This week I would like to focus my garden column on the topic of tree biology. Aborist Phil Frazee has compiled these interesting notes for all us tree lovers out there.

In the area of root physiology and its relationship to developments in the tree canopy, Phil assures us that many of the problems that manifest themselves in the tree canopy crown begin below. Many instance of decline, loss of vigour, deadwood development, or death of trees can be traced to damage of the root system.

Trees establish a tap root in their early years but after seven years of age, begin to lose this system. In its place, the trees root system looks much like a wine glass on a dinner plate. The goblet is the canopy, the stem the trunk and the root zone the dinner plate. Research in the field of the tree root systems has consistently shown that the root systems in maturing trees rarely penetrate more the 18 inches to 24 inches in depth. The root system of a deciduous tree extends out 5-7 times the drip line of the tree. The root zone of a pine or native eucalypt can reach out as much as the height of the tree.

Root zones are comprised of 20% anchor roots and 80% fine hair-like absorbing roots. On germination a tree develops a tap root to stabilize it and reach down to higher moisture levels, roots are opportunistic and go to the source. If water is applied intermittently and near the surface the roots will stay at that level. Species that have a history of shallow rooting will, in urban or building sites, cause problems. Better to give maximum water penetration in the first three years of its growth and then ease off to very little water or none once the root system is established. However water needs to be in place to help the tree in times of drought.

Damage Control;

If the anchor roots are severed by trenching, cutting or crushed by compaction (vehicles, livestock, road building), then the risk of tree failure is increased proportional to the damage inflicted. There is a direct correlation between the decline of the canopy and limbs of a tree and damage to the root system. Some trees species will show this directly over the root damage zone, others show the die back on the opposite side of the tree.

Mulch Therapy;

In an effort to mitigate the effect of severe heat and loss of moisture after intrusion into the root zone the use of compost and mulch has proven to be of great benefit. Placing 20 mm layer of compost under the drip line followed by a top dressing of 75 mm of mulch works wonders for the tree. The compost and mulch must be of good quality that allows water to flow through it easily. (Not hydrophobic)

Organic Recycling

“Turn don’t burn” The addition of organic materials through mulch therapy provide the energy source for the mycorrhiza fungus that cohabits on and in the tree roots. These “good” fungi enhance nutrient uptake and drought tolerance by vast amounts thus greatly increasing the tree survival rates.

Tree Roots and Public Safety.

Best practices in primary root management help reduce the threat to public safety as well as improving the quality of urban tree assets of the community.

When root systems are entered for necessary installation of utilities, gas, telephone, sewer, water and other infrastructure, proven low impact options are available. Plan before you dig. Consult with a certified Aborist before losing a valuable tree of considerable appraised valuation and incurring expensive removal costs.

Trees do not always show immediately the effects of serious damage to their root systems. If best practices are not used during incursions into the root zone of a tree, it may take up to 7-10 years before it dies.

Before stressing established trees during activities such as construction, road building, excavations etc, prepare the tree first. (Like a pre-season training in footy)

In the years prior to impacting the tree and its root system, have it pruned by a certified Aborist to Australian Tree Pruning Standards. Create a tree protection zone around the tree with strong fencing out to the drip line or beyond. Use water and mulch therapy to build strength in the tree. Keep equipment, building by-products such as paint thinners, concrete slurry etc out of the root zone. Fence out all animals off the root zone to stop soil compaction, which will crush the life giving oxygen out of the soil. Use a strong barrier or electric fence to insure this.

It was interesting that Phil said you can’t feed a tree, it creates all it needs through the leaves!