Seed biology influences recruitment, demography, restoration success, and population persistence of endangered Dalea carthagenensis var. floridana (Fabaceae)

Authors: MASCHINSKI, JOYCE - Fairchild Tropical Botanic Garden; POSSLEY, JENNIFER - Fairchild Tropical Botanic Garden; Walters, Christina; Hill, Lisa; WALTERS, DON - Fairchild Tropical Botanic Garden; KREUGER, LISA - Fairchild Tropical Botanic Garden; HAZELTON, DALLAS - Miami-Dade County Parks, Recreation And Open Spaces Department

Submitted to: Restoration Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2017
Publication Date: 10/16/2017
Citation: Maschinski, J., Possley, J., Walters, C.T., Hill, L.M., Walters, D., Kreuger, L., Hazelton, D. 2017. Seed biology influences recruitment, demography, restoration success, and population persistence of endangered Dalea carthagenensis var. floridana (Fabaceae). Restoration Ecology. 26: 636-641.

Interpretive Summary: Seed biology provides important clues on how plant populations naturally establish and maintain viable population size. Populations of the study species, Dalea carthagenensis var. floridana, were dwindling at an alarming rate and prompted a planting of seeds to sites. Germination of the seeds was initially low, but years later there was a pulse of seedlings. Laboratory studies showed that germination of Dalea carthagenensis var. floridana seeds was inhibited by a hard seed coat,that could be abraded by relatively gentle treatment. Seeds of D. carthagenensis maintained high viability even when exposed to humid conditions – largely because the water-impermeable seed coat kept the seed dry. The study postulates that activities implemented to rehabilitate sites (e.g., raking) or lower than normal temperatures during winter could have provided sufficient treatment to stimulate germination. The study shows that an understanding of germination and emergence requirements increases the success of restoration projects that use direct seeding.

Technical Abstract: Soil seed banks buffer populations from environmental variation; yet unpredictable seedling emergence poses challenges for assessing and restoring rare plant populations. Using wild and restored populations of endangered Dalea carthagenensis var. floridana (Fabaceae), we tested the hypothesis that germination is regulated by rare dormancy releasing cues that subsequently limit seedling emergence, population persistence, and restoration success. Over 7 to 10 years we monitored three wild populations and studied climate and human-disturbance events associated with recruitment. Laboratory trials examined germination percent and speed of seeds exposed to cold and scarification. Field trials varying habitat and seed pretreatment tested seedling establishment and maturation. PVA models projected population persistence with and without germination cues from 2007-2013. High seedling emergence in wild populations was associated with cold winters and human disturbance. Laboratory tests confirmed that seeds are hard seeded, remaining viable for 600 days even when moist. Freezing and scarification triggered higher and more rapid germination than controls implicating weather and disturbance effects on germination. Using a freezing pretreatment increased field germination and maturation in natural pine rockland habitat, but little germination occurred in novel habitat. PVA models simulated germination cues that increased population growth in most years, except 2010-2011 when high seedling mortality occurred. Weather and disturbance events can trigger high germination. Seed pretreatments improved field seedling emergence and persistence, but only in suitable habitat. The frequency and timing of germination-stimulating events, mortality events, and climate interact with microsite to determine population growth.