Trees for the future

By the time the still-vigorous remnants of the recent hurricanes and tropical storms began roaring through our region, there was little anyone could do to mitigate their fury. And once the rains and winds subsided, the evidence of nature’s power was clear. Watercourses had overflowed their banks, flooding streamside areas and washing away or simply drowning vegetation; and large, seemingly healthy trees had simply broken at the base or tipped over, exposing massive root systems.

But maybe once we’ve cleaned up, grieved for what’s been lost, and begun to adjust to the changing landscape, we can acknowledge that although the damage wasn’t fully preventable, there are some things we can do over time to help grow strong and healthy trees that will be better prepared to survive the assaults of future storms.

The recent flooding was unusual for this region. And unless you live or work in areas along streams or rivers that periodically flood, you may never think twice about the type of plant material that’s best suited to flood conditions. But you don’t have to be near water to know that wet or poorly drained soils won’t grow trees.

The types of soils typically found in urban sites pose some of the same challenges. Like flooding or excessive moisture, compaction displaces the oxygen in the soil, slowly suffocating plant roots. Immediate symptoms will include browning of the foliage and even early leaf drop. But this is an immediate stress response — it in no way indicates that the tree is totally lost. It’s best to wait until the following spring, when the new leaves emerge, to determine the true extent of damage. No one will venture to say for sure, but a general rule of thumb is that the chance for plant survival is reduced if it’s submerged for more than 72 hours.

The time of year when the flooding occurs also makes a difference. In general, plants are more flood-tolerant during the dormant winter months than during the active months of early summer. Our flooding came in early fall — a fair compromise, since the plants were neither in active growth nor fully dormant. Because their systems were already slowing down in anticipation of winter, the long-term effects may not be as great.

In addition, plants vary in their ability to tolerate tough conditions, and even the experts concede that there are gray areas. We need only look to bottomland habitat to see that many native plants survive and even thrive in these wet conditions. Flood-tolerant trees include red maple, birch, green ash, sweet bay magnolia, black gum, plane tree, pear, willow and bald cypress. Shrubs include button bush, tartarian, red osier, silky dogwood and winterberry holly. In the end, however, only time will tell what survives and what doesn’t.

The other piece of the recent weather equation that had disastrous results is wind. Wind combined with rain is what I call a “double whammy.” This is particularly true when a lot of rain falls — enough to fully saturate the soil — and then more rain arrives within a few days. But if that second rain comes accompanied by high winds, it spells trouble. The leaves provide resistance to the wind, putting the trees in motion. Eventually, the roots of a particular tree can no longer hold, and the trunk can’t withstand the gyrating motion. So it topples, either pulling up or breaking off entirely. Either way, it dumps the trunk, branches, leaves and all onto whatever lies below — a house, a car, a utility line or other plants. I won’t spend time here reviewing the multiple problems created when one of these behemoths falls, since I’m sure many readers have been there (and may still be there).

What concerns me, however, is that when an area sustains this level of destruction, even people who merely saw tree damage on TV may suddenly become wary and want all trees removed from their surroundings, “just in case.” As I see it, the potential for damage is a risk we take in order to maintain the important place trees have in our lives and our world. And rather than indiscriminately chopping them all down, we can learn to be more observant of the trees around us — learn what compromises tree health, how to recognize when a tree has become more of a liability than an asset, and when and where to seek help.

Overall tree health can be compromised in many ways. Weak branching and poor overall form — resulting from improper pruning, inappropriate plant selection for the site, and inadequate root development — are easily overlooked but have a definite influence on a given tree’s chances of having a long, healthy life. Too much or too little water, pruning, vandalism, topping, trunk wounds, filling or removing soil and paving over roots will, over time, have a slow but insidious harmful effect on trees. The key point here is that the decline of a tree’s health usually begins with something we humans do. Later, insects and disease gradually move in, weakening the root system (or some other part of the tree) so that when a severe weather event occurs, all or part of the tree will give way.

Learning to recognize when a tree’s health is in decline can take practice; in most cases, it’s best left to someone with experience. But learning to recognize basic symptoms can mean the difference between seeking skilled care for your living tree and calling in someone to clean up the debris and patch the damage once it’s gone. Begin by asking these questions:

* Does the tree have any large, dead but-still-attached branches?

* Are there any dead, detached branches hanging in the tree or lying on the ground below?

* Are there any cavities or areas of rotten wood in any of the branches, along the trunk or at the base of the trunk?

* Does the tree have cracks or splits along the trunk or where branches attach to the trunk?

* Are mushrooms present at the base of the trunk or on exposed roots?

* Does the tree have a strong lean?

* Do most of the branches originate from the same point on the trunk?

* Has there been recent construction in the vicinity or around the root system — such as grading that would raise or lower the soil level, installation of pavement or other utilities, sidewalk repair or trenching, or lawn or landscape development?

* Have the leaves developed an unusual color or become smaller?

* Have adjacent trees recently died or declined?

* Has the tree been topped or heavily pruned?

Over time, these important questions can help determine both when tree care is needed and how it’s provided. Some things we can do ourselves long before problems develop, such as pruning properly, choosing the right tree for the site, avoiding construction in the root zone, and providing regular, proper care. Sometimes, even removing a questionable tree and replacing it with a more appropriate, healthy one can be a good decision.

When in doubt, seek advice from someone who knows trees; it’s a very worthwhile investment. And since the work may be expensive and the trees are our future, you’ll want to seek out a qualified service provider, much as you might choose, say, a doctor. Look for a certified arborist; this professional accreditation is voluntary and means that the person has completed an extensive training-and-examination process that covers all aspects of tree care. They’ll perform only acceptable practices and must continue to train on a regular basis to maintain their certification. Beyond the proper credentials and experience, be sure your hire has proof of insurance (personal, property and even worker’s comp). Ask for references, get more than one estimate, and don’t always go with the low estimate — you want quality work. The International Society of Arboriculture’s Web site (www.treesaregood.com) offers excellent information on tree care and hiring certified arborists.

In the meantime, The North Carolina Arboretum is hosting a program titled “Tree Care Strategies” on Monday, Nov. 8 from 10 a.m. to noon. Arborist Dan Flinn will lead a discussion and workshop on pruning, the best tools for specific tasks, suggestions for protection in inclement weather, and defining situations that may require professional attention. This is an excellent opportunity to get your questions answered — and to start making plans for providing sound tree care — before the turn of the season brings the onslaught of (take a deep breath) winter weather.

[Alison Arnold is director of horticulture at The North Carolina Arboretum. She can be reached at: aarnold@ncarboretum.org.]