Collecting wild trees (yamadori) for bonsai is one of the best ways of acquiring new material for development as bonsai. Though it is unlikely you will ever collect a 'ready made' bonsai, well developed trunks with naturally created trunklines can be acquired that might otherwise take decades to produce from cuttings or nursery material.
The thrill of finding a wild collectible tree, can only be beaten by the feeling of accomplishment when the tree is finally collected and bought home. The reward of a unique yamadori bonsai is a worthwhile prize for spending days, months or years searching for potential material.

This isn't a 'how to' article; however it does discuss some of the most important aspects of collecting trees for bonsai.

Over the past few years many of us have seen some of the beautiful yamadori that has been displayed on the internet on websites and forums. Contorted and striking Pines and Junipers from the Alps, Larch with meandering almost snake-like trunks and heavy-trunked deciduous trees.
Unfortunately, a series of photos describing the evolution of a yamadori on a forum does not convey the skill, knowledge and patience of the collector. It does not show the true time-scale of developing a yamadori nor does it show the daily care necessary just to keep a collected tree alive for the first few years after collection.

This article isn't a tirade against those who wish to learn how to collect wild trees nor those (like myself) that do. However, a recent post at the Internet Bonsai Club where an enthusiast had ripped up an ancient Pine from a rock face, leaving almost all of the rootsystem behind and a tree condemned to die, illustrated that there is a need to warn enthusiasts that collecting trees and yamadori is not simply a case of digging up a nice wild tree and putting it into a pot where it will miraculously turn into a world class bonsai.

Many collected trees have only ¼ or (much) less of the total rootball lifted with the tree and bought back home. The rootsystem of any wild tree can spread a considerable distance from the trunk; to dig up and bring home the whole rootsystem, or even a large part of it, is often impossible, would also be physically beyond the majority of us. Removing any portion of the rootsystem of a tree (as we all should know) puts a certain amount of stress on the health, vigour and survival of that tree.
Anyone who was to rootprune away 75% or more of the roots on one of their bonsai would (or should) have serious concerns for the health of that tree. If you add other factors integral to collecting wild trees such as the time the roots are exposed to the air while the tree is taken home, possible inferior health and vigour in comparison to a cultivated tree (bonsai), simultaneous removal of branches and trunk chopping, changes in environment and climate, the risk of stress and death on the collected tree is increased tenfold.
For these reasons, a collected tree must be treated like a fine piece of antique porcelain; for it to survive, positioning, soil quality, watering, feeding, humidity and temperature exposure must be of the highest standard. The exact nature of this care is hugely dependent on the species of tree collected, the climate the tree has been growing in and the your local climate where the tree is to recover, the vigour of the individual tree and even the soil the tree was growing in before collection.
There is no doubt that trees have been collected and survived with minimal roots, at the wrong of the year or with minimal care and attention. In these cases, survival of the tree is an exception rather than the rule and the trees survival is due to great skill of the collector or more commonly, large amounts of luck.

It should be noted at this point that there is a huge difference between a well-collected, healthy, vigorous yamadori and a tree that has barely survived collection through lack of knowledge of care and skill of the collector. A poorly collected tree might survive and produce a few leaves and shoots the following year but will be practically useless if it lacks the vigour to recover enough to be developed into a bonsai.
Some of my earliest collected trees that I recovered from old gardens (while working as a gardener) would leaf out during each growing season but would barely grow. Any plans I had of growing a new branch structure or new section of trunk were completely unrealistic, as the trees would lack sufficient vigour for growth.

The correct skills needed to collect yamadori can be learnt by anyone; there are no mystical skills involved, just a lot of common sense and horticultural knowledge. Experience is also necessary; it not only teaches you the necessary horticultural skills but most importantly, it teaches you patience. Patience is a skill that means you are able to prepare a tree in the ground for a number of years before collecting it. Patience is a skill that teaches you not to plant your new yamadori into a bonsai pot as soon as you get it home. It also teaches you how to wait 5 years before even contemplating styling or wiring the tree.
The best way to learn how to collect trees is to start with old garden shrubs and trees or trees destined to be removed to make way for building development. Unwanted garden material can yield some excellent material for bonsai and in many cases will have been planted in relatively good quality, moisture retentive soil leaving a relatively small, easily collectible rootball. Most importantly (assuming you have the full permission of the land owner) if the tree does die, the loss is your own and you are not responsible for the loss of a tree from the wild.
Again, trees destined to be bulldozed for development are a good opportunity to gain experience; trying to rescue an otherwise condemned tree cannot be seen as morally or ethically wrong as long as permission of the landowner is obtained.

Learn how to recover a tree and how it reacts, not just in the short-term but over 2,5 or 10 years. Learn that working on a collected tree too early and inappropriate care after collection will either kill or slow the recovery of a tree considerably.
And finally, learn that collecting a tree from the wild is an art in itself. Appreciate that when you see Walter Pall, Wolfgang Putz or Harry Hirao display a beautiful yamadori bonsai, they are not just 'lucky' to find such material but are also accomplished horticulturalists.