Yamadori is a term used by the Japanese to describe trees collected from the wild. A yamadori tree is a wild tree growing in the mountains and sculpted by nature. They are great subjects for bonsai; in fact, once they've successfully been moved and replanted in a container for development, they can often carry large price tags and are highly sought after by bonsai hobbyists and professionals.
Whether you’ve had the chance to visit the mountains and experience the presence of a large yamadori juniper in its natural habitat, or only ever seen a yamadori bonsai in a container at an exhibition, you may still appreciate these thoughts and considerations on how a juniper grows and what makes them such great subjects for bonsai.
Lets start by discussing the Scofield Juniper, the longest-lived of all known and accurately-dated juniper trees; it was situated near Sonora Pass in the Sierra Nevada Mountains and began life around 1520BC. The cross section shown in Figure 1 is about 5 feet across from the bottom where the tree started to the top where it died around 1,155AD at an age of 2,675 years. Having been long-deceased when discovered, the tree was cored by the Oxford Tree-Ring Laboratory staff and with permission from the forest service they cross-sectioned it. While the age is impressive, it's actually the shape of this cross-section that is of particular interest to the bonsai enthusiast. It demonstrates the principle adaptation of juniper trees that allows for fantastically-shaped trunks and branches: the growth of lifelines on isolated sections of the wood.
Figure 1. A cross-section of the Scofield Juniper from near Sonora Pass in the Sierra Nevada mountains of California.
We can trace the story of the tree through the shape of the cross-section: it shows that for about 100 years the tree grew with nearly-complete bark coverage. Then a small section between two live sections on the upper left side died, resulting in a narrow strip between the two strongly-growing lifelines. Over the next 400 years that strip became a narrow channel between the parts of the tree that made it past 500 years in age; the majority of the rest of the lifeline coverage on the lower-right, weaker side died during that period. The section is showing fewer than 600 rings on about 75% of the circumference of the tree. Then the tree grew for another 400 years with 4 separate lifelines, appearing like fingers heading upward in the figure, before two of those eventually died leaving a strong lifeline and a relatively narrow and weak one. For the last 1600 years of its life the tree seems to have found a better resource for nutrients and was able to grow strongly along the last lifeline.
Lifelines on a juniper are formed like strings running directly between particular roots and their corresponding foliage. When the branch grows strongly it allows the corresponding root to grow more strongly and the converse is true as well. As the tree ages, strong-growing branches create more wood along the lifeline connecting to their roots than weak growing branches, causing the irregularly or even ribbon-shaped trunks. When weak branches die, the section of the trunk connecting them to the roots dies, and eventually the bark falls off leaving the wood exposed. It is possible to re-direct the lifeline slowly from one trunk section or root to another, and this may account for some of the twisting that we see in wild trees.
The forces that shape the lifeline in the juniper’s natural environment are numerous: wind, snow, sun versus shade, rock crevice constrictions versus open soil, and drought among many others. At the same elevation and location some trees will grow relatively straight while others will grow in a twisted and gnarled mess of wood and branches.
In Figure 2 we see an example of a Sierra juniper growing in a rock crevice at about 8,000 feet elevation. The tree is situated on the southwest side of a large granite ridge that is in the middle of a larger canyon. There is an obvious wind influence in the tree’s foliage mass indicating that the wind primarily comes from the right of the foliage mass. The lifeline wraps from the leeward side of the foliage down under a large mass of deadwood that protects it from much of the damaging wind, ice, and snow.
The remarkable things about this particular tree other than the present pleasing shape is the remnants of what seems to be the original base of the tree on the left. The wood is completely separated from the ground: did it fall over and survive or did the base of the trunk rot off? The lifeline many years ago would have been more to the left of the photo.
Figures 3 and 4 show another Sierra juniper sculpted by wind and snow. The tree is about 7 feet tall and has the shape of a bonsai after many years. This tree shows that under harsh conditions we see that the lifeline on the top of the tree or on the windward side is frequently killed while the lifeline that is more protected is the portion that soldiers on, gaining protection from some of the environmental harshness from the deadwood sections. Where the wind and snow conditions are particularly harsh the successive killing of portions of the lifelines can cause the live sections of some branches and trunks to seem to melt over the dead sections that they neighbor.
The photo at the top of this article is of a tree that started it’s life on one side of a boulder but found that the shelter on the other side was a better place for growing leaves. The process of getting from one side of this boulder to the shelter on the other side probably took a long time. The tightness of the trunk to the rock is the most remarkable part.
This last photo shows a tree that grew relatively straight when it was younger but has added more twists as it ages. Junipers start life straight and round, but often end up making fin shapes and wings as hard angles get closed up by decades or centuries of new wood growth. The lines in the deadwood tell the story.