ADAPTING EUCALYPTUS STANDS TO ACT AS EFFICIENT FIREBREAKS TO PROTECT THE URBAN INTERFACE FROM FUTURE FIRES - NORTHOAKS ESTATE, HOUT BAY, WESTERN CAPE, SOUTH AFRICA.
OUR CLIENT’S NEED
NCC Environmental Services was approached by the Northoaks Estate, Hout Bay, and requested to clear a fire break along the bordering mountainside. A firebreak acts as a zone from which to fight and prevent the downward spread of the inevitable future wildfires that are synonymous with the Western Cape and its urban interface.
DESIGNING A CUSTOMISED SOLUTION
The abutting property on the slope above the Estate consists of mature Eucalyptus trees, a somewhat controversial tree species in the Western Cape owing to their exotic nature, combustibility and thirsty water consumption. Whilst many of these trees are listed as invaders owing to their foreign nature, they also poses some beneficial properties, particularly in regard to being excellent honey bee forage with plants providing nectar in the form of carbohydrates and pollen providing protein, hence they enjoy some special regulations
What many people do not realise about gum trees, is that in a seemingly direct contradiction many, of these species were planted around the Cape Town urban interface several decades ago to act as an effective fire breaks. The reason behind this stems from knowledge of fire behaviour and the growth habits of gum trees themselves.
Fire requires three elements to survive, heat, oxygen and fuel. All firefighting efforts involve removing at least one of these elements. In the case of wildfire the fuel is plant matter such as branches, leaves and twigs. The lighter the fuel (e.g. grass and dry brush), the easier it is for fire to start and spread through the area.
Gum trees are known to have alleleopathic properties, which mean they release a chemical into the surrounding soil. This chemical acts as a poison of sorts and prevents other plant species from being able to grow underneath, thereby reducing competition for limited nutrients and water. We now know this to be incredibly damaging and undesirable in the fragile and threatened fynbos eco-systems, however past management authorities would have viewed fire breaks as purpose driven and unnatural zone. By preventing undergrowth, the gum trees themselves reduce the fuel load and likelihood of fire spread beneath them.
The second important trait is that gum trees generally grow with a single thick vertical stem, with very few lateral branches on the lower reaches of the trunk. It is these lateral branches or “ladder fuels” that allow ground fires to climb up the stems of large trees and into the canopy. With ladder fuels being for the most part absent in gum stands, and with little to no ground fuels (smaller plants) as a result of the alleleopathic poisons in the ground, it is almost impossible for fire to move through a section of barren ground and thick stems of a well planted and maintained gum tree groves.
When life gives you lemons, make lemonade. Gum tree stands in the Western Cape are damaging to the fragile fynbos ecosystems and consume large amounts of water, and as such should be eradicated where possible. If however resources and budget are not available to implement the eradication properly, then it is best to maintain them in a manner that at least allows them act as an effective firebreak. These firebreaks will also provide some shade, a cooler climate, block some wind, provide perches for birds and forage for honey bees.
Figure 1: Removal of fine ground fuels in the firebreak by NCC wildland firefighters.
NCC utilised their team of professional wildland firefighters, who often in their “off” season are required to conduct integrated wildfire operations in the form of invasive alien vegetation clearing and firebreak maintenance. For this particular site, they cleared and removed all the low growth and dead material to allow this gum tree stand to act as a firebreak. The work itself replicates the result of a fire sweeping through the area; removal of leaf litter and small bushes via brushcutting and raking and the amputation of low ladder fuel branches on the trees known as ‘limbing’. The result is an understorey that is almost impossible for a fire to move through. As a second line of defence, an area between the fence line and the gum tree fire break has also been completely cleared in the unlikely case that a fire does manage to spread through the gums.
Figure 2: Fine fuels removed and trees limbed. It is now unlikely that a fire can move through the shaded gum tree fire break with ease.
Many people identify a grove of alien gum trees as being a significant fire hazard, when in fact, if managed and maintained correctly, can be the complete opposite. Although unnatural, unfavourable and detrimental to the local fynbos ecosystems, there are a few advantages to a properly managed and maintained grove. The key learning point however remains that if you practice a disciplined reduction and management of flammable fuel loads, you will in all likelihood reduce the suppression requirements of uncontrollable wild fires when they do occur, thereby mitigating your potential loss and liability.
ACHIEVING REAL GROWTH
NCC continually strives to achieve its vision of real growth for people, planet and business. By better preparing the urban interface for the upcoming wildfire season, it not only provides off season work for the firefighting teams, but also safeguards the residents and the firefighters themselves, who may be called upon to put their lives at risk attempting to protect these areas. The better prepared the urban interface is, the safer they will be and the lower the risk of loss to life, livelihood, property and environment.