The role of reintroductions to conservation of Florida scrub

Background/Question/Methods

While habitat loss and fragmentation remain the major threats to the persistence of rare and endangered plant species, low reproductive success may also contribute to extinction risk. As a result, introductions have become a necessary component in the recovery strategy of many imperiled species. We carried out two experimental introductions and three augmentations on three Florida scrub or sandhill endemic plant species:  Crotalaria avonensis, Dicerandra thinicola, and Ziziphus celata. All species have extremely narrow ranges, have suffered severe habitat loss, and have few protected populations. Two of the three species have low reproductive success. Introductions and augmentations were designed experimentally to incorporate a variety of propagation techniques (seeds, seedlings and tissue culture plantlets), microsite locations and habitat quality. We followed vital rates on each introduced plant/seed to measure the success of the introduction.  Specifically, we focus here on one multi-genotype introduction of the federally endangered Z. celata using seeds and seedlings into a range of habitats varying in quality, three augmentations of the federally endangered C. avonensis into a preferred microhabitat using tissue culture material, and one introduction of Florida-threatened D. thinicola into an unoccupied, newly protected site.

Results/Conclusions

Low germination (<5%) combined with low cumulative seedling survival (<35%) were weaknesses for introduced seeds of Z. celata.  Cumulative survival of Z. celata transplants was 66.1% after 3.5 years (annualized survival=88.8%), and varied significantly among habitats. Relative growth rates of Z. celata seedlings and transplants have remained positive but are minimal. Propagation and rooting of C. avonensis tissue culture material has been relatively successful; however, survival after transplanting from rooting media into native soil was low (mean=34.6%) for all three augmentations. For D. thinicola, mean seed germination was 5.8% in the first year and seedlings sowed into burned plots had higher flowering percentages. D. thinicola seedling survival has remained high, the majority of early seedlings flowered by their second year and several small patches recruited a second, larger generation. Introductions and augmentations were designed to create genetically diverse self -sustaining populations in protected areas within a species' known historic range. By incorporating an experimental component to our introductions, we are able to increase our knowledge of rare species’ biology, seedling vital rates, microsite preferences and habitat requirements.