Posts tagged ‘trees’
The Smithsonian Gardens Tree Collection currently consists of over 1,850 trees, approximately 1,400 of which are located on the downtown Washington, D.C. and Anacostia campuses. These trees add beauty to our grounds, and they offer myriad environmental and health-related benefits. Unfortunately, it seems that trees are constantly under attack by a host of problems, ranging from severe climate, to native and exotic pests and diseases, to damage from construction and development projects, to the tough urban environment in which they grow. Once these plants become stressed, it’s more likely that they will suffer due to one or more of these issues. In addition, as trees grow, certain structural defects can develop which may cause problems in the future, especially when severe weather events can exploit the inherent weaknesses in these defects.
For these reasons, we at Smithsonian Gardens take a proactive, rather than reactive, approach to caring for these green assets. Oftentimes, defects, cultural stressors, or insect and disease infestations that have gone unnoticed for a time can be difficult, if not impossible, to reverse. Therefore, a thorough health and structure assessment of these trees was completed at the end of 2014. This assessment consisted of a top-to-bottom, 360 degree visual evaluation of each tree. All defects and other potential issues were noted and assigned a rating based on the severity of the condition observed.
What we had at the end of the evaluations was a complete list of trees, their problems (if they had any), and recommendations for correcting anything of concern. Based on the ranking system, we now have an organized and detailed list of what maintenance and tree care work is needed, with a clear indication of where we need to start. This has enabled Smithsonian Gardens to find and fix issues before they become more serious, and gives us the ability to be proactive with our tree management. It also gives us a better idea of how to budget for upcoming maintenance needs. Prevention is the best medicine, and any time we can find and correct an issue before it becomes serious it allows us to keep our trees happy and healthy for many years to come.
-Greg Huse, Smithsonian Gardens Arborist and Tree Collection Manager
Ever heard of the pawpaw tree? Ever tasted its fruit? Did you even know it had fruit? Though it may not have the name recognition of an apple or a peach tree, pawpaw trees have a long and important history in the United States. In 1541, Hernando de Soto observed Mississippi Valley Native Americans growing pawpaws and eating the fruit. According to scientist Neal Peterson, the Spanish mistakenly named the pawpaw fruit “papaya.” Spanish explorers selected this name because they observed pawpaw fruit to have a similar green skin and orange flesh to a papaya. Overtime, the English language transformed the fruit and tree species name from papaya to pawpaw (Asimina triloba).
According to James A. Little in his 1905 A Treatise on the Pawpaw, pawpaw fruit helped sustain Native Americans and early American settlers in times of harvest failure. Little wrote that pawpaw trees needed little maintenance in order to survive in the wild, unlike apple, pear, or peach trees. Thanks to its resilience, Native Americans and early pioneers enjoyed pawpaw fruit as a dependable source of fiber and nourishment. Even members of the Lewis and Clarke Expedition survived on pawpaw fruit during their long journey west in 1804-1806.
Found between Georgia and Northern Michigan, pawpaws extend across eastern portions of the United States. Unlike the tropical members of the Annonaceae family to which it belongs, pawpaw trees thrive in harsh conditions of snow and ice. Despite this resilience, pawpaws still struggle to reproduce. Scientists believe the tree is ineffective at attracting flies and beetles to pollinate its flowers, thus creating challenges for reproduction.
The pawpaw tree produces a very nutritious and delicious fruit, which is actually a berry. The pawpaw berry is also called a “custard apple” and is said to taste like a mix between a banana and a pear, with a hint of vanilla. The name custard apple derives from the creamy texture of the fruit.
Smithsonian Gardens currently has seventeen pawpaw trees in its Tree Collection. They can be found in the Native Landscape garden at the National Museum of the American Indian, the Butterfly Habitat Garden adjacent to the National Museum of Natural History, and the National Air and Space Museum.
Next time you stop by one of the Smithsonian gardens keep an eye out for this beautiful tree with a deliciously-interesting past.
-Jessica Brode, Archives of American Gardens intern
As we gaze around at the beautiful autumn colors that our trees are showing us, we’re trying not to think about the arrival of the cold and snowy weather of winter. However, arrive it will, and now is the time to prepare your trees for those coming winter months. Although all trees are potentially susceptible to winter injury, young and/or thin-barked, and broadleaf evergreen trees require the most preparation.
Excessively cold temperatures, wind, and quick temperature changes can cause drying, browning, and death of evergreen foliage. This problem is most prevalent on broadleaf evergreens such as rhododendrons, laurels, boxwoods, and hollies. To help prevent this damage, construct a barrier of heavy burlap, like a fence, to block drying winds from their prevailing direction. If the entirety of the plant is exposed, loosely wrap it in burlap. In either case, be sure to leave the top of the plant exposed so light and air penetration can still occur. In addition, it is important to keep watering your trees up until the time of the first hard frost. A 4-6 inch layer of mulch over the root zone will also help the soil retain warmth and moisture. (Remember not to pile the mulch up against the trunk of the tree.)
Another issue of concern, which is also caused by rapidly fluctuating temperatures, is sunscald. This occurs when the sun has warmed the trunk of the tree, and then that trunk is rapidly cooled upon sudden shading from a cloud, etc. This condition results in elongated, dried and cracked areas of dead bark. This can be prevented by wrapping the trunk with commercial tree wrap (available at most home and garden centers) or other light-colored material. This will reflect sunlight and keep the bark at a more consistent temperature. The wrap should be placed on the tree in the fall and removed in the spring, after the last frost.
Broadleaf evergreen foliage damage and frost cracks are influenced by many factors, including plant species, location, drainage, natural protection, and how well established a plant is in the landscape. There is no specific temperature at which damage occurs, but if the forecast calls for temperatures below the average seasonal low (29-33°F for Washington, D.C.), it is best to utilize the protection methods outlined above.
Tree branches can be prone to breakage from heaving snow and ice loads and by strong winds. Weakly attached, overextended and broken limbs should be pruned. Trees with an upright form, such as juniper, arborvitae, and clump birch, can be wrapped in burlap, or held together by wrapping the branches collectively with twine or rope. Any wrapping material should be removed in the spring.
When natural food sources grow scarce in the winter, rodents may feed on the young bark and cambial tissue of trees. Plastic tree guards or a cylinder of ¼” wire mesh placed around the trunks of young trees will help prevent this damage. Be sure to remove these guards once the spring has come so the tree does not wind up growing into them.
Trees possess an extraordinary ability to withstand severe winter weather, with some being more hearty than others. However, with proper care and attention, your trees should come through the winter ready to show off their new flowers and foliage for spring.
-Greg Huse, Smithsonian Gardens Arborist & Tree Collection Manager
Smithsonian Gardens manages the health and maintenance of 1,873 trees in the Washington, D.C. area. As you walk around the Smithsonian gardens and museums you may notice a common theme: many of these trees are mature specimens with historical context and connection to the museums they surround. This is extremely evident as you walk the grounds of the National Museum of Natural History, where the extensive American elm plantings bring us back to a time when Ulmus americana was the predominant street tree in America. In fact, the large specimen on the corner of 9th Street and Constitution Avenue predates the museum, which celebrated its centennial in 2010.
As Dutch Elm Disease (DED) has wiped out the majority of stately American elms throughout the U.S., we at Smithsonian Gardens work diligently to monitor and manage our trees in order to prevent the spread of this lethal disease.
It is with this management strategy in mind that we carefully select replacements when elm trees at the Smithsonian need to be removed. When one of the younger elms on the north lawn of the National Museum of Natural History was critically damaged during a storm, we once again debated and discussed which “resistant” elm to replace it with. One of the best choices for a true Ulmus americana replacement is the ‘Jefferson’ Elm (Ulmus americana ‘Jefferson’), selected through the collaborative efforts of the National Park Service and the USDA’s Agricultural Research Service (ARS).
This tree was selected for its excellent DED resistance and the fact that as a true species, it exhibits the classic American elm form, unlike some of the resistant hybrids.
‘Jefferson’ elms leaf out earlier in the spring and maintain their green color better in the summer than other U. americana specimens. We were very lucky to receive this tree from the National Park Service as it is just becoming available in the commercial trade at this time, and can be difficult to find. The National Park Service propagates ‘Jefferson’ by cuttings from the original tree, located on the National Mall, and grows the seedlings for six years at its National Capital Region Nursery. It is a long process and a difficult one, as only about 5% of the cuttings live to become mature trees. Hopefully this selection will become more common in the nursery trade so that we can once again plant these majestic trees with confidence. Until that time, we are very thankful for the ongoing collaboration between the National Park Service and Smithsonian Gardens to ensure that the American elm still graces the Washington, D.C. landscape.
-Jonathan Kavalier, Smithsonian Gardens Supervisory Horticulturist
As Abraham Lincoln once said, “We cannot consecrate-we cannot hallow-this ground. The brave men, living and dead, who struggled here, have consecrated it, far above our poor power to add or detract.” In honor of Veterans Day in 2010, Brian Thacker, a recipient of the Congressional Medal of Honor was joined by representatives from the Medal of Honor Foundation, the National Air and Space Museum, and many veteran Smithsonian staff and volunteers to dedicate The Medal of Honor Tree on the grounds of the National Museum of American History (NMAH). Traditionally, red oaks (Quercus rubra) lined the north side of the museum. However, over time many of these trees were lost. To fill in the spaces left by the missing trees, Smithsonian Gardens collected trees from placed of historic significance to the United States such as the Lexington Green, the Trail of Tears, and the Manassas Battlefield. Brett McNish, Supervisory Horticulturist with Smithsonian Gardens, originally had the idea to seek out these historic trees and in conversation with a close friend in the museum community came up with the idea for the Medal of Honor Tree.
The tree commemorates recipients of the Congressional Medal of Honor. This award was created on July 12, 1862 when the bill S.J.R. No. 82 was signed into law by President Lincoln. The law designated that Medals of Honor were to be “presented, in the name of Congress, to such non-commissioned officers and privates as shall most distinguish themselves by their gallantry in action, and other soldier-like qualities.” Following the establishment of the Medal of Honor, soldiers quickly began receiving the medals for their valiant efforts in battle. The largest number of Medal of Honor recipients in one day of battle (120) took place at the Battle of Vicksburg on May 22, 1863. Since its creation, 3,463 service men and women have received the Medal of Honor. A variety of individuals have received the Medal of Honor representing the complex fabric of our nation. Medal of Honor recipients include one woman (Mary Walker), eighty-seven African Americans, forty-one Hispanic-Americans, thirty-three Asian-Americans, and thirty-two American Indians. Since 1918, Medals of Honor can only be given to members of the U.S. Armed Forces. However, exceptions have been made in special circumstances. Sixty-one Canadians, for example, hold the Medal of Honor, many of them from actions in the American Civil War. While the Medal of Honor now must be given to a member of the U.S. Armed Forces, they do not have to be U.S. citizens. The most recent Medal of Honor was awarded to Captain William D. Swenson on October 15, 2013.
To dedicate the Medal of Honor Tree, consecrated ground from 16 battlefields relating to 11 different wars that the United States was involved in were collected and added to the soil at the base of the tree. McNish discussed the immense task of collecting soil samples from these battlefields: “My goal was to get at least one soil sample from every war the US fought. Then it came down to what was possible to obtain. I think I came close to getting most of them. It took me about six months to get everything.” The process of collecting the soil involved many helping hands from the USDA, Department of State, Department of Defense, the American Battle Monuments Commission, and others, along with “a hefty FedEx bill” McNish noted. He created little collection kits made out of heat-resistant plastic containers.
A number of interesting stories grew out of the soil collection project. The soil collected from Luxembourg was from General George Patton’s grave at the Luxembourg American Cemetery and Memorial. The soil from Iwo Jima had its own history; it had been previously been collected by a Marine who visited the island on a pilgrimage. The soil then made its way to numerous veterans who took a little of it for themselves. McNish received the remaining soil from a retired Air Force officer in an airport VIP lounge. Then U.S. Ambassador to the Republic of Korea, Honorable Kathleen Stephens, collected Korean War soil from the Pusan Perimeter, an area that witnessed some of the first fighting of the Korean War. Soil from Haiti was collected by a group of Smithsonian curators working on post-earthquake relief for Musée National d’Haiti (the National Museum of Haiti). Because of difficulties mail, obtaining soil from Afghanistan was very difficult. The soil went through numerous hands before it was finally spread under the tree by an SI employee who had just returned from a tour of duty in Afghanistan.
Since its planting in 2010, the Medal of Honor Tree at NMAH is decorated every Veterans Dhistoay with a large red, white, and blue ribbon with a yellow center to highlight its significance in remembering the sacrifices of our nation’s service men and women.
-Mattea Sanders, Smithsonian Gardens intern
When people walk through the landscapes of Smithsonian Gardens, they often take pleasure in the beauty and majesty of the trees that are found throughout. The large spreading canopies, colorful spring and summer blooms, and brilliant autumn colors make for a feast for the eyes. Although we take great pride in the appearance of the trees here at Smithsonian Gardens, we also manage them for the numerous benefits that they provide, many of which are often not recognized.
Urban trees provide myriad contributions to the areas where they grow. Some of those benefits include:
- Storm water runoff and flooding reduction. It has been found that trees absorb the first 30% of most precipitation events through their leaf systems, and up to another 30% can be absorbed and held by their root systems.
- Traffic calming. Research shows that tree lined streets have fewer and less severe traffic accidents than those with no trees.
- Reduction of air pollution. Tree crowns capture and trap air pollutants, including automobile exhaust gasses and particulate matter. The severity of asthma and other negative health impacts are reduced in the presence of trees.
- Carbon sequestration. Trees absorb and retain carbon, thereby contributing to the reduction of greenhouse gasses. A US Forest Service study found that the average annual carbon sequestration of urban areas in the U.S. is approximately 26 million tons totaling a $2 billion value.
- Lowering of air temperatures. Urban areas can become extremely hot, as all of the concrete, asphalt and other hardscapes absorb heat throughout the day. In areas with trees, air temperatures can be reduced by 3-10°F, and properly shaded neighborhoods can realize energy cost savings of up to 35%.
- Improve your health. The findings of one study show that areas that have many trees can lower blood pressure, have a calming effect on teens and adults with ADHD, and contribute to overall emotional and psychological health.
- Add to property values. Realtor based estimates of street tree versus non-street tree comparable streets show a $15,000-$20,000 increase in home or business value.
So, the next time you’re enjoying the trees here at Smithsonian Gardens, remember all of the wonderful and helpful things they’re doing for us!
-Greg Huse, Smithsonian Gardens Arborist and Tree Collection Manager
This year, Smithsonian Gardens is pleased to be hosting its second annual Arbor Day Tree Planting Celebration! Although we have a great diversity of tree species here at the Smithsonian, we are always looking to add more to diversify our collection. There are many wonderful exotic, non-invasive species that are well-suited to the growing environment in the Washington, DC area. However, we are currently concentrating on adding more native tree species. This year, we have chosen two different natives to plant.
Carolina Silverbell (Halesia tetraptera)
Carolina Silverbell is a native hardwood understory tree that is typically found along slopes and streams in ravines in hardwood forests. They favor north and east-facing aspects with moist, well-drained acidic loam soils. They thrive in full and partial shade and have a core range in the southern Appalachian Mountains, but stretch as far as eastern Oklahoma, northern Florida, and southern Illinois. This tree typically grows to be 30-40 feet, but can grow as high as 80 feet. Its primary feature is beautifully bell-shaped white flowers that hang in clusters and are borne in the spring.
White Fringe Tree (Chionanthus virginicus)
The White Fringe Tree is another native hardwood tree that is found in its natural range which stretches from southern New Jersey to Florida, west to Texas. The species is very variable, and no two trees seem to be alike in all characteristics. The Fringe Tree can grow in a variety of conditions, and is cold hardy to minus 30 degrees Fahrenheit. As with the Carolina Silverbell, this tree’s most striking feature is the flowers. Six to eight-inch fleecy white, fragrant flowers appear in May and June and make this a beautiful addition to the landscape.
On Arbor Day, Friday April 26, we will be having two tree plantings. The White Fringe Tree will be planted at the Anacostia Community Museum, and the Carolina Silverbell will be planted at the National Museum of Air and Space, on the south side of the building adjacent to the observatory. The Smithsonian Gardens’ Arborist and other horticulture staff will be on hand at the Air and Space event to demonstrate proper tree planting techniques and to answer questions. The planting will take place at noon. We hope you can join us!
-Greg Huse, Smithsonian Gardens Arborist