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Virginia Working Landscapes (VWL) is a program of the Smithsonian Conservation Biology Institute (SCBI) that promotes the conservation of native biodiversity and sustainable land use through research, education and community engagement.

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Surveying
Smithsonian scientists and interns, George Mason University graduate students, and a network of trained citizen scientists, have just completed the fourth year of the VWL grassland biodiversity study. This report contains the overall and property-based results for inventory surveys conducted on birds, pollinators, plants and soils from March to October 2013.

Methods

In 2013, the VWL grassland biodiversity survey was conducted at 21 locations within the northern Shenandoah Valley and northern Piedmont, from Wheatlands Farm in Swoope to Banshee Reeks Nature Preserve near Leesburg, with most located on private property.

Surveys were conducted on properties either with fields of predominantly warm season grasses (WSG) or cool season grasses (CSG), or both. This year’s field sites incorporated a variety of land uses including hay production, pasturing of livestock, recreational use (i.e. hiking, horseback riding and hunting) or have been managed specifically for wildlife habitat.

VWL surveyors inventory sampled (i.e. occurrence and relative abundance) for birds, pollinators, plants and soil, typically at one site per property; however some properties had multiple study sites.

Three survey poles (labeled A, B and C) served as starting points for each survey sample. Pole locations were at least 100m from forest edge and approximately 200m from each other. Birds were sampled during the spring nesting season, while pollinators and plants were sampled in both spring and late summer to account for seasonal differences in species composition. Twenty-four soil samples were taken from each site in the late summer or fall for laboratory analyses. Due to the nature of sampling methods, the species lists do not necessarily reflect all species that may potentially occur on a particular property.

Bird Survey

Birds were sampled by point count method for 10 minute intervals; VWL researchers identified each bird seen and heard within 100m of predetermined points relative to survey poles. Each site was visited four times between May 15th and June 30th with surveyors conducting three point counts during each visit (totaling 12 point counts for the season).

Values are reported as occurrence in rank order, which represents the number of times that a species was observed (i.e. point counts) during the sampling season (maximize of 12 observations for a species). In cases where fields at the same location were distinguished by native grass ratio, they are presented as CSG and WSG fields respectively. Species of regional or continental concern are noted, as are VWL target species.

Information on species of regional and continental conservation concern was obtained from Partners in Flight. VWL Target Species are those SCBI researchers have identified as dependent on grassland/shrubland habitats and therefore are important components of the grassland communities. Incidentals are species observed either before or after survey periods, outside the survey boundaries or observed as flyovers. Birds recorded as incidentals are not included in the final dataset for scientific analysis by SCBI researchers.

Plant Survey

Plants were sampled as counts of identified species per square meter (m2) at 21 plots along three transects at each survey site during each of the two survey seasons. At the time of data collection, other features such as weather, percent cover, tallest plant, etc. were recorded. Plants are presented identified to species (as possible, some specimens lacked the characteristics necessary for correct identification) with common names provided, and occurrence is reported as the number of times the species was recorded in 21 plots. Species are rank ordered by occurrence in both survey seasons. Each species is also reported as native or introduced and categorized by its growth form (woody, grass, or forb [nonwoody, non-grass plant species]).

Pollinator Survey

Pollinator surveys focused on the important and conspicuous -- bees and butterflies. Butterflies were sampled as counts of individuals identified to species along four independent transects walked for 20 minutes each. Bee species were sampled by placing twenty small colored plastic bowls filled with soapy water (known as bee bowls) along 100 meter transects starting at each survey pole. Bowls were left in the field for 24 hours. Each site was surveyed once in spring and once in late summer. Specimens were collected for later identification by VWL pollinator experts. Specimens were identified to genus; common names are provided as applicable. The occurrence of pollinators is presented as the number of individuals seen or collected during the survey season. Butterfly species and bee genera are rank ordered by occurrence in both survey seasons.

Soil Sampling

Eight soil samples were taken at each survey pole (A, B and C) at each site for a total of twenty-four samples. Results represent the soil community within 100 meters of the survey poles. Samples were analyzed by A&L Eastern Laboratories. for several aspects of soil fertility (i.e. organic matter, phosphorus, potassium, calcium, magnesium, pH, acidity and cation exchange capacity (CEC)). Values for organic matter and minerals indicate the abundance in the soil sample. Parts per million (ppm) can be converted to pounds per acre by multiplying by two. For more information on how to interpret soil analyses, visit http://www.aleastern.com/showpdf2.aspx?spdf=31.


Combined Survey Results and Discussion

Surveys at all 24 sites combined (Figure 1.1) recorded 97 bird species, 47 butterfly species, representatives of 23 bee genera, and 422 plant species (Tables 1.1-1.4). Fourteen birds observed were of regional conservation concern; three of continental concern; three were of both regional and continential concern, and 24 were VWL target grassland or shrubland species (Table 1.1).

Two important patterns emerged from the bird survey data:

  • 01Grassland obligate bird species abundance increased in areas with more than 50 contiguous acres of grassland habitat (Figure 1.2 and Figure 1.3).
  • 02Grassland and shrubland bird diversity increased with an increase in the proportion of native warm season grasses (Figure 1.4).

Among the 47 butterfly species observed, the cabbage white (2978 individuals), the clouded sulfur (1752 individuals), and the orange sulfur (1174 individuals) were the most numerous, making up 61% of the total butterfly abundance (Table 1.2). The Sweat Bees (Lasioglossum) were the most common bees, accounting for 51% of the total bee abundance (Table 1.3).

Surprisingly, there was no apparent connection between pollinator diversity and native grass proportion (i.e. CSG v. WSF fields). Pollinator richness and abundance did not vary with native grass proportion (Figures 1.5 and 1.6). Not surprisingly, pollinator richness differed from spring to summer; each site reported new butterfly species and bee genera for the summer that were not present in the spring (Figure 1.5).

Butterfly abundance was often more than double that of bee abundance (Figure 1.7), and may be a function of the proportion of native grasses and forbs. However differences in sampling methods might also explain some of this variation. The relationship between the ratio of native grasses to forbs and pollinator richness is being investigated further.

The 422 plant species recorded include 54 woody, 87 grass and 282 forb species. This total includes 140 (33%) non-native species, of which 21 (15%) are considered invasive (Table 1.4; embolded).

This list of invasives (Table 1.5) was compiled in January 2014 by the VWL plant team based upon the Virginia Department of Conservation and Recreation’s Invasive Alien Plant Species of Virginia website and consultation with experts, and then refined to the 20 most frequently encountered invasive grassland species of the region.

Four main patterns among the relationship of grasses, forbs, and woody plants appear in the plant data:

  • 01Forb richness decreased when the percent grass cover (density) increased, though there was variablility between sites (Figure 1.8; site names and codes are provided in Table 1.6).
  • 02Some variability was reduced when native warm season grasses were separated from the introduced cool season grasses.
  • 03Native warm season grasses have highest forb richness at intermediate density; however this is not the same for introduced cool season grasses (Fig. 1.9). Forb richness is highest at an intermediate native grass proportion (Figure 1.10), with 30% more species then either extreme of CSG or WSG.
  • 04Forb richness increases with increased woody plant abundance (woody abundance is the best measure of field age as it increases with time from the last disturbance; Figure 1.11).

Therefore, older fields typically have twice the forb richness as younger fields; however the oldest fields are transitioning out of grassland into shrubland.

The soil sampling results presented in Table 1.7 reflect those for all of the sites and will be used to examine the relationship of soil fertility with plant, insect, and bird species community composition.

VWL would like to thank all of the citizen scientists (Table 1.8) whose hard work made this year’s surveys possible. Forty-seven people volunteered their time and donated over 3,000 hours to this project from March to October 2013. VWL would also like to thank all landowners and managers (Table 1.9) for participating in this year’s surveys and for their continued support. Nineteen landowner and land managers allowed SCBI staff and volunteer citizen scientists access to their properties and provided valuable orientation and logistical support on a nearly weekly basis from March to October 2013. Their support helps further efforts to promote the conservation of native biodiversity and encourage the sustainable use of working landscapes through research, education and outreach.


Map of Survey Locations

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