by Josh Spencer
Tree sculpture, pleaching and grafting make use of the biological principal of inosculation.
In nature inosculation occurs when branches cross and rub in the wind, wearing through the cork, phelloderm, and pholem layers, exposing the vascular cambium. Being tissues of the same hardness and cohesion on both branches they will both wear to the cambium at the same time. Both branches cambium being in contact will cause new growth not between the two, but to the outside edges, eventually binding the branches. As the growth continues, the two will share sap and grow as one.
Inosculation can also conjoin separate specimens, joining their vascular systems. A hedgerow, for example is a series of plants, usually of the same species, planted in line and grafted together to grow as a unified organism. The vascular tissue of each plant essentially pools the resources with the rest.
Grafting is a horticultural/agricultural use of inosculation, it is often used as a type of asexual reproduction, “surgical” repair of injured plants, and hybridization of species for desired traits.
Asexual reproduction via grafting involves planting a compatable species with rapid root growth and allowing it to spread its roots for several years. The plant which is to be propagated has a section of the shoot system removed when dormant (usually). This is the plant scion. The scion, depending on the technique and situation, may be as much as the whole shoot system or as little as a section of budding axil. The scion and rootstock are cut to expose the vascular cambium to one another and are bound together to inosculate. A wax seal is often used to prevent infection at the grafting site. The scion will grow with the vigor of the rootstock plant, thus producing an adult offspring in greatly accelerated time as compared to propagation by cuttings.
Grafting may also repair otherwise irreparable damage due to root loss or girdling ( amputation of the phloem from root to shoot system). In the case of root structure damage, several saplings (of the same variety as the damaged plant) with healthy roots are planted close to the ailing plant. The saplings are pulled into contact with the ailing plant, their tops are removed and they are grafted on.
The saplings become root donors to the ailing plant. This is known as inarch grafting
In a girdled plant, a bridge graft can save the life of the plant. Several scions are be prepared from branches of the same tree, and cut to replace the phloem and/or cambium which has been lost in the girdle.
Grafting is often used in hybridization programs in order to produce flowers in less time than by seed propagation alone.
Purposeful human inosculation, known as pleaching, of branches, trunks, or roots, sometimes between several specimens, have both aesthetic, horticultural, and structural advantages.
The aesthetic and artistic purpose of pleaching is a beautiful and breathtaking medium. Notable artist Axil Erlandson grew dozens of living sculptures in the medium of pleached sycamores and other inosculate trees. Some examples of his “Tree Circus” are below:
Hobbiests are able to grow stools from manufactured forms. Three saplings of maple, sycamore or other suitable tree are planted and a jig is placed with wire ties to train the growth along the form. When the growth at the intersections are thick enough they are grafted together. The apical growth is allowed to continue up the form to the top, in order to form a mounting surface for the seat of the stool. After five years growth, the stools are ready to be cut and have a seat mounted.
The tradition of keeping large hedge mazes originated in medieval Europe, though not intended to actually trap or confuse those who walked it, the grandeur and impenetrability of solid, living walls was an impressive show of timeless affluence and high class. The pleached shrubs produced foliage so thick that the walls were opaque.
Modern living fences are both artistically and structurally sound, some are produced from trees crisscrossed into a chain link pattern, and grown together to make a living barrier.
In medieval Europe, flooding of inhabited regions made life difficult. The solution to this issue was building on orchards which had been topped and pleached to produce a continuous pathway across the tops. Structures atop these joined trees were safe from flood waters, received fruit and shade from the trees they were built upon.
Contemporary methods for growing a living house are more similar to the above mentioned grown stool project: Computer drafts of growing forms are input into a CNC printer. Reusable 3-D scaffolds are placed on site where a series of trees are then planted and grown, trained around arches pleached and ultimately integrated into an insulated contained living space made of bioplastic. The aim of the project is to reduce the need for consumable resources. The waste water from the inhabitants are used to sustain the trees. The trees seem to be more the framework, and the living space appears to to be the bioplastic covered with pleached saplings, vines and other cover growth.
Much of the appeal of this structure is its “green” appeal, a living home that providing shelter while acting as a carbon sink.
Another advantage sited is having lumber with an immune system is beneficial to prevent decay and insect infiltration.
Inosculation is a powerful mechanism that can create interesting curiosities, valuable horticultural techniques, and beautiful living sculpture.