Frequently Asked Questions

Should trees be topped?

As mentioned earlier, "topping" can be an emotion-charged term. In the context of view management it usually means the removal of a substantial portion of the upper tree trunk in conifers and the cutting of all branches at a particular height for deciduous trees. Illustrations 10 and 11 show typical topped trees.

Topping is not advised

Opinions vary on the usefulness and dangers of tree-topping. For years trees have been topped for a variety of reasons: to reduce height; to minimize wind resistance; to afford views; and to install television antennas. However, it has been clearly demonstrated that topping trees is a poor and damaging practice.

A topped tree requires periodic maintenance to maintain its reduced size. That can become expensive in the long-term. Also, conifers will often form a weakened top as the side branches all try to grow up as shown in Illustration 10. In addition, the cut top often becomes an entry site for decay organisms, that weaken the tree and increase the danger of a top breaking in high winds.

For broad-leaved trees such as maple, madrone or oaks severe topping is even more damaging. It can seriously harm the tree's health and cause various safety hazards. Illustration 11 shows a radically topped deciduous tree. There may be rare circumstances where the owner of bluff property may decide that the situation warrants topping a tree, but all alternative options should first be explored. Readers who seek more information can contact the International Society of Arboriculture or Plant Amnesty (see Links).


What are alternatives to tree removal and topping?

Given the importance of tree cover on potentially unstable slopes and the advisability of retaining them for erosion control purposes, a landowner should explore alternative options to tree removal or topping.

Several trimming practices can be used successfully on conifers. They are listed below and can be used in combination to create views without compromising tree health or slope stability.

View-enhancing Pruning Alternatives for Conifers

  • Windowing
  • Interlimbing
  • Skirting-up

Note: In any pruning practice or combination, a minimum of 60% of the original crown should be retained to maintain tree health and vigor. The removal of too much live foliage can reduce the tree's ability to supply food to the roots, thereby weakening them.

Windowing. This pruning practice allows a view "window" through the existing foliage of the tree's canopy (Illustration 12-A). In pruning major limbs and branch whorls, sections that obscure a view are removed. Many people find that this technique creates an aesthetically pleasing effect.

Interlimbing. The removal of entire branch whorls or individual branches throughout the canopy allows more light to pass through, as well as reducing wind resistance of the tree. As seen in Illustration 12-B, this practice can be used in conjunction with windowing to improve views.

Skirting-up. Limbing the tree up from the bottom allows a clear line of sight (Illustration 12-C). Instead of an obscuring mass of foliage, the tree trunk is the only object between you and the view. This technique is useful when the tree in question is located high on the bluff face or upon the tableland. Relatively more branches can be removed with this technique because the lower branches contribute less nutrients to the tree than higher branches.

Pruning Broad-leaved Trees

Pruning and trimming of broad-leaved trees is usually more complicated, especially for trees grown in the wild. The occurrence of these trees where they obscure views requires the landowner to weigh and consider the many factors discussed previously to decide if pruning or removal is a smart option. Generally, short-lived species such as alder, willow and Bitter cherry are not worth pruning, while trees like madrone, White oak, Bigleaf maple, and Vine maple will warrant the expense. Basically, proper pruning of broad-leaved trees entails removal of some limbs as shown in Illustration 13. Note the difference between "B" and "C". Refer to Recommended Reading and Links for information on proper pruning.

If a tree must be cut, should the stump and roots also be removed?

Stumps and root systems should be left undisturbed when a tree is cut on a slope. The beneficial nature of roots for erosion control has been discussed. Trees removed for foundation excavations, septic system construction, road building, or gardens should be removed during site development. Stumps remaining when trees are cut for view or hazard considerations should generally be left. They can be cut flush with the ground or be incorporated into a landscape design. In some cases stump grinders can be employed to remove the stump without causing the disturbance associated with pulling or digging the stump out.

Should groundcovers and brush be removed?

Extensive clearing of bluff properties is very common, especially on uplands. Since heavy equipment is on the property, people decide they may as well make the most of the machinery's presence. Rather than planning what requires site preparation (septic system, well site, house site, access road) they have the entire area scraped at one time. While it may appear simpler and less expensive to conduct site development this way, in the long run you may be setting the stage for chronic slope stability problems and greater expense. Keep in mind the processes at work on bluff properties and the benefits of vegetation, as well as the results of altering local hydrology, topography and vegetational cover. It makes sense to proceed carefully and thoughtfully in clearing your property.

Leave and maintain a buffer of groundcover and brush between the construction site and the crest of the bluff. If the vegetation is suitable it can be incorporated into a landscape scheme. Many native brush and groundcover species are effective as noise and site barriers between you and your neighbors. They are already established and require little care. If your property supports species such as Oregon grape, salal, snowberry, Wild rose, Sword fern, Evergreen huckleberry and Butterfly bush, then you have a wide range of valuable plant materials with which to work. On disturbed sites where plants such as blackberry, Scot's broom, thistle, dock, tansy and Bracken fern predominate, you may want to judiciously clear them out and establish native or ornamental plantings. This can require a lot of work and dedication on the part of the landowner. It should be done by hand to reduce damage to potentially unstable areas. In the case of horsetail, be fore-warned that trying to dig them out only makes them thrive, but sometimes establishing a dense growth of evergreen shrubs will discourage their growth. Refer to Slope Stabilization and Erosion Control Using Vegetation for some helpful suggestions.

Note: English ivy is common on many sites. It has a tendency to climb trees and can constrict tree growth and contribute to mortality. It should therefore be removed from the trunks of trees. Ivy also tends to cascade over sheer bluff faces. While it offers little rooting protection it does protect exposed bluff faces from wind and rain erosion. Ivy is emphatically not recommended for new plantings, but if it exists on a site it can be of some protective value. It is almost impossible to eradicate once it has become established.

When is the best time to cut back vegetation?

Generally, the best time to trim woody vegetation is the period between late fall and early spring, when the plant is dormant. The frequency of trimming should not be so often that the food reserves needed for growth are depleted. Generally, a five-year maintenance schedule for most brush species will be adequate. Severity of pruning or trimming should be commensurate with the ability of the plant to tolerate the pruning damage.

Should I install a lawn?

Bluff-top property owners often install large expanses of lawn subsequent to land clearing. Lawns are relatively inexpensive to establish and maintain, and allow free access and open space around residences. They are especially good groundcovers for septic drainfields because of their shallow rooting. However, the shallow rooting of most grasses that makes them attractive cover for drainfields means their erosion control values are limited.

On sites where soil erosion and surface water runoff could be of concern it would be wise to limit the area of lawn. While low-growing or closely cropped vegetation (like lawns) helps filter and trap sediments to some extent, its capacity to do so is limited when compared to other groundcovers. During heavy rain periods, areas covered by lawns soon become saturated since rooting is shallow, water retention capacity is minimal, and canopy interception is not available. Surface water can pool in depressions and runoff occurs.

Lawns on upland sites should be bordered on the downslope side by a buffer of deeper rooted, more effective groundcover like salal, Oregon grape, Wild rose, trailing blackberry, kinnikinnick or other low-growing plants. Lawns should not extend to the crest of a slope, nor should they be established on erosion-prone sloping areas that would tend to drain over the bluff.

Are some trees better than others?

Previous sections of the guide have discussed factors that contribute to a particular species' usefulness as an erosion control element. Generally, short-lived deciduous trees are of less value and require more management than longer-lived species. Conifers, maples, and the evergreen broad-leaf tree, Madrone, are the most valuable and every effort should be made to retain and safeguard them. The relative value of a tree is a function of the physical characteristics of the site, the natural processes influencing the property, and the property owner's needs and goals.

What about construction damage during site development?

Trees retained on a development site often die as a result of various construction-related influences. Understanding these damaging construction practices can help the property owner and contractor be more effective in preserving trees as well as increasing property values.

Construction Damage to Trees (see Recommended Reading) is required reading. This informative publication discusses major construction-related impacts that should be avoided. These are:

  • Grade changes around trees
  • Soil compaction by heavy machinery
  • Mechanical injury caused by heavy machinery

Tree thinning

Give the trees you retain plenty of room. Keep machinery back at least to the edge of the dripline of the canopy. Do not bury roots when grading. Even a foot of fill over the existing grade can cause the death of a mature evergreen. Wounding of the tree by equipment can stress the tree directly as well as offer entry paths for decay organisms. Installations of temporary exclusion fencing during construction can be helpful.

Soil compaction is a common occurrence on construction sites. Hand clear brush surrounding trees rather than using heavy machinery. Compacted earth restricts root development and reduces water-holding capacity. Exclusion fencing will reduce soil compaction.

As mentioned, thinning of trees on the bluff top should be done only after consideration of factors such as species, rooting, hydrology, wind patterns, tree health, and age have been assessed. The economic value of the timber should be of secondary importance. The extra initial expense of careful site development will be a worthwhile investment.

Note: There are several general site development and construction-related practices that property owners should be aware of. Since they are beyond the scope of this guide, they are not discussed here. Refer to the Shorelands Technical Advisory Papers in Recommended Reading.

What to do with clearing debris

The process of site development invariably creates a large volume of plant debris. The disposal of this material can become a major concern. The location of debris on your property will dictate the best disposal method to employ.

Upland areas, where development and home construction occurs, generate the largest volume of debris. The best way to deal with this material is by chipping. The resultant chips can be used on rustic walkways and as free mulching materials to discourage weeds. Other options include piling and burning or disposal off-site. In densely populated areas burning may be restricted and burning in rural areas may require a permit. Contact the Washington State Department of Natural Resources or your local Fire Department. Disposal off-site may be expensive but some counties have large-scale composting programs that accept clearing debris.

Never dump material over the bluff edge or allow your equipment operator to do so. Stumps and clearing debris can cause slope damage, add unwanted weight, disturb and smother vegetation, and make access difficult in the future. Yard waste and construction debris can also cause problems and a steep bluff is no place to dump toxic chemicals such as paint or solvents. It is up to you to make sure your contractor understands your concerns.

Are there any problems to consider in using the existing trees in my landscaping?

Often when trees are retained and integrated in a landscape design, they are damaged inadvertently by typical yard maintenance practices. Remember that native trees evolved over time to become suited to regional conditions such as rainfall, shade, and wind. Radical changes should be avoided or done gradually to allow the tree to adjust to new conditions over time.

One notable example is Pacific madrone. This tree is intolerant of root disturbance. Established madrones should never be watered in the summer. Because madrone is such a striking tree, it is often used as a major landscape element with flower beds surrounding it. As a result, the area is tilled and watered. Both of these practices can kill madrone within a few years. Madrone, while valued by many, can be a problem as a landscape element because it tends to shed leaves all year. Its value as wildlife habitat and its excellent erosion control qualities make it worthwhile nonetheless.

Bigleaf maple can often prove to be a maintenance concern because of heavy leaf-fall and a tendency to drop large limbs. Again, wildlife and erosion control benefits often outweigh these drawbacks. Maple branches should be removed where they present a hazard to residences but in general the tree should be retained. At present, there is little information available that deals with maintaining native vegetation in residential settings. The best practice is to alter local conditions as little as possible.

Why did my trees blow over?

After site development and construction is completed, and sometimes even after several years have passed, the retained trees on a property will blow over. This can cause property owners considerable expense. To safeguard against this occurrence it is necessary to understand the nature of the inter-dependence of trees in the original stand. This has been discussed in the question Should Trees Be Topped? and in the question concerning construction damage. Briefly, trees blow over due to increased exposure to wind, root damage and decline, and changes in hydrology caused by vegetation removal and soil compaction. Careful consideration of factors discussed in this guide during site planning and careful construction practices during development will reduce subsequent tree loss. Blowdown often occurs as a result of tree removal or clearing on adjacent properties. Talk with your neighbors.

Why do the trees on my bluff look so scraggly?

As discussed in the section on "Factors Influencing Vegetation" in Section 2, trees exposed to severe environmental stresses such as exposure to wind and salt-laden air will develop differently than trees that have grown in protected environments. Trees growing on exposed bluff sites often are twisted, stunted, and smaller than their inland cousins. They often have many broken branches and tops. Their foliage can be sparse and of a different color than less-exposed trees of the same species.

Trees adjust in various ways to local conditions and show the wear and tear of time. These trees often protect the ones behind them from the full force of the elements. They are a valuable asset on a bluff site. Any pruning done on them should be carefully considered and properly executed. They should not be removed unless conditions absolutely warrant it.

Is this tree a hazard?

The question of hazard trees often comes up during site development. The conditions existing on a particular site and the specific tree characteristics dictate the hazard potential present. The erosion control values of a tree on bluff properties are an additional consideration in determining whether a tree should be removed or pruned.

Two major considerations contribute to the hazard present. First, a determination of the nature, probability, and severity of a failure must be made. Second, the worst-case damage resulting from a potential failure should be determined. For example, even if a tree is in poor shape with a broken top, an old unhealed trunk wound and perhaps other defects, if it will not cause property damage or personal injury when it falls, it is not a hazard. Conversely, if a tree is healthy and sound but has a large heavy branch overhanging a bedroom or nursery it could be a hazard and the limb should be removed. Remember Bigleaf maple's tendency to drop branches.

If a potentially hazardous situation exists and you cannot decide what to do, contact a qualified arborist or other competent person. Be sure to explain your concern regarding the stability of the site.

Note regarding snags: Snags are dead, standing trees. They have died for a variety of reasons: old age, insect attack, disease, past disturbances. In the case of conifers, they are seldom a blowdown hazard and may persist for many years. (Large conifer snags can remain standing for as long as 100 years.) They offer nesting and perching sites for many wildlife and bird species, including Bald eagles. If they are located so as not to constitute a hazard to structures, they should be retained. Smaller conifers and most hardwood trees will not last nearly as long (madrone and oak are exceptions). Generally snags will not be a threat to bank stability.

If I have existing slope erosion problems on my land how do I solve them? Can vegetation help?

Often, properties already have problems resulting from past practices like those described in the Introduction. There are many ways that low-cost solutions using vegetation can be implemented. A companion volume to this guide dealing specifically with the use of vegetation to control erosion is available from the Washington State Department of Ecology. Ask for Slope Stabilization and Erosion Control Using Vegetation.

Back to top

Previous page > Next page