Japan is famous for three pine species, Japanese black pine (Pinus thunbergii), Japanese white pine (Pinus parviflora), and Japanese red pine, (Pinus densiflora). The focus of this article is on the latter species, that like its cousins, is an iconic plant in Japan, used in traditional gardens as a dwarfed tree, but more rarely as a bonsai subject. Moreover, since its wood burns very hot, it makes a great fuel for pottery kilns, and has been used in construction for its durability, strength, and lightness. It is closely related to the Eurasian mainland species, scots pine, Pinus sylvestris.
Pinus densiflora is a large coniferous tree growing to 35 meters, but is usually much smaller, not more than 20 meters or so. Specimens found on moister sites with richer soils grow to large sizes and their straight, red barked trunks are unmistakeable from a distance. Trees found on cliffs, rock barrens, or dry ridge lines with impoverished soils are far less stately, often standing no more than a few meters tall. The bark is a bright orange-brown color and peels off in paper-like sheets except older bark low on trunks which forms into plates and is silver-gray . The evergreen needles come two per fascicle (or bundle), are a dark green, and up to 12 cm long. Branching is tiered and upswept, forming a distinct, elegant look. Pollen cones appear in early spring, are conical and elongate and orange-yellow in color. The seed cones start at the same time and are yellow to purple in color. These female cones mature by fall and are small, not more than 6 cm long, occurring alone or in clusters. The winged seeds are about 1.5 cm long.
This is a widespread tree in Japan found from northern Honshu and southward to Kyushu and Shikoku. It is most commonly seen growing in low mountains and hillsides, but can be found up to 2500 meters elevation in parts of its range. Its typical habitat are dry ridge lines with poor soils that have been subject to recent disturbance as this is a colonizing species, and is usually one of the first trees to seed in after a fire or other disturbance. For this reason, you often see near pure stands of it here and there, no doubt due to forest fire. I’ve noticed it also colonizes abandoned mines on shear cliffs alongside other weedy pioneer tree species such as Mallotus japonicus and Rhus sylvestris. It is believed that in times past it was much more uncommon a plant since disturbance due to fire was very limited prior to human habitation. It is one of the few trees than can withstand growing in windswept rock barrens.
Where this species is found in mixed stands with Japanese black pine, Pinus thunbergii, the unusual hybrid called akakuromatsu (red-black pine) sometimes results (known under the Latin name. P. x densi-thunbergii). These hybrids have the red bark of P. densiflora while retaining the darker, more stout needles of P. thunbergii.
P. densiflora has long been used in traditional Japanese gardens as a dwarfed tree. In nature it is represented by three separate varieties, v. densiflora, the commonly seen variety in Japan, v. ussuriensis, found in Russia, and v. zhangwuensis, limited to China. In Japan there also is a very unique form, f. umbraculifera, called tanyoshou in Japanese. This tree sends out multiple trunks low on the tree and forms an umbrella-like crown – for this reason it is a favorite garden subject. All varieties sport bright red trunks and branches, as well as soft needles.
In times past P. densiflora was an important lumber species. Many of the remaining old temples contain akamatsu wood, in particular the beams since the wood is both strong and light, and highly resistant to rot. This resistance to rot made it important in bridge building in ancient times by virtue of the submerged wood standing the test of time better than most other trees. The reason for its durability is the wood’s high content of resins, which also makes the it very good as a hot burning fuel. To this day, P. densiflora firewood is preferred over hardwoods for pottery kilns due to the intense heat it can generate and the fact that little ash is left afterward. In times past the tree’s resin was collected and used in votive candles as well and the resulting soot itself was saved as a high quality ink. Historically it was also used in charcoal production.
An interesting relationship exists between this tree and the terrestrial orchid, Cephalanthera falcata. C. falcata is partially dependent on mycorrhizal fungi for its nutrition and the appropriate fungus species is found in P. densiflora‘s decaying needles. For this reason C. falcata is most commonly seen growing near red pine stands. One orchid grower told me that if I ever tried to grow this plant I should get some humus from under a red pine to inoculate the growing medium. I did attempt this once, but after a few seasons the orchid failed to come up. I wouldn’t call the experiment a failure exactly – it could be that additional humus added each year may have kept the orchid happy.
Like its cousin, Pinus thunbergii, P. densiflora has been under attack by the North American pinewood nemetode, Bursaphelenchus xylophilus, causing the condition known as pine wilt. A native long horned beetle known as the Japanese pine sawyer, Monchamus alternatus, is implicated in spreading these nematodes from tree to tree, sometimes wiping out whole stands. The nematodes live in the respiratory tract of the beetle and are spread from tree to tree as the beetles bore into the bark, depositing the tiny worms. It is not uncommon to see many dead and dying trees on hillsides – all victims of the beetle/nematode double punch. It is said that problems with pine wilt brought on by the invading exotic nematodes started soon after the American occupation of Japan after WWII. Logically, the nematodes were unwittingly brought over by the US occupying force.
The species epithet, densiflora, is derived from the Latin words densus, meaning dense or thick, and flos, meaning flower, rendering “densely flowered” – an odd designation for a non-flowering plant. Its Japanese name is akamatsu from the words aka meaning “red” and matsu, “pine” – giving the straightforward name “red pine” in English. Most often Japanese names are pretty darn obscure, but in this case their name makes a lot more sense!
Beyond the issue of pine wilt, this is a fairly straightforward tree in cultivation. It prefers well drained, acidic soils, but is likely to be more water tolerant than P. thunbergii since it is believed that in ancient times it grew along rivers. As with most pines, to grow well it requires full sun. It can handle both heat and cold well being found naturally from Kyushu and up to the very eves of Siberia. It is said to be cold hardy to USDA cold hardiness zone 4 with an absolute minimum temperature of -30 C to -25 C being the lethal limit, though I’d imagine that zones 6 and 7 would be optimal, at least in the eastern USA. The natural hybrid of P. densiflora and P. thunbergii, P. densi-thunbergii, is considered a good omen and so is planted in gardens throughout Japan, and should be cold hardy to at least zone 6.
Here is a unique and lovely pine species that deserves a place in any suitable garden. If you ever get the chance to see its bark glowing in the fading afternoon sun, you very likely will be hooked and want one for yourself.