The genera Hymenolobusand Hornungia(Cruciferae) in the flora of Dagestan: notes on botany and geography

The genera Hymenolobus and Hornungia in the flora of the Caucasus occupy a special place among the Cruciferae. First of all, both genera are relatively close, hence the repeated attempts to unite them in one genus (Hayek, 1924; Appel, Al‑Shehbaz, 1997; German, 2005); secondly, they are spring ephemerals; thirdly, the plants of these genera are of extremely small size; fourthly, the ecological niches of representatives of these genera are very limited, although they are different among themselves. Hymenolobus procumbens was first discovered in the Manas‑Samur region of the Eastern Caucasus. The northernmost known population of H. puberulus was found in the Verkhne‑Sulak botanical and geographical region of the Eastern Caucasus. Ecology of a Hornungia angustilimbata population in the Talginsky Canyon has been studied in detail.

Seasonal dynamics of shoot biomass of dominant clonal herb species in an oak–hornbeam forest herb layer

Seasonal fluctuations of light availability, nutrient concentrations, and moisture affect plant population traits like density, standing biomass, and flowering. We analyzed seasonal changes of density and shoot biomass of the four most frequent herb species growing in an oak–hornbeam forest community, i.e., Anemone nemorosa, Ficaria verna, Galeobdolon luteum, and Galium odoratum. In 2010 and 2011 plant biomass was harvested from 7 to 10 randomly situated square sample plots (0.36 m2) in the homogenous oak–hornbeam forest community every week in the spring and every two weeks in the summer and autumn. The highest abundance of Anemone nemorosa reached over 1000 shoots per m2, of Ficaria verna 459.5 shoots per m2, of Galium odoratum 83.6 shoots per m2, and of Galeobdolon luteum 98.4 shoots per m2 (means for 2010 and 2011, based on all sample plots). We did not observe negative correlation between density and shoot biomass. Growth rates of vegetative shoot biomass amounted to 0.857 mg day−1 for Anemone nemorosa, 0.467 mg day−1 for Ficaria verna, 0.722 mg day−1 for Galium odoratum, and 0.448 mg day−1 for Galeobdolon luteum (means for 2010 and 2011). Spring ephemerals had much higher densities of shoots than summer-greens. Summer-greens reached higher biomass of individual shoots than spring ephemerals. Flowering shoots constituted only 4, 2, and 11% of all shoots for A. nemorosa, F. verna, and G. odoratum, respectively. More resource availability resulting in high shoot biomass did not translate to higher share of flowering shoots.

Canopy effects on abundance and leaf traits of a spring ephemeral: Erythronium americanum

Spring ephemerals take advantage of the high light levels available in the spring by completing the aboveground portion of their lifecycle before the canopy develops and while few other understory plant species are growing. The spring is marked by high resource availability, yet spring ephemerals are variably abundant throughout forests. Research indicates that canopy conditions can influence the growth of spring ephemerals; consequently, we tested whether the variation in canopy conditions predicted variation in the abundance of Erythronium americanum Ker Gawl. across 50 forest plots. We also tested whether the specific leaf area (SLA) of E. americanum in plots was predicted by variation in plot-level canopy conditions, reflecting E. americanum‘s ability to adapt to different canopy conditions. The abundance of E. americanum was significantly lower in the plots with greater hard canopy closure (i.e., permanent cover: tree architecture + evergreen leaf cover), and significantly higher under canopies that reached full development earlier. Canopies with greater hard canopy cover at the start of the growing season were associated with significantly higher SLA, quantifying local adaptation by E. americanum to variable canopy conditions. Erythronium americanum takes advantage of the high light levels available in the spring. It is unclear at this time why higher abundance of E. americanum is associated with canopies that close earlier.

Soil characteristics drive Ficaria verna abundance and reproductive output

Lesser celandine (Ficaria verna Huds.), an invasive plant from Europe, is becoming widespread in river valleys throughout the northeastern United States and the Pacific Northwest. Its high rate of asexual bulbil and tuber production creates dense infestations threatening native spring ephemerals. Ficaria verna abundance and reproductive output (seeds, bulbils, and tubers) were examined in invaded transects spanning a disturbance gradient away from a river. Site characteristics (photosynthetically active radiation [PAR], soil pH, moisture, texture, and nutrients) were quantified to examine their roles in plant abundance and reproduction. A larger-scale study examined random transects not specifically chosen based on F. verna infestations. Soil characteristics and slope were hypothesized to drive F. verna abundance and reproduction; we also hypothesized that reproductive output and biomass would be highest at intermediate distances from rivers, where disturbances are infrequent. Ficaria verna abundance and reproductive output varied considerably by site; soil characteristics, rather than landscape placement, appeared to drive plant abundance and reproduction. Lower percent sand was associated with significantly higher F. verna stem density and bulbil and tuber production. CEC was significantly negatively related to F. verna biomass and tuber counts. In the larger-scale survey, slope and PAR were significantly negatively related to F. verna presence and percent cover, respectively. Overall, these findings suggest that soil texture and slope can help explain higher abundance and reproductive outputs. However, reproductive output and biomass were not significantly greater at intermediate distances, contrary to expectations. We did not observe any seed production in any of the plots, although we did see a few plants with seeds outside our study area in the second year, demonstrating a near-complete reliance on asexual reproduction in these populations. This study expands on the current limited understanding of F. verna and can help management by identifying areas likely to support dense infestations.

When spring ephemerals fail to meet pollinators: mechanism of phenological mismatch and its impact on plant reproduction

The flowering phenology of early-blooming plants is largely determined by snowmelt timing in high-latitude and high-altitude ecosystems. When the synchrony of flowering and pollinator emergence is disturbed by climate change, seed production may be restricted due to insufficient pollination success. We revealed the mechanism of phenological mismatch between a spring ephemeral ( Corydalis ambigua ) and its pollinator (overwintered bumblebees), and its impact on plant reproduction, based on 19 years of monitoring and a snow removal experiment in a cool-temperate forest in northern Japan. Early snowmelt increased the risk of phenological mismatch under natural conditions. Seed production was limited by pollination success over the 3 years of the pollination experiment and decreased when flowering occurred prior to bee emergence. Similar trends were detected on modification of flowering phenology through snow removal. Following snowmelt, the length of the pre-flowering period strongly depended on the ambient surface temperature, ranging from 4 days (at greater than 7°C) to 26 days (at 2.5°C). Flowering onset was explained with an accumulated surface degree-day model. Bumblebees emerged when soil temperature reached 6°C, which was predictable by an accumulated soil degree-day model, although foraging activity after emergence might depend on air temperature. These results indicate that phenological mismatch tends to occur when snow melts early but subsequent soil warming progresses slowly. Thus, modification of the snowmelt regime could be a major driver disturbing spring phenology in northern ecosystems.

Early-Season Treatment of Fig Buttercup (Ranunculus ficaria)

Fig buttercup is a perennial herb native to Europe, temperate Asia, and northern Africa. In eastern North America, fig buttercup competes with native spring ephemerals, complicating control techniques. If chemical control could be shifted earlier in the year, the potential to negatively impact spring ephemerals would be reduced. We tested glyphosate applications on fig buttercup in northern Virginia under three early phenological phases (preflowering, early flowering, and 50% flowering) to assess the effectiveness of early-season treatment. Treating when approximately half of the plants in the population were in flower resulted in a 95% decline in fig buttercup. Treating when the first flower in the population had emerged resulted in a 90% decline. No later phenological phases were treated. Control of fig buttercup led to an increase in cover of Japanese stiltgrass, an invasive grass.