Trees often decline for apparently no clear reason. However, if you look carefully at the conditions the tree has experienced over the years, the reason might be right there in front of you.
Although they don’t have child care, rent, or job considerations, plants do experience stress. Many factors affect trees adversely, and when compounded over time, can eventually lead to their decline. Trees are long-lived and over a period of years may be subject to insect attack, disease, severe weather conditions, and other environmental effects, all of which can result in an accumulation of adverse effects on the physiology of the tree.
The root system is especially vulnerable to changes in the soil environment. Grade changes resulting in root damage from soil removal, or root smothering by addition of fill dirt, changes in water drainage, and mechanical damage to roots from trenching or construction projects are examples of non-living (abiotic) stress factors affecting root systems. Soil compaction from construction equipment, vehicular traffic, or foot traffic will reduce aeration of the soil, which is needed for healthy roots.
As important as roots are to tree health, the trunk is also key. Whacking the bark with a string weeder, mower, or just recreational hacking on the tree will create wounds that can admit fungal decay organisms, such as this wood rot fungus pictured below.
A tree with root or trunk problems will show thinning of the foliage in the canopy overhead, where there is more sky visible than leaves (pictured here in a sweetgum). If the problem is advanced, as shown here, the tree is too far gone to try to revive. Once young trees begin to decline, palliative action may help to reverse the trend, but unfortunately people don’t usually notice the situation until it is too late, and for a tree of this size, it simply isn’t possible to reverse the damage.
Prevention is key.
Trees are not like telephone poles that are content once in place. Trees are living organisms that need TLC, especially if it looks like there are fewer leaves present than the year before. Take special care to keep the tree well-watered according to the needs of the species, especially during the heat of the summer. Be sure that water from sprinklers does not hit the trunk, which can lead to decay. Mulching with wood, leaves, or other organic material will encourage the growth of fine feeder roots. Apply very light amounts of fertilizers, no more than 1 lb. of nitrogen /1000 square feet of root area in the early spring, and again in the summer prior to August. High amounts of nitrogen may stimulate the stressed tree to exhaust its energy reserves, so do not assume that “more is better.” Finally, some selective pruning may be necessary and desirable to remove dead and dying branches to improve the tree’s appearance.