Life stages, demographic rates, and leaf damage for the round-leaved orchids,Platanthera orbiculata(Pursh.) Lindley andP. macrophylla(Goldie) P.M. Brown in a northern hardwood forest in New Hampshire, USA

Abstract

Life stages, demographic rates and leaf damage for the round-leaved orchids, Platanthera orbiculata (Pursh.) Lindley and P. macrophylla (Goldie) P.M. Brown in a northern hardwood forest, New Hampshire, USA. rates for a species pair of rare round-leaved orchids (Platanthera spp.) in a northern hardwood forest. Marked individuals were measured over five years, including: leaf area, damage by herbivores and pathogens, flowering and seed production. Germination trials were also conducted. Vital rates were very similar for the two species, which were about equally abundant despite large differences in seed production. Mortality was twice as high for juvenile as for adult stages and juvenile abundance was markedly lower than for adults. Both species are vulnerable to leaf damage by invertebrates and fungi and exhibit clear leaf area thresholds for progression across life stages, both suggesting a delicate carbon balance for these mixotrophic orchids. The likely role of mycosymbiont distribution in facilitating seedling establishment deserves further detailed study to inform conservation efforts as these and other orchid species face an uncertain future owing to rapid environmental change and increasing pressure from white-tailed deer herbivory in the northern part of their range.

Roots Mediate the Effects of Snowpack Decline on Soil Bacteria, Fungi, and Nitrogen Cycling in a Northern Hardwood Forest

“…The ericoid mycorrhizal community was mainly composed of three fungal genera (Rhyzoscyphus, Sebacinales, and Leptodontidum) that are known to colonize the roots of orchids (Nguyen et al, 2016). Cleavitt et al (2017) recently observed that two round-leaved orchid species ( Platanthera orbiculate and P. macrophylla ) at Hubbard Brook may be experiencing a population bottleneck evidenced by a higher proportion of orchids at adult-compared to juvenile life-stages as well as low juvenile survivorship. Seed establishment and juvenile survivorship of orchids during early mycoheterotrophic life-stages are known to be highly dependent on close association with the fungal symbiont (McCormick et al, 2018), and the results from our study suggest the distribution of these fungal symbionts will decline with future reductions in winter snow depth at Hubbard Brook.…”

Population dynamics and comparative demographics in sympatric populations of the round‐leaved orchids Platanthera macrophylla and P. orbiculata

“…Given the observed recent increase in loss of flowering individuals to deer herbivory (2016 onward), we were particularly interested in how much impact loss of flowering individuals would have on the two species demographic rates. Cleavitt et al (2016) reported P. orbiculata produced more flowers per spike and was more likely to flower consecutive years than P. macrophylla. Do these differences lead to more stable or growing populations for P. orbiculata?…”

“…We use the species pair of the round-leaved orchids, Platanthera macrophylla and P. orbiculata, to explore potential differences in their vulnerabilities to such looming environmental changes. Previous work on these orchids found critical thresholds for leaf area pertaining to both individual life stage transitions and survival (Cleavitt, Berry, Hautaniemi, & Fahey, 2016). Both species are forest dwelling, terrestrial orchids endemic to North America, and are variously listed as rare, threatened, endangered, or extirpated throughout parts of their range in Canada and the United States (NatureServe, 2015; USDA-NRCS, 2015).…”

First-Year Vitality of Reforestation Plantings in Response to Herbivore Exclusion on Reclaimed Appalachian Surface-Mined Land

“…Herbivory can greatly influence vegetation communities. Individual plant factors, such as species, life stage, nutrient quality, and defensive chemical potency [13][14][15][16], contribute to the extent of herbivore damage to plant communities. Community-level impacts, including floral dynamics [17,18], herbivory timing and intensity [19,20], and trophic interactions [21,22], also dictate the influence of herbivory.…”

“…The loss of apex predators in the eastern U.S. has aided in the overabundance of primary consumers, specifically white-tailed deer (Odocoileus virginianus Zimmermann), a species noted for its impact on plant composition and structure in eastern U.S. ecosystems, including the biodiverse mixed-mesophytic forests of Appalachia [23]. Vulnerable plants, such as American ginseng (Panax quinquefolius L.) and several understory forbs, have experienced sharp declines in numbers and population viability as a result of increased deer browsing [14,24,25]. Areas with high deer densities commonly experience regenerating forests with compositions reflective of differences in plant species palatability and defensive mechanisms to reduce browsing; less palatable and more defensive plant species become more common in these areas, which dictates compositional and structural changes manifested with forest aging [26].…”