This is information based on the choice of host trees
Oaks Quercus robur, Quercus ilex, Quercus coccifera
Hazelnuts
Other varieties – stone pines
General Principles
In experiments done to ascertain where the truffle gets its carbon for growth, this experiment found that there was little from the soil around the truffle, and most of the food from the tree comes as simple sugars. “It appears evident that Tuber ascocarps are dependent on their hosts throughout their development. These results contradict the statements of well-recognized truffle handbooks and could be of some importance for improvement of truffle cultivation methods, for example, through using caution regarding tree pruning at truffle primordium production and during truffle growth.” Source.
Pruning early after the truffle is harvested seems current best practice. On the WA Govt Truffles site however it suggests that “both hazelnuts and oaks are best pruned in autumn or spring. Pruning should be undertaken in dry weather where possible to reduce the risk of fungal infections to the pruning wounds.”
Marcos Morcillo has a good blog entry here and he suggests differently
“As a rule, pruning will start in the second or third winter, depending on the tree’s development. The holm oak usually forms two or three dominant trunks, which it is better to cut from the beginning when they are young and still small in diameter. Pruning has traditionally been carried out at the end of winter, but in climates where trees grow too fast we recommend green pruning in summer, because pruning at this time limits the tree’s vegetative growth.”
Acidification of soil can come from from pruned vegetable matter. Rotting leaves, chipped branches and mulch all lower the soil pH. So clearing these and fallen leaves also ensures that pests are less likely to breed. Some truffieres leave the leaf litter, eg. Truffle & Wine Co in Manjimup.
Photo.
Auxins (plant hormones) produced in the twig’s terminal buds stimulate root growth. Gibberellins (plant hormones) produced in the root tip stimulate canopy growth.
The tree balances root growth versus canopy growth by these hormones. Soil factors that limit root growth will in turn influence canopy growth.
Storm damage or excessive pruning may reduce auxins, slowing root growth. Following storm damage, trees often put on heavy growth of water sprouts due to a low auxins/high gibberellins ratio (coupled with unobserved, limited root growth). This is followed by a decline in the canopy caused by the reduced root growth.
Author: David Whiting Colorado State University Extension
Canopy Management
Hazelnut trees are commonly grown to a vase shape, a V with one main trunk.
They have a natural tendency to form a bush, with several stems and a bushy canopy. Pruning back to a main stem after the third year will still allow you to choose a parallel shoot if the main one becomes damaged. The reports from Western Australia say that “Several growers are allowing two or three ‘trunks’ to develop as insurance against the single trunk being damaged and leading to death of the entire tree”. However trees in Europe were often ‘coppiced’ with only a few seasons disruption to full production.
Oak trees are usually grown with one main trunk and are gradually pruned up the stem so that you, and the truffle dogs can move clearly around the tree without getting eye damage. Canopy pruning is again an open V so that sunlight and water can move through. Air flow is also important to minimise diseases growing in damp dark areas. Starting with the right variety of oak, one that doesn’t show a tendency to ‘weep’ will such as Quercus ilex ilex can save a lot of work in future years. Because oaks such as Quercus robur can grow very large and with considerable spread, pruning out the tops is often the only way to ‘open up’ an established orchard. This has become accepted in European truffières but with our relatively young trees, is still untested and viewed with fear of disrupting production.
Again, Marcos says “Note that Holm oak leaves can stay in the tree for over 3 years, but the old leaves just breathe and waste sugars produced by the new leaves, so competing with truffles for nutrients. It is advisable to prune trees inside the canopy, so that this is aerated and permits rain to pass through it and wet the soil. Otherwise, the Holm oak tends to form an umbrella and gather rain water at the base of its trunk as a funnel.
It is now known that the truffle extracts all its carbon and sugars from the tree, which is why it is necessary to maintain a tree healthy and vigorous. No heavy pruning should be carried out that curbs the tree’s development or significantly impairs its photosynthetic capacity. Therefore, heavy or green pruning should be carried out, above all, during the early years, before entry into production. Once production begins, pruning should only be done at the end of the truffle gathering season (end of winter), to generate new shoots and new leaves with a higher photosynthetic rate.”