Progress 09/01/06 to 08/31/10
Outputs
OUTPUTS: Summary presentations were given at a number of national and regional meetings, including annual meetings of the Weed Society, Ecological Society of America, Natural Areas Society, and the Northeast Section of The Wildlife Society. These presentations have lead to a number of discussions with organizations involved with cost-sharing programs for habitat management, including NRCS, U.S. Fish and Wildlife, and New Hampshire Fish and Game Department. Field demonstrations have been scheduled. PARTICIPANTS: John Litvaitis (PI) involved with all aspects of study, especially in insect inventory, breeding bird responses, and management decision tree. Tom Lee (Co-PI) involved with all aspects of the study, especially in green house experiments and effects of logging. Serita Frey (Co-PI) involved in soil feedback experiments. Kris Vagos (graduate research assistant) involved with greenhouse experiments and assisted in all aspects of the study. James Panaccione (graduate research assistant) involved in breeding bird inventories and all aspects of the study. Johanna Fickenscher (graduate research assistant) involved in insect inventories and feeding trials. Ryan Bechtel (graduate research assistant) involved in several inventories and greenhouse experiments. TARGET AUDIENCES: Land managers and government staff responsible for cost-share programs. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
In the northeastern U.S., many rare native species occur in early-successional shrublands (thickets). Abundance of thickets has declined in recent decades; those that remain are often dominated by exotic shrubs. We investigated the effects of invasive shrubs on 1) insect abundance and diversity, 2) bird abundance and diversity, 3) abundance of native shrubs, and 4) influence on soil quality. We also examined how exotic shrubs respond to thicket habitats created by logging. We compared insect abundance, richness, and phenology among field sites differing in exotic shrub coverage. Habitats with a large proportion of coverage by invasive shrubs tended to have an abundance of generalist and pest insects, while sites dominated by native shrubs had more lepidopterans, more herbivorous insects, and more rare species. In feeding trials, captive lepidopteran larvae avoided invasive foliage and a majority of larvae fed invasive foliage died. Clearly, invasive shrubs can alter insect communities, change that could reduce the suitability of thicket habitats to nesting songbirds. Related to these findings, an examination of breeding birds in thicket habitats revealed that the abundance of birds that are restricted to these habitats (obligates) was negatively correlated with the proportion of invasive shrub coverage. Territory size of obligates was positively correlated with invasive shrubs coverage, suggesting a numeric response. In a greenhouse study, we examined whether competition between native and invasive shrubs influences thicket invasion. A pair-wise experiment was conducted using three native (Sambucus canadensis, Spiraea alba, Viburnum dentatum) and three invasive (Euonymus alatus, Frangula alnus, Lonicera morrowii) shrubs planted in field soil. Treatments included no competition, intraspecific competition, and interspecific competition. Invasive shrub species were better competitors than the natives. Competition likely enhances the ability of invasive shrubs to succeed in thickets. Another greenhouse study examined the effect of invasive and native shrubs on soil biota (soil feedback) to determine whether soil feedback influences thicket invasion. We found that soil feedback effects were species specific, stronger in non-tilled than tilled soils, and not likely to facilitate invasion. We tested the hypotheses that invasive shrubs were more abundant in successional habitats (canopy gaps) created by logging than in uncut forests and that invasive abundance increases with gap size in hemlock-pine-hardwood forest. Invasive Frangula alnus was nearly 100 times more abundant in logged areas than in uncut forest, was rare in single-tree gaps and was abundant and reproducing in gaps >0.06 ha. The enhancement of thickets is a management priority in the region, yet activities that maintain these habitats (e.g., logging, burning) increase exotic plant invasions. We developed a decision tree to assist habitat managers responsible for creating and maintaining thicket habitats. Nodes of the tree attempt to identify circumstances when control measures are likely to be most cost effective. Field trials of the decision tree are pending.
Publications
- Burnham, K.L. and T.D. Lee. 2010. Canopy gaps facilitate establishment, growth, and reproduction of invasive Frangula alnus in a Tsuga canadensis dominated forest.Biological Invasions 12(6):1387-3547
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Progress 09/01/06 to 08/31/07
Outputs
OUTPUTS: We are examining soil-plant interaction via soil feedbacks to native and invasive shrubs using soils with two different land-use histories. Soils were collected from adjacent field (with tilled soils) and forests (with non-tilled soils), sieved, bulked, and placed in growing pots according to land-use history. We then planted 50 seedlings for each of 6 species of shrubs (3 native and 3 exotic/invasive) in pots that contained tilled or non-tilled soils (total seedlings planted = 600). This initial planting can be considered Phase #1 or the "culturing phase". Here, individuals plants will be allowed to grow in the soil for a minimum of 10 weeks before being removed. This should allow the soil biota to interact with the plant species and become uniquely "cultured" to the plant species. Phase #2 of the experiment will be the measurement of soil feedback. A new round of plants will be transplanted into the pots. This time, however, each species will be allowed to grow in soil
cultured by the same species, called "home" treatment, and also in soil cultured by other species, "foreign treatment" . Growth rates of invasive and native shrubs will then be compared by soil treatment to determine of native or invasive shrubs respond differently to how soils were cultured. Animal responses to invasive shrubs were examined by sampling insect abundance and species richness among sites colonized by varying amounts of native and exotic/invasive shrubs. Insect collection occurred over four sites, two sites with minimal exotic shrub invasion (<25%) and two sites that were almost entirely invaded (>90%). Within each site, 10 flight intercept traps were set up to monitor whole-site insect communities. After 16 weekly sampling periods, 640 total samples of multiple insects were obtained. Individual shrubs also were sampled using a beat method to gain an understanding of shrub-to-shrub differences. We sampled 5 invasive and 5 native shrubs/site. All insects collected were
placed in sealed bags and frozen for identification this fall and winter. We are also examining nesting songbird responses as key insect consumers. To examine avian responses, we are comparing territory size of insectivorous songbirds to the abundance of exotic/invasive shrubs within their territory and examining if seasonal fecundity is reduced at sites with a high percentage of invasive shrubs. Territory size was assessed by spot mapping common yellowthroat pairs at four of the study sites. A total of eight pairs were observed during the nesting and fledgling stages (July and August). Each pair was monitored for a minimum of eight observational hours throughout the nesting/fledgling season. Although an attempt was made to locate the nest within each territory, we only found 2 of 8 yellowthroat nests. However, seasonal fecundity was evaluated for each study site by monitoring the success of all species nesting within the study sites. Nest searching and monitoring occurred from May
21, 2007 to September 6, 2007, resulting in a total of 81 nests observed. Once discovered a nest was checked every three to four days until fledging (success) or failure.
PARTICIPANTS: PIs Litvaitis, Lee, and Frey supervised data collection schedules and techniques. Three graduate students (MS candidates) and 1 undergraduate technician were trained in field data collection.
Impacts
Because preliminary samples have yet to be examined, we are not reporting any outcomes.
Publications
- No publications reported this period
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