Military installations in the Southeast are subject to extensive encroachment by urban development, and increasingly the burden of conserving listed and at-risk plant species falls to the Department of Defense, which manages much of the remaining suitable habitat. The overall objective of this project was to conduct an operational-scale demonstration of recently developed propagation protocols for reintroducing one endangered (Lysimachia asperulifolia) and four at-risk plant species (Amorpha georgiana, Astragalus michauxii, Lilium pyrophilum, and Pyxidanthera brevifolia) that occur across multiple military installations in the Southeast. The primary objectives were to (1) demonstrate successful reintroduction of four populations per target species at an operational scale, (2) optimize the cost of establishing self-sustaining populations using data collected from natural and reintroduced populations, and (3) secure user acceptance.

Technologies both necessary and sufficient for reintroduction of the target species exist in the form of newly established propagation protocols, test-plot field trials, and state-of-the-science population reintroduction best-practice guidelines. Using comparative demographic modeling methods, the project team sought to assess the separate contributions of survivorship, growth, and reproduction by transplants of different age/size class to population growth rates and the cost per capita for establishment of different outplanted classes.

The project team propagated and outplanted 6,075 transplants for four of the five target species over three successive years. These outplants, and more than 1,500 individuals within natural populations, were demographically monitored over four years. Propagation challenges and high transplant mortality ultimately forced abandonment of P. brevifolia as a demonstration species. Averaged across the four reintroduced populations of each species, approximately 22.1%, 13.4%, 24.0%, and 24.2% of outplants became established for A. georgiana, A. michauxii, L. pyrophilum, and L. asperulifolia, respectively. All four species exhibited limited reproduction within one or more reintroduced populations.

One qualitative and seven to nine shared quantitative performance objectives were evaluated for each of the species. End users showed general acceptance of the technologies based on responses to a post-demonstration questionnaire. Three quantitative performance objectives based on comparisons of population growth rates (λs) or vital rates between reintroduced and natural populations were unmet, because λs and vital rates in reintroduced populations were lower than those in natural populations. The researchers demonstrated improved cost-effectiveness of vegetation-removal near L. pyrophilum bulbs at outplanting, but no improved cost-effectiveness was demonstrated for supplemental watering of A. georgiana and A. michauxii transplants. Establishing populations via seed addition versus outplants for A. georgiana and L. pyrophilum was not effective or cost efficient, and irrigation of A. georgiana seed-addition plots did not enhance recruitment. Cost optimization for establishing self-sustaining populations could not be evaluated because λs were less than 1.0 for each species four years post-reintroduction. However, for A. georgiana and A. michauxii, the project team alternately showed that a population of 100 individuals can be established five years post-outplanting for under the specified $10,000 threshold. At the demonstration site on Fort Bragg, North Carolina, the researchers estimated that a population of 100 A. georgiana individuals can most cost effectively be established five years post-outplanting using the largest size class and at a cost of $3,358. In contrast, a population of 100 A. michauxii individuals can be established most cost effectively five years post-outplanting using the smallest size class and at a cost of $9,780. Furthermore, propagation and outplanting costs for establishment of the most cost-efficient size class were substantially lower (mean = $25.42) than the $175 threshold established for all species.

Prior use of reintroduction as a strategy for rare plant conservation and mitigation has exhibited varying success. Although many of the ambitious performance objectives established for this demonstration were unmet, the observed mean percent survival of individuals of A. georgiana, L. pyrophilum, and L. asperulifolia was comparable (~20%) to that reported in a recent review of reintroduction success for 249 species (Godefroid et al. 2011). The survival rates of the other two species (A. michauxii and P. brevifolia) were reduced by small outplant size during one or more years. Because size is generally correlated with survival, the researchers explored the efficacy and cost-efficiency of three age/size classes in our test design. Although this allowed the project team to identify, for each species, outplant size classes that provided the greatest contributions to population growth rates, it also undoubtedly negatively impacted the vital rates and growth rates of reintroduced populations. Moreover, natural populations exhibited low recruitment, with only two species (A. georgiana and L. pyrophilum) having λs greater than 1.0. Consequently, it may have been overly optimistic to expect positive population growth rates within reintroduced populations within such a short timeframe. Additional monitoring will be needed to determine the ultimate fate of the populations reintroduced during this demonstration. The researchers remain optimistic about the expanded conservation strategies and new opportunities to share conservation responsibility with partner agencies and organizations that are made possible by our propagation and reintroduction protocols. However, scaling up may be constrained by propagule procurement limitations, and a lack of staff and funding. Use of the demonstrated technologies should not be a substitute for active conservation of the remaining natural populations of the five species, especially given the modest success of the demonstrated reintroduction efforts compared to the effort invested.