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Last week we reviewed some root disease problems and symptoms that might be seen with thinning leaves and branches at the tree crowns (the top most range of branches.)
This column looks at the difficulties with construction and the effect of logging in an area on the remaining trees.
Construction around trees causes major disruptions to the tree roots, disruptions that can result in trees becoming hazardous. Again this week, Dennis Tompkins, certified arborist, has contributed to this column.
In order to understand the effect of construction on big tree health, it's necessary to imagine how the root structure looks underground. Many people believe that tree roots descend dozens of feet into the ground, balancing the big top of the tree with a similar underground mass. This doesn't happen. If you've ever seen the roots of a wind-rocked Douglas fir, you've seen the "pancake" like shallow wad they make. Roots are essentially shallow, even on big trees.
Most feeder roots that take up nutrients lie within two feet of the surface. They are located near the outer edges of tree root systems and usually extend well beyond a tree's drip line. Large anchoring roots located closer to the trunk typically extend down another two to three feet.
Soil compaction by heavy equipment, trenching for water or utility lines or changing the grade for landscaping can damage or cut roots. Also, grading, bulldozing, and rearranging or adding soil over a large area may change natural drainage systems. The resulting standing water or saturated ground can also weaken or kill trees. Extra soil piled up on tree roots reduces the oxygen available to the roots and often results in tree death.
Indications of problems caused by construction may not become visible for months or even a few years after the damage has occurred. Very large trees may die 5 to 10 years after the damage. For example, if over 30 to 40% of a root system has been affected, a tree's vigor may decrease over two years or more. It's possible to move into a landscape without knowing all the construction stresses trees have endured.
Weakened trees usually attract insects that tunnel through the cambium layer (the "green layer) just beneath the bark. Cambium carries the tree's vein system and must be healthy to provide the exchange of minerals and nutrients between the roots and the leaves (or needles.) Many of the insects that invade weakened trees are bark beetles, and they may eventually overwhelm the tree's remaining natural defenses and contribute to its death. Bark beetles are sometimes referred to as "nature's undertakers" because they generally go after trees that are destined for decline and death.
A tree that has previously been shaded will be exposed to sun when surrounding trees have been removed. Sunscald during the summer and even freezing temperatures in the winter can cause cracking or peeling of the bark. Decay organisms can enter the trunk through some of the wounds where bark has peeled. Disturbance of root systems can weaken trees remaining as buffers along the edges of logged areas. Again, such damage will attract bark beetles and other tree enemies.
Loss of protection from neighboring trees can also reduce a newly exposed tree's ability to withstand heavy gusts of wind, particularly during saturated ground conditions. This can be a very serious problem where root rot is also affecting trees. When the stand of trees was intact, nearby trees protected those with decay from winds that now could topple them.
If tree failures occur following a logging operation, hazard evaluations of remaining trees that have potential house or outbuilding targets should be considered.
So, if high winds make your family nervous, inspect the trees around your home. If any of the conditions are present, certified professionals are available to help homeowners evaluate the health and safety of their trees. It's better to plan ahead, because getting qualified help during and after a storm is often impossible.
Hortsense: Managing plant problems with Integrated Pest Management
