By Dave Meadows
Pioneer Columnist
Rarely is poor plant health the result of one simple factor; the cause is usually a combination of living and nonliving stress factors. Primary agents first stress the plant and start the decline process, which predisposes the plant to secondary agents, such as pests and diseases. Tree stress and decline may or may not be deadly, but often these secondary agents get the blame while the primary agent goes undetected.
Early symptoms of stress and decline might include reduced growth, thinning of the upper canopy, abnormal foliage color, vigorous watersprouting, or premature leaf drop. The most common causes of tree stress are site and environment related. If a tree is not well suited for the site in which it has been planted, it is more likely to become stressed. A good example of this is birch trees, which are naturally found in bottomland, swamp fringe areas, where they have access to full sun and wet roots. This is a difficult environment to reproduce in a residential yard or garden landscape!
There are only five factors needed for tree survival — moisture, sunlight, nutrients, temperature and space. Trees suffer when any of these factors are in excess or limited. Poor drainage is often a contributor by creating an unfavourable environment for tree survival. However, excess or inadequate irrigation water is the most common problem associated with tree decline. Newly planted trees require 68 litres of water, per inch of tree diameter, each week. Therefore, a 3-inch caliper tree, requires 204 litres of water each week and the proper drainage to percolate that water!
Another issue leading to long-term tree stress and decline is planting too deep. Back in 2000 (Smiley and Booth, USA) discovered that 93 per cent of all professionally planted trees were planted too deep. This was primarily due to nursery stock being too deep in the containers prior to planting. Every tree that I have planted so far, twenty years later, still requires soil removal to find the correct position of the root flare PRIOR to digging the hole. Most trees are 3 to 10 inches too deep in the root balls and potted containers. Expect more on this topic in an upcoming Branching Out article this spring. It will be dedicated solely to this chronic tree planting problem!
The idea that rapidly growing trees are more tolerant to stress and resistant to pests and diseases is far from true. In fact, a large number of studies show that rapid growth can result in LESS tolerance and resistance. Another myth is the general belief that cultural practices, such as fertilization, often optimized tree growth and enhanced insect and pest resistance. However, it has been proven fertilization often increases tree susceptibility and actually reduces natural defences.
Hopefully, this article helps homeowners as well as contractors, understand the five factors required for tree survival and recognizing the complex interactions of primary and secondary agents that can confuse matters when trees show visible evidence of stress and decline.
Dave Meadows has been an ISA, Certified Arborist since 1996. Dave owned and operated Invermere Tree Care until his retirement this year. Dave also works part time for the District of Invermere, Public Works, helping with municipal tree care operations, and planting new trees for the Urban Forest.
