Successional tree species often form soil seedbanks, suggesting that extended seed dormancy may also facilitate regeneration in nonnative species. We examined seed dormancy in Ailanthus altissima, which is currently spreading into long-established forests of Europe and eastern North America. Ailanthus seeds were sewn into replicated nylon mesh bags and buried in 10 second-growth stands in southeast Ohio, USA. North- and south-facing slopes were included as a coarse-grained test for environmental control. Bags were recovered at 2-mo intervals and seeds were tested for viability and germination. Fifty percent of Ailanthus seeds survived the full length of the study (24 mo) after an initial phase of partial germination (51–79% of viable seeds). Remaining seeds returned to a state of induced dormancy, allowing a second flush of germination (3–28%) after 18 mo. After the first 5 mo no further decline in seed number was observed, suggesting persistence in the soil well beyond the 2-yr length of this study. No slope-aspect effect was observed. Long-term seed dormancy potentially facilitates Ailanthus invasion by buffering against extended canopy closure or allowing passive dispersal with movement of soil. Complete eradication of a population will depend on elimination of the soil seed bank, which may require many years. Management should avoid creating canopy openings near existing populations with the goal of suppressing sexual reproduction and seedling establishment.

Old-growth forests dominated by shade-tolerant tree species are among the plant communities most likely to be in equilibrium. However, the assumption that these forests show long-term stability has rarely been tested. In this study, we resurveyed plots established 86 yr before in an old-growth beech-maple-hemlock forest in northeast Ohio to examine changes in tree community composition, diversity, and structure. Species richness and diversity remained constant from 1932 to 2018, but we found dramatic shifts in the relative abundances of species and the size structure of populations. Fagus grandifolia remained the most frequent and abundant tree species in the forest, while changing dramatically in size structure; larger Fagus grandifolia trees died and were replaced by large numbers of root suckers, increasing the overall stem density of the forest by 50%. Tsuga canadensis declined in frequency and stem density, shifted away from smaller size classes, and had almost no saplings. Plots dominated by Tsuga canadensis in 1932 showed the greatest magnitude of compositional change over time, shifting toward dominance by Acer saccharum, which along with Acer rubrum, increased greatly in frequency, stem density, and basal area. Eight species including Castanea dentata and Sassafras albidum were lost from the plots. In sum, Fagus grandifolia and Acer saccharum are displacing Tsuga canadensis in this stand. Tree diseases, pests, and deer herbivory likely contributed to these compositional shifts. Given the time scale of the directional changes we observed, even relatively undisturbed communities such as old-growth forests might be best viewed as not in equilibrium.

Shortleaf pine (Pinus echinata (Mill.)) can sprout after stem injury or top kill. Currently, evidence regarding the effects of seedling age and disturbance timing on sprouting potential are limited. The objectives of this study were to determine the effects of clipping and season of burning on shortleaf pine seedling survival, number of sprouts, and total seedling height at three different seedling ages. Treatments included: a March clip, an April burn, a July burn, a November burn, and a control. All treatments were applied to 1-, 2-, and 3-yr-old planted shortleaf pine seedlings located in Morgan County, TN. Seedling survival did not differ by season of burning for any age tested. Sprout production of early season disturbances were similar for each age tested. Total heights of sprouts were greater with treatments conducted early in the growing season rather than later for the second and third growing years, but not the first year. Some 2-yr-old seedlings burned in November and most 3-yr-old burn seedlings burned in either burn treatment were large enough that they were not top-killed by the treatment burns. Burning of artificially regenerated shortleaf pine seedlings should be delayed for at least 3 yrs after planting in the Cumberland Plateau and Mountains regions to reduce top-kill rates, growth losses, and mortality experienced by younger seedlings.

Ice storms are a major source of tree mortality in some regions of the eastern North American deciduous forest, but are rare in the boreal forest. As climate changes, ice storms are predicted to be more common in the boreal forest, creating new challenges for forest management. In 2012, an ice storm damaged Pinus banksiana (Lamb.) stands throughout southeast Manitoba, Canada. We assessed damage in a 98- and a 32-yr-old stand. In both stands, half the trees broke near the base of the crown. Trees with a deeper crown were more likely to break in the young stand and less likely to break in the old stand. In the young stand taller trees were also more likely to break. There was no relationship between tree diameter and the probability of a tree breaking in either stand. Tree mortality increased the bare area around surviving trees by 52% and 119% in the young and old stands, respectively. This resulted in a 42% increase in canopy openness in the old stand but did not alter the pattern of spatial distribution of trees. Before the storm, trees in the young stand showed a dispersed distribution, indicative of density-dependent mortality. This dispersion was lost after the storm and suggests that, along with selection of shorter trees, ice storms reorganize the structure of forests undergoing self-thinning.

Stylophorum diphyllum (Michx.) Nutt. is an endangered plant of rich floodplain forests in southern Ontario, Canada. Prior to 2015 there were only four known populations in Ontario. I built a species distribution model (SDM) based on the known occurrences, and tested it by surveying 156 forest sites that varied in their predicted suitability. An indicator species analysis showed that sites predicted to be suitable had significantly higher frequency and abundance of common species usually associated with S. diphyllum, demonstrating the ability of the SDM to pinpoint similar habitat, although none of these sites contained S. diphyllum. The most important predictors used by the SDM to determine habitat suitability were growing season precipitation, surficial geology, and soil texture. I discovered a new population of S. diphyllum more than 50 km north of the known populations, at one of the sites not predicted to be suitable. This demonstrates a clear example of SDM overfitting, which may occur when models are built based on few, spatially limited occurrence records. Nonetheless, the key environmental predictors remained the same in an updated SDM including the new record. Stylophorum diphyllum provides a case study of both the value and the limitations of using SDMs to predict suitable habitat for very rare and geographically restricted plants, and the need for more rare plant surveys even in human-dominated landscapes.

We evaluated several mechanisms that enable saplings of Yucca filifera (Chabaud) to endure water shortage. Saplings were exposed to water shortage and subsequent rewatering inside a greenhouse. The response variables were maximum quantum efficiency (F_v/F_m), effective quantum yield of photosystem II (Φ_PSII), nonphotochemical quenching (NPQ), electron transport rate (ETR), leaf relative water content, titratable acid (ΔH⁺), pigment content (chlorophylls a and b, total carotenoids, chlorophyll a+b/carotenoids ratio, and chlorophyll a/ b ratio), antioxidant activity, and proline accumulation. We hypothesized that Y. filifera saplings tolerate water shortage, and that rewatering favors the sapling development. We found that F_v/F_m and Φ_PSII values as well as ΔH+ and chlorophyll a/b ratio were strongly affected by water shortage, and their values reverted after rewatering. We also found higher NPQ, antioxidant activity, and proline content during the water-shortage treatment, which might represent mechanisms for preventing photodamage. The high ability of Y. filifera saplings to withstand stress caused by water shortage indicates that it could be a key species for conservation and restoration of degraded arid ecosystems.

A sizable population of the jester lichen, Cladonia leporina Fr., is here reported from dune habitat in Floyd Bennett Field, Brooklyn, NY. Marking a new record for New York, and the northernmost known record of this species, this study is a reminder that the Atlantic Coast likely still holds hidden diversity in its urban lichen communities.