Mapping Severe Invasive Plant Infestations in our Parks
Fairfax Tree Rescuers PRISM
Thank you for helping to find and document the very worst infestations of invasive plants in our parks so we can work as a community to figure out how to get the situation under control! Our park managers cannot possibly know where trouble has hit in all 40,000+ acres of parkland in Fairfax. We hope to have all of FCPA surveyed by summer of 2026 and all the parks surveyed by the end of 2026, which will take many volunteers, each going on a whole lot of walks, including in obscure parks that are rarely visited.
Below are instructions for how to do this simply and quickly, using a mobile app while you are walking through the parks. (If you also would like to do more detailed mapping, see this document for instructions.)
Note: When you have made your first observations, please email Jean Lockhart
It’s as easy as 1 2 3!
- Assess the site. Take a walk in any park in Fairfax (includes parks owned by Fairfax County, Falls Church, the other independent jurisdictions, NOVA parks, and state and federal agencies), looking for any horrible infestations of invasive plants. You may find it more fun (and possibly feel safer in the obscure parks) if you take along a companion.
- Document the overall Site Condition. Once you have walked the park, and gotten a feel for the level of overall condition with respect to invasive species, please complete this site survey form to report on the overall condition of the park.
- Document Severe Infestations. When you see a nasty infestation, use the iMapInvasives mobile app, snap a photo, click on a few dropdowns, put in a short comment, and move on! The app will document your location automatically.
How thorough and how often to survey:
Our hope is that you will walk all the trails of the sites that you agree to survey and document severe infestations. If you go at a time of year when you can readily identify most of the species on our list, then you really only need to survey each park one time. If you feel like you may have missed something because you weren’t there when you would expect to see an ephemeral species (like lesser celendine that is out in the spring and then hard to detect after June), then you should plan to revisit at a later date.
Here is what we are looking for.
- Severe vine infestations: English ivy, porcelain berry, or wintercreeper reaching up high into multiple trees. Strangling vines severely affecting multiple trees. Smothering invasive vines blanketing the canopies. Big patches of vines obliterating the shrubs and ground layer underneath. We always consider wisteria and kudzu severe, even if there isn’t that much of it. The most common other examples are Japanese honeysuckle and Oriental bittersweet.
- Severe tree infestations: Large areas dominated by invasive trees. The most common example is callery pear (aka Bradford pear). It’s good to document tree-of-heaven even if there isn’t a lot of it.
- Severe shrub infestations: Large areas where invasive shrubs are covering almost everything underneath. The most common examples are multiflora rose, Amur honeysuckle, Japanese barberry, autumn olive,and burning bush.
- Severe ground-layer infestations: Large areas where the ground-layer is almost entirely occupied by forbs (annuals or perennials such as lesser celandine) or grasses (such as Japanese stiltgrass or Chinese Silvergrass). Sometimes these can be quite tall - like Japanese knotweed (which is good to document on public land even if it’s a small area).
How do we define “Severe?” An invasion might be considered severe even in an area less than half an acre if the invasive species is dominating the canopy, covering more than about 30% of the ground cover or understory, or is having a serious ecological impact such as obviously outcompeting or covering native species. Use your judgement! We are really looking for the very worst infestations, but don’t stress about overlabeling invasions that you see as “severe.” We’d rather err on the side of caution and know about the bad guys out there that may be gaining a foothold.
Priority species
If you see Asian Wisteria, Kudzu, or Five-leaved Akebia anywhere in the county (parks or elsewhere), please add them to the map and use the same “Severe invasive plant infestations” project code that we do for park surveys. We want to get on top of these species, which are devastating but not yet so common that we can’t get a grip on them.
Note: You may still document invasive species occurrences that are not considered severe, but be sure not to enter them as “Severe Invasive Plant Infestations” in the mobile app. See below for instructions.
Instructions
EVALUATING SITE CONDITION
Once you have a sense of the overall condition of the park with respect to invasive species infestations please fill out this site survey form . This form will help identify the severity of invasive species infestations in cases where, perhaps no single invasive species is dominant, but that the site overall is dominated by a combination of invasive species. This form is also especially useful to document high quality parks that you visited and did NOT detect any severe infestations. Please bookmark this form so you don’t forget to fill it out.
In the comment section, tell us who owns the park if you know it (such as FCPA or NOVA Parks), and give us an idea of where you looked (so we know how much of the park was searched).
DOCUMENTING SEVERE INFESTATIONS
1. Set up your iMapInvasives account using the web version.
You must be an official “member” of Fairfax Tree Rescuers for us to be able to use your data.
- Create a free account on https://imapinvasives.natureserve.org/imap/login.jsp Choose Virginia as your jurisdiction.
- Navigate to https://imapinvasives.natureserve.org/imap/services/page/OrganizationList.html. Search for and choose Fairfax Tree Rescuers, then click on Request to Join Organization. (Do not try to do this from your account page - it doesn’t work, for some reason).
- You should receive an email from us to let you know when we have done that. It may take a few days for approval since volunteers are doing the approval.
Make a note of your login information. You will need it later to login to the iMapInvasive mobile app that you will use in the field to document observations of invasive species..
2. Go to the App store or Google Play and download iMapInvasives Mobile app.
IMPORTANT NOTE!! Users with very current model Androids may not be able to download the iMapInvasives app at this time due to a new compatibility issue. It is expected to be resolved sometime in January. If you are highly motivated to still survey and have patience for additional complexity, contact
3. Login to the mobile app. If you have trouble logging into the app, first check that you have entered the right username and password. You can do this by trying to log into the online version iMapInvasives.org. If you can’t get in there, then you are not entering the username and password correctly.
If the username and password are correct, then try removing the iMapInvasives app from your phone and reloading it.
4. Set your preferences (click on the upper left to get the dropdown.)
- Jurisdiction Species List - Virginia
image - Username
- Password
- Retrieve iMap LIst - click on that to update your organization and project options
image - Customize Species List - click on anything you might use (see suggestions at the bottom of this document). It’s very helpful to do this since it will limit the number of species you have to scroll through.
image - Default Project - Pick “Severe Invasive Plant Infestations” This is key! But please note: if you are documenting an invasive species that is not dominating the area, be sure to change the Project so it doesn’t lump it with the severe invasive species infestations.
- Default organization - Fairfax Tree Rescuers. This is also key!
- Save
You’ll want to play with the app a little and try this next part at home before heading for the field.
5. Walk through the park, looking for severe infestations. Stop at each, and…
6. Create a survey
- Click Add Observation in the upper right corner of the screen
- Take a photo that shows enough detail of the plant for someone to identify the plant. Leaves are important, and flowers or fruits are a bonus.
- Enter the species name using the drop down. Note: in the case of mixed species infestations, choose whichever is most dominant.
- It’s pretty important that we get a correct identification of the species. If you aren’t sure, apps like iNaturalist, Seek, and others can help you with this.
- Click “species detected”
image
Note: If your phone had a good GPS signal when you took the photo, the location will automatically choose the place where the photo was taken. If you don’t have a good signal, create the record in the field, but don’t upload. When you have a signal edit the record and uncheck the gps box to manually enter the location. Save and upload.
IMPORTANT NOTE: In the Short term, the basemap is not showing up on the app interface, but the GPS is still working. Make sure to keep “GPS” field checked to allow the app to automatically set the location.
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- Take a guess about the size of the infestation.One acre is about the size of three quarters of a football field, 0.5 acre is about the size of 4 tennis courts, and 10 sq. feet is about the size of standard dining table.
NOTE. If you are documenting an invasive species that is present, but the infestation is NOT severe, please uncheck “Severe invasive plant infestations” and check the blank line below the last value on your list.
image - Pick one of the choices for Distribution of Invasive
image - In the comment section, and give us an idea of where you looked (so we know how much of the park was searched). (You only need to tell us this once for each walk you take.)
image - Save
IF you survey a park and do not see ANY severe infestations and feel pretty confident about that…
- Do a little happy dance.
- Complete the Site Survey Form -see above. This will allow you to document that you visited the site but did not identify any severe infestations.
7. Upload your Observations to iMap
- Once you are satisfied with the data you collected for the observation, check the box for the observations you are ready to upload.
image - Click on the dropdown in the upper lefthand corner. Upload Selected.
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8. Check out your observations online if you’d like.
You can check out your observations on the online applications iMapInvasives.org. Zoom into the site that you visited. Open the “Layers On/Off” dropdown and select “Unconfirmed Presence” and you will see a purple dot for each observation you entered.
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Once your observation has been confirmed by an administrator, it will show up as a green dot on the map on the web version of iMapInvasives.
In those situations where a mess of the same invasive species extends for a very long way, please make a fresh observation every 30-50 yards or so and make a note in the comment section that you are looking at a continuous infestation. The administrators can then draw a line on the map to indicate that.
Some common invasive plants causing severe infestations in Fairfax
These are ones that are relatively easy to recognize and that tend to obliterate everything in their path.
A Fake Species (Use this when you can tell that it is something really bad, but you are either too far away to identify the species, or too inexperienced to be sure. In the latter case, please take a bunch of closeup photos and email them to us so we can edit it afterwards.
- Amur honeysuckle: Lonicera maackii
- Autumn olive: Elaeagnus umbellata
- Bradford pear: Pyrus calleryana
- Chinese lespedeza: Lespedeza cuneata
- Chinese privet: Ligustrum sinense
- Chinese wisteria: Wisteria sinensis
- English ivy: Hedera helix
- Five-leaf akebia: Akebia quinata
- Fountain grass: Cenchrus purpurascens
- Garlic mustard: Alliaria petiolata
- Golden Bamboo: Phyllostachys aurea
- Incised fumewort: Corydalis incisa (not too common yet, but big trouble. Document wherever you find it.)
- Japanese barberry: Berberis thunbergii
- Japanese honeysuckle: Lonicera japonica
- Japanese knotweed: Fallopia japonica
- Japanese stilt grass: Microstegium vimineum
- Japanese wisteria: Wisteria floribunda (distinguishing that from Chinese wisteria is unimportant. If in doubt, list it as Chinese wisteria.)
- Kudzu vine: Pueraria montana
- Lesser celandine: Ranunculus ficaria
- Linden viburnum: Viburnum dilatatum
- Mile-a-minute: Persicaria perfoliata
- Mugwort: Artemisia vulgaris
- Multiflora rose: Rosa multiflora
- Oriental bittersweet: Celastrus orbiculatus
- Porcelain-berry: Ampelopsis brevipedunculata
- Silver grass: Miscanthus sinensis
- Tree-of-heaven: Ailanthus altissima
- Wavyleaf grass: Oplismenus hirtellus (not too common yet, but big trouble. Document wherever you find it)
- Wintercreeper: Euonymus fortune