Metabolomic responses of indigenous and nonindigenous plants to deer exclosure fencing and deer herbivory in a suburban forest

Trees and shrubs in suburban forest understories can be subject to chronic herbivory from abundant white-tailed deer. An undocumented consequence of this stress may be shifts in secondary metabolite production associated with defense. We aimed to learn whether plants protected from deer exhibited different metabolomic profiles compared to those exposed to deer. We tested the indigenous species Nyssa sylvatica and Lindera benzoin and the invasive, nonindigenous species Rosa multiflora and Euonymus alatus within a suburban forest understory in New Jersey, USA, in unfenced plots and plots fenced for 5.3 years. We did untargeted metabolomics by sampling leaves from three plants of each species per 6-7 fenced and unfenced plots, conducting chloroform-methanol extractions followed by LC-MS/MS, and conducting statistical analysis on Metaboanalyst. We also scored each species for deer browse frequency over eight years, and compared their heights and percent cover between unfenced and fenced plots. The analysis identified 2,333 metabolites. The global metabolome diverged significantly between fenced and unfenced plots pooled across species, but for individual species only N. sylvatica exhibited a significant fencing effect. Nyssa sylvatica was one of the most browsed species and was the only one with both greater cover and height in fenced plots, suggesting greater susceptibility to deer browsing. The metabolites most responsible for the fenced/unfenced divergence also were affected by the species-fencing combination, with increases in certain species but decreases in others. The most significant metabolites that were upregulated in fenced plants include some involved in defense-related metabolic pathways, e.g. monoterpenoid biosynthesis. Further study of more species in multiple sites is needed to learn how common metabolomic responses to deer are among forest species, how the intensity of deer pressure influences the responses, which types of metabolites are most affected, and if there are ecological consequences at the physiological, population, and/or community levels.

Fire history and dendroecology of Catoctin Mountain, Maryland, USA, with newspaper corroboration

Background Our study was designed to reveal a detailed forest fire history at Catoctin Mountain Park, Maryland, USA. We compared the ages of living trees to known fire dates in the dendrochronological record. Seasonality and years of fires in the dendrochronological record were juxtaposed with specific dates of fires recorded in newspapers. Results Twenty-seven pines (Pinus L.) captured 122 fire scars representing 58 distinct fire years between 1702 and 1951. Climate was significantly hotter and drier in the years of burns that affected at least two trees and was wetter two years prior. Thirty-three fires described in local newspapers were reported largely in the spring and fall months (68% between March and June, 32% between September and December). Ninety-one percent of fire scars in our tree-ring chronology had dormant seasonality. The mean fire interval was 5.47 ± 10.14 (SD; standard deviation) yr, and the Weibull median fire interval was 3.22 yr during the entire chronology. The longest fire-free interval was from 1952 to 2018. The size structure of living trees was biased toward smaller black gums (Nyssa sylvatica Marshall) and oaks (Quercus L.) that recruited in the 1930s and 1940s. Most living pitch pines (Pinus rigida Mill) recruited between 1890 and 1910, but a few individuals recruited before the 1850s. Diversity of tree stems smaller than 10 cm diameter at breast height (DBH) was generally lacking; the youngest tree >10 cm DBH in our study area had recruited by 1967. Conclusions The Catoctin Mountains experienced frequent fire during the 1800s and early 1900s. The causes of fires were diverse, including accidental ignitions and purposeful cultural burning for berry (Vaccinium L.) production. The current forest developed during a period of low deer density and after the demise of the charcoal iron industry ended an era of logging. The lack of fire since the 1950s has encouraged the development of a black gum dominated mid- and understory. Management with frequent fire would facilitate pine and oak regeneration.

Dwarf Blackgum (Nyssa sylvatica) Contains Datable Fire Scars that Complement an Existing Fire History

Blackgum (Nyssa sylvatica) is a “consummate subordinate” hardwood tree species consigned to the mid-canopy of many eastern North American forests. Despite its wide distribution and ecological amplitude, blackgum is an underutilized tree species in fire history reconstructions within its range. In this study, I analyzed cross-section samples collected from 19 fire-scarred blackgum trees at a dry, nutrient-poor ridgetop study area in northeastern Pennsylvania. All but two of these samples were successfully crossdated, each containing between one and six fire scars. Fires recorded by blackgum occurred frequently, with site-level mean fire intervals between approximately three and five years. There was an increase in blackgum growth within two years following fire events, but this increase was not statistically significant and it was dependent on local fire regime characteristics. In addition, the blackgum fire-scar data increased the temporal and spatial resolution of an existing local fire history. These results provide evidence for the potential use of blackgum in fire history reconstructions, but applications may be limited by tree age, complacent growth that prevents crossdating, and the degree of rot resistance after scarring.

Pretreatment Effects on Seed Germination of Two Nyssa Species

The genus Nyssa L. includes several woody species with traits valued by horticulturists, but only black gum (Nyssa sylvatica Marsh.) is prevalent in the nursery trade. A congener, swamp tupelo (Nyssa biflora Walt.), might be a marketable shade tree, but little is known about propagating it from seeds. Because cold, moist stratification overcomes embryo dormancies of black gum, we compared germination of cleaned seeds (surrounding pulp of fruits removed) of swamp tupelo and black gum that were stratified at 5 °C for 0, 14, 28, 42, 56, 70, 84, and 112 days. Seeds of swamp tupelo within intact drupes were also stratified. Across all durations of stratification, 79% of cleaned seeds of swamp tupelo germinated, whereas 11% of seeds within drupes germinated. Germination value of cleaned seeds of swamp tupelo increased from 1.26 to 3.23 as duration of stratification increased. Although cleaned seeds of black gum responded similarly, the benefit of stratification was more pronounced, and the mean germination percentage was lower than for swamp tupelo (66% vs. 79%). In a second experiment, irrigation with low and high concentrations of an extract of fruit pulp of swamp tupelo reduced germination of seeds of basil (Ocimum basilicum L. ‘Superbo’), spinach (Spinacea oleracea L. ‘Bloomsdale’), zinnia (Zinnia ×marylandica Spooner, Stimart, and Boyle ‘Double Zahara Cherry’), and swamp tupelo by 25% to 63% (low concentration) and 40% to 70% (high concentration). Propagators should remove the surrounding pulp from seeds of swamp tupelo and cold stratify them at least for 4 weeks.

Nyssa sylvatica, der Wald-Tupelobaum, ein spektakulärer nordamerikanischer Herbstfärber

Der Wald-Tupelobaum (Nyssa sylvatica) ist ein mittelhoher Baum mit einer spektakulären Herbstfärbung. Im Oktober färben sich seine Blätter gelb, leuchtend rot bis purpurviolett. Es handelt sich um eine interessante Art für Solitärstellungen in großen Gärten und Parkanlagen, die mehr Beachtung finden sollte.

Growing Blackgum Whips in Ground Beds Increases Survival and Growth Following Transplanting to Field

Difficult-to-transplant species can be produced in containers and transplanted with high survival. However, circling roots can develop even in containers designed to prevent root malformation, requiring root pruning before transplanting and this results in transplant shock. In order to determine the effect of different containers and substrates on whip growth and survival after transplanting, blackgum (Nyssa sylvatica Marsh.) whips were grown in four container types (Spinout®-treated plastic, tall or short fiber containers or in ground beds) and two substrates (pine bark: Com-Til™ and Haydite: Com-Til™). Container-grown whips were overwintered in unheated polyhouses; bed-grown were overwintered out-of-doors with no winter protection. Two year branched whips grown in Haydite: Com-Til™ were bare rooted and root pruned before transplanting. Whips grown in containers required root pruning to correct root malformation, while whips grown in pine bark: Com-Til™ in ground beds were root pruned as part of the harvesting process. Container and substrate treatment did not affect whip stem diameter, but whips grown in ground beds in pine bark: Com-Til™ were the tallest. Overwinter survival for container-grown whips ranged from 77 to 88% and averaged 85% for whips grown in ground beds. The percentage of whips reaching 1.2 m in height ranged from 53 to 97% for whips produced in tall fiber containers in Haydite: Com-Til™ substrate and in short fiber containers in Haydite: Com-Til™ substrate, respectively. Two years after whips were transplanted, survival averaged 98% (174 of 178). Two years after transplanting, whips produced in beds in pine bark: Com-Til™ substrate had the greatest caliper. Whips produced in ground beds in pine bark: Com-Til™ offer an acceptable alternative to container-produced blackgum whips; they had high overwintering and transplant survival; they were taller at the end of the two year whip production period, and two years after transplanting to field plots they had the largest trunk caliper.