The persistence of Quercus forest ecosystems in eastern North America is uncertain with replacement of Quercus spp. by other trees, invasion by nonnative plants, and alteration of native ground layers through deer herbivory and other factors. In northwestern Ohio, we examined changes in tree strata and ground layers (herbs, shrubs, and tree seedlings) at eight Quercus forest sites measured in 2002, 2015, 2018, and 2019. Mortality averaged 2.0% per year for small (1–40 cm in diameter at 1.4 m) and 0.7% per year for large (≥ 40 cm in diameter) Quercus trees. Assuming continued lack of recruitment and linear continuation of mortality rates, live Quercus trees would be absent on these sites by the year 2042 in the small size class and by 2165 in the large size class. Despite their density declining by half between 2002 and 2019, Acer rubrum, Sassafras albidum, and Prunus serotina remained the most abundant tree species in the understory (stems 1–10 cm in diameter). Contrasting with many studies, nonnative plants remained nearly absent, never exceeding 0.2% cover (compared with 27–48% average cover of native ground layer plants among years). A major change in the ground layer was a nine-fold increase in cover of deer-preferred, native forbs between 2015 and 2019. This increase coincided with deer management after 2015 and three consecutive wet early summers from 2017–2019. Based on the long-term dataset, we discuss five scenarios of future ecosystems under different potential conservation strategies, ranging from managing for forests with canopy gaps encouraging Quercus regeneration, to facilitating transitions to non-Quercus forests. Although lack of Quercus recruitment highlighted uncertainty in persistence of Quercus trees, trends in ground layer communities suggested sustained dominance by native plants.

We assessed Rubus seed bank abundance and variability in 39 stands located throughout northern Pennsylvania as part of a replicated chronosequence of age classes. Seed abundance declined precipitously after stand age 60 in the Allegheny hardwoods or after stand age 50 in the northern hardwood and oak forests. Variability among sites increased with stand age, resulting in less predictability of Rubus seed abundance. Rubus seed banks were more than twice as abundant in Allegheny and northern hardwoods as in mixed oaks. Rubus seed bank abundance decreased as percent clay in the soil increased. Given that Rubus seed bank abundance declines with age and seed abundance becomes more variable, we suggest that there will be less Rubus immediately following the stand-replacing disturbances in older stands, potentially changing plant competition dynamics and wildlife food sources.

Acer saccharum (Marsh.) is an ecologically and economically important overstory tree species with a widespread distribution in eastern North America. As climate change is predicted to modify the temperature and precipitation regimes throughout the range of the species, it is important to understand how climate has impacted the growth of the species in the past to predict how it may be affected in the future. However, limited research has been conducted on the growth responses of A. saccharum to climate in the western half of the species range. Because climate varies substantially over the range of A. saccharum, becoming warmer and drier at sites in the west and south, there is a need for additional research in this portion of the range. A dendroecological study was conducted at sites in Michigan, Indiana, Kentucky, and Missouri to determine how past variation in temperature and precipitation has affected A. saccharum growth, and how these growth responses varied spatially and temporally. Acer saccharum radial growth correlated strongest with maximum temperature, precipitation, and Palmer Drought Severity Index during the months of June–August of the year the annual growth ring formed. The strength of the growth-climate correlations with June–August precipitation: maximum temperature ratios decreased over the last century. Climate had a stronger impact on radial growth at the study sites in the western part of its range compared to eastern populations examined in other studies. However, differences in growth-climate correlations across a latitudinal gradient did not show a consistent pattern of variation along the climate gradient. These results suggest that A. saccharum populations in the western part of the species range may be more vulnerable to increasing temperature, drought frequency, and drought intensity compared to populations in the eastern part of the species range.

Threatened species frequently have a J-shaped population structure, which indicates a reduction in seed set and poor or nonexistent recruitment. Altered population structures may be due to disrupted demographic processes that result in low reproductive success or small population size. Peyote—Lophophora diffusa Croizat (Bravo)—is a rare, threatened cactus species that is subject to overexploitation because of psychedelic tourism and medicinal and religious uses that decrease its effective population size. We analyzed peyote population structure and identified attributes of its reproductive biology that may limit population persistence. The population's size structure (based on plant size in square centimeters) was determined by census in 2014 and 2015 (n = 420 individuals). Determination of the breeding system of peyote was based on floral morphology and evaluation of herkogamy, dichogamy, and pollen/ovule ratio, and controlled pollination experiments were used to determine the outcrossing rate and whether the species was pollen limited. Additionally, behavior and frequency of floral visitors were recorded to establish the pollinator guild. Peyote's population structure showed the presence of seedlings, juveniles, and adults in both years, indicating some recruitment and low adult mortality. Flowers were herkogamous, homogamous, and diurnal, with a 2-day longevity and high pollen/ovule ratios. These floral traits suggest that peyote is xenogamous, and pollination experiments indicated that it is a facultative outcrossing species, which needs pollinators to set fruit. The time of pistil receptivity coincided with the maximum activity of floral visitors (small solitary bees and small beetles) searching for floral rewards. Evidence indicates that peyote has an outcrossing system with partial self-incompatibility and is pollen limited. Positive factors, such as moderate seedling recruitment, a similar population structure during the two study periods, and a large number of reproductive individuals (close to 50%), indicate natural regeneration and increase the likelihood of population persistence. However, low fruit set and strong dependence upon efficient pollinators reduce reproductive success and increase species vulnerability.

We analyzed the floral biology of a population of the threatened/endangered Veratrum virginicum (L.) W.T. Aiton at the Shaw Nature Reserve (Missouri, USA), comparing our results to the first and only study of this species by Charles Robertson (1896). We confirmed most of Robertson's original descriptions regarding floral presentation, protandry, and insect pollination but found the following new information. Each flower lived 9–11 days and smelled of raw liver and latex. We discerned four floral stages based on gradual changes in style and stamen orientation, which might assist in insect-mediated pollination. We determined that stigmas became receptive by the fifth day of anthesis. The generalist pollination system included three Lasioglossum species (Halictidae) and the beetle Chauliognathus marginatus Fabr. (Cantharidae). Most floral foragers showed a geometric mean of body dimensions between 2–3 mm. Approximately 40% of foraging insects carried heterospecific pollen loads, combining the host flower's pollen with grains from up to seven co-blooming taxa. Field observations suggest that all bees foraged on multiple inflorescences whereas beetles remained on the same inflorescence for hours. Larger Apidae species showed symptoms of nectar poisoning. Epifluorescence showed that flowers exposed to visiting insects contained < 5 pollen tubes per gynoecium. Fruit set was 3% for bagged flowers and 51% for exposed flowers. However, the conversion rate of ovules into seeds was low in both bagged (2%) and exposed (6%) flowers. We interpret low reproductive success as one explanation for current declines in populations of this species.

Secondary (flowering) sex ratio of a wild population of the dioecious woody shrub Lindera benzoin (spicebush) in Maryland has been persistently female biased over a time span of ∼ 17 years. Female-biased secondary sex ratios are relatively uncommon in dioecious woody plants, and are not readily explained by differential costs of reproduction, which are generally higher in females. In fact, prior studies of reproductive adults in L. benzoin populations have shown higher growth rates in males. This leads to questions concerning the source of female-biased sex ratios in some populations. Using seeds collected from 15 maternal plants at the Maryland site in 2013, a potted plant study was conducted from 2014–2020 in which periodic flowering censuses were taken, and plant size parameters were recorded. This study improves upon an analogous common garden study conducted under highly competitive conditions that induced considerable preflowering mortality. In the current study, plants were grown in pots to eliminate root competition and in a loose array to minimize shoot competition; mortality was thus kept to ∼ 1% after seed germination. Like the source population, genet sex ratios in the current study were significantly female-biased, partly due to a trend toward female-biased sex ratios in the offspring of a number of maternal plants. Estimates of plant size were generally higher for females in 2018, just prior to the onset of significant fruit production, supporting earlier results suggesting that females may compensate for differential costs of reproduction that can manifest after fruiting begins. Even in the absence of biased primary sex ratios, formation of female bias in wild populations could involve development of a relatively larger size in the pre-fruiting stage that gives females a temporary advantage over males. This could lead to relatively greater survival and/or earlier flowering of female plants in the early stages of population establishment, and could thus explain observed patterns of sex ratio bias.

Agave colimana, subgenus Littaea (Asparagaceae) is a wild plant that belongs to the Asparagaceae family, and in this species, the formation of its female reproductive system is unknown, probably because it has no commercial use. However, A. colimana recently has been considered as a candidate for marketing as a succulent plant because of its floral and growth architecture. Knowledge about aspects of the formation of the embryo sac is useful for understanding its sexual reproduction, which is important for propagation by seed and breeding purposes. Megasporogenesis and megagametogenesis were studied using Feulgen staining under confocal microscopy. Megasporogenesis resulted in the formation of a linear tetrad with the functional megaspore attached to the chalazal end. Subsequently, megagametogenesis from the functional megaspore was followed by three mitotic divisions generating an embryo sac with seven cells: two synergid cells, one egg cell, three antipodal cells, and one central cell with a 2n nucleus. The embryo sac of Agave colimana was found to be monosporic of the Polygonum-type considered as the typical type in the majority of angiosperm plants. Also, abnormal embryo sacs were observed, following possible errors during meiosis.