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Butterfly habitat enhancement at unoccupied acub sites – Treatment and Monitoring at Mima Mounds Natural Areas Preserve


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FY08 ACUB Project

Butterfly habitat enhancement at unoccupied ACUB sites – Treatment and Monitoring at Mima Mounds Natural Areas Preserve

David Wilderman and Birdie Davenport

Department of Natural Resources

PO Box 47014

Olympia WA 98504-7014

(360) 902-1556; 596-5144



david.wilderman@dnr.wa.gov

roberta.davenport@dnr.wa.gov

Executive Summary

Based on existing knowledge of habitat on the site, in conjunction with Prairie Habitat Quality data, a 70-acre management unit was identified for Mardon skipper habitat enhancement. In spring 2008 we mapped nectar plants to refine our assessment of nectar resources, using a protocol and criteria developed by the project team. Results indicate that Camassia quamash is the most abundant nectar source, followed by Fragaria virginiana, Lomatium utriculatum, and Viola adunca. Camassia quamash was found abundantly in nearly all swales, and occasionally on mounds, within the most of the management unit.


Ten 8m-radius “enrichment” plots were established on mounds within the management unit in spring 2008. Five of these (Phase 1) will be planted in fall 2008, while the other five (Phase 2) will be burned and planted in fall 2009. Locations for these plots were selected for good Roemer fescue (host plant) cover within or adjacent to the plot, low to moderate abundance of nectar plants, and low cover of highly competitive invasive species. M
Figure 2. 2008 tall oatgrass treatment and monitoring plots on Mima Mounds NAP
ost plots were located adjacent to a nectar plant patch that met criteria for high abundance of the particular species.
Within the ten enrichment plots, we controlled invasive species including shrubs, introduced grasses, and introduced forbs, using Poast and Milestone herbicides, hand-pulling, and cut-stem treatments. In addition, bracken was mowed within one of the plots. Cut-stem treatments were also used in a portion of the management unit, where both native and non-native shrubs were forming dense patches.
Pre-treatment vegetation data were collected from within each of the enrichment plots, with a total of 100 sampling quadrats in each Phase of treatments.

Introduction

Reintroduction of Taylor's checkerspot (Euphydryas editha taylori) and mardon skipper (Polites mardon) is a primary goal of the Fort Lewis ACUB program. However, many ACUB prairie sites do not currently support appropriate habitat for either species. Invasive weeds have had particularly deleterious effects and larval hostplants as well as nectar species have declined, creating unfavorable habitat conditions. Availability of suitable receiving sites is the primary limiting factor for reintroduction of these butterflies. This project would work toward supplying appropriate habitat suitable as receiving sites for captive-reared or translocated animals.


Mima Mounds Natural Area Preserve has been identified as a prime location for re-introduction of Mardon skipper, which was last observed on the site in 1994. The site generally supports good-quality prairie habitat, particularly with regard to cover of Roemer’s fescue, the Mardon skipper ‘s primary larval host plant. This report provides an update on the status of this project through August 2008, including:


  • identification of management unit

  • assessment of butterfly habitat with the unit

  • a summary of treatments conducted; and

  • a summary of monitoring data.



Identification of Management Unit and Habitat Assessment

Based on existing knowledge of habitat on the site, in conjunction with Prairie Habitat Quality data, a single 70-acre management unit was identified for Mardon skipper habitat enhancement (Figure 1). This unit was selected using the following factors identified by the ACUB group working on this project:




  • density and diversity of known nectar plants;

  • density and diversity of known host plants, particularly Festuca roemeri for mardon skipper,

  • presence and density of invasive plants;

  • heterogeneity in habitat features, such as mounds and swales, forest edge, water features;

  • adjacency to other potentially suitable habitat patches/sites; and

  • planned management activities on the site.

Habitat within the unit was initially assessed in 2007, and described in our work plan of October 2007 as follows:


Except for the extreme north end and along the forest edge, the unit has good to excellent fescue cover (30-60%) virtually throughout (see Figure 2). Nectar plant abundance and diversity appears moderate overall (to be determined during spring nectar surveys in 2008), with higher abundance in the southern portion of the unit, which has more Viola adunca (see Figure 3). Primary nectar species are Viola adunca and Lomatium utriculatum. Access to the bases of fescue plants is moderately good -- invasive grasses, litter accumulation, and lichen/moss inhibit access somewhat. There is generally little bare soil present due to litter accumulation and invasive herbs, resulting in relatively few sites for forb germination.
Habitat structure and heterogeneity are provided by mounded topography and a forest ecotone on east edge of the unit, although much of the forest edge is linear and could be “rougher”. Potential sink habitat is present in the adjacent landscape (gun club, residential properties), mainly due to lack of nectar sources, but most of this is >100m from the unit. Dispersal barriers, in the form of forest and dense Scotch broom, are present primarily along the east edge and north edges, but also along a portion of the west edge. Dispersal would be primarily to the south, into the southern portion of the NAP and potentially toward Glacial Heritage.
In general, invasive species are at moderate levels in the unit, with considerable variation within. Scotch broom is present primarily as sparsely scattered short individuals (<1’ tall), although there are a few patches and scatterings of more mature shrubs (3-4’ tall) and denser patches of 1-2 year old plants especially along the northwest edge of the unit. Tall oatgrass occurs in relatively small (5’x5’ to 20’x20’) patches and as scattered individuals throughout the unit, but concentrated in the eastern third. It has been increasing rapidly in recent years and 2007 treatments had little apparent effect. Invasive forbs and grasses (hairy catsear, oxeye daisy common, St. John’s wort, velvet grass, sweet vernal grass, Agrostis) are present in moderate amounts, although there are dense concentration on the tops of some mounds. Bracken fern is present throughout the unit, and is dense over a considerable portion, particularly on mound tops. Himalayan blackberry is present but not abundant. The native trailing blackberry is dense on some mounds, primarily those where trees were removed in the past. Shrubs (cascara, snowberry, etc.) and Garry oak trees form occasional dense patches that may need treatment in the near future.
Although vegetation within the unit is relatively homogenous, it does have pronounced mound and swale topography, providing a variety of soil and aspect conditions. The conifer/oak tree line along the east unit boundary provides edge habitat, although the edge is generally straight, rather than “rough”. Scattered patches of shrubs, and to a lesser extent, Garry oak, provide some heterogeneity within the unit, but are also a threat to open prairie. There are no water sources or major swales within or near the unit.
A number of additional units of similar size could be identified within the NAP. Glacial Heritage Preserve is located 1 mile to the south-southeast. Intervening habitat is rural residential and agricultural fields, with a few patches of semi-natural and degraded prairie habitat in close proximity to the NAP. Exchange between the two sites may be possible, especially with habitat improvements (broom control, prairie plant landscaping) on portions of the intervening land.
Projected management activities within the unit and adjacent portions of the NAP include:


    • Continued tall oatgrass control, primarily with Poast (possibly Fusilade) herbicide, throughout most of site

    • Continued broom control with hand-pulling and triclopyr herbicide (backpack application), throughout most of site

    • Conifer removal in wooded areas for oak release (approx 8 acres by 2009; possibly more in subsequent years). Note, this is not located adjacent to prairie habitat.

    • Collins experimental plots (small-scale treatments)

    • “Large-scale” Collins plot (approx. 2 acres planned for Poast and burn treatments 2008-2009)

    • Invasive shrub treatments (cut-stem herbicide) and possible Garry oak thinning

    • Targeted treatment of invasive forbs

    • Prescribed burns (extent & location TBD)


Nectar Survey In spring 2008, we mapped nectar plants to refine our assessment of nectar resources within the Mima Mounds management unit and for the entire Rocky Prairie Natural Area Preserve (the Rocky Prairie map is also included in this report). This mapping was conducted at a number of other ACUB sites as well, using a protocol and criteria developed by the project team (see attached Nectar Survey Protocol). We conducted the mapping at Mima Mounds and Rocky Prairie May 13-20, 2008. Results indicate that, for the Mima Mounds management unit, Camassia quamash is the most abundant nectar source, followed by Fragaria virginiana (37 patches), Lomatium utriculatum (32 patches), and Viola adunca (9 patches) (Figure 4). Camassia quamash was found abundantly in nearly all swales, and occasionally on mounds, within the area shown for this species in Figure 4. The nectar species were not concentrated in any particular portion of the unit, although the largest Viola adunca patches were located toward the south end, and PHQ data also indicate somewhat higher density of this species in the southern half of the unit (see Figure 3).

Nectar resources at Rocky Prairie were somewhat more diverse, with significant amounts of Camassia quamash (37 patches), Balsamorhiza deltoidea (22 patches), Fragaria virginiana (18 patches), Viola adunca (8 patches) and Lomatium utriculatum (7 patches), as well as dense patches of secondary nectar species Cerastium arvense and Rubus ursinus. Except for Camassia quamash, nectar species were more densely distributed at Rocky Prairie, which contains approximately 25 acres of prairie habitat compared to the 70-acre unit at Mima Mounds.


Establishment of Enhancement Plots Ten 8m-radius enhancement plots, similar to the “enrichment plots” described in Fimbel (2004), were established on mounds within the management unit in spring 2008 (Figure 5). Locations for these plots were selected based on the following criteria:


  • Roemer fescue (host plant) cover >30% on or immediately adjacent to the mound

  • Presence of a some nectar plants but not enough to be considered adequate (nectar plant augmentation is the primary focus of the enrichment plots)

  • Low cover of Scot’s broom and other shrubs, tall oatgrass, and bracken, i.e. species that would be particularly difficult to control and would compete heavily with plant augmentation


Figure 2. 2008 tall oatgrass treatment and monitoring plots on Mima Mounds NAP

Most plots were located adjacent to a mapped nectar plant patch that met the mapping criteria for nectar plants (see attached protocol).



Enhancement Treatments Conducted
Invasive Species Control All enrichment plots were treated with 1.5% Poast in mid-May to control invasive grasses, primarily Holcus lanatus and Anthoxanthum odoratum. A small amount of tall oatgrass was present in some plots. In late-June the plots were treated with Milestone herbicide (1/8th oz/gallon plus 0.32 oz/gallon Spreader 90 surfactant) to control invasive forbs including Hypochaeris radicata, Leucanthemum vulgare, Senecio jacobea, and Hypericum perforatum. This herbicide was applied with a hand-held bottle in order to minimize contact with desirable plants. In some cases, Hypericum perforatum was hand-pulled instead of sprayed due to the difficulty of avoiding contact with desirable species. One plot with significant bracken cover was also mowed with a weedeater in late-June.
Shrubs were controlled in the north-central of the unit (see Figure 5), where both native (snowberry, serviceberry, Indian plum, cascara, hazelnut, rose) and non-native (cherry) species were forming dense patches. Treatment included mowing for snowberry and cut-stem herbicide treatment with Garlon 3A for all other species. In a given patch, we targeted 70-90% of the total shrub cover, in order to leave some shrubs for habitat heterogeneity. We favored species that are more limited to open habitats (serviceberry, cascara) for leave individuals, while more heavily controlling the introduced cherry and native species more common in forested settings.
Additional 2008 treatments within the enrichment plots will include hand-removal of dense trailing blackberry patches, a second mowing of bracken, and cut-stem treatment of shrubs similar to that described above. Additional herbicide may be applied to the Phase 2 plots in spring 2009 depending on success of the 2008 treatments.
Seed Collection & Plant Propagation Seed have been collected throughout the spring and summer of 2008, including species to be used in the enrichment plots: Viola adunca, Lomatium utriculatum, Festuca roemeri, and Danthonia californica. Amounts of seed collected are yet to be determined. In addition, plugs of these same species are currently being grown at Shotwell’s Landing nursery for fall 2008 planting in five of the enrichment plots (the other five will be planted in 2009 following prescribed burning).
Monitoring
Methods We collected pre-treatment vegetation data from each of the enrichment plots. Within each plot, we estimated percent cover of all vascular species in 20 1mx1m plots using the following cover classes: <1%; 1-5%; 6-15%; 16-25%; 26-50%; 51-75%; 76-100%. Four 1mx1m plots were placed on each of five transects radiating from the center of the plot on randomly generated compass bearings. Combining the data from the five “Phase 1” treatment plots and the five “Phase 2” treatment plots separately will yield samples sizes of 100 for each treatment type (Phase 1 has no burning; Phase 2 will be prescribe burned).
Results 19 species were encountered in the Phase 1 (no burn) sampling plots, and 23 in the Phase 2 (burn) plots. Data are summarized in the following tables, showing all species with >4.5% mean relative cover and including the species of interest for Mardon skipper:


Phase 1

Species

Mean

Absolute % cover

(90% CI)

Mean

Relative % Cover

Festuca roemeri

16.7 (3.2)

27.5

Hypochaeris radicata

14.2 (1.9)

26.4

Leucanthemum vulgare

8.6 (1.8)

15.3

Holcus lanatus

2.0 (0.4)

4.6

Fragaria virginiana

1.4 (0.8)

2.4

Viola adunca

1.3 (0.4)

2.7

Lomatium utriculatum

0.2 (0.1)

0.4



Phase 2

Species

Mean

Absolute % cover (90% CI)

Mean

Relative % Cover

Hypochaeris radicata

13.4 (2.1)

24.9

Fragaria virginiana

8.1 (2.2)

12.6

Festuca roemeri

5.6 (1.2)

11.6

Anthoxanthum odoratum

4.5 (1.3)

9.1

Agrostis spp.

3.9 (1.2)

7.2

Leucanthemum vulgare

3.7 (1.0)

6.3

Hypericum perforatum

2.8 (0.5)

5.8

Danthonia californica

2.8 (0.8)

4.7

Viola adunca

2.2 (0.6)

4.4

Lomatium utriculatum

0.3 (0.2)

0.8

As the data tables show, the Phase 1 plots had higher Festuca roemeri than the Phase 2 plots, but somewhat lower cover of the Mardon skipper nectar species Fragaria virginiana, Viola adunca, and Lomatium utriculatum. Both Phase 1 and Phase 2 plots had significant cover of introduced forbs, primarily Hypochaeris radicata, Leucanthemum vulgare, and Hypericum perforatum, and to a lesser degree, introduced grasses. Total introduced species cover was 32.2% in both Phases. Treatments targeting invasive species should result in a comparable amount of open space for planting and seeding. Post-treatment data will be collected in spring 2009.




Figure 1. Mardon skipper management unit location at Mima Mounds NAP.


Figure 2. Fescue cover at Mima Mounds NAP as recorded in 2007 Prairie Habitat Quality monitoring plots.

Figure 3. Viola abundance at Mima Mounds NAP as recorded in 2007 Prairie Habitat Quality monitoring plots.

Figure 4. 2008 nectar survey map, Mima Mounds NAP.






Figure 5. Enrichment plot and 2008 shrub treatment locations, Mima Mounds NAP.



Figure 6. 2008 nectar survey map, Rocky Prairie NAP.

Nectar/Host plant Survey Protocols for

ACUB Unoccupied Site Butterfly Enhancements

Timing

The main consideration in timing the surveys is that the plants to be mapped will be readily visible and identifiable. Because we are focusing on nectar species, the surveys should be done during, or close to, the flight season of the butterfly species, when the primary nectar plants will be flowering. For the south Sound, the following time windows should be used:




  • Units with both butterfly species: Ideal timing is May 1-May 20, but could be done as late as June 1. If possible, all surveys should be done during this window regardless of which butterfly species is targeted, in order to gather the most complete information for future use.

  • Mardon skipper units: May 15-June 15

  • Taylor’s checkerspot units: May 1- May 30



Protocol


  • Use GPS or air photo for mapping

  • Walk the entire area, in a systematic manner, in bands approximately 20m wide (marking with pin flags recommended to track progress), and map concentrations of each species as follows:


Primary Nectar Plants

    • Viola adunca: map patches w/ ≥ 40 plants or >10% cover within a 4 m2 area (derived from Hays et al. 2000). NOTE: this will be recorded by PQP for all of our highest priority sites (Mima, Glacial, Scatter Ck), plus either Morgan or Wolf Haven this year.




    • Balsamorhiza deltoidea: map areas that are ≥100m2 and contain ≥15 plants/100m2.




    • Lomatium utriculatum/triternatum: map areas that are ≥100m2 and contain ≥40 plants/100 m2. Hays et al. (2000) indicates 0.4 plants/m2 as a target level for Mardon skipper.







    • Vicia sativa: map areas of dense cover, i.e. >5%, within an approx. 100m2 area or larger. Based on Chappell plot data & Rocky Prairie plot data, typical coverage is in the 1-5% range, and maximum coverages are around 20-30% for this species.




    • Fragaria virginiana/vesca: map areas of dense cover, i.e. >5%, within an approx. 100m2 area or larger. Based on Chappell plot data & Rocky Prairie plot data, typical coverage is in the 1-5% range, and maximum coverages are around 20-30% for this species.


Other Nectar Plants

For the following species, note & map any particularly large/dense concentrations that are incidentally encountered:




Amelanchier alnifolia

Armeria maritima

Berberis spp.

Cerastium arvense

Crataegus monogyna

Eriophyllum lanatum

Linanthus bicolor

Malus sp.

Marah oreganus

Mimulus spp

Plectritis congesta

Ranunculus occidentalis

Rubus ursinus

Saxifraga integrifolia

Sedum spp.

Viola praemorsa

Zygadenus venenosus


Host Plants


    • Castilleja hispida: map groups of plants and count the number of clumps per group. (NOTE: this will be recorded by PQP for all of our highest priority sites (Mima, Glacial, Scatter Ck), plus either Morgan or Wolf Haven this year.




    • Plantago lanceolata: map patches w/ ≥ 40 plants or 10% cover within a 4 m2 area (derived from Hays et al. 2000). NOTE: this will be recorded by PQP for all of our highest priority sites (Mima, Glacial, Scatter Ck), plus either Morgan or Wolf Haven this year.

This method will produce a map identifying areas of higher densities of nectar and host plants. This will aid in identifying where nectar plant augmentation would be most beneficial, i.e. areas with good host plant abundance but with poor or only moderate nectar plant abundance/diversity.



Resulting GPS files could also be overlaid on the PQP grid for placing this data in context with the PQP data and for comparing these variables with the same variables collected in the PQP (e.g. Viola adunca, Balsamorhiza deltoidea.
Prepared by ACUB Butterfly Habitat Enhancement Group 4/11/08
Poast plot 3






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