Botanical History of Northern Loudoun County (VA)

For the past few months I have been preparing a talk for the Lovettsville Historical Society in Loudoun County, Virginia.  This talk focuses on the importance of native plants to the functioning of the ecosystem, how native plant populations have changed overtime, and their relationships with humans.  It also looks at important species for the indigenous peoples in the Northern Piedmont of Virginia and many of the native species that are hiding in plain sight.

Here's a link to the video Zoom presentation.  It does run a bit more than an hour.  There were just so many plants that I I wanted to talk about!

While doing the preparation for this presentation I did learn many new things.  Here are just a few of the things I learned:

• The new digital Flora of Virginia is a fantastic app for your smart phone.  Not only is there information on all the plants found in Virginia there is a ton of background information on the history of the land from its geology to forest use.
  
  
• I based my talk on the ecoregions and physiographic regions contained in Loudoun County.  These are defined by the climate and the soils present in the area.  While the soils in northern Loudoun County tend to be acidic there are a number of locations with calcium-rich soils.  These sites have a greater diversity of plants.  Some of the rich-soil sites are in the Blue Ridge ecozone where you would normally expect to find thin, acidic soils.
  
  
  

  

  From Sweet Run State Park you can find several different forest types.

  
  
• Sweet Run State Park has just opened in the northwestern corner of Loudoun County.  Here there is hiking access to a variety of forest types from dry oak forests, some calcareous oak forests and riparian woodlands in the  northern part of the Blue Ridge Ecoregion.
  
  
• To identify the vegetation types at specific locations in the county I used the interactive maps on Landfire.  Landfire is cooperative venture of the Dept. of the Interior and the Forest Service to map out vegetation coverage across the US as a means of better controlling wildfires.  This allows identification of forest types down to less than one acre resolution.  You can then look at an attached document that gives details about what constitutes each vegetation type.  It was a little clunky going between the maps and the descriptions, but there was a ton of information buried there.
  
  
• I also learned a lot more about the Pawpaw tree (Asimina triloba).  For example it is the largest tree fruit native to North America and that there is evidence for its presence on what is now North America from the Miocene period, 23-5 million years ago.
  
  

  

  These pawpaw fruits are not quite ripe.

  
  
• During the discussion afterward it was mentioned that researchers at MSU have isolated a gene from resistant elm trees that may impart resistance to the Emerald Ash borer.  A crop of potentially resistant trees is being grown.  This brings great hope for returning this significant tree to our forests.

Spring Finds 2023

 

A weakened garlic mustard.  Arrows pointing out insects on
the stem and leaf and a weakened flower stalk.

While out evaluating the effectiveness of winter spraying and pulling up garlic mustard this spring I noticed aphids on the plants that I had not noticed before.  These might be the garlic mustard aphid, Lipaphis alliariae.  These are native to Europe but have been showing up in the US of late.  I first noticed these dark colored aphids on plants that had been sprayed with glyphosate.  As I became aware of them I found scattered populations on the untreated garlic mustard as well.  Plants that were heavily infested with aphids were not coming into bloom.  Fortunately this species is host specific, meaning it only feeds on a single host plant, in this case garlic mustard. If you see them you can report the sighting on iNaturalist or EDDMaps, a web-based app for reporting and tracking invasive species.  

Close up of aphids on a garlic mustard leaf.  Coloration and
markings are consistent with the garlic mustard aphid.

The aphids on this garlic mustard are
interfering with blooming.

The area to the left of the line was sprayed with glyphosate in late February. 
The effects of spraying didn't show up until the weather began to warm in April. 
This photo was taken about 2 month after spraying.

As I mentioned in my last blog post one of my to dos was to spray a number of invasive plants with glyphosate before the native species broke dormancy.  I was a little late in getting this done so I had to be very careful not to spray the emerging native plants.  It took a long time to see any effect of the treatments. It became clear where I had sprayed after the weather got a little warmer and the Japanese honeysuckle started greening up.  The sprayed areas were definitely browner.  However, there is new growth of Virginia creeper, ash seedlings and grasses.  The box elders that were covered with honeysuckle took some damage, but they are now beginning to leaf out.  The targeted spraying technique that I have been using limits damage of non-target species and reduces the amount of pesticide applied but it also allows a lot of target plants to be missed.  As practiced, it is one of several tools I use to control invasives.  Pulling, cutting and replacing are all important components in my battle. While not 100% effective using my technique, it did set back the early growth of Japanese Honeysuckle and garlic mustard and multiflora rose.  This spraying has little effect on Oriental bittersweet, which does not put out foliage until much later. The cut stump method seems to be more efficient for shrubs and climbing vines (less overspray).  I will try to do the spraying in November this year after most of the native have died back.  There are studies that indicate that glyphosate treatments for garlic mustard at that time are more effective than in the spring.

Rattlesnake, or common grape fern, has a distinctive triangular shape

While putting out tick tubes a week ago (this is nearly a month later than I had planned) I came across a fern I had not seen before.  It has distinctly triangular appearance, quite unlike the Christmas and wood ferns that are pretty common here.  A photo sent to the ‘Seek’ app on my phone identified it as rattlesnake fern, Botrychium virginianum.  This is one of the grape ferns, named for the clusters of sporangia on the fertile frond that may look like a cluster of grapes.  The fern that I spotted lacked a fertile frond.

A Christmas fern (left) and an unusual form (right)

The pinnae of this fern are distinctly toothed, many with spiny edges.

Another unusual fern I spotted was in a clump of Christmas ferns, Polystichum acrostichoides.  Usually the margins of the pinnae (leaflets) are nearly smooth.  On this fern the margins of the pinnae were distinctly toothed, many were spine-tipped.  The pinules do have the enlarged lobe at the base, common to Christmas ferns.  So this probably is a variant of the regular Christmas fern.

The blue-green foliage of these twinleaf plants forms an effective ground cover.

I have been working on finding native replacements for vinca in a dry shady location for quite a while.  One plant that continues to impress me is twinleaf, Jeffersonia diphylla.  While its native habitat is rich moist woods, it seems to have found a home in the dry shade of this driveway planting bed.  After taking a year or two to settle in it has been doubling its spread each year for the past 3 or 4 years.  The flowers last for only a few days in early spring but the interesting foliage persists until fall. 

The branching habit of this violet sets it apart from most of the others
growing here. The large, toothed stipules indicate that this is pale violet.

Springtime is when most of the violets come into bloom.  By far the most common here are, appropriately, common blue violet, Viola papilionacea.  So when I saw a white violet in the woods I stopped to examine it.  Besides the white color, what distinguished this violet was its branching flower stalk.  Most violets only have basal leaves.  Checking in my Newcomb’s guide led me to ID this as pale violet, Viola striata.  Canada violet, another similar white violet has yellow coloration in the throat of the flower and lacks significant stipules.

Some of the flowers in my early May lawn.  Most noticeable
 are the Philadelphia fleabane (native) and the bulbous buttercup (not).

 No mow May?  I still haven’t mowed yet this year.  I have been allowing the fleabane and other natives time and space to flower and go to seed.  However, this also allows bulbous buttercup to do the same.  There are several aspects of looking at the ‘No Mow May’ trend.  It is valuable if your lawn contains early blooming plants that benefit insects/pollinators.  Natives like fleabanes, selfheal, spring beauties and violets, can benefit the local insect population.  If your lawn is a near monoculture of turf grasses skipping the mowing in early season will save on gas, but do very little to help the pollinator population.

 

Saw lots of salamanders in the pool this spring.

After opening the swimming pool this past month I found about a dozen salamanders hanging out in the cold water, about 58°F.  Normally salamanders are tricky to get out, but these were relatively sluggish and were easily caught in the basket skimmer.  These were most likely red-backed salamanders, Plethodon cinereus.  At this size these were probably a year of two old, old enough to be looking for a mate.

 

 

 

Plans for 2023

 2022 was a particularly bad year  for me in the vegetable garden.  Conversely it was a great year for our local ground hog and rabbits.  The chicken wire fencing that I had sunk in around the perimeter had sufficiently rusted away to allow too many access points to control.  So may first garden job this year is to  rebuild the subsurface groundhog fence.  I've adopted a design I found on the Massachusetts Audubon site.  The key feature is that it extends the fencing horizontally outward from the fence.  This is supposed to make it more frustrating for critters to dig under the fence.  In preparing the area for the new fencing I needed to clear out the wild blackberries that are encroaching on the garden.  A future headache will be when blackberries start growing up through the horizontal welded wire.

Here's the garden last spring.  You can see the dense growth of
blackberries on the left that is encroaching from the outer fence. 
The inner fence need to be re-established at the base. 
I'm planning on transplanting a fig to the center.

Here's the plan for the buried welded wire fencing that should
keep the ground hog from burrowing under.  The loosely attached
chicken wire creates an unstable barrier that the ground hogs
find difficult to climb on.

While many folks do not like these somewhat weedy blackberries, with a little management they can produce some good quality fruit.  The secret is to prune back the long flowering branches to 4-8 buds in late winter/early spring.  This reduces the number of berries produced, but increases their size and sweetness.  In fact last year the blackberries were the best performing food plant in the garden.  In addition the tall blackberry canes around the garden help deter the deer from jumping over the double fence.  For a good resource for keeping deer out of a garden take a look at Deerproofing your Yard and Garden by Rhonda Hart.

Last year I started growing a 'Brown Turkey' fig outdoors in the ground.  It should do fine with the cold, it's cold hardy in USDA zones 5-9.  It does, however, get browsed by deer.  For this reason I will move one out to the center of the fenced in vegetable garden.  

Replacing Exotic Spireas

Over the past couple of years I have been accumulating native some native shrubs as replacements for exotic spireas and forsythia.  First was New Jersey tea (Ceanothus americanus).  This grows about 3' tall and wide in part to full sun and dryish, slightly acidic soils.  A major drawback is that deer and rabbits like to eat it. I will be using those in the pool enclosure where at least the deer are excluded.  Sizewise this is a good replacement for the spireas that I currently have.  

I have been growing meadowsweet, Spiraea alba for awhile.  This species is a vigorous grower with a rather rangy habit.  It is better suited as background plant, rather than a feature.  Last year I got a couple of shinyleaf meadowsweet, Spiraea corymbosa.  This Mid-Atlantic native has a habit more similar to that of its Asian relatives.  I will give this one a try in pool enclosure as well.

Another plant that I have been seeking for a long time is prairie willow (Salix humilis).  This Northeastern native willow is early spring blooming and only grows 4-6' tall.  It seems to be a good visual substitute for forsythia.  A couple have overwintered well in the ground.  If these continue to perform well I should be able to make more, since willows are particularly easy to propagate.    

this is the shinyleaf meadowsweet as it arrived last summer. 
If it has overwinter successfully, I will get it in the ground later this spring.

Woodland Management

Managing a landscape is as much about taking plants out as it is expanding and adding new plants.  In one area that is an early successional woodland (trees 15-20 years old) I have been aggressively killing off Tree of Heaven (Alianthus altissima).  As the larger ones are coming down the canopy is opening up and I'm seeing an increase in the undergrowth.  I need to manage this area by selective removing killing invasive species like multiflora rose (Rosa multiflora) and garlic mustard (Alliaria petiolata).  Late winter/early spring is a good time to hit these with herbicide, while the native species are dormant.  For the larger roses I've been doing cut stem treatments (apply 20% glyphosate to freshly cut stumps with foam paint brush).  Garlic mustard and dense masses of rose with leaves get the standard foliar spray.  

I'm trying to eliminate the Tree of Heaven that has dominated
this young woodland.  Most of the trunks laying on the ground
are ones that I have successfully treated using the Hack and
Squirt method.  In the center is one of the musclewoods
that grow well in this mostly shady area.

These trees were treated two years ago with a commercial
mixture of 2,4-D and dicamba.  The one in front is being
helped along by some currently unknown critter.

My goal here is to maintain this as a high quality woodland.  A couple of years ago I started adding some young 2 gallon oaks and red maples, but these did not survive in this minimally cared for location.  There is some debate about how effective humans are at forest regeneration and that letting trees grow from the natural seed bank may be more effective.  So now I am just adding protective cages around desirable seedlings especially oaks, maples, black cherry and musclewood (Carpinus caroliniana).  The most prolific native tree in these woods are box elders (Acer negundo).  These don't need any protection.

I am, however, adding some bare root evergreens to our windbreak to the north and west of our house.  The white pine trees here are aging out and I would like to get some replacements established before these have to come out.  This year I am adding some red cedar (Juniperus virginiana) and Canaan firs (Abies balsamea var. phanerolepis).  Of the fir trees I've tried to grow here in the neutral pH soil in Pleasant Valley, the Canaan fir seems to be the happiest. 

This Canaan fir is still in the wire cage I
put around it to protect from deer rubbing.

Shade Management

Another bit of shade management I did was to take out a rapidly growing tulip tree that was too close to the house and swimming pool and would soon cast too much shade on some smaller trees and shrubs.  I figured I could cut it myself this year while it was under 40' tall, any bigger and I would want professional help.  Many of the other tulip trees here are 80+ feet tall.  I really hated removing a native tree like this but in this location it would soon dominate the landscape.

The tulip tree I removed was only about 10 years old
(see inset) but was already nearly 40' tall.  It was
casting a lot of shade on a nearby persimmon. 
The box elder may be next.

This nearby tulip tree is probably in the 70-80' range
and growing.  A good choice here, but much to big to
be close to the house.

Invasives Management

And of course I'm am continuing a broad fight against the invasive plants.  In addition to early spraying for garlic mustard and multiflora rose, I am starting to go after the Japanese honeysuckle growing on the ground.  I have just a little more time to treat these with glyphosate before the spring ephemerals come out in force.  Also with the warm winter we've had it is almost time to apply a pre-emergent  herbicide to control the Japanese stiltgrass that will start sprouting in early May.  These pre-emergent treatments have been very effective at reducing the amount of stiltgrass growing in the lawn.  They also seem to have reduced that amount of hairy cress (Cardamine hirsuta) in the lawn.

Dealing with Invasives in Winter

This is a pretty typical scene when English ivy gets established
in a tree.  This ivy is robbing light from the tree and also weighing
 it down, leading to limb breakage.  Cutting a section of each vine
around the base of this tree will kill all the vine above the cut in a month or so.

Wintercreeper grows up trees with the aid of sticky rootlets. 
Its evergreen foliage shades the host trees as well as
the surrounding area.  In areas with plentiful deer the bottom 4'
 are often stripped of foliage.  The same can be seen with English ivy.     

Winter is a very good time to have an impact on Mid-Atlantic invasive plants.  Many of these still have leaves and are susceptible to herbicide treatments.  It’s also easier to see where plants are (though identification can be trickier). Most native species are dormant during winter so there is less risk of damage from herbicides or from tromping through the landscape.  In can be more comfortable to work in cooler weather.  As long as it is above 45°F, many herbicides are still effective (see below). 

When I look out at unmanaged areas infested with invasive plants I see many opportunities to have a large impact on reducing the spread of many of these species without a lot of effort.  For some species just keeping them from climbing up the tree will have a huge impact on controlling their spread.  OF course complete removal for most of these species will take several years of consistent effort, but just keeping them from climbing trees can limit their spread and be much healthier for your established trees and large shrubs. 

Among the species that need to climb in order to bloom and produce seeds are English ivy, Japanese honeysuckle, winter creeper, and oriental bittersweet.  These vining species produce flowers when they are growing upwards or over the tops of other plants.  You can significantly reduce their seed production by keeping them from growing upwards.  Most simply this can be done by cutting the vines growing into trees and larger shrubs close to ground level.  Applying the appropriate herbicide to the stump will go one step further in eliminating that plant from the landscape.  If you aren’t using herbicide, clear the invasive from a zone around the base of a tree to help slow re-establishment of the invasive vine. 

The bittersweet, wisteria and honeysuckle grow upwards by twining around their hosts.  These vines grow tightly around the trunks and branches of their host plants in effect strangling them.  While English ivy and wintercreeper don’t twine as much (they climb with the help of sticky rootlets growing from the stem) its dense evergreen foliage gets very heavy, especially in winter, and can bring down branches or even whole trees.

Oriental bittersweet can grow vertically by twining around itself. 
Once it finds a suitable host it will continue upward
growing around the host.  I cut this one high last spring so
that I could come back later and treat a fresh cut with herbicide.

This Japanese honeysuckle was cut last season.  You can see
 the damage caused by this tightly twining vine.

The table below summarizes how to treat several of the invasive species in fall and winter.  All this information was taken from the references cited.  For details check out the links to the references for each species.  Before using herbicide read and follow the label directions.  Don’t forget to wear proper protective equipment.  Another important safety practice in dealing with vines is to NOT pull them out of the trees after you cut them.  You risk damaging the tree and yourself.  They will dry up and fall out on their own.

Invasive	Common name	Winter treatments	timing	Reference
Celastrus orbiculatus	Oriental Bittersweet	Cut stump treatment with 20% glyphosate or  trichlopyr. Digging/pulling partially effective, but plants can regrow from root fragments.	Fall-Winter when temps above 40°F.   Digging can be done anytime.	Bugwood CO
Lonicera japonica	Japanese honeysuckle	Foliar treatments with glyphosate (0.75-1.5%) effective.  Later in season higher concentrations are more effective.  Use for easily accessible foliage (ground level).	After first frost but before hard frost are very effective.  Mid-winter treatments were less effective.	Bugwood LJ
		Cut stump (25% glyphosate) for climbing honeysuckle vines	Cut stump most effective June-Winter	PRISM
Euonymus fortunei	Wintercreeper euonymus	Cut back climbing vines to prevent flowering and fruiting.  Small infestations can be dug out, but plants can regenerate from stem fragments.	Anytime, the sooner the better.   Flowers form in summer with ripe fruits in fall on climbing vines.  Dig plants when soil is soft and easily worked.	Forest Service
		Cut stem treatment with 25% glyphosate for climbing vines. Foliar spray with glyphosate or triclopyr (2%) for large infestations on ground	When temperatures are above 40°F.  Treat immediately after cutting. Mid to late fall when other species are dormant.  Best at or above 65°F.	TN Exotic Plant Management Manual
Hedera helix	English ivy	Cut vines growing up trees close to ground and again 1-2’ up.  If possible, treat cut stump with 25% active ingredient glyphosate or triclopyr amine.	Cut stump method is effective year round.  Herbicide treatment best when temperatures are above 55°F.	Invasive.org
		Foliar treatment with these chemicals (2-5%) when temperatures are above 55°F are partially effective.	Foliar treatments most effective from mid-summer through fall.  Partially effective in winter.  Apply during mild periods (above 55°F) while other plants are dormant.
		Smaller non-climbing infestations can be manually removed.  Plants can resprout from any remaining roots or vine.	Pulling can be done anytime.  There are fewer competitive plants in winter.
Wisteria sp.	Wisteria	Cut vines about 2” from the ground.  Treat with 25% glyphosate or trichlopyr.  Plants will resprout if not treated with herbicide. Small infestations can be dug out, but resprouting is possible from pieces left behind.	Cut stump treatment can be done anytime that the ground is not frozen.	Bugwood

NOTE: In most jurisdictions a home owner can apply OTC herbicides to their own properties, but they are restricted from doing so on public lands or on another person’s property.  In most cases a certified pesticide applicator is need to apply herbicides to any property but your own.

Before attacking the invasive species it is important to be able to know which plants are desirable and which are not.  Some species are easy to identify in winter (e.g., English ivy and wintercreeper).  Others like oriental bittersweet, can be difficult to distinguish from their domestic relatives.  Check out this guide from the Delaware Department of Agriculture for help in identifying invasive plant species.  Of course any vine that is threatening the life of a desirable tree or shrub is a candidate for removal.  

This adolescent hickory tree sustained damage from
Japanese honeysuckle a few years back.  The truck is swollen
due to sap being restricted from flowing up the tree.  I'm not sure
if this tree will continue to survive into maturity.

In looking over the nearby woodlands I noticed that most of the native vining species do not spiral tightly around their host.   Deciduous native vines like Virginia creeper and native grapes do not twine so they do not strangle trees, and, since they lose their leaves in the fall they do not add a lot of weight through the winter.  Native vines growing high into trees can reduce the amount of light penetrating the tree canopy.  One of the bigger problems on my property with vines growing up in the canopy is that they join trees together so that when one falls it can damage other trees that are connected through the vines.  An important benefit of these native species is that their berries are an import food source for many birds, poison ivy included.

Catbrier (Smilax sp.), the green stems here, is a native species that twines
loosely on itself as well as on other nearby plants.  While it can
 be a nuisance due to its stiff thorns it plays well with other established plants.

Another group of invasive species that can be attacked in winter are woody shrubs and herbaceous species that are still green and active in the winter months.  These include multiflora rose (Rosa multiflora), wineberry (Rubus phoenicolasius) and garlic mustard (Alliaria petiolata).  Last year I wrote a more detailed post  on how to deal with these species in the winter. 

As an update to that post, I did test whether burning the crowns of wineberry with a garden torch was sufficient to kill it.  In most cases the answer was no.  Most of the crown resprouted later in the spring. Another action took was to  cut back the long arching branches in late summer and fall.  This shoud reduce its spread since it can form roots wherever a branch tip contacts the ground.  The effectiveness of this effort will be difficult for me to measure but I hope to get a sense if there are fewer of these out there.

For a general overview of Mid-Atlantic invasive species see Plant Invaders of  Mid-Atlantic Natural Areas  For detailed instructions on how to treat you should look to nearby state resources or University cooperative extension services.

What else can you do?

Aside from managing your own property there is not a lot an individual can due by themselves or without permission.   There are a number of ways to volunteer to do plant conservation or get involved with removal of invasive species.  I first got started working with native plants by becoming a plant conservation volunteer with what was then the New England Native Plant Society (now the Native Plant Trust).  A number of our projects involved clearing out invasive species from public and some private lands.  We were trained on how to identify our target and how to remove it.

To work on public lands you need training and or supervision.  Contact the public lands supervisor for the areas where you want to help.  Some other places where you can look for opportunities are plant conservation groups and state or regional native plant societies.  In Maryland there are several counties with ‘Weed Warrior’ groups (for example see  Weed Warriors  for Montgomery County).  In Northern Virginia there are the Tree Rescuers.  Also in Virginia there is  Blue Ridge Prism, a group dedicated to removing invasives from the forests of the Blue Ridge Mountains.  The USDA website has some general information including a few specific links to projects around the country.  The Nature Conservancy has a volunteer site that can be searched by location and date.