DC’s Famous Cherry Trees: Keeping Them Healthy in the Face of Pests, Floods, and More

a collage of cherry trees showing pink and white flowers
A collage of cherry (Prunus spp.) blossoms, some of which can be found in Washington DC. The species and varieties vary in blossom color, size, and shape. Credit: LiveJapan

Just across Maryland’s border, millions of people flock to Washington, DC at this time of year to witness the spectacular display of 3,000+ cherry trees in bloom around the Tidal Basin. Keeping these famous trees healthy from pests, predicting the timing of peak bloom, and mitigating the threat of rising tides from climate change are among the challenges that need to be addressed to keep these cherished plants in top form for people to enjoy now and for many years to come.

Dr. Lauren Schmitt, an ecologist working with the Burghardt lab in the University of Maryland’s Entomology Department, gives us a close look at the history of these magnificent trees, how pests are managed using an Integrated Pest Management (IPM) approach, how peak bloom times are predicted, and how some of the non-pest threats such as soil compaction and flooding are being addressed.

Read her two part-series on DC’s Famous Cherry Trees:

Part 1: A Case Study For IPM 

Part 2: Variation In The Trees And Varied Threats To Their Health 

Lauren Schmitt, Ph.D. is an ecologist working at the intersection of ecosystem ecology and community ecology. A member of the University of Maryland Burghardt Lab, her research focuses on linking biodiversity and ecosystem function. Much of her work takes place in a forest diversity experiment, “BiodiversiTREE” to assess how tree diversity shapes communities and ecosystem processes.

Dead Trees “Snag” Lofty Praise as Habitat

snag
A snag at Patuxent Wildlife Refuge, North Tract. Photo: N. Allred

Chad Hanson, a University of California-Davis researcher and Sierra Club board member observes, “We are trapped by an outdated cultural idea that a healthy forest is one with nothing but green trees. An ecologically healthy forest has dead trees, broken tops, and down logs.”

Over the last several years, you may have noticed an increase in dead and dying trees in our watershed, particularly oaks. There are a number of factors at play, including soil compaction from development, old trunk wounds, storm damage, environmental stressors such as heat and drought, opportunistic diseases and insects, and just plain old age. If you think the only response to a dead tree is to cut it down, think again!

chickadee explores a tree cavity
Insect-feeding songbirds like chickadees find food and shelter in snags. Photo: Christa R.

It has been estimated that dead trees, called snags when they are still upright, and trees with decaying wood provide important habitat for about 25 percent of the forest wildlife species in the northeastern United States. Add aquatic species and that number climbs even higher.

Did you know that more than eighty birds in North America are cavity-nesters, include 10 species of owls, 7 ducks, 2 falcons, all 21 woodpeckers, and about 40 songbirds? They raise their young in hollowed out sections of dead and dying trees. In addition to providing a place for birds to nest, cavities also protect birds from predators and offer shelter from the elements. Dead branches serve as a perch from which birds can survey their surroundings, hunt, eat, and dry their wings and rest. If that weren’t enough, a dead tree offers a smorgasbord to insect-eating birds and other animals, with holes, depressions and cracks that double as places to store seeds, nuts and other food.

red-bellied woodpecker in a dead tree
Red-bellied woodpecker (Melanerpes carolinus). Photo: Lip Kee

Logs on the ground also provide a bounty of food and shelter for a range of critters. Hollow logs provide cover and protection for small mammals like foxes, rabbits, skunks and raccoons. The wood itself may be home to ants, beetles, and carpenter bees that tunnel into it, while bark beetles build extensive chambers under the bark. These insect residents are, in turn, a good source of protein for turtles, toads and lizards. No walk in the woods is complete without flipping over a log to see what lies beneath –
beetles, worms, centipedes and, if you’re lucky, a salamander. Don’t forget to roll the log back over gently, lest you destroy someone’s happy home. Continue reading

How to plant a container-grown tree – Featured Video

Late-winter through mid-spring and early through mid-fall are the best times to plant woody ornamentals, so this is a good time of year to start planning your process if you are interested in adding shrubs or trees to your landscape this year.

Take a look at this video showing you how to plant your container-grown tree, and for more information, view the HGIC page on the planting process.

Our Favorite Trees

What are your favorite trees? The Watershed Restoration Specialists from the University of Maryland Extension Sea Grant Program recently shared what their favorite trees are and why.

As Watershed Specialists, we spend a lot of time helping people decide which species of trees might be best for a particular project based on a variety of factors including
sun, soils, and size. Every now and then, people will also see if they can add their favorite tree to the project. Now the number of reasons why people like a particular tree is
probably rivaled by the number of grains of sand on the beach and there’s not enough room in this article to list them all. But this got me to thinking; we spend so much
time talking to other people about trees, I wonder what our favorite ones are? Well, below is the answer to that very question. And after reading this, drop any one of us an email and let us know what your favorite tree is and why.

paw paw tree flowers and fruits
Paw Paw

Amanda – Paw Paw (Asimina triloba)
As an eastern North American native species, not only does Paw Paw have a very distinctive flower, it produces one of the largest edible fruits of all our native trees. The main reason this is Amanda’s choice of favorite native tree is that her son loves the fruit! And because of recent interest in Paw Paw fruit, it has earned the nickname Hipster Banana.

Jackie – Red Maple (Acer rubrum)
Red Maples live up to their name: they give us that first shimmer of red in early spring with its flowers and seeds and wraps up the year with fiery red leaves in the fall. Even
though its nickname is Swamp Maple, Jackie appreciates Red Maples not only for their color, she’s actually made syrup from its sap!

red maple tree and flowers
Red Maple

Kelsey – Willow Oak (Quercus phellos)
A tree she grew up with in her home state of Michigan, Kelsey’s favorite is the Willow Oak. This fast-growing species produces plenty of acorns which keeps the squirrels busy, it also casts a great shadow on her apartment, something she appreciates during the summer months.

willow oak trees and acorn
Willow Oak

Jennifer – Tulip Poplar (Liriodendron tulipifera)
Earning its name from a coffee-cup sized flower that people don’t often see since they’re so high up in the tree, the Tulip Poplar is Jen’s favorite. This tall growing tree is important to a number of birds and butterflies. And its cat-shaped leaf reminds her of the two felines that are really in charge of her house.

tulip poplar tree flower and leaf
Tulip Poplar

Eric – Black Gum (Nyssa sylvatica)
My fave is the Black Gum. I grew to appreciate it over time because of the wide variety of conditions it grows in. And when people tell me they love the red color of a Burning Bush, which can invade natural areas, I often suggest that plants like Black Gum not only have a beautiful red color, they produce flowers and fruit that are beneficial to native insects and animals.

black gum tree red foliage
Black Gum

By Eric Buehl, Senior Agent Associate, Sea Grant Extension Programs. This article was published originally in the Maryland Sea Grant Headwaters Newsletter, October 2019.

Why are so many oak trees dying this year?

dead oak tree
Rapid decline of an oak tree in an area with a restricted root zone. Photo: D.L. Clement, University of Maryland Extension

This season (2019) the Home and Garden Information Center has received a tremendous number of questions on rapid browning and death of many of our oak trees in urban landscapes and forest situations. Even though it would be convenient to point to a single reason for this dieback it is most likely a combination of weather, disease, and insect factors.  

A logical starting place to look for an explanation would be the often-overlooked gradual health decline of our trees due to old age, restricted root zones, soil compaction in work zones, old trunk wounds, storm damage, poor pruning, urban stress such as reflected heat and drought, and opportunistic diseases and insects. These decline factors can extend over many years, leaving trees to try and cope with less than ideal growing conditions.

Last season these conditions were further worsened by the excessive rainfall that continued into this spring which resulted in standing water at many locations that had low spots, compacted soil, or water collection points. Flooded soils and saturated root zones further weakened trees by allowing root pathogens such as Phytophthora a chance to reduce the overall number of healthy roots. 

area of flooding near oak trees
Flooding near oak trees, Spring 2019. Photo: D.L. Clement, University of Maryland Extension

dead oak tree
Dying oaks in the same location as above, Fall 2019. Photo: D.L. Clement, University of Maryland Extension

In general, red, black, chestnut and white oaks don’t tolerate poorly drained soils. Trees can tolerate some reduction in root health, as long as temperatures remain cool, water demands aren’t high, and adequate time is allowed for root regeneration. As a root system loses the ability to support the tree’s water needs, dieback will occur especially in the upper branches.  

When the high summer temperatures began this season in mid-July and the low rainfall extended into this fall these conditions accelerated the loss of tree vigor and resulted in sudden browning of tree leaves and canopy dieback. Compromised tree health often allows pathogens such Armillaria and Hypoxylon to invade, which further accelerates dieback and death. In addition, opportunistic insects such as Ambrosia Beetles and Two-lined Chestnut Borer, will attack tree trunks and continue tree demise.  

frass on oak from ambrosia beetles
Evidence of a boring insect infestation. Photo: D.L. Clement, University of Maryland Extension

There are a few positive steps that may alleviate some tree stress. It is very difficult to reverse decline in stressed oaks so select trees that still have green foliage and irrigate near their bases during this period of high drought stress. Even minimal amounts of water can help recovery and prevent drought stress before winter dormancy. Practices that open up compacted soils to increase drainage and raise soil oxygen levels (e.g., vertical mulching) will often help as well.  

As we continue to receive information about dying oaks across the state, we still have many unanswered questions. We will continue to collect data on tree species, age, and pest occurrence, in coordination with other agencies across Maryland.

By Dr. David L. Clement, Principal Agent, University of Maryland Extension, Home & Garden Information Center and Dr. Karen Rane, Director, University of Maryland Plant Diagnostic Laboratory

For Those Who Are Looking, There Are Sycamores

sycamore tree
American sycamore tree in winter. Photo: Paul Wray, Iowa State University, Bugwood.org

I knew I had to go back to school to study horticulture when I was in my mid-twenties. Every day on my way to work I found myself looking out the windows at trees instead of watching the road. The Catoctin mountain forest was particularly enticing. Route 15 was a much quieter road then, and fortunately, there were no mobile phones to provide additional distractions. Although I admired the landscape in general, there was one tree that stood out amongst the others: the sycamore. Against a blue daytime sky or a sunrise dancing with pink and purple hues, its white bark was remarkable. The shape of this towering tree with its dazzling bark and color contrast inspired me to leave a secure job in search of knowledge for the things that ignited curiosity in me. Continue reading