2011 Annual Report
1a.Objectives (from AD-416)
Determine the effect of habitat and repeated foliar damage on the growth, reproduction, and survival of black and pale swallow-wort plants, and document the survival and longevity of swallow-wort seed in the soil seed bank.
1b.Approach (from AD-416)
Established seedlings of pale and black swallow-wort will be tagged within three habitat types and annually censused for survival, growth and time to first seed production. Mature plants of pale and black swallow-wort will be planted into a common garden and receive damage treatments consisting of clipping, 50% or 100% defoliation at different frequencies over six years. Various growth and reproductive parameters will be measured. Subsets of plants will be harvested during that time to assess changes in plant biomass. Seed of pale and black swallow-wort will be placed at various depths into pots sunken into the ground and assessed for germination and survival rates over four years.
Various studies of pale and black swallow-wort (SW) biology are being conducted to help determine what factors affect their population growth and spread and what life stages should be targeted for disruption through biological control. Data collection continues for a field study established in fall 2007 of the effect of habitat (field, forest edge, and forest interior) on SW seedling survival, growth, and time to first flower. After the third season of growth (2010), survival of black SW was greater than pale SW. Juvenile black SW remained 2.5-3.5 times taller than pale SW. To date, only four black SW plants have flowered (one in 2009 and three in 2010), but none of the plants produced seed. The relatively low seedling establishment levels observed in this study, especially for pale SW, are surprising given that this species typically thrives in high light, open habitats in the region. However, the dense cover of resident vegetation in the old field may have suppressed pale SW establishment and growth more than the larger seeded black SW. A long-term field experiment examining the effects of different types (50% or 100% defoliation, clipping) and frequencies (1, 2, or 4 times) of foliage removal on field-grown SW performance continues. Stem lengths and mass were unchanged from 2009 to 2010. Root dry mass increased from 2009 to 2010 in all damage treatments except plants clipped four times – their root mass was unchanged. Branching generally increased with increasing damage frequency. Viable seed production decreased for black SW, but not pale SW, clipped 2x or 4x compared to controls. Pale and black SW display a high tolerance to above-ground tissue loss in high-light environments (without plant competition). The potential efficacy of a defoliating insect against field populations of SWs appears questionable. However, it is not uncommon that several seasons of damage are needed before perennial species, such as SWs, begin to decline in vigor. A two-year herbicide/mowing study for pale SW was conducted in an old field and adjacent forest understory near Ithaca, NY. After two years, SW cover and density of large SW stems (>5cm) in the old field decreased from initially measured values with herbicidal treatments but increased with mowing. Small (<5cm) stem density decreased in all treatments. In the forest understory, reductions in cover and large stem density occurred in all treatments. Small stem density changes were variable depending on the herbicide used. Findings suggest that management of pale SW using herbicides in combination with mowing can be effective but may vary with habitat. Progress is being monitored through bimonthly meetings with the Cooperator, as well as by telephone calls, e-mail, field site visits, and the receipt of written reports.