Hazards associated with campus trees

Campus gardens are as much a facility of a university as are its buildings, roads, street lights and other infrastructure needing regular attention and maintenance. Because of the great age that trees can attain and because of the unique hazards they often present to lives and property they are of special importance.

Much can be said about their selection, tree planting schemes or themes, their uses and benefits, maintenance, etc. However, this article deals solely with the hazards that campus trees may present and the steps that can be taken to negate these hazards. A brief search on the internet will quickly give numerous accounts of campus trees around the world that have resulted in death, injury or major damage to property due to total or partial failure of a tree. I can sense that the immediate reaction of some people might be; “Statistically, what is the chance of this happening on our campus?” Well my response to this is; “How many incidents are you aware of where a student or staff member has died of electrical shock or gas inhalation or fell to his or her death because of an unsafe balustrade? Yet there is legislation governing these issues”. (It could be argued that this low incidence is because of strict legislation that is in place). It is a fact that unsafe trees can usually be identified before they fail and the possibility that a university can be held accountable for incidents of death, injury or damage to property, due to negligence, is very real. Accountability aside, I am of the opinion that one death or injury on campus, or one major unnecessary repair cost due to tree damage, that could have been prevented, is one too many.

An article in the “North Eastern Tribune, Alex News” in October 2011 describes an incident where a tree on a school premises fell onto a classroom of a primary school in Alexandra in the Johannesburg Metro (also read). As a result of this incident a pupil was seriously injured and both his legs had to be amputated.

Unsafe trees

An unsafe tree is one that potentially poses a threat to life or property and could fall into one of three categories. It could be because the tree is incorrectly situated – for example planted too close to a building, or the tree is a species that has inherent weaknesses – for example a species that has a tendency to drop limbs or lastly, a tree that’s integrity has been compromised due to injury or disease. During the time that I was the groundsman at Wits University I regularly encountered all three categories on campus, and I am sure similar situations exist at other South African educational institutions.

Trees sited incorrectly

Probably the most common mistake made by people planting trees, including qualified horticulturists, is to under-estimate the size that a newly planted tree will eventually attain. This results in trees being planted too close to structures such as buildings, roads and other infrastructure. It is imperative that the ultimate size of a selected tree is known or properly researched before it is selected for planting – keeping in mind these recorded sizes are average sizes and exceptions to the rule do occur. The natural habitat of the tree in relation to the site it is intended to be planted in must also be considered. For example yellow-wood trees (Podocarpus spp) grow much larger in their natural habitats than they do on average in Johannesburg.

Knowledge of the characteristics of a tree being considered for planting must also be considered. Does the tree have shallow roots or are the roots invasive? Probably the best known example is where common willow trees (Salix babylonica) are growing near drains or water reticulation systems. This is a sure recipe for disaster. Other common root invasive problems are where trees with shallow root systems are planted near to roads and foot paths. At Wits this is an on-going problem with damage caused by trees such as the Jacaranda (Jacaranda mimosaefolia).

Trees growing too high or with canopies that are too wide can also be a cause of concern in later years. Gutters and roofs need to be regularly cleaned to prevent possible rain damage during heavy down pours. At Wits there is an extensive preventative maintenance program to clear roofs of leaves and plant debris. Depending on the problem, roofs are cleaned; weekly, monthly, bi-monthly or quarterly. The roofs being cleaned weekly are those of the Wits Staff Club buildings which are surrounded by English Oaks (Quercus robur) and Poplar trees (Populus deltoides).

Trees along boundary fences or walls can result in increased security risks as these can be used by unauthorised persons wanting to access or egress the property.

Other characteristics such as trees with weak structures or trees that tend to drop branches, or discard hazardous seeds or flowers will also be dealt with in this article.

In considering all these factors and tree characteristics at the time the trees are selected for planting, many risks and associated costs associated with these risks can be reduced from the on-set. A Water Wise publication by the Rand Water Board, entitled “Tree Rooting Habits and their implications for the infrastructure of Rand Water” (Author: Dr R J Poynton) (more information) sets out guidelines on the safe distances that are recommended when planting trees near to servitudes and other infrastructure, and is a worthwhile acquisition in any maintenance department.

It must also be stated that there are cases where mature trees exist on site when a decision is taken to build a building adjacent to it, often resulting in similar hazards being experienced.

Trees with poor characteristics

Some trees have inherent poor characteristics such as invasive root systems, roots with poor anchoring ability, or trees that have trunks and branches which are susceptible to tearing or breaking. If these negative characteristics are known, trees with these weaknesses should be avoided.

Some examples are; Sweet thorn acacias (Acacia karoo) have shallow root systems and tend to become top-heavy and topple over. Belhambra trees (Phytolacca dioica) have the most invasive roots of all trees which I am familiar with.

There are trees, especially bluegums (Eucalyptus spp.), that have a tendency to drop limbs for no apparent reason and do not need wind or adverse weather for this to happen – this is known as “Sudden Limb Failure”. If this phenomenon is researched on the internet you will find that many accidents and deaths are attributed to “sudden limb failure”. Some cities have even taken steps to remove existing bluegums as a preventative measure against this phenomenon. Some bluegums also have weak root anchoring abilities. During the time I was employed at Wits this was one of the most common tree problems I encountered. In February 2008 a large bluegum fell across a small building used as an office in the Wits Parktown Campus and not long after this incident a large bluegum came down in a parking lot on the University’s West Campus, demolishing a mini-substation in the process. Fortunately there were no casualties as both incidents happened on Sunday evenings.

Some trees seem to attract lightning strikes more frequently than others. At Wits the trees which appear to attract lightning strikes more often than other species are the common Christmas trees (Cedrus deodara). The problem with lightning strikes is that the symptoms of the strike may only become evident sometime after the event took place. Often the tree may take a year or more to die.

Various bacteria, viruses and fungi attack trees and cause health decline to the point where parts of the tree die – or the whole tree dies, making it hazardous to life and property. These diseases can be recognised by looking for various tell-tale signs. For example; white powdery substance on the leaves (powdery mildew), leaf blisters, mushroom-type of growth on branches or roots of trees, sap oozing from tree wounds or rotten branches or cavities in tree trunks. On Wits campuses oaks, plane trees and Australian acacias are trees that commonly became hazardous due to disease attacked. (Blister on the leaves of Coral trees (Erythrina spp) are the result of wasps and are not disease related).

Poor tree specimens

It makes no sense in selecting a tree species that has the necessary positive characteristics, but the specimen selected is a poor one. If the tree is “root- or pot-bound” in its container it can develop a poor root system. (Roots usually circle the container and are very compact).

Trees should commonly have a dominant straight trunk or “leader”. If the tree has two or more leaders (Co-dominant) tree trunks this can result in the tree having a tendency to split when it matures. It is a good indicator if the tree has a straight erect main trunk with smaller side branches.

Branches should form an “open” junction with the main stem and not a “closed” junction. In the latter case bark of the tree can become embedded in the joint causing a weak union where the branch can tear off at a later stage.

Natural aging of trees

Trees are subject to natural death as are all other living organisms. A tree that is in state of health decline may actually be dying of old age. Such trees can present hazards due to dying branches and roots making the tree or parts of it unstable. At Wits many of the Australian acacia’s (Now mostly declared Category 1 and 2 Invasive trees), planted in the last 30 years have already died or are dying due to old age.

Other hazards that may be associated with trees.

– Leaves, fruit, seeds and even flowers of some trees can create hazardous situations, which may not be as serious as the imminent falling of a dead branch, but are never-the-less still hazardous. The following examples were all recorded as hazards while I was employed at Wits University;- Falling palm leaves. Falling leaves of the date palm (Phoenix canariensis) can cause serious injury to persons or damage to vehicles and should be avoided in car parks and areas frequently used by people.

– Flowers that fall on smooth surfaces, such as paved walkways, often create a slipping hazard. At Wits this is true of Jacaranda (Jacaranda mimosaefolia) and Australian Flame (Brachychiton populneum) trees.

– The seed pods of bluegum trees, due to their roundness, become as dangerous to walk on as are small ball-bearings if they are not regularly swept off smooth walking surfaces.

– A monkey-puzzle tree (Araucaria bidwillii) on the University’s West Campus is situated near a food outlet with surrounding seating. The cones produced by this tree are very large and an individual cone can weigh up to 3.5 kg. If such a cone fell from a height of 10m and struck someone, it will certainly cause serious injury to that person.

– Often trees have dead branches in them which may become dislodged and fall to the ground. (Not to be confused with “Sudden Limb Failure Syndrome”). These trees shed branches because of abscission (a physiological process similar to leaf abscission where leaves are shed at the onset of winter). This usually happens because of adverse weather conditions, aging or loss of vigour.

Trees can also indirectly be the cause of hazards to a staff member or persons. The following two examples do not describe injury or damage hazards but, I am sure you will agree are non-the-less hazards. The first example is where trees have insects, such as the spittal bugs, that excrete fluids which can land on persons below the trees. Most commonly associated with Tipuana trees (Tipuana tipu). The second example is where hadedah or other like-minded birds roost on dedicated branches from where they bombard the area below. At the Wits Staff Club, one such area chosen by hadedah’s is directly above the outdoor seating area of the club. As a remedial step, the branch that the birds regularly roost on, can be removed – this may however, not always be practical.

Prevention is better than cure

I feel it is important that universities employ a staff member or person that is knowledgeable, such as a qualified horticulturist, to take responsibility for the campus gardens. Even then it may be necessary for this person to consult with tree experts, such as aboriculturists, regarding some of the important decision making in the selection and maintenance of trees on campus.

At Wits a monthly meeting was held between the grounds management and the senior persons in the Botany Division, where amongst other issues, the planting and removal of trees was discussed and agreed upon. The safety officers of the various grounds and external sports regions were required to report monthly on the state of campus trees in their regions. (Provision is made for this on the standard safety report used in the grounds department). Weekly inspections of the grounds was undertaken, where amongst other issues the state of trees were considered.

In summary it can be said that it is important to select suitable tree species when considering new plantings and to consider their characteristics when choosing the site where they are to be planted. Only select healthy specimens that have strong single leader stems and that are not root-bound. It is also important to regularly inspect all trees that are growing on your campus to ensure they are safe and to take the necessary action where trees are considered to be hazardous. Remember; “rather lose a tree than a life”.


The Development of a Tree Appraisal Model for the Urban Environment of South Africa, research dissertation submitted in partial fulfilment of the requirements for the Magister Technologiae, Nature Conservation, Florida, South Africa. UNISA – Marx C W (2005).

– Internet article presented at the 58th Annual Conference of the International Society of Aboriculture, in Louisville, Kentucky, on August 10, 1983 titled “Summer Branch Drop” cited on the “Artistic Treeworks” webpage. – Richard W Harris (1983).

– Internet article entitled “Dieback and what to do about it”. Centrefor Natural Resources, NSW Department of Land and Water Conservation. – Christopher Nadolny (2002).

Internet article titled Understanding Lightning and Associated Tree Damage” on the Tree Care Kit website – Wayne K Chatterbuck, David S Vandergriff, Kim D Coder.

– Internet article titled “Trees: Damage” on the NC State University website. – Erv Evans (2000).

– Efekto’s Identification of Garden Pests and Diseases”. Ekogilde CC. – A S Schoeman (1977).

Andries Norval

(Nat. Diploma: Horticulture, Nat. Diploma: Parks and Recreation Management).

(All photographs depicted in this article, with the exception of the first photograph, were taken on the campuses of the University of the Witwatersrand, Johannesburg).