Sunday 22 June 2008

Like Lightning Striking Again....

Like the lines of Lou Christies smash hit, “again and again and again”, every summer I see the tragic consequences of this all to common occurrence.

The people who track these things indicate that you are more likely to be struck by lightning that win the lottery. I know trees don't by lottery tickets but plenty of them get hit by lightning.

Its is extremely rare for a mature tree to survive a lightning strike with out major damage.

In my experience large single trees on rocky out crops get hit with lightning all to often. This is the preferred habitat for oak trees and they have long been listed as the tree most likely to be struck by lightning. In fact oak is the favored tree of Zeus, the Greek god of thunder, for just that reason.

Lightning takes the path of least resistance to the ground, this may be on the wet bark on the outside of the tree, or it may penetrate into the moist cambium layer and heart wood. The tremendous energy super heats the moisture in the tree causing it to explode. This can be quite dramatic, throwing splinters and debris for great distances. The force of the explosion can even break windows and in one case blew the wall paneling off the interior walls of the house.

More often than not the lightning flashes across from the tree into the houses electrical system causing extensive damage to appliances and electronics.

The solution to this problem is a simple as Ben Franklin's kite and key experiment.

Lightning protection in trees typically consists of a thick copper conductor running from the top of the tree to a ground rod driven deep into the ground. It sounds simple and it is.

The top of the conducting wire is attached to an air tip, a conductive rod that terminates the copper lead. The lead is held to the tree with bronze stand offs that are driven into the bark. If the tree is extremely wide or has more than one main trunk several leads may branch off from the central conductor. All metallic objects in the tree must be bonded to the central lighting conductor. This includes bolts and cables used to support the structure of the tree. Specialty hardware is used to connect the system together ensuring a good electrical contact.

Lightning protection, when properly designed and installed, can reduce the risk of lighting flashing across into your home.

Does this improved grounding of the tree make it more susceptible to lightning strikes?

Probably not, but it does make it more likely to survive a direct hit. The materials are expensive and the skills needed to install the system are beyond the average home owner. Have your certified arborist inspect large trees close to your house to see if they are candidates for lightning protection. The results will pay out more reliably than the lottery.

Saturday 21 June 2008

Bored to Death!

There are few trees that can rival white birch for its four season beauty in the landscape.

There are also few trees that can be so heartbreakingly disappointing when they suddenly fail. Growing up my parents had a large European white birch that gracefully dominated the front yard of our house. Every spring we would dutifully treat it to prevent bark borers.

One by one the birches in our neighborhood were removed after the slow process of dying back from the top down. Last year we took the birch down, not because of borers, it had gown so large that it no longer fit the landscape and was mechanically unstable.

The nemesis of most white birch trees is the bronze birch borer, Agrilus anxius, this North American beetle has caused extensive die offs of native birches in the past.

Most white barked birch trees are susceptible. European variety's are so prone to attack that they are not recommended for planting. In the wild birch trees prefer moist north facing slopes that allow them to have full sun on the crown of the tree and shade to keep the roots cool. This is a far cry from conditions most birches face in urban and suburban landscapes. Most birches in peoples yards are under stress. Stress makes birch trees attractive to bark beetle infestation.

The beetles lay their eggs on the rough patches of bark normally near the attachment point of branches. Eggs hatch and the larva tunnel into the cambium layer excavating zig zag tunnels around the tree cutting off the flow of sap as they destroy the trees vascular system.

Healthy trees may be able to wall the larva off by forming a callus layer around the insect and preventing it from excavating the tree tissue. More often the tree is stressed and slow to respond to the invasion and loses the battle. The callus tissue forms a lumpy mound over the larval tunnel that can be seen on the outside of the bark. The process from egg to adult can take a year or more and is dictated by the weather. Cold conditions slow the process down.

The result is active adult emergence and egg laying throughout the summer months starting in early June.

If you see the tops of your birch trees dying back you may have birch borers. Close examination of the dead branches will probably reveal raised tunnels under the bark can dark “D” shaped exit holes on the bark. Pruning out infested branches to below areas with any visible activity will be helpful. There are treatments available that can be applied to the bark or systemically to the root zone to limit the impact of the borers. Heavily infested trees should be removed from the area to prevent infestation of adjacent trees. Maintaining vigor and reducing stress factors present will be of great benefit. Properly mulching the area below the tree will help reduce root temperature and increase the vitality of existing plantings. Acting before you have any signs of borers will be of greater benefit than trying to catch up once they are present. The long term key to preventing birch decline is to chose resistant species and maintain the vigor of those that are susceptible. Contact your certified arborist for recommendations on birch trees to plant as well as maintenance regimes for your existing birches.