Effects of habitat, microsite and seed density on recruitment limitation in native scrubland and scrub undergoing restoration

Background/Question/Methods

Recruitment influences population and community dynamics by determining the replacement of older individuals, decreasing population expansion and reducing/excluding a species from a community. There is insufficient information on the relative importance of mechanisms affecting seed availability and how interactions between recruitment limitation, other life history stages and environmental variables affect plant demography. Seed availability is pertinent to restoration projects, in which the establishment of native plant populations is a priority. We hypothesize that seed and seedling dynamics are affected by seed production, predation, and microsite characteristics, which may differ among habitats with different human disturbance. We compared seed production, and will evaluate seed predation and seedling establishment of two opportunistic native herb species (Chamaecrista fasciculata, Balduina angustifolia) in disturbed scrub and native rosemary scrub. We predicted that these species would have higher seed production and seedling establishment in the disturbed scrub, and that seed removal may differ in the two areas due to contrasting suites of animal species. We expect seed density to further influence the extent of animal-mediated seed removal and germination success.

Results/Conclusions

B. angustifolia was found to produce significantly more seed heads in disturbed scrub than in native scrub, while there was no significant difference in C. fasciculata seed pod production between the habitat types. Preliminary evidence indicated that seedling number increases with seed density. However, lower observed germination probabilities compared to expected estimates (binomial probabilities) in locations with > 7 seeds suggested increasing density dependence with seed density for C. fasciculata. Germination for this species was not significantly different between habitats in our precursory trial. Our work suggests that seed dynamics affect population persistence and should be considered during management of Florida scrub.