Monday 19 July 2010
Few tree failures are as tragic as ones caused by girdling roots. This condition, caused by roots that have circled the main trunk growing to eventually strangle the tree, results in a slow decline and eventual death of trees in their prime.
This condition can occur with a wide variety of trees, maples, cherries, plums and pines are a few on the ones I have personally observed in the last few months.
Normal root systems extend from the root flare at the base of the main stem and move away from the stem like the spokes of a bicycle wheel. The roots that cause trouble, circle around the tree and constrict the main stem. Tree roots that cross other roots further away from the main stem cause little damage and my even form unions or grafts that result in no damage at all.
If you let the girdling roots go unchecked they will eventually cause the tree to die back and decline to the point of failure.
Fortunately you can easily observe tell tale signs that are indicative of root problems on your own trees.
Trees should have a basal flare where the main stem meets the soil surface. This sometimes pronounced swelling should lead from main stem to root in smooth curve.
Flattening of one side of the stem can indicate a buried root that is pressing on the main stem and causing stress on the trees vascular system. The root actually compresses the tissues of the tree preventing the movement of water up the stem and nutrients down to the roots. You may even see decline on that side of the tree. Small leaves and reduced growth on one or more sides is another typical symptom. If you are able, grasp the tree and slowly shake or try to move it, it should be firm and not rotate. Small trees with girdling roots will move like the stick shift in a manual car.
Occasionally, the tree will not display any outward obvious symptoms yet will fail when extreme weather conditions overwhelm the trees circulatory system. Periods of drought or extreme heat can result in this type of failure. Once the tree has failed a close examination will reveal the obvious signs of girdling roots. Take a look for these telltale signs:
Large roots that are visibly crossing the trunk of the tree
Lack of typical root flare on one or more sides of the tree
Yellow or smaller leaves on one side of a tree
Recessed, inverted or flattened root flares that curve inward like the point of a pencil
Instability in small trees when manually shaken or pushed
I.S.A.Certified Arborists are knowledgeable in identifying and correcting girdling root problems. Take the time to consult with your Certified Arborist if you suspect your tree has rooting problems. You may be able to limit the damage caused by girdling roots and prolong the life of your tree.
Thursday 15 July 2010
Dutch Elm Disease, a typically fatal vascular fungal disease of North American elms, has been around a long time. It was first described in the 1920's in Northern Europe but soon made its way to North America and was wide spread in Eastern North America by the 1950's. Shade tree committees and tree surgeons alike mobilized or try prevent or slow the spread of the disease. Depending on climate and success in controlling elm bark beetles, a vector for spreading the disease, there were some successes. There were however tremendous losses in areas where the type and behavior of elm bark beetle was not conducive to control or where people were slow to organize to control the spread of the disease. While elm bark beetles are the primary vector for spreading the fungal disease they need habitat that is suitable for them to survive and thrive. Native elm bark beetles have a life cycle that is limited to one generation per year and they overwinter by burrowing into the bark at the base of elm trees. This leaves them susceptible to control methods that target them while they are overwintering. European elm bark beetles have a different life cycle that does not allow them to be controlled using these methods. However European elm bar beetles, do not survive extremely cold winters and this has prevented them from migrating much further north than the State of Minnesota. Winnipeg, Manitoba along with other Western Canadian cities now have the largest intact urban elm forests in the world. The survival of these forests would not have been possible without cost or the ongoing efforts of generations of concerned professionals and citizens alike. These costs are minor compared to the value of the resources protected.
But what lessons have been learned from this on going battle? Beyond the species and disease specific lessons, the need to actively care for and manage urban trees and the greater urban forest has been the most important lesson learned. Many of the current generation of I.S.A. Certified Arborists had there first experience in arboriculture in the battle to fight Dutch Elm Disease.
The second great lesson learned is the necessity for diversity in our urban plantings. In some areas at the height of uncontrolled Dutch Elm Disease epidemics, towns and villages lost in excess of 50 percent of their forest canopy. The planting of single species urban forests should have stopped but this was not always the case. In many areas towns and villages are now losing their replacement canopies of ash to emerald ash borer.
The third lesson that should have been learned is that trees add tremendous value to our urban environment. Not only the intangible “feel goods” but real dollars and cents benefits. Increased property values, effects on heating and cooling, storm water retention are just a few of the benefits that we can actually calculate.
I.S.A.Certified Arborists are knowledgeable in tree preservation, selection and planting. Take the time to consult with your Certified Arborist before you undertake tree planting and your landscape will maintain it's diversity and value for years to come.