Brescacin, Stormy Haynes, Matthew Gordon, Katherine Grablow, Leesa Souto, Joseph Waddell, and Annalisa Weiler-Lazarz helped collect soil and seed samples. Lisa McCauley assisted with GIS.