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Understanding demographic vital rates and the factors that affect those rates are key components of successful conservation strategies for many threatened and endangered rare plant species. Lindera subcoriacea is a rare dioecious shrub that occupies isolated wetland habitats in a small number of locations in the southeastern United States. The species faces a number of threats to its continued persistence, including habitat destruction, invasive species, and population isolation. From 2011 to 2019, we collected demographic information from 290 L. subcoriacea individuals within 28 populations on Fort Bragg, North Carolina and used the data to estimate demographic vital rates in unburned populations and after being exposed to prescribed fire. We then constructed population matrices and estimated population growth rates under a 3-, 5-, and 10-year return interval. Results indicated that L. subcoriacea individuals have high survivorship in both burned and unburned populations, seed production was reduced 1- and 2-year post-fire, seed production was highly uneven across individuals, seedling recruitment was extremely low, and simulated population growth rates were only above 1.0 under the 10-year fire return interval. Taken together, these results indicate that (1) L. subcoriacea populations are persisting with population growth rates close to one, (2) the short-term impacts of fire on the overall population growth rate of L. subcoriacea, while only 2–3% may determine long-term population viability, and (3) extremely uneven seed production and limited recruitment of seedlings into larger size classes make L. subcoriacea populations vulnerable to stochastic demographic processes.

Seed dormancy is a trait that has evolved to maximize germination when environmental conditions are optimal for successful recruitment of new individuals into a population. Physical dormancy is one such trait common in legumes and release from this condition is often associated with disturbance events, such as fire. Changes to the specific conditions (e.g., climate, fire regimes) that release seeds from dormancy can have negative effects on populations, especially of rare species. Therefore, understanding the species-specific requirements needed to release seeds from dormancy and induce germination provides insight into ecological processes, effects of changing environmental conditions, and potential conservation actions. Amorpha georgiana (Fabaceae) is a rare subshrub with indehiscent fruits (pods) found in fire-maintained longleaf pine habitats in the southeastern United States. The germination ecology of this species is largely unknown. The goals of this study were to determine the presence of physically dormant seed in A. georgiana and then, through a series of laboratory-based experiments, resolve the fire related factors that effectively overcome dormancy and promote germination. The seeds of A. georgiana exhibit physical dormancy and show significantly higher germination after brief exposure to hot water (94 °C) compared to all other temperatures and treatments assessed. Regardless of treatment, seeds have low germination when retained in their pods, but the pod is not the cause of physical dormancy. We found enclosure within an indehiscent pod and exposure to pyrogenic temperatures (> 80 °C) both affect dormancy release and germination of A. georgiana. The 3.5-fold increase in germination at pyrogenic temperatures suggests the response is highly fire-adapted and fits the definition of obligate pyrogenic dormancy release. While season of fire exposure was not significant in our study, we did find consistent negative effects on the germination response. Our results suggest pulses of heat from periodic growing season fires are likely necessary to promote recruitment and maintain populations of this rare species.

The causes of species rarity are of critical concern because of the high extinction risk associated with rarity. Studies examining individual rare species have limited generality, whereas trait-based approaches offer a means to identify functional causes of rarity that can be applied to communities with disparate species pools. Differences in functional traits between rare and common species may be indicative of the functional causes of species rarity and may therefore be useful in crafting species conservation strategies. However, there is a conspicuous lack of studies comparing the functional traits of rare species and co-occurring common species. We measured 18 important functional traits for 19 rare and 134 common understory plant species from North Carolina's Sandhills region and compared their trait distributions to determine whether there are significant functional differences that may explain species rarity. Flowering, fire, and tissue-chemistry traits differed significantly between rare and common, co-occurring species. Differences in specific traits suggest that fire suppression has driven rarity in this system and that changes to the timing and severity of prescribed fire may improve conservation success. Our method provides a useful tool to prioritize conservation efforts in other systems based on the likelihood that rare species are functionally capable of persisting.

Fire controls tree cover in many savannas by suppressing saplings through repeated topkill and resprouting, causing a demographic bottleneck. Tree cover can increase dramatically if even a small fraction of saplings escape this fire trap, so modeling and management of savanna vegetation should account for occasional individuals that escape the fire trap because they are "better" (i.e., they grow faster than average) or because they are "lucky" (they experience an occasional longer-than-average interval without fire or a below-average fire severity). We quantified variation in growth rates and topkill probability in Quercus laevis (turkey oak) in longleaf pine savanna to estimate the percentage of stems expected to escape the fire trap due to variability in (1) growth rate, (2) fire severity, and (3) fire interval. For trees growing at the mean rate and exposed to the mean fire severity and the mean fire interval, no saplings are expected to become adults under typical fire frequencies. Introducing variability in any of these factors, however, allows some individuals to escape the fire trap. A variable fire interval had the greatest influence, allowing 8% of stems to become adults within a century. In contrast, introducing variation in fire severity and growth rate should allow 2.8% and 0.3% of stems to become adults, respectively. Thus, most trees that escape the fire trap do so because of luck. By chance, they experience long fire-free intervals and/or a low-severity fire when they are not yet large enough to resist an average fire. Fewer stems escape the fire trap by being unusually fast-growing individuals. It is important to quantify these sources of variation and their consequences to improve understanding, prediction, and management of vegetation dynamics of fire-maintained savannas. Here we also present a new approach to quantifying variation in fire severity utilizing a latent-variable model of logistic regression.

Rare species reintroductions are an increasingly common conservation strategy, but often result in poor survival of reintroduced individuals. Reintroduction sites are chosen primarily based on historical occupancy and/or abiotic properties of the site, with much less consideration given to properties of the larger biotic community. However, ecological niche theory suggests that the ability to coexist with other species is determined in part by the degree of functional similarity between species. The degree to which functional similarity affects the survival of reintroduced plants is poorly understood, but has important implications for the allocation of limited conservation resources. We collected a suite of abiotic, biotic, and functional trait variables centered on outplanted individuals from four reintroduced rare plant species and used logistic regression and model selection to assess their influence on individual survival. We show that higher functional similarity between reintroduced individuals and the local community, measured by differences between their multivariate functional traits and the community-weighted mean traits of their immediate neighbors, increases survival and is a stronger predictor of survival than local variation in abiotic factors, suggesting that the functional composition of the biotic community should be incorporated into site selection to improve reintroduction success.

Canebrakes formerly occupied hundreds of thousands of hectares across the southeastern USA, but habitat conversion and fire suppression have reduced their size and extent. Currently, canebrakes are among the rarest vegetative communities in the southeastern USA. Research has focused on Arundinaria gigantea (river cane), with very little focus on Arundinaria tecta (switch cane). The fire history, area, associated flora, and species frequency of 13 canebrakes, dominated by switch cane, were examined at three Department of the Army locations and one game land in the Sandhills physiographic region. We determined canebrake area by identifying its unique vegetative signature in aerial photography at three time steps: earliest aerial photography, the beginning of the recorded burn history, and current aerial photography. We compared fire-return intervals to changes in canebrake area. We created a checklist and tallied 330 taxa of vascular plants (plus Sphagnum sp.) from the 13 canebrakes in our study a...

The US Department of Defense is taking proactive steps to conserve rare species that occur primarily on lands under its stewardship, including Astragalus michauxii (Kuntze) F.J. Herm. (Sandhills milkvetch; Fabaceae). We completed a series of evaluations to determine effective means of germinating and propagating A. michauxii . We collected A. michauxii seed from Fort Bragg, an Army Installation located in the Sandhills ecoregion of North Carolina. While previous work described a germination protocol and suggested the presence of chemical dormancy, we determined that A. michauxii possesses only physical dormancy, which can be successfully broken by mechanical scarification yielding a 94% germination rate. We also developed an effective method for large-scale propagation of A. michauxii by directly sowing seed into media, rather than transplanting seedlings from Petri plates. This method resulted in an emergence rate comparable to the observed germination rate and a 69% survivorship of seedlings ex situ . Our simplified germination and propagation protocols can effectively be used to provide individual plants for use in reintroduction and restoration.

Prioritizing management of invasive plants is important for large land management entities, such as federal and state public land stewards, because management resources are limited and multiple land uses and management objectives are differentially impacted. Management decisions also have important consequences for the likelihood of success and ultimate cost of control efforts. We applied multi-criteria decision analysis methods in a geographic information system using natural resource and land use data from Fort Bragg, North Carolina. Landscape-scale prioritization was based on a hierarchical model designed to increase invasive plant management efficiencies and reduce the risk of impacts to key installation management goals, such as training-land management and protected species conservation. We also applied spatial sensitivity analyses to evaluate the robustness of the prioritization to perturbations of the model weights, which were used to describe the relative importance of different elements of the hierarchical model. Based on stakeholders' need for confidence in making management investments, we incorporated the results of the sensitivity analysis into the decision-making process. We identified high-priority sites that were minimally affected by the weight perturbations as being suitable for up-front management and evaluated how adopting this strategy affected management area, locations, and costs. We found that incorporating the results of the sensitivity analysis led to a reduced management area, different target locations, and lower costs for an equal area managed. Finally, we confirmed the distinctiveness of the approach by comparing this same subset of prioritized sites with locations representing species-centric strategies for three invasive plants and their aggregate distribution. By supplying pragmatic information about the localized effects of weighting uncertainty, spatial sensitivity analyses enhanced the invasive plant management decision-making process and increased stakeholder confidence.