Treasure At Home
Japanese black pine bonsai. Photo: Wikipedia commons
In Japan, the black pine (Pinus thunbergii) holds a deep cultural significance as a symbol of strength, endurance, and longevity. Japanese folklore speaks of it as a tool to bridge the gap between the mortal and spiritual realm.
These pines are left in pots outside homes to welcome in the new year, planted in traditional Japanese-style gardens, and painted in theatre backdrops.
During World War II, an incarcerated Japanese-American man named Juzaburo Furuzawa was even sent Japanese black pine seeds from his relatives as a sign of resilience. He grew the seeds in a tin can, and the now 84-year-old bonsai still exists today.
One of the most iconic conifers used for bonsai, Pinus thunbergii is prized for its vigor, its thick, plated bark, and its deep coloration. It was widely planted throughout Japan as a street tree, along the coast, in gardens, and as a privacy screening.
In the wild it plays several important ecological roles. Its deep roots knit sandy soil together; the tree provides protection against extreme weather; and evergreen branches diffuse high winds, allowing unique coastal plant communities to form.
Terror Overseas
However, this prized “king of bonsai” has brought chaos to North American shores. Here its vigorous growth forms widespread infestations in ecosystems defined by full sun and well-drained soil. In the Cape and Islands region, our globally unique grasslands and heathlands offer ideal habitat for this non-native pine.
Japanese black pine infestation. Photo: Rich Couse
Japanese black pine was first brought to the United States in 1855 and was then introduced to the Cape and Islands in the early 1900s. It has since spread to open areas such as roadsides, coastal margins, and disturbed sites. Initially intended to be used for dune stabilization and as a windbreak, this aggressive conifer proved to be a little too good at its job.
Many coastal Northeastern states have recorded observations of Japanese black pine spreading into wild areas. Natureserve Explorer lists plantations in five states: Delaware, Massachusetts, New Jersey, New York, and Rhode Island. But iNaturalist, EDDmaps, and USDA data shows observations not just across those five states, but in South Carolina, North Carolina, Tennessee, Virginia, Ohio, and Maryland as well. Observations often feature more than one individual specimen.
Delaware recognizes Japanese black pine as invasive and has spent more than a decade removing it from coastal parks. In 2009, aerial surveys showed that Japanese black pines dominated up to 40 percent of the coastline.
Our neighbors at Nantucket’s Invasive Plant Species Committee and the Town of Nantucket Conservation Commission have designated Japanese black pine as a highly invasive species. The Linda Loring Nature Foundation has put considerable effort into removing Japanese black pine in a grassland restoration project since 2018. They have seen their work pay off as rare grassland species emerge near the restoration site.
Reproduction
Japanese black pine with cones. Photo: Robyn Graygor
A single tree can produce hundreds of cones each year, each holding as many as 55 seeds. Germination rates are high, and seeds can persist in the seed bank for years.
Japanese black pine typically takes 10-20 years to reach full maturity but can begin reproducing in as little as four years. Pines are monoecious, meaning both male and female cones develop on the same tree. Male cones release pollen and are soft and short-lived. In the early spring, you might see clouds of pollen floating off of these alien-like cones.
Female cones begin their two-year life cycle as small pink buds clustered on the tips of new shoots. They collect wind-blown pollen from the male cones in the spring, and after being pollinated they turn green, fuse together, and bend downward to enter dormancy through the winter. In their second spring and summer, the cones elongate and begin turning brown as the seeds mature. By the second fall and winter, the cones turn woody and crack open to disperse little winged seeds.
A Fleeting Reign
Despite its quick claim on the landscape, Japanese black pine often succumbs to insect pressures soon after it reaches maturity. There are a variety of stressors that cause these pines to die: sawyer beetles, European pine tip moth, blights, rusts, cankers, and needle cast.
Our native black turpentine beetle (Dendroctonus terebrans) bores into the lower trunk and acts as a vector for blue-stain fungus (Leptographium sp.) and the pinewood nematode (Bursaphelenchus xylophilus), which feeds on the vascular system of non-native pines.
Pinewood nematode (Bursaphelenchus xylophilus). Photo by Y. Mamiya, Bugwood.org
The resulting rapid death leaves groves of highly flammable standing dead wood behind, making them a serious public safety concern.
Identification
Japanese black pine can fly under the radar of the untrained eye. It resembles our native pitch pine (Pinus rigida), which is an important component of our coastal canopy layer. Pitch pine has evolved to grow alongside native plants and wildlife on Martha’s Vineyard, similar to how Japanese black pine has evolved to be ecologically important in Japan.
There are few main ways to differentiate between these pines. First, look at the needles. Pitch pine needles come in bundles of three, whereas Japanese black pine needles come in bundles of two.
Japanese black pine needle bundle. Photo: Robyn Graygor
Pitch pine needle bundle. Photo: Keith Kanoti, Maine Forest Service, Bugwood.org
If you’re still not sure, look at the tips of the branches. In the winter, Japanese black pine will have bright white terminal buds that are covered with dense, woolly hairs. By the spring, that bud will break its dormancy and begin extending to create a woolly elongated shoot or “candle.” This is quite different from a pitch pine, which has a resinous, brown terminal bud.
Japanese black pine winter buds. Photo: John Ruter, University of Georgia, Bugwood.org
Pitch pine winter buds. Photo: Wendy Cutler
Pitch pine cones also have scales with distinct thick spines, which makes the cone prickly. Japanese black pine cones are smaller and smoother and may have small points that are not as noticeable as the pitch pine.
Japanese black pine cone. Photo: Robyn Graygor
Pitch pine cones. Photo: Ansel Oommen, Bugwood.org
Management
Japanese blackpine seedlings under three feet tall can be pulled or clipped. If you are only dealing with a few trees that aren’t in a hazardous location, girdling may be an easy option. These isolated trees will not pose much of a fire risk. However, it may be better to cut down expansive groves that are more hazardous to human health.
Unlike many invasive trees, Japanese black pine will not resprout vigorously after being cut. So conveniently, mature trees can be cut down and chipped without risking vegetative spread. Cutting should be done between October and March, when bats are least likely to be using trees as roosting sites. There are state-mandated restrictions on any pine removals during June and July when female bats may be roosting in trees with pups.
Pinecones can be clipped from branches and gathered from the ground. All pinecones should be disposed of as garbage in black plastic contractor bags to avoid further spread.
Replacements
The following native trees can serve an alternative planting/replacement for Japanese black pine:
Pitch pine (Pinus rigida)
Red cedar (Juniperus virginiana)
The following native shrubs can also be used:
Common juniper (Juniperus communis)
Beach plum (Prunus maritima)
Bayberry (Morella caroliniensis)
Groundsel tree (Baccharis halimifolia)
Shadbush (Amelanchier spp.)
Carolina rose (Rosa carolina)
Virginia rose (Rosa virginiana)
