Recruitment Experiment—Germination

Fruits were collected from two G. triacanthos trees at the Tessentee Bottomland Preserve (35°04’03.57”N; 83°23’00.53”W) near Franklin, NC (U.S.). Seeds were extracted from the fruit pulp, and any seeds that were poorly formed or damaged by beetle larvae were removed. The remaining seeds were mixed and stored at 4°C for 6 months. In April 2009, the seeds were soaked in 90% concentrated sulfuric acid for two hours and rinsed thoroughly with water. The scarification of seeds is consistent with megafaunal dispersal (including cattle and horses) as the large seed pods pass through the digestive system, or Native American cultivation that including soaking or boiling the pods [30, 35, 36].

Scarified seeds were placed in a peat medium, randomly placed in 12 covered germination trays and exposed to 100% ambient sunlight (n = 36), 50% ambient sunlight (n = 36), 100% soil moisture saturation (n = 36) and 50% soil moisture saturation (n = 36). Ambient sunlight was ameliorated using 50% shadecloth (International Greenhouse Co., Georgetown, Illinois, U.S.). Light measurements were taken five times during the germination experiment with a LiCor LI-191 Line Quantum Sensor (LiCor Biosciences, Lincoln, NE, U.S.). Soil moisture saturation was controlled by adding water until the peat medium was 100% saturated without standing water in undrained pots. For 50% saturation, 50% the amount of water required for saturation was added, and the container bottoms were perforated to allow drainage.