Forest fire shields or barriers, no-fines concrete, living fences.
PROTECTION AGAINST FOREST FIRES
November 2019. My sympathies go out to those affected by fires in Australia at present, and wherever they may occur around the world.
Topics on this page include forest fire shields (e.g. hedges made of succulent plants such as Aloe arborescens, and walls made of no-fines concrete, which provide a protective shield or barrier for houses against bushfires), bushfires, forest fires, fire shelters, fire-retardant plants, autoclaved aerated concrete, firescaping, firewise plants, no fines concrete (or pervious concrete), scoria, pumice, my “wet wall” invention, fuel reduction browsing, prescribed browsing, living fences, hedges, windbreaks, Aloes, Aloe arborescens, Aloe ciliaris, succulents, Aloe arborescens hedge, Atriplex nummularia, Brachychiton populneus, Myoporum insulare, vegetation management, fodder trees, pest control, pollination, biodiversity, habitat creation.
“There is always a way to do it better… find it.”
“Fire shields” (shields or barriers which protect people, livestock and property from fires), firescaping and fire-retardant plants.
The ideas presented here offer no guarantees of course, but should reduce the intensity of an approaching fire, or divert it, so that it should be possible to reduce loss of human life, livestock, and property. The “wet wall” invention, and hedges of the succulent Aloe arborescens, may even be able to stop an approaching fire completely in suburban situations, or at least deflect it around and past a house.
Countries or regions with a Mediterranean climate often have the worst fires, because they have a wet winter/spring, which causes plants to grow and increases the fuel load, followed by long summers which are hot and dry (and often windy) which dry out the fuel, resulting in perfect conditions for intense fires. Added to this, the leaves of plants in these regions commonly contain highly flammable substances (oils, resins, etc.), and sometimes strips of dry bark hanging from the trees, with tinder-dry grass beneath – a recipe for disaster.
Most of the ideas, recommendations and suggestions presented here are from someone who has personal experience of living in fire prone areas of Australia and South Africa, but can be applied, perhaps slightly modified and adapted, to work in other Mediterranean climate, sclerophyll vegetation regions which are particularly prone to fires, such as Southern California and other parts of the USA, Chile, countries around the Mediterranean Sea including Israel, Greece, Italy, the South of France, Spain and Portugal, and countries on the southern coast of the Mediterranean.
I wrote an article titled “Fire Shields”, which was published in the May 2009 issue of “Small Farms” magazine in Australia. Click here for the article: Fire shields for protecting people, livestock and property. and here: fire shield 131211.
The basic idea is that each shield, e.g. a frontline windbreak of low flammability trees, a hedge (of succulent plants such as aloes for example), succulent climbers growing on a fence, or a wall; intercepts, possibly deflects, slows down, and reduces the intensity of an approaching fire, in a step-down process. The fire therefore becomes less destructive and more manageable, and may even be stopped, before it reaches people, livestock, houses or other property, or could be deflected around them. Some of the photos, information and ideas are presented further down this page, and on the “Articles” page.
I would also recommend that you visit http://www.gardeninggonewild.com/?p=7205, a site by Debra Lee Baldwin on “Firewise Plants”, and read the following articles by David Mason-Jones: Proper Grazing 1 , Proper Grazing 2 , Using Livestock 1 , Using Livestock 2 , Using Livestock 3 , and visit the “Articles” page (click on the button at the top of this page).
The firescaping with fire-retardant succulent plants, low-flammability plants and other measures suggested here are intended to be extra precautions in addition to the well known preparations such as screening windows against flying ember attack etc., that can be found on the internet on Australian rural fire service (also try CFA, Country Fire Authority) web sites, in books, etc. Also, more manufacturers are now providing products for fire protection, such as fire fighting pumps and roof mounted sprinklers, e.g. http://www.totaleden.com.au/
“Fuel reduction browsing” or “prescribed browsing” – to create a firebreak by reducing the fuel load… and/or to change a flammable vegetation type to a less flammable vegetation type (Alternatively, “Fuel reduction grazing” or “Prescribed grazing”).
Reducing the number of fires and the intensity of forest fires by changing fire-prone and fire-promoting vegetation to less flammable plant species has already been done. In the Tijuca forest in Rio de Janeiro, from 1991 to 2000, there was an average of 75 fire occurrences a year. “To decrease fire damage, sites with high fire frequencies and density of invasive (flammable) vegetation were planted with less flammable species. Results indicate that fire frequency decreased and density of invasive (flammable) vegetation declined. This approach appears to prevent fire incidence, reduce the need for fire fighting, and preserve existing biodiversity.” (Silva Matos et al 2002).
Utilising livestock grazing/browsing to reduce fire or protect against fire
Livestock can be used to reduce the fuel load and thus fire incidence and intensity – they can be bunched together to heavily graze dry grass in a strip to produce fire breaks. A quote from the Australian Farm Journal, May 2012, pg. 27: “Use cattle to create a firebreak: Ian Mitchell-Innes, a mob-grazing guru in South Africa, uses overgrazing to prevent fire on his pastures. “In a conference he said all his neighbours burn their pastures – a horrible waste. He wants a firebreak around his perimeter so he puts all his cows on his border and moves them around it, letting them create the firebreak so his neighbours’ fires don’t spread onto his property. This is part of the philosophy of letting the cows do all the work. Don’t mow a firebreak; let the cows graze it heavily in the right places,” he says.”
Livestock that browse (eat leaves of trees and shrubs) as well as graze (eat grass), such as Galloway cattle, Bali cattle, eland, and goats, can also be concentrated in an area of trees, shrubs, and grass, where fire threatens people, stock or property, to reduce the fine fuel load of the vegetation, and so reduce the intensity of fires. Goats can be used “to reduce vegetative fuel loads in fire-vulnerable ecosystems” (Ekarius 2008). This could be done on the edge of and into bushland/forest to produce a protective strip or buffer zone (perhaps 20-100 metres wide).
Repeated browsing could also be used to retard the growth of vegetation which promotes fire (sclerophyll vegetation which is common in infertile soils in Mediterranean climate regions with hot, dry summers, including, for example, eucalyptus and pine trees), and control the seedlings of fire-promoting plants such as eucalyptus/pines which germinate after fire. Fire promoting plants often have a shape that facilitates the spread of fire up from the ground and into the tree canopy (providing what is sometimes called a fuel ladder, e.g. pines and eucalyptus), as well as containing flammable oils, resins etc. (e.g. pines and eucalyptus again). Browsing the under-storey vegetation such as dry grasses reduces the intensity of the ground fire, and so reduces the chance of the fire going up into the trees, and thus may prevent or delay a more intense crown fire.
The browsing animals could also be fed with seeds beforehand (mixed in with palatable supplementary fodder plus perhaps molasses to entice them to ingest the seeds) of indigenous fire-retardant (or at least low-flammability) plant species, (see “Fire shields” plant list, “Articles” page), which would be deposited in their manure, and some of the seeds would germinate later in their manure. See the AID plus seeds article on the articles page or at the bottom of the home page for more information on this technique, and click here: https://reforestation.me/animal-improved-dung-fmnr/. This could change the balance or dominance from fire-promoting to fire-retardant/low-flammability plant species/vegetation, in one operation. Repeated treatments will probably be necessary.
Change a highly flammable vegetation type to a less flammable vegetation type
Another possibility – the vegetation could potentially be shifted to a later successional stage (towards a wetter type of forest, made up of less flammable plants), which should be less fire-prone and less fire-promoting. This would have the additional ecological benefit of producing a patchy, more biodiverse forest. This could be achieved by feeding livestock the seeds of later successional stage plants (or spread the seeds first and then let the livestock in), plus deficient nutrients (e.g. in many cases, phosphorus), and perhaps brown coal dust (a way to increase soil organic matter, and therefore water infiltration, and water holding capacity), to suit these plant species (later successional stage species). Utilising livestock in this way (or adding seeds and soil improvers by other means) will speed up the natural process of succession. If fire can be excluded, reduced in intensity, or is less frequent, the soil will naturally increase in organic matter and nutrient levels, and the vegetation will naturally progress towards a later, less fire-prone and less fire-promoting, successional stage.
If a fire does burn the buffer strip of browsed vegetation, the fire should be reduced in intensity, but the process of browsing and adding seeds and soil improvers will need to be repeated.
An oversimplification no doubt, but the practice of fuel reduction burns (prescribed burns), which is common in Australia, reduces the fuel load, and reduces the intensity of fires, but also tends to favour the establishment and survival of plant species that are adapted to fires, and these plant species commonly also promote fires, potentially perpetuating a vicious cycle. Fuel reduction burns are likely to continue to be necessary for reduction of fuel loads in large areas of forest, but the edges of bushland may be better managed through fuel reduction browsing, perhaps in a buffer strip, at least near houses. Fuel reduction browsing is also safer near houses, compared to prescribed burns, and could be implemented before a prescribed burn, in case the prescribed burn gets out of hand (and perhaps burns down houses), which is not uncommon.
The illustration below shows natural succession:
Silva Matos et al (2002). “Fire and restoration of the largest urban forest of the world in Rio de Janeiro City, Brazil”. Urban Ecosystems, 6: 151-161.
Ekarius, Carol. 2008. Storey’s illustrated breed guide to sheep, goats, cattle, and pigs. Walsworth Publishing company. Pge. 142.
Fire shields and firescaping with fire-retardant plants
A “fire shield” (a term I have coined) or “fire barrier”, is a barrier made of non-flammable or fire-retardant materials such as concrete, or low-flammability/fire-retardant plants. These can be built or grown at right angles to the direction from which a fire is likely to approach (which can be predicted in many cases) or in a “^” shape, pointing towards the fire. In Switzerland, where avalanches are a hazard, rock and earth walls are built uphill from houses – the walls are built in a “^” shape (looking at the walls from above) so that the walls do not stop an avalanche but deflect it around both sides of the “^” and around both sides of the house. It is easier to deflect an oncoming avalanche (and probably a fire), than to attempt to stop it head-on. The plan for a stock shelter further down this page incorporates this strategy.
Fire-retardant succulent plants (and other low-flammability plants such as Atriplex nummularia) grown as hedges/climbers to form a water-filled fire shield.
The photo above shows the succulent Aloe arborescens used as a hedge. The leaves are full of a viscous watery sap, and are effectively a way of storing water above ground – a wall of water. An Aloe hedge has the potential to stop a fire, and thus protect people, livestock and property; see www.debraleebaldwin.com., and click on “Firewise landscaping”, on the left hand column, to see where a house in California was saved by Aloe arborescens plants, while other houses nearby burnt down, and http://www.gardeninggonewild.com/?p=7205 .
Aloe arborescens prefers well-drained, sandy soils and full sun, but will tolerate clay soils and can even grow under trees in the shade. It is not tolerant of heavy frosts.
In South Eastern Africa, this plant, as well as Aloe ferox, and in colder, higher altitudes in Lesotho, Aloe striatula, is traditionally used to form stockpens (called kraals in Southern Africa, and bomas in East Africa, where Aloe kedongensis is used). The plants are bitter and unpalatable to stock and wildlife. The plants are stockproof, and largely fireproof and peopleproof.
Aloe arborescens is found near Caledon in the S.W. Cape, South Africa (Mediterranean climate, winter rains, hot dry summer), the Southern Cape coast (cooler, with year-round rains, and coastal exposure), through to higher altitudes in tropical Malawi (warm, summer rains, dry winter). The plant is generally adaptable, but suitable provenances could be sought or even improved for a specific climate.
The flowers produce nectar and attract birds such as sunbirds, which may also eat pest insects, and attract bees for good quality honey. Aloe arborescens also has medicinal properties, especially the treatment of burns, especially radiation burns, and may be equal to or better than Aloe vera in this respect, according to research in Russia. The plant does not seem to be invasive, although it has naturalised on or near the coast in Northern New South Wales and Southern California. Aloe ferox is more likely to be an environmental weed.
An Aloe arborescens hedge is likely to have a useful life of fifty years or more (Aloe dichotoma has been known to live three hundred years).
Climbing succulent plants as fire shields
A fire shield of succulents can be produced more quickly if a fence of metal posts and wire mesh is constructed, and faster-growing climbing succulents are used. Perhaps the best plant for this would be the climbing aloe, Aloe ciliaris, which is fast-growing, tough and adaptable, (but not resistant to heavy frosts), and the next best might be the even faster Senecio tamoides (Senecio angulatus) climbing to three metres or more. The Senecio is not frost tolerant, and grows best in sandy soils in coastal areas (it can be a weed). Aloe ciliaris should climb to two metres, and may reach 4.5 metres, providing a fire shield of water-filled leaves. It can also form a mounding groundcover, as can Aloe tenuior.
Aloe ciliaris was once quite popular in Australia, commonly used to cover outdoor toilets. The Senecio should climb to three metres or more, but has less succulent leaves than aloe species. The plants should ideally be thoroughly watered before a possible fire, so that their leaves are full of water.
Ivy pelargonium (Pelargonium peltatum hybrids/cultivars) also has fleshy to succulent leaves and can grow 1.8 to 2 metres tall up a fence or trellis. They are not particularly frost tolerant but they will grow in almost any soil. They prefer full sun, or at least sun for half the day.
Any of these plants grown over an existing wooden fence could result in the fence taking longer to ignite, and perhaps burn less vigorously, or perhaps not burn at all.
Ground covers to catch and trap burning embers
During a fire in Canberra, it was very obvious from TV footage that larger, heavier, burning embers were being blown along at a low level (mostly less than 50cm? above the ground). These embers can get under houses and set them alight. A succulent groundcover, backed up by a hedge, next to a house, could catch and trap most of these embers.
Most of the plants mentioned below grow best in full sun and sandy soil (or at least well drained soil in raised beds), and are not very tolerant of frosts and cold.
Combined fibre-cement sheet and sprinkler fire shield
Growing plants takes time. If fires are imminent, the quickest (but relatively expensive) fire shield may be a fibre-cement sheet fence (cement sheets bolted to steel posts which are set in concrete in the ground), with the fireward side painted with fire retardant paint.
Fibre-cement sheets may crack and be destroyed under sustained intense heat, but should survive long enough to do their job and for a fire to pass by, especially if they are painted with fire retardant paint. To be an effective fire shield against blowing embers and radiant heat, a fibre cement sheet wall would need to be close to the house, on the probable fireward side, and be at least 1.5 meters high, and preferably more than two metres high. For a recipe for relatively cheap fire retardant whitewash paint, read the fire shields article (see the “Articles” page).
A metal sprinkler system on top of the fence, spraying water onto the roof and walls of the house, and outward towards the the fire, would greatly enhance effectiveness. In a fire, sprinkler systems should ideally have an independent water and power source such as a dam, pond or pool, and a pump.
The wall could have fire retardant climbing plants or shrubs planted on the fireward side as an additional measure to reduce the intensity of the radiant heat.
Succulent plant shields continued…
Most Aloes (and other succulents, including cacti) can be grown from large cuttings placed directly in the ground (preferably a raised bed, dug over, with some compost added, and perhaps a mulch of stones) in the wet season, or other times of the year if they can be watered (including the Aloes, Senecio and ivy pelargoniums, and ground covers mentioned above). Some other succulents that can form fire shields include Euphorbia spp., Cereus and related genera, eg. Mexican fence cactus, prickly pears Opuntia spp. (only where they are not a weed), etc.
There are mail order nurseries that mail out cuttings of succulents (without roots), which can then be planted directly into prepared ground (the cheapest option), or into pots to get roots growing before planting out. In Australia, South Africa, California and around the Mediterranean, it should not be too difficult to obtain these succulent plants. In California there are nurseries that supply fire-retardant plants.
A few mail order options (in Australia):
Paul Forster http://www.cssq.org.au/ , click on “Buy plants” and look for his name. Paul has provided me with good plants and service in the past. He may have Aloe arborescens (various forms), Aloe ciliaris, Aloe barberae, Aloe kedongensis and a giant form of Portulacaria afra. Email: email@example.com.
http://www.cactusland.com.au/ Aloe arborescens and Aloe ciliaris.
http://www.roraimanursery.com.au/ Aloe ciliaris.
Succulent plant flammability/fire-retardant experiment
Sometimes you may read, or hear someone say in a sage-like manner, that “all plants burn”.
It is a platitude. It is not true.
As proof, the aloe vera leaves in the photo below combusted (in the sense that they can be reduced to ash under a sustained flame), but they did not themselves ignite, much less support a flame, after five minutes held in the flame of a cigarette lighter.
Even dead and dry aloe leaves are hard to burn.
The photo above shows a flammability experiment. A constant flame from a lighter held under a leaf of Aloe vera for one minute, and five minutes (the cut end of the leaf was in the falme all the time). In both cases the sap bubbled and boiled, and ultimately the leaf charred, but did not support a flame/fire, i.e. there was no ignition, and the leaf did not act as fuel for the flame. A truly fire-retardant plant.
I am reasonably confident that Aloe arborescens, A. striatula, A. ciliaris, and most other aloes, (and perhaps many other similarly watery and succulent plants), would be the same.
The photo above shows the leaves of Aloe barberae (previously A. bainesii). This is a tree aloe, and could protect livestock and property from the danger of falling, burning embers (most houses burn down in bush fires/forest fires from fires started by wind-blown embers). The upward pointing rosettes of leaves of this Aloe should be good for catching embers. Aloe cv. ‘Hercules’ may be even better (a hybrid between A. barberae and A. dichotoma). Brachychiton populneus and Myoporum insulare (potential weed outside its natural range) should also work well, but these plants are not especially succulent, and are best described as “low- flammability” plants, rather than “fire-retardant” plants. See photos further down this page.
Stock shelter, garden design and windbreaks
The two illustrations above show how firescaping with multiple fire shields, including fences (painted with fire-retardant paint), walls, fire-retardant trees, hedges, climbers and sprinklers can intercept burning embers, deflect fires, slow them down, and absorb the initial blast of radiant heat. Each shield reduces the intensity of a fire as it approaches, shielding what’s behind it, reducing the threat to people, livestock and property. The top illustration is a cross-section of a design for a fire shelter for livestock (see plan view below). Note how the shape of the windbreak and livestock shelter point towards the fire (see below), so that the winds and fire may be deflected around them.
Fire shelter for livestock, plan view
The design above would provide livestock with shelter from fires and extreme hot and cold weather. Some plants that might be suitable:
The front row of the stock shelter could be Aloe arborescens, Atriplex nummularia or Myoporum insulare.
Second row: possibly Myoporum insulare or Lagunaria patersonia.
Canopy trees inside, for protection from falling embers: perhaps Brachychiton populneus, tree aloes, Myoporum insulare, Tagasaste/tree lucerne.
The frontline windbreak could be Atriplex nummularia or Myoporum insulare on the fireward side, backed up by trees such as Lagunaria, Brachychiton, or Casuarina cunninghamiana.
Kurrajong tree Brachychiton populneus – potential windbreak species, and possible fire protection for livestock and houses.
Boobialla Myoporum insulare. This low-flammability plant could provide some protection for livestock or houses (especially with an overhead sprinkler system). Foliage down to ground level makes it a good radiation shield, and plants behind the shield could be pruned underneath to provide a refuge for smaller livestock such as sheep or goats from falling embers. It is likely to be a weed outside Australia (and outside of its natural range within Australia).
Atriplex nummularia, Old Man Saltbush, a low-flammability plant which is very adaptable, coping with frost, heat and drought. It is also a good fodder plant.
Semi-underground fire shelter.
The illustration above is a simple concept plan for a semi-underground fire shelter which could be used for people, pets, or personal valuables. It is similar to the Anderson shelters used in London during the Second World War for protection against bombing during the Blitz (my father told me about Anderson shelters – he was in London at the time). The design above could be called an Anderson fire shelter, instead of an Anderson bomb shelter. The catenary arch shape provides structural strength. The loose scoria, pumice or no-fines concrete (see photos below) on top provides insulation against the heat of the fire, and scoria could be used as a mulch as well. The optional succulent plants and sprinkler system on top provide additional protection.
Scoria is a volcanic rock which contains air bubbles, providing insulation against fire. Scoria (or pumice) could be used as aggregate in concrete for overhead/roof construction of semi-underground shelters, and walls which act as fire shields.
Additional overhead protection is provided by a sprinkler system, and the water-filled leaves of succulent plants (eg. Aloe arborescens, A. striatula, A. tenuior, A. ciliaris, Carpobrotus spp., Crassula ovata (syn. C. argentea, C. arborescens, use large, not dwarf forms), Sedum spp., Senecio tamoides (syn. S. angulatus), Aptenia cordifolia, or other fire-retardant/low flammability plants (eg. Atriplex nummularia, Prunus laurocerasus, Hakea salicifolia – these are more frost-tolerant than most succulents).
A door with a handle on both sides could possibly be made of an aerated concrete panel (eg. “Hebel” panel, see photo below), or fibre-cement sheet, cut to size and perhaps covered with a wet woollen blanket on the ouside of the door but which comes over the edges of the door, and wedged in place to provide a seal.
This concept design aims at economy and simplicity, and obviously more sophisticated, effective and expensive shelters are possible and desirable if finances are sufficient. It may be better to leave early (if there is an early warning, and if the fire isn’t approaching too quickly, which can and does happen), and to build shelters based on some of these concepts inside the house. If a shelter is built outside, access to the shelter will need to be protected from radiant heat. Fire shelters do not guarantee safety of course, but some of the alternatives, such as staying to defend a house which has no fire shelter, losing the battle, and then being stuck in a house which is burning down; or trying to leave and then finding yourself stuck in a burning car surrounded by a fire, are far worse.
The fire front usually passes within ten to thirty minutes, and the shelter could be stocked with water, torches (flashlights), self-contained breathing aparatus, woollen blankets, etc.
There is a great deal more information about fire protection in books (e.g. Joan Webster) and on the internet.
CONCRETE, CONCRETE WALLS AND THE WET WALL INVENTION
Autoclaved, aerated concrete, or AAC concrete
The air bubbles in autoclaved aerated concrete panels, and the air pores/tunnels in no-fines concrete (also called pervious concrete, see photos below), provide insulation and protection against fires. The panels are light in weight and can easily be made into walls, and even carved into desired shapes. NASA uses tiles on the space shuttle made of silica with fine bubbles in it for insulation against the heat when re-entering the Earth’s atmosphere.
No-fines concrete (or pervious concrete or permeable concrete)
No-fines concrete is made with aggregate, cement and water, without the usual fine sand – see photos below. This leaves pores or tunnels in the gaps between the aggregate chips. Large size aggregate, perhaps 2-5 cm, results in larger tunnels or pores, which provide insulation, and allow water to flow through. Scoria or pumice could be used as aggregate to provide additional insulation (from air bubbles within the scoria or pumice).
It is usually possible to predict the direction from which a fire may come, and no-fines concrete could be cast into panels (which could be tilted up – they would no doubt need some form of internal steel mesh re-inforcing), bricks or blocks to make a protective wall or shield near the house, on the fireward side. Alternatively the concrete could be poured into vertical formwork, with re-inforcement, to make a no fines concrete wall.
The “wet wall” invention
A metal sprinkler system on top of a wall made of no-fines concrete would provide additional fire protection, and some of the water would trickle down through the pores/tunnels in the wall, and out to the surface, (see photo below) producing a “wet wall”, which should be very effective against an approaching fire. Alternatively sprinkler uprights could be flush with the wall, on the protected side. Another possibility would be a wall built with gabions (wire baskets filled with rocks).
The no fines concrete wet wall could also have wire mesh attached on the outside, and fire-retardant climbing plants or creepers planted on the fireward side (e.g. Aloe ciliaris, Senecio angulatus, ivy pelargonium). A garden bed of fire-retardant plants (e.g. Aloe arborescens, Atriplex nummularia, Hakea salicifolia, Photinia spp., Prunus laurocerasus, Pittosporum spp., Myoporum insulare), could be grown on the fireward side of the wall, all providing extra protection.
In this example of no fines concrete the aggregate size ranges from approx. 1 cm to 2.5 cm. Larger aggregate would result in larger tunnels for water to flow through. Smaller aggregate would result in smaller air pores which may provide better insulation, and/or slower passage of water. A range of aggregate sizes, as in this example, would produce a range of pore/tunnel sizes, where larger tunnels would allow the quick passage of water, medium pores the slower passage of water, while smaller, enclosed air pores/bubbles would provide insulation.
Water was poured into the top of the block on the left which flowed down through the tunnels in the concrete and out through the side, in seconds.
The pores can be clearly seen in this close up photo. Walls made of no-fines concrete could be made more attractive and colourful if iron oxide powder is mixed into the cement, or plants can climb up over them, or trail down them.
No-fines concrete is also used locally (Captain Cook Highway between Cairns and Port Douglas, Australia), at the base of road cuttings (slightly out from the base) to catch rocks and soil that may go onto the road, or fall on cars, while allowing water through. It could possibly be sprayed or poured on to sloping roadside cuttings and embankments, perhaps with a few holes kept to plant groundcovers (or other plants) later.
A retaining wall made of solid concrete blocks. With sufficient rain, water pressure builds up behind the blocks. A retaining wall made of solid concrete blocks is much more likely to fail than a wall made of no-fines concrete blocks, where more water can flow through the pores.
No-fines concrete could be useful for making artificial coral reefs such as reef balls, with the pores allowing water and nutrients to pass through, and providing additional micro-habitat/homes for small creatures. See www.reefball.com/. Since no-fines concrete is more brittle than solid concrete, the walls of a reef ball would need to be thicker, perhaps no less than 15 cm (6″).
No-fines concrete could prove useful for breakwater construction. Wave action would be dissipated as the water enters into the pores of the concrete. A disadvantage could be that the shape would have to be simple, as the concrete is relatively fragile compared to solid concrete made with sand, and protruding arms are likely to break during placement, or from rocking with wave action. As mentioned above, the pores would provide habitat for marine life.
No-fines concrete block details
Blocks stock-piled for later placement.
View of block from the top
Approximate dimensions of a no-fines concrete block, starting at the top of the photo above, and going clockwise:
top, or outward face: 600 mm
face pointing towards the top right: 370 mm
face pointing towards the bottom right: 700 mm
base, or bottom of photo: 840 mm
height 1000 mm.
top right corner: 140 degrees
right corner: 115 degrees
bottom right corner: 105 degrees.
Recessed bolt at the top of the block, presumably to enable placement by crane. The bases of the blocks can have a step/cutaway design so they can be seated on top of each other, especially for sloping retaining walls.
More fire retardant plant photos
Sedums are good groundcover or trailing plants, frost-tolerant and fire-retardant. This is Sedum acre cv. ‘Gold moss’. Visit the articles page for more information and lists of fire-retardant plants.
A succulent groundcover, Aptenia cordifolia, trails down a rock wall in Fern Tree Gully, Melbourne, Australia.
Carpobrotus spp. are more robust succulent groundcovers, and probably more effective at catching and trapping embers, and could be grown over the roof of a semi-underground or underground fire shelter.
Living fences/hedges and larger scale windbreaks can be multi-functional e.g. contain livestock, fire-protection, fodder, (e.g. Atriplex halimus, A. nummularia, tree lucerne/tagasaste) and are a great opportunity to add biodiversity, and habitat (including nectar and pollen) for beneficial birds and insects (which may control pests on adjoining crops or pastures for example) on a farm. They can form important corridors for wildlife and plant dispersal/pollination, linking remnant patches/islands of natural vegetation and reforested areas.
An example of pest control: the larvae of scarab beetles feed on the roots of pasture grasses and herbs (decreasing leaf production, as well as livestock kicking up patches of grass where the roots have been cut) and in low rainfall periods can have significant negative impacts on pasture production. In fertilized pastures, there may be greater root mass, which may support an unnaturally large population of larvae. Once they become adults, these unnaturally large populations of beetles may cause disproportionate damage by feeding on the leaves of the few trees left after clearing (e.g. Eucalyptus die back in Australia).
Tachinid flies; thynnid, sphecoid, tiphiid, and scoliid wasps feed on the larvae of scarab beetles, and thus indirectly increase pasture productivity, but they need nectar from flowering shrubs for their food (McIntyre et al. 2002). Thus, in a roundabout way, livestock production can be increased and trees protected by growing a variety of flowering plants which provide a constant supply of nectar for beneficial insects.
The value of pollinators (which need a variety of plants flowering at different times) is generally unappreciated – “the value of pollination by native animals to the US agricultural economy ranges between US$4 and 6 billion a year” (McIntyre et al 2002).
In North Queensland (and this will probably work wherever it is grown), Premna serratifolia flowers provide nectar and the plant seems to be one of the best for attracting a wide variety of bees, wasps, flies, beetles and butterflies. It also produces small berries, which are eaten by wildlife and people. It is native from East Africa through India, Sri Lanka, China, Japan, Taiwan, Philippines, Malaysia, Indonesia, PNG, Australia, Samoa and Fiji (Brock 2001). It could be a weed if it is grown outside of its natural range.
Micromelum minutum attracts beneficial insects.
Insects are attracted to flowers with easily accessible nectar.
Flat flowerheads made up of small flowers generally provide nectar which is easily accessible to a wide range of insects, and provide a convenient landing platform. Some others: Sambucus, many herbaceous plants in the Apiaceae, Rosaceae and Asteraceae families, Rhus taitiensis, Alphitonia, Micromelum minutum etc.
The plants attract insects, and the insects in turn attract birds.
Erythrina x Bidwilli ‘Blakei’. Coral trees fix nitrogen, attract birds and bees, and the leaves of most species can be used as fodder. They can be propagated by using large branch/stump cuttings pushed straight into the ground at the beginning of the wet season (in the tropics), often combined with Napier grass (Pennisetum purpureum) to form a living fence. Coral trees are very useful in reforestation and agroforestry.
Erythrina indica, Coral tree.
Butea monosperma is similar to Erythrina, and native to India. Like Erythrina, it produces copious quantities of nectar and is very attractive to birds, but is slower-growing, and therefore not as useful in reforestation.
Tithonia is perhaps not strong enough by itself to contain larger livestock, but could be a component of living fences, providing nectar, pollen, and biodiversity, where it is native, or already introduced (it can be an invasive weed). The closely related Montanoa spp. are also likely to be useful (and may also be a weed). The leaves are high in nitrogen and phosphorus (around 4% of each) and can be used to make compost or steeped in water to make a fertilizer tea. The dried stalks can be used as fuel wood. Useful in agroforestry (where it is native or already introduced), and potentially in reforestation, where it can be usually established by placing cuttings straight into the ground.
Calliandra cv. ‘Pink Poodle’ in my garden. Calliandras make good living fences – many species are nitrogen-fixing, soil-improving, wildlife attracting, and provide fuelwood and fodder. Some can be invasive weeds. Calliandra ‘PinkPoodle’ is an attractive and delicate, feathery looking plant in gardens, but species such as Calliandra calothyrsus are more robust and more likely to perform in reforestation/agroforestry situations.
Leptospermum spp., and Kunzea spp. Tea trees form a moderately prickly hedge, and are generally very good at attracting beneficial insects such as parasitic wasps, and the nectar makes good honey (Manuka honey). Tea tree oil comes from the related Melaleuca alternifolia.
Euphorbias of various species are commonly used as spikey living fences in Africa and India.
Melaleuca, formerly Callistemon, are tough plants that attract birds and bees. This is the cultivar ‘Perth Pink’.
Many nectar-eating birds are attracted to red, orange or yellow flowers (often, but not always, tubular in shape), and eat insects and spiders as well as nectar.
Acacia holosericea can be used as a living fence/windbreak, is tough and very adaptable (one of the most adaptable Acacias in the tropics), nitrogen-fixing and provides edible seeds, fuelwood, as well as being useful in reforestation, and soil improvement (possibly as a long-term covercrop or a component of a mixed, improved fallow). Photo: James Cook University, Cairns.
Pinus caribaea is easy to grow and has the desired permeability for an effective windbreak, but is allelopathic, fire-prone, and has limited value for wildlife.
Grevillea ‘Honey Gem’. Grevillea hybrids are excellent for attracting birds and bees, and the hybrids are likely to be sterile and therefore not become weeds. G. banksii ‘fosteri’ has become a weed in South Africa.
Hybrids between G. banksii and G. pteridifolia are likely to be vigorous and floriferous, and make good living fences, or at least a component of a living fence/hedge. Grevillea foliage can also be used as fodder for goats.
Brock, John. (2001). Native Plants of Northern Australia. Reed New Holland. ISBN 1 877069 24 8. Pg. 288.
McIntyre, S., McIvor, J. G. and Heard, K. M. (Editors). (2002). Managing and conserving grassy woodlands. CSIRO Publishing. ISBN 0 643 06831 7. Pgs. 84, 118.
Grevillea ‘Robyn Gordon’.