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National Park Service U.S. Department of the Interior

Natural Resource Stewardship and Science

National Capital Region Network 2006-2009 Forest Pest, Pathogen and Exotic Plant Status Report Natural Resource Technical Report NPS/NCRN/NRTR—2012/650

ON THE COVER Kudzu vine grows in Fort Circle Park. Fourteen exotic plant species are found in this plot. Photograph by NCRN forest vegetation monitoring crew.

National Capital Region Network 2006-2009 Forest Pest, Pathogen and Exotic Plant Status Report Natural Resource Technical Report NPS/NCRN/NRTR—2012/650

John Paul Schmit John Parrish J. Patrick Campbell National Park Service Center for Urban Ecology 4598 MacArthur Blvd. NW Washington DC 20007

December, 2012 U.S. Department of the Interior National Park Service Natural Resource Stewardship and Science Fort Collins, Colorado

The National Park Service, Natural Resource Stewardship and Science office in Fort Collins, Colorado, publishes a range of reports that address natural resource topics. These reports are of interest and applicability to a broad audience in the National Park Service and others in natural resource management, including scientists, conservation and environmental constituencies, and the public. The Natural Resource Technical Report Series is used to disseminate results of scientific studies in the physical, biological, and social sciences for both the advancement of science and the achievement of the National Park Service mission. The series provides contributors with a forum for displaying comprehensive data that are often deleted from journals because of page limitations. All manuscripts in the series receive the appropriate level of peer review to ensure that the information is scientifically credible, technically accurate, appropriately written for the intended audience, and designed and published in a professional manner. Data in this report were collected and analyzed using methods based on established, peerreviewed protocols and were analyzed and interpreted within the guidelines of the protocols. This report received informal peer review by subject-matter experts who were not directly involved in the collection, analysis, or reporting of the data. Views, statements, findings, conclusions, recommendations, and data in this report do not necessarily reflect views and policies of the National Park Service, U.S. Department of the Interior. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the U.S. Government. This report is available from National Capital Region Network I&M Network website (http://science.nature.nps.gov/im/units/ncrn/index.cfm) the Natural Resource Publications Management website (http://www.nature.nps.gov/publications/nrpm/). Please cite this publication as: Schmit, J. P., J. Parrish, and J. P. Campbell. 2012. National Capital Region Network: 2006-2009 forest pest, pathogen and exotic plant status report. Natural Resource Technical Report NPS/NCRN/NRTR—2012/650. National Park Service, Fort Collins, Colorado.

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Contents Page Figures........................................................................................................................................ xviii Tables .............................................................................................Error! Bookmark not defined. Abstract ........................................................................................................................................ xix Acknowledgments........................................................................................................................ xix Introduction ..................................................................................................................................... 1 Pests and Diseases of Forest Trees .......................................................................................... 1 Chestnut Blight ................................................................................................................... 1 Hemlock Woolly Adelgid and Hemlock Scale ................................................................... 1 Dogwood Anthracnose........................................................................................................ 2 Butternut Canker ................................................................................................................. 2 Emerald Ash Borer ............................................................................................................. 2 Exotic Plants ............................................................................................................................ 2 Scope of This Report ............................................................................................................... 4 Methods........................................................................................................................................... 5 Site Selection ........................................................................................................................... 5 Measurements .......................................................................................................................... 6 Pests and Pathogens Monitored ............................................................................................... 7 Exotic Species Monitored ........................................................................................................ 8 Trees and Shrubs ................................................................................................................. 8 Vines on Trees .................................................................................................................... 8 Forest Floor Species ............................................................................................................ 8 Plant Pests and Pathogens in the NCRN ....................................................................................... 11 Dogwood Anthracnose .......................................................................................................... 11 xiv

Contents (continued) Page Hemlock Woolly Adelgid ...................................................................................................... 11 Gypsy Moth ........................................................................................................................... 12 Exotic Plants in the NCRN ........................................................................................................... 15 Trees, Saplings and Tree Seedlings ....................................................................................... 15 Trees .................................................................................................................................. 15 Saplings ............................................................................................................................. 16 Tree Seedlings ................................................................................................................... 16 Shrubs and Shrub Seedlings .................................................................................................. 17 Shrubs ............................................................................................................................... 17 Shrub Seedlings ................................................................................................................ 18 Forest Floor Species .............................................................................................................. 18 Vines ...................................................................................................................................... 20 Antietam National Battlefield ....................................................................................................... 21 Trees ...................................................................................................................................... 22 Forest Floor Exotics ............................................................................................................... 22 Vines ...................................................................................................................................... 22 Catoctin Mountain Park ................................................................................................................ 23 Trees ...................................................................................................................................... 23 Tree Seedlings ................................................................................................................... 24 Forest Floor Exotics ............................................................................................................... 24 Vines ...................................................................................................................................... 25 Chesapeake & Ohio Canal National Historical Park .................................................................... 27 Trees ...................................................................................................................................... 27 xv

Contents (continued) Page Saplings ............................................................................................................................. 28 Tree Seedlings ................................................................................................................... 28 Shrubs .................................................................................................................................... 29 Shrub Seedlings ................................................................................................................ 29 Forest Floor Species .............................................................................................................. 29 Vines ...................................................................................................................................... 32 George Washington Memorial Parkway....................................................................................... 33 Trees ...................................................................................................................................... 34 Tree Seedlings ................................................................................................................... 34 Shrubs .................................................................................................................................... 34 Shrub Seedlings ................................................................................................................ 35 Forest Floor Exotics ............................................................................................................... 35 Vines ...................................................................................................................................... 37 Harpers Ferry National Historical Park ........................................................................................ 39 Trees ...................................................................................................................................... 39 Saplings ............................................................................................................................. 40 Tree Seedlings ................................................................................................................... 40 Forest Floor Exotics ............................................................................................................... 40 Vines ...................................................................................................................................... 41 Manassas National Battlefield Park .............................................................................................. 43 Trees ...................................................................................................................................... 43 Saplings ............................................................................................................................. 43 Tree Seedlings ................................................................................................................... 44 xvi

Contents (continued) Page Shrubs .................................................................................................................................... 44 Shrub Seedlings ................................................................................................................ 44 Forest Floor Exotics ............................................................................................................... 44 Vines ...................................................................................................................................... 46 Monocacy National Battlefield ..................................................................................................... 47 Trees ...................................................................................................................................... 48 Saplings ............................................................................................................................. 48 Forest Floor Exotics ............................................................................................................... 48 Vines ...................................................................................................................................... 49 National Capital Parks East .......................................................................................................... 51 Trees ...................................................................................................................................... 52 Saplings ............................................................................................................................. 53 Tree Seedlings ................................................................................................................... 54 Shrubs .................................................................................................................................... 54 Shrub Seedlings ................................................................................................................ 54 Forest Floor Exotics ............................................................................................................... 54 Vines ...................................................................................................................................... 55 Prince William Forest Park ........................................................................................................... 57 Trees ...................................................................................................................................... 58 Tree Seedlings ................................................................................................................... 58 Shrubs .................................................................................................................................... 58 Forest Floor Exotics ............................................................................................................... 58 Vines ...................................................................................................................................... 59 xvii

Contents (continued) Page Rock Creek Park ........................................................................................................................... 61 Trees ...................................................................................................................................... 61 Saplings ............................................................................................................................. 62 Shrubs .................................................................................................................................... 62 Shrub Seedlings ................................................................................................................ 63 Forest Floor Exotics ............................................................................................................... 64 Vines ...................................................................................................................................... 65 Wolf Trap National Park for the Performing Arts ........................................................................ 66 Discussion ..................................................................................................................................... 69 Forest Pests and Diseases ...................................................................................................... 69 Exotic Plants .......................................................................................................................... 69 Literature Cited ............................................................................................................................. 71

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Figures Page Figure 1. Layout of the monitoring plots. ...................................................................................... 7 Figure 2. Location of observed gypsy moth and hemlock woolly adelgid occurrences in Catoctin Mountain Park. ........................................................................................................... 12 Figure 3. Location of observed gypsy moth occurrences in Harpers Ferry National Historical Park. ............................................................................................................................. 13 Figure 4. Forest monitoring plots (green symbols) at Antietam. ................................................. 21 Figure 5. Forest monitoring plots (green symbols) at Catoctin. .................................................. 23 Figure 6. Japanese barberry and Japanese stiltgrass are common in and around this plot (CATO-0271) in the south-west corner of Catoctin. ............................................................. 25 Figure 7. Forest monitoring plots (green symbol) along the C&O Canal.................................... 27 Figure 8. Garlic mustard on plot CHOH-0983 near Brunswick, MD. ......................................... 31 Figure 9. Forest monitoring plots (green symbols) along George Washington Memorial Parkway. ....................................................................................................................... 33 Figure 10. Exotic vines smother trees on Daingerfield Island. .................................................... 38 Figure 11. Forest monitoring plots (green symbols) in Harpers Ferry. ....................................... 39 Figure 12. Common periwinkle dominates the forest floor in this Harpers Ferry plot................ 41 Figure 13. Forest monitoring plots (green symbols) in Manassas. .............................................. 43 Figure 14. Japanese stiltgrass covers this plot in the southwest part of Manassas. ..................... 45 Figure 15. Forest monitoring plots (green symbols) in Monocacy. ............................................. 47 Figure 16. Exotic plants dominate the forest floor in this plot in Monocacy. ............................. 49 Figure 17. Forest monitoring plots (green symbols) in National Capital Parks East................... 51 Figure 18. English ivy covers the floor of a plot dominated by exotic trees in Anacostia Park. ............................................................................................................................. 53 Figure 19. Forest monitoring plots (green symbols) in Prince William Forest. .......................... 57

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Figures (continued) Page Figure 20. One of the few plots in Prince William with a high cover of Japanese stiltgrass. ....................................................................................................................................... 59 Figure 21. Forest monitoring plots (green symbols) in Rock Creek. ........................................... 61 Figure 22. This plot along the Rock Creek and Potomac Parkway is dominated by English ivy and Siebold’s arrowwood .......................................................................................... 64 Figure 23. Forest monitoring plot (green symbol) in Wolf Trap. ................................................ 66

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Tables Page Table 1. Monitoring effort by park................................................................................................. 6 Table 2. Forest tree pests and diseases monitored. ........................................................................ 8 Table 3. Exotic plant species monitored on the forest floor in the NCRN monitoring plots. ................................................................................................................................................ 9 Table 4. Tree species affected by gypsy moth in NCRN monitoring plots. ................................ 14 Table 5. Exotic tree species recorded in the NCRN monitoring plots. ........................................ 15 Table 6. Exotic sapling species recorded in the NCRN monitoring plots.................................... 16 Table 7. Exotic tree seedling species recorded in the NCRN monitoring plots. .......................... 17 Table 8. Exotic Shrub species recorded in the NCRN monitoring plots...................................... 17 Table 9. Exotic shrub seedling species recorded in the NCRN. .................................................. 18 Table 10. Exotic plant species recorded on the forest floor in the NCRN monitoring plots. .............................................................................................................................................. 19 Table 11. Exotic vine species recorded on trees in the NCRN monitoring plots. ........................ 20 Table 12. Exotic tree species recorded in Antietam monitoring plots. ........................................ 22 Table 13. Exotic plant species recorded on the forest floor in Antietam monitoring plots. .............................................................................................................................................. 22 Table 14. Exotic vine species recorded on trees in Antietam monitoring plots. .......................... 22 Table 15. Exotic tree species recorded in Catoctin monitoring plots........................................... 24 Table 16. Exotic tree seedling species recorded in Catoctin monitoring plots. ........................... 24 Table 17. Exotic species recorded on the forest floor in Catoctin monitoring plots. ................... 24 Table 18. Exotic vine species recorded on trees in Catoctin monitoring plots. ........................... 25 Table 19. Exotic tree species recorded in the C&O Canal monitoring plots. .............................. 28 Table 20. Exotic sapling species recorded in the C&O Canal monitoring plots. ......................... 28 Table 21. Exotic tree seedling species in the C&O Canal monitoring plots. ............................... 29

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Tables (continued) Page Table 22. Exotic shrub species in the C&O Canal monitoring plots. .......................................... 29 Table 23. Exotic shrub seedling species recorded in the C&O Canal monitoring plots. ............. 29 Table 24. Exotic species recorded on the forest floor in the C&O Canal monitoring plots. .............................................................................................................................................. 30 Table 25. Exotic vine species recorded in trees in the C&O Canal monitoring plots. ................. 32 Table 26. Exotic tree species recorded in GWMP monitoring plots. ........................................... 34 Table 27. Exotic tree seedling species recorded in GWMP monitoring plots. ............................ 34 Table 28. Exotic shrub species recorded in GWMP monitoring plots. ........................................ 35 Table 29. Exotic shrub seedlings at GWMP. ............................................................................... 35 Table 30. Exotic species recorded on the forest floor in GWMP monitoring plots. .................... 36 Table 31. Exotic vine species recorded in GWMP monitoring plots. .......................................... 37 Table 32. Exotic tree species recorded in Harpers Ferry monitoring plots. ................................. 40 Table 33. Exotic sapling species recorded in Harpers Ferry monitoring plots. ........................... 40 Table 34. Exotic tree seedling species recorded in Harpers Ferry monitoring plots. .................. 40 Table 35. Exotic plant species on the forest floor in Harpers Ferry monitoring plots. ................ 41 Table 36. Exotic vine species on trees in Harpers Ferry monitoring plots. ................................. 42 Table 37. Exotic tree species recorded in Manassas monitoring plots......................................... 43 Table 38. Exotic sapling species recorded in Manassas monitoring plots. .................................. 44 Table 39. Exotic tree seedling species recorded in Manassas monitoring plots. ......................... 44 Table 40. Exotic shrub species recorded in Manassas monitoring plots. ..................................... 44 Table 41. Exotic shrub seedling species recorded in Manassas monitoring plots. ...................... 44 Table 42. Exotic plant species recorded on the forest floor in Manassas monitoring plots. .............................................................................................................................................. 45 Table 43. Vine species recorded on trees in Manassas monitoring plots. .................................... 46 xvi

Tables (continued) Page Table 44. Exotic trees in Monocacy. ............................................................................................ 48 Table 45. Exotic sapling species recorded in Monocacy monitoring plots. ................................. 48 Table 46. Exotic plant species recorded on the forest floor in Monocacy monitoring plots. .............................................................................................................................................. 48 Table 47. Exotic vine species recorded in trees in Monocacy monitoring plots. ......................... 49 Table 48. Exotic tree species recorded in NACE monitoring plots. ............................................ 52 Table 49. Exotic sapling species in NACE monitoring plots. ...................................................... 53 Table 50. Exotic tree seedling species recorded in NACE monitoring plots. .............................. 54 Table 51. Exotic shrubs in NACE. ............................................................................................... 54 Table 52. Exotic shrub seedling species recorded in NACE monitoring plots. ........................... 54 Table 53. Exotic plant species recorded on the forest floor in NACE monitoring plots. .............................................................................................................................................. 55 Table 54. Exotic vine species recorded in trees in NACE monitoring plots. ............................... 56 Table 55. Exotic tree species recorded in Prince William monitoring plots. ............................... 58 Table 56. Exotic tree seedling species recorded in Prince William monitoring plots. ................ 58 Table 57. Exotic shrub species recorded in Prince William monitoring plots. ............................ 58 Table 58. Exotic species recorded on the forest floor in Prince William monitoring plots. .............................................................................................................................................. 59 Table 59. Exotic vine species recorded on trees in Prince William monitoring plots. ................ 60 Table 60. Exotic tree species recorded in Rock Creek monitoring plots. .................................... 62 Table 61. Exotic sapling species recorded in Rock Creek monitoring plots. ............................... 62 Table 62. Exotic shrub species recorded in Rock Creek monitoring plots. ................................. 63 Table 63. Exotic shrub seedling species recorded in Rock Creek monitoring plots. ................... 63 Table 64. Exotic plant species recorded on the forest floor in Rock Creek monitoring plots. .............................................................................................................................................. 65 xvii

Tables (continued) Page Table 65. Exotic vine species recorded on trees in Rock Creek monitoring plots. ...................... 65 Table 66. Exotic plant species recorded on the forest floor in Wolf Trap monitoring plots. .............................................................................................................................................. 67

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Abstract Four hundred permanent forest vegetation monitoring plots were established across the eleven parks in the National Capital Region Network. Each year one hundred of these plots are monitored. This report presents the results of the first four years of monitoring for forest pests, pathogens, and exotic plants. Gypsy moth was the most commonly found pest species in the parks, particularly at Catoctin and Harpers Ferry. Dogwood anthracnose and hemlock woolly adelgid were also encountered. Exotic plants are very common in the parks, and are found in over half of all monitoring plots. Species most frequently encountered include the tree of heaven, Amur bush honeysuckle, Japanese stiltgrass, and Japanese honeysuckle. There are numerous examples in the scientific literature of exotic plants that have negative impacts on native vegetation. As monitoring continues we will be able to determine which exotic plants are spreading and how quickly. We will also be able to compare regeneration, growth, and mortality of native vegetation on plots with and without exotic species as a measure of what impact exotic plants are having on the forest.

Acknowledgments We would like to thank our forest vegetation monitoring crewmembers: M. Bright, K. Felix, M. Housholder, B. Hwang, E. Johnson, N. Khan, E. Margulies, C. Nye, S. Schmid, J. Smith, and T. Watts. Useful advice was proved by members of the I&M eastern forest group including J. Comiskey, M. Marshall, K. Miller, B. Mitchell, S. Perles, and S. Sanders. M. Frey and M. Nortrup provided helpful reviews of an earlier draft of this repor.t Finally we would like to thank the other members of the NCRN I&M program who provided a variety of field and data support, including S. Carter, M. Lehman, M. Nortrup, T. Paradis, and G. Sanders.

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Introduction Forests are the dominant natural vegetation of the parks of the National Capital Region Network (NCRN) and the surrounding area. Overall approximately 69% of the area of the parks is forested (Fry et al. 2011). Within the parks, only marshes and managed open areas are not wooded. The marshes are small and are primarily found along major rivers such as the Potomac and the Anacostia. Open areas of the parks have a variety of uses, including crops, pasture, and planted grassland used to preserve historic landscapes; as well as mown areas used for recreation. In light of the importance of forests, exotic forest plants and forest pests and pathogens were chosen as “vital signs” for the NCRN. Vital signs are key attributes of the natural resources of the parks that are monitored to determine the overall condition of the parks. Pests and Diseases of Forest Trees Native forest trees are affected by a wide variety of insect pests and microbial diseases. In most cases these do not cause dramatic reductions in the populations of affected trees. In a few cases however, introduced pests and diseases have been devastating and have almost eliminated certain tree species. Several serious pests and diseases are currently present in the NCRN. Several of these species are particularly notable in that they have already caused a sharp decline in the populations of some tree species. Chestnut Blight

Perhaps the most well-known example of a decline due to disease is that of American chestnut (Castanea dentata). While once a dominant tree in eastern deciduous forests (Southgate 2006), it is now largely absent. This drastic decline took place in the early decades of the twentieth century and was caused by the chestnut blight (Cryphonectria parasitica) an introduced fungal pathogen (Anagnostakis 1987). According to data in NPSpecies, chestnut trees are currently or historically known from all NCRN parks except Manassas. Due to chestnut blight, most American chestnuts now grow as sprouts from stumps of trees that were felled by the disease. The stump sprouts survive for several years, typically to the point where they are large enough to flower and produce nuts, and then succumb to the disease only to sprout again. This cycle could continue indefinitely, but deer browsing and rubbing is also causing mortality of the sprouts and slowly reducing chestnut populations (Sherald 2011). However, at least two trees in the NCRN are known to be large (50 foot +) nut bearing individuals. The current abundance of American chestnut is not known, but it still occurs throughout its range in low numbers (McWilliams et al. 2006). In addition to being a common tree species, chestnut trees were also prolific producers of nuts. It has been estimated that if chestnuts had not been affected by the blight, the additional nut crop available to wildlife would be on the order of 20-50% of the current crop of all nuts (Paillet 2006). Hemlock Woolly Adelgid and Hemlock Scale

Eastern hemlocks (Tsuga canadensis) are found in eastern North America where they are regarded as the most shade tolerant tree species (Burns and Honkala 1990a). Hemlock trees are 1

found in small dense stands in the NCRN – typically on the north facing slope of moist shaded valleys. Locations of ~28 hemlock stands are known in 6 NCRN parks – Catoctin, C&O Canal, Harpers Ferry, Manassas, Monocacy, and Prince William. Several other stands are known to be on the border between these parks and private lands and may extend into park lands. Hemlock trees are threatened by two exotic insect pests: hemlock woolly adelgid (Adelges tsugae) and elongate hemlock scale (Fiorinia externa). These two pests are present in the NCRN and have caused widespread mortality to hemlocks (Danoff-Burg and Bird 2002). Uncontrolled, these pests can kill entire stands of hemlocks and could eliminate them from much of their current range in the Eastern US, including NCRN parks (Orwig and Foster 1998). Dogwood Anthracnose

Dogwood anthracnose is a fungal disease which infects dogwood (Cornus spp.) trees. Anthracnose was first found to infect flowering dogwood (Cornus florida) in New York and Connecticut in 1978 and 1979 (Hibben and Daughtrey 1988). By 1983 the disease had spread to Catoctin Mountain Park (Mielke and Langdon 1986) and the fungus responsible for the disease, Discula destructiva, was first described based on material collected in Catoctin (Redlin 1991). Dogwood anthracnose caused substantial mortality to dogwoods in Catoctin in the 1980s (Sherald 1996), and has spread throughout the NCRN and the Eastern US. Butternut Canker

Butternut canker is a fungal disease which infects butternut (Juglans cinerea) trees. Butternuts are shade intolerant understory trees with a typical lifespan of less than 100 years (Farlee et al. 2010). They are found throughout the eastern U.S. and adjacent areas of Canada (Burns and Honkala 1990b). Butternut decline was first noticed in 1967 (Renlund 1971) and the causal agent Sirococcus clavigignenti-juglandacearum was described in 1979 (Nair et al. 1979). The disease is fatal to butternut trees. In some states there has been an 80% decline in the population of butternuts (Ostry et al. 1994). There is no treatment for infected trees. Emerald Ash Borer

Emerald ash borer is an insect pest that infects ash (Fraxinus spp.) trees. The insect is an exotic Asian beetle, Agrilus planipennis, which was first found in Michigan in 2002 (Siegert et al. 2009). The insects have since spread through much of the Eastern US, including Maryland, West Virginia and Virginia. Larvae of the beetle feed by burrowing in the sapwood of living trees. A tree infested with these larvae will typically die in three to four years (Cappaert et al. 2005) Exotic Plants Exotic plant species are a pressing concern for all of the parks in the National Capital Region Network. As this report documents, a variety of exotic species are commonly found in forested areas in the parks. Many exotic plant species are also present in open fields and non-forested wetlands, but these are not currently monitored by the NCRN. Edge habitat, such as the border between forests and fields can also harbor many exotic plant species. While some of the monitoring plots include the forested part of the edge, these habitats were not extensively sampled. In recent years there has been extensive research on the impacts of exotic species on native communities. It is beyond the scope of this report to review all of this information. It is worth 2

noting that many of the exotic plants found in NCRN parks have been studied. These species have been shown to have a wide variety of impacts. One of the most commonly demonstrated impacts is to reduce the abundance of native plants through competition. For example, the exotic tree of heaven (Ailanthus altissima) has been shown to compete with black locust trees (Robinia pseudoacacia – Call and Nilsen 2005). Japanese barberry (Berberis thunbergii), an exotic shrub, has been shown to reduce the biomass of native plants (Silander and Klepeis 1999). The exotic vine mile-a-minute (Persicaria perfoliata, formerly Polygonum perfoliatum) has been shown to overgrow and kill native vegetation (Kumar and DiTommaso 2005). The presence of the exotic plants Japanese honeysuckle (Lonicera japonica) and multiflora rose (Rosa multiflora) has been shown to prevent native plants from becoming established (Yurkonis et al. 2005). Tree seedlings have been shown to be vulnerable to competition from exotic plants. Biomass and/or the abundance of native trees seedlings is reduced when they compete with Amur honeysuckle (Lonicera maackii – Yost et al. 1991, Collier et al. 2002), garlic mustard (Alliaria petiolata – Meekins and McCarthy 1999) and porcelainberry (Ampelopsis brevipedunculata – Yost et al. 1991). It has also been shown that tree seeds suffer greater predation when they are under Amur honeysuckle or multiflora rose than when they are in the open (Meiners 2007). Many exotic plants produce chemicals that can inhibit the growth of native plants, a phenomenon called allelopathy. Tree of heaven has been shown to have allelopathic effects on native plants, including inhibiting the growth of sugar maple and red oak (Lawrence et al. 1991, GómezAparicio and Canham 1998). Amur honeysuckle is allelopathic and has been shown to inhibit the growth of other plants and to lessen their ability to respond to added nutrients (Cipollini and Dorning 2008). Garlic mustard (Alliaria petiolata) is also allelopathic and can reduce the abundance of tree seedlings and the diversity of native plants on the forest floor (Stinson et al. 2007, Rogers et al. 2008). Most plants form a beneficial relationship with fungi, which aids the growth of both the fungi and the plants. This “mycorrhizal” relationship occurs when the fungi extend from the roots of the plants into the soil to absorb nutrients and water. In return for providing these to the plants, the fungi receive sugars produced by photosynthesis.. Garlic mustard has been shown to harm native plants by inhibiting mycorrhizae of herbaceous plants (Callaway et al. 2008) and trees (Stinson et al. 2006, Wolfe et al. 2008). Exotic plants can also have negative impacts on vertebrates. There has been some concern that exotic plants may cause changes in native plant communities that lead to the decline of bird populations. Northern cardinals and American robins that nest in exotic honeysuckle (Lonicera spp.) and multiflora rose have been shown to suffer greater nest predation compared to nesting in native shrubs (Borgmann and Rodewald 2004). The combined effects of Japanese stiltgrass (Microstegium vimineum) and browsing by deer have been shown to alter forest structure and reduce the abundance of birds that nest in the subcanopy (Baiser et al. 2008). Finally, exotic plants can also have adverse impacts on populations of invertebrates. For example, caterpillars that feed on garlic mustard develop poorly (Keeler and Chew 2008). The abundance and activity of cursorial leaf litter spiders (those that actively search for food rather than build webs) is reduced in common periwinkle (Vinca minor) compared to native vegetation (Bultman and DeWitt 2008). 3

Scope of This Report This report presents the result of the first four years of monitoring for the forest pest and exotic plants vital signs. Data was collected from 400 forest plots randomly scattered throughout the NCRN. Each of the plots was visited once and will be revisited between 2010 and 2013. As a consequence of the single visit, this report only covers the status of these vital signs and does not present any information on trends. While it is generally believed that exotic plants are rapidly spreading in the NCRN we cannot measure this increase until the plots are revisited. A status report on forest vegetation monitoring from 2006 to 2009 is also available (Schmit et al. 2012).

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Methods Data on pests, pathogens, and exotic plants is collected as part of the NCRN forest vegetation monitoring program. This program also collects data on native forest vegetation (for protocol see Schmit et al. 2009, for results see Schmit et al 2012). In designing the vegetation monitoring program, it was decided to use the US Forest Service Forest Inventory and Analysis (FIA) program as a model (Stolte et al. 2002). The FIA protocol is used by the Forest Service nationwide and includes an FIA plot in Catoctin Mountain Park. Furthermore, based on informal discussion it was clear that the FIA protocol was going to be the basis for forest vegetation monitoring by other eastern I&M networks. Therefore, FIA was chosen in order to maximize the benefits of data sharing. While FIA is the basis of the NCRN protocol there are some differences. Not all of the data collected on FIA plots is collected on NCRN plots. NCRN plots have the same area, but a more compact design than FIA plots in order to accommodate the numerous small patches of forest found in the network. For a full description of the NCRN monitoring protocol see (Schmit et al. 2009). Site Selection In 2005, the NCRN developed a network-wide, 250 meter square grid across the network parks. The grid exists as a spatial dataset in the GIS system. Points defined by intersections of the grid are potential monitoring locations. The purpose of this grid is to establish a consistent basis for sampling that will allow the NCRN to co-locate sampling sites and integrate results from a variety of monitoring protocols. The grid is currently used for both forest vegetation and forest bird monitoring. Two-hundred fifty meters was chosen as a grid size as many NCRN parks have long narrow forests (e.g., C&O Canal, Baltimore-Washington Parkway, and George Washington Memorial Parkway) that would be missed with a larger grid. A smaller grid was not used as forest bird monitoring relies on audible point count data (i.e., listening for bird calls). Point counts closer than 250m apart run the risk of counting a single bird in two listening points, even if the bird stays in the same location. Each point on the grid on park owned land can be considered a potential sampling location for forest vegetation monitoring, assuming it has forest vegetation, is safe to access and the park approves of the monitoring location. Old fields that are becoming forests and gaps within existing forests are also potential monitoring locations. A randomized procedure was used to choose which of the grid points would actually be used for forest monitoring. Sampling locations were selected by using generalized random-tessellation stratified survey (GRTS – Stevens and Olsen 2004). GRTS was chosen over simple random sampling as GRTS creates a random sample that is spatially balanced – points are not clumped in a single part of the study area. Monitoring locations are randomly placed across the entire network and parks with more forested area have more monitoring plots. This method was chosen as NCRN parks are not eleven distinct and compact park units. Parks in the NCRN, particularly in the DC region, are 5

fragmented and intermingled. Parts of Rock Creek are contiguous with the C&O Canal, parts of George Washington Memorial Parkway are surrounded by the C&O Canal and the border between the small forest fragments managed by Rock Creek and by National Capital Parks - East is an arbitrary line drawn for administrative convenience. Outside of DC, Harpers Ferry is bisected by the C&O Canal. Additionally, George Washington Memorial Parkway and the C&O Canal are long linear parks, so forest conditions at one end of the park may differ markedly from those at the other end. All of these considerations would reduce the benefits of stratification by park, as we may wish to analyze the data by a group of neighboring parks, or break longer parks into smaller regions. These types of analysis can be easily done post hoc if we select all of our sampling sites from a regional design. The NCRN has decided to sample 400 plots in total (Table 1). The plots are divided into four panels of 100 plots each. One panel is sampled per year, so that each plot is sampled once every four years. If a site becomes unusable at some point in the future (e.g. land is transferred out of the park system, forests are felled etc.), then a replacement site will be added. Table 1. Monitoring effort by park. Park Antietam National Battlefield Catoctin Mountain Park Chesapeake and Ohio Canal National Historical Park George Washington Memorial Parkway Harpers Ferry National Historical Park Manassas National Battlefield Park Monocacy National Battlefield National Capital Parks East Prince William Forest Park Rock Creek Park Wolf Trap National Park for the Performing Arts

Park Abbreviation ANTI CATO CHOH GWMP HAFE MANA MONO NACE PRWI ROCR WOTR

Plots Monitored 4 49 73 20 21 19 3 46 145 19 1

Measurements Each forest monitoring location consists of a 15m radius circular plot with an area of 707 m2 (Figure 1). All trees, including exotic trees, ≥10cm dbh (diameter at breast height, 1.37 m) are identified, tagged, and mapped in the plot. The diameter of each tree is measured at breast height. The trees are marked at breast height with forestry paint so that future measurements will be made at the same location on the tree. The diameter is used to determine the “basal area” of the tree, which is the area of the cross section of the trunk. Basal area is used to compare the sizes of trees. Also recorded is the presence of vines on each tree, targeted insect pests and diseases, and other conditions that could increase tree mortality. Within the main plot are three 3m radius circular microplots, with a combined area of 85m2. All saplings (trees between 1 and 10 cm dbh) and shrubs are identified, measured, and tagged on these microplots. Saplings are measured at breast height and shrubs are counted. Shrubs are woody species that are generally multi-stemmed. In practice, the field crew is provided with a list of species which are to be measured as shrubs.

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Finally, twelve 1m2 quadrats (0.5 x 2 m) are placed in the microplots and along three 15m long transects that radiate out from the center to the edge of the plot. Percent cover of select exotic and native herbaceous species and seedling regeneration is measured in the quadrats.

Figure 1. Layout of the monitoring plots. Trees are monitored within the 15m radius large circle. Saplings and shrubs are monitored within the 3m radius grey circles. Seedlings and select exotic and native herbaceous plants are monitored in the 1m2 black quadrats.

Pests and Pathogens Monitored A large number of insect pest and microbial pathogen species infest trees in the NCRN. In general, it is not the goal of the monitoring program to monitor the course of every pest or pathogen in the network. Rather, we focus on a small number of exotic pest and pathogen species that have the potential to cause widespread loss of trees in the region (Table 2). The list is reviewed annually, and new species are added if warranted. During forest vegetation monitoring, every tree on the monitoring plots is inspected for signs of the targeted pests and pathogens. In many cases, a pest or pathogen only occurs on a single host tree species, but all trees are checked regardless of tree species.

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Table 2. Forest tree pests and diseases monitored. Pest or Disease Beech bark disease Butternut canker Dogwood anthracnose Emerald ash borer Gypsy moth Hemlock scale Hemlock woolly adelgid Other significant insect damage

Scientific Name Nectria spp. Sirococcus clavigignenti-juglandacearum Discula destructiva Agrilus planipennis Lymantria dispar Fiorinia externa Adelges tsugae various

Year Monitoring Began 2006 2006 2008 2009 2006 2008 2006 2006

Occasionally the monitoring crews will encounter a tree without the targeted species, but with evidence of other insect or pathogen damage. This can include symptoms such as a large number of leaves with holes in them or a lack of chlorophyll in the leaves. In these cases the symptoms are noted, but no attempt is made to identify the cause of the symptoms. Exotic Species Monitored Trees and Shrubs

Exotic trees, saplings, shrubs, and seedlings are monitored in the same manner as their native counterparts. All exotic trees and shrubs found on the plots are tagged and recorded. Some plants that might reasonably be called shrubs, such as Japanese barberry (Berberis thunbergii) are monitored as understory species instead. This applies to thorny species which form dense thickets. It is difficult to delineate and mark these species, so we do not monitor each individual shrub. Instead we monitor how much area they cover. In practice, field crews are provided with a list of known exotic species in the NCRN and how each one is to be monitored. As more exotics are found the list is updated. Vines on Trees

Exotic vines are monitored in two ways — as vines on trees and as cover on the forest floor (see next section). As each tree is monitored, the field crew records the species of vines growing on it. The vines are not measured in any other way (e.g. no dbh measurement is made). However, the field crew also notes if the tree has vines growing in the crown of the tree. These vines are potentially more harmful to the tree, as vines in the canopy can shade the leaves of a tree. If there are several species of vines in a tree, the crew will not attempt to determine which species are in the crown, as it is difficult to do this from the ground. Forest Floor Species

Not all plant species found on the forest floor are monitored as this would be too time consuming. Instead, the field crew looks only for species which have been targeted for monitoring, and this takes place only in the 12 quadrats. The list of targeted exotic species (Table 3) was developed in consultation with the NCR Exotic Plant Management Team and the National Capital Region’s Integrated Pest Management Coordinator. Field crews estimate what percent of each of the 12 quadrats is covered by each of the targeted exotic species encountered.

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Table 3. Exotic plant species monitored on the forest floor in the NCRN monitoring plots. Latin Name

Common Name

Akebia quinata Alliaria petiolata Ampelopsis brevipedunculata Berberis thunbergii Celastrus orbiculatus Centaurea stoebe ssp. micranthos Cirsium arvense Clematis terniflora Duchesnea indica Euonymus fortunei Fallopia japonica Ficaria verna Glechoma hederacea Hedera helix Hemerocallis fulva Lespedeza cuneata Lonicera japonica Lysimachia nummularia Microstegium vimineum Murdannia keisak Oplismenus hirtellus ssp. undulatifolius Persicaria maculosa Persicaria perfoliata Polygonum caespitosum Pueraria montana Rosa multiflora Rubus phoenicolasius Viburnum dilatatum Vinca minor Wisteria floribunda Wisteria sinensis

chocolate vine garlic mustard porcelain berry Japanese barberry oriental bittersweet spotted knapweed Canada thistle sweet autumn clematis Indian strawberry winter creeper Japanese knotweed fig buttercup / lesser celandine ground ivy English ivy orange day lily Chinese lespedeza Japanese honeysuckle creeping jenny Japanese stiltgrass marsh dewflower wavyleaf basket grass Asiatic tearthumb mile-a-minute Oriental ladysthumb kudzu multiflora rose wineberry Linden arrowwood common periwinkle Japanese wisteria Chinese wisteria

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Year Added 2006 2006 2006 2006 2006 2006 2006 2006 2006 2006 2006 2006 2006 2006 2006 2006 2006 2008 2006 2009 2009 2008 2006 2008 2006 2006 2006 2006 2006 2011 2006

Plant Pests and Pathogens in the NCRN Between 2006 and 2009, three of the targeted pest species were found in monitoring plots. Dogwood anthracnose and hemlock woolly adelgid were seen on two trees each, while gypsy moths were found on 247 trees. Two additional species –hemlock scale and chestnut blight were observed in the parks, but not on trees which were in the monitoring plots. Neither emerald ash borer nor butternut canker was observed. No butternut trees were found in the monitoring plots, and very few were seen in the parks at all. Ash trees are fairly common both on and off the plots, but as of 2009 we could find no signs of infestation. Dogwood Anthracnose A total of 84 dogwood trees (Cornus florida) from 42 plots in seven parks were monitored (see Schmit et al. 2012 for information on forest vegetation for each park). Of these only two trees (2.4%) were found to currently be exhibiting signs of infection with dogwood anthracnose. One of these was located on plot CHOH-0847 near Antietam in the C&O Canal. The other was on plot PRWI-0014 in the northwest of Prince William Forest. A previous study of dogwood anthracnose in Catoctin revealed that, by 1984, 97% of dogwoods in the park had some symptoms of the disease (Sherald et al. 1996). Between 1976 and 1992 the number of dogwood trees and saplings in the park declined 77%, from 128/ha to 29/ha. Based on the 2006-2009 data (Schmit et al. 2012) the number had declined still further to 10.2/ha. The disease was not found in the park, but only two trees and four saplings were monitored, so the disease may still be present, infecting trees outside of the plots. Currently, the C&O Canal has 19 dogwood trees and saplings per hectare. Prince William has the highest dogwood density in the network at 74/ha. Manassas has the second highest density at 64 dogwoods/ha. Hemlock Woolly Adelgid Eastern hemlock trees (Tsuga canadensis) are uncommon in the NCRN. Only 26 trees and 11 saplings were found on the monitoring plots. Twenty-tree of the trees and all of the saplings were found in Catoctin on plots CATO-0294 and CATO-0365 on the south side of the park along Big Hunting Creek. The remaining three trees were found in Rock Creek in plots ROCR-0180 in Dumbarton Oaks and ROCR-0186 along Rock Creek Parkway. Hemlock woolly adelgid (Adelges tsugae) and hemlock scale (Fiorinia externa) are commonly observed outside of the plots in Catoctin. Within the plots, hemlock scale was not observed, but the woolly adelgid was found on one tree in each of the Catoctin hemlock plots (Figure 2).

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Figure 2. Location of observed gypsy moth and hemlock woolly adelgid occurrences in Catoctin Mountain Park.

Gypsy Moth Gypsy month (Lymantria dispar) was by far the most common pest species found. An outbreak of gypsy moth occurred in 2007, but it was quickly contained through aerial spraying. They were found on 247 trees on 42 monitoring plots. Catoctin and Harpers Ferry were the hardest hit. Twenty-seven (55%) plots were infested in Catoctin (Figure 2) and in Harpers Ferry 8 (38 %) were infested (Figure 3). Gypsy moth was found on two plots in C&O Canal and one plot each in George Washington Memorial Parkway, Manassas, and Monocacy. 12

Figure 3. Location of observed gypsy moth occurrences in Harpers Ferry National Historical Park.

Gypsy moths affected twenty species of trees (Table 4). In most cases, gypsy moth infested only a few individual trees of each species. Chestnut oak (Quercus prinus) northern red oak (Quercus rubra), and sweet birch (Betula lenta) had the highest percent infestation. The two oak species are common in both Catoctin and Harpers Ferry, while sweet birch is mostly found in Catoctin.

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Table 4. Tree species affected by gypsy moth in NCRN monitoring plots. Latin Name Acer rubrum Acer saccharinum Acer saccharum Betula lenta Carya alba Carya glabra Carya ovata Cornus florida Fagus grandifolia Fraxinus americana Liriodendron tulipifera Nyssa sylvatica Prunus avium Quercus alba Quercus coccinea Quercus prinus Quercus rubra Quercus velutina Sassafras albidum Tilia americana

Common Name red maple silver maple sugar maple sweet birch mockernut hickory pignut hickory shagbark hickory flowering dogwood American beech white ash tulip poplar black gum sweet cherry white oak scarlet oak chestnut oak northern red oak black oak sassafras American basswood

Total Monitored 1132 154 167 92 234 277 27 84 908 296 1236 637 17 750 244 426 282 146 85 30

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# with Gypsy Moth 27 1 7 10 1 2 3 1 10 1 3 7 1 9 3 119 35 4 1 2

% Infested 2.4 0.6 4.2 10.9 0.4 0.7 11.1 1.2 1.1 0.3 0.2 1.1 5.9 1.2 1.2 27.9 12.4 2.7 1.2 6.7

Exotic Plants in the NCRN Exotic plant species are common throughout the NCRN parks. Exotic plants were present in all of the forms of vegetation we monitor—trees, shrubs, vines, and understory species. Trees, Saplings and Tree Seedlings Seventeen species of exotic plants were recorded as trees, saplings, or tree seedlings in the monitoring plots. Additionally there were a few individuals of apples (Malus spp.) and pears (Pyrus spp.) that are exotic but could not be identified to species. Trees

While less than 2% of all trees are exotic, they were found in over 15% of the plots, indicating that they are widespread and could become more abundant (Table 5). Wolf Trap was the only park where exotic trees were not found, but that is due to the low number of monitoring plots in the park, not a lack of exotic trees. Tree of heaven (Ailanthus altissima) is the most widely distributed and abundant invasive tree and has the highest total basal area. Other widespread species include sweet cherry (Prunus avium), white mulberry (Morus alba), and Norway maple (Acer platanoides). Many invasive species however, were found in less than one percent of the plots. Table 5. Exotic tree species recorded in the NCRN monitoring plots. Latin Name Acer platanoides Ailanthus altissima Catalpa bignonioides Maclura pomifera Magnolia grandiflora Malus prunifolia Malus sieboldii Morus alba Paulownia tomentosa Prunus avium Pyrus betulifolia Pyrus communis Pyrus pyrifolia Pyrus spp. Ulmus pumila Total

Common Name Norway maple tree of heaven southern catalpa Osage orange southern magnolia plumleaf crab apple toringo crab apple white mulberry princess tree

% Plots with species 2.50

Density (Trees/ha) 0.50

% of Total Density 0.12

Basal Area (cm2/ha) 74.0

% of Total Basal Area 0.03

6.50

2.00

0.51

1100.0

0.38

0.75

0.11

0.03

29.0

0.01

1.25

1.20

0.30

470.0

0.17

0.25

0.25

0.06

250.0

0.09

0.25

0.04

0.01

3.4