Bush Fires: Part 1 – Effects and Management

This is the first of four articles on fire, its’ impact on the environment and its’ use as an environmental management tool. The others are:

• Bush Fires: Part 2 – Feedback Loops That Shape Grasslands
• Bush Fires: Part 3 – Bush Fires: Part 3 – Management of Fire in Conservation Areas
• Bush Fires: Part 4 – Fire as a Bush Management Tool

Introduction

Africa has been referred to as the ‘fire continent’ and is considered as the most fire-prone continent in the world. Much of Sub-Saharan Africa once consisted of a vast landscape of tropical and subtropical fire-prone savannas, and its’ fire-influenced woodlands and shrublands have been shaped by the longest history of human involvement with fire in the world. The hot, dry winters experienced in Zimbabwe, combined with abundant dead grass and ready sources of ignition (both lightning and human) ensure that fires are a regular feature of savanna landscapes.

Types of Fire

Before proceeding with this topic it is important to be aware that bush fires can be classified according to the intensity of their burning and can be described as either ‘cool’ or ‘hot’. “Intensity” is a measure of the release of heat energy per unit time, per unit length of fire front.

Cool fires usually occur early in the dry season (late April to June) when there is still moisture in the grass and leaves and they are typically of low intensity. Cool fires leave a mosaic of burnt and unburnt patches and lick at the smaller twigs of trees but do not, on the whole, set fire to mature trees.

Hot fires usually occur late in the dry season (August to September) when the grass and trees are very dry, and massive heat energy is released. Hot fires are often made hotter and more destructive by the windy conditions in August, September and October and they are a combination of surface and crown fires (see below). Hot fires which occur during the driest part of the year are often very destructive. They completely wipe out all ground cover and kill many shrubs and trees.

Fires are also distinguished by where they occur in the landscape:

• Ground fires  burn beneath the surface in deep accumulations of humus, peat, coal, or tree roots. They move very slowly, often without flames, and can smoulder for days or months.

• Surface fires are the most common type, burning surface litter, twigs, grass, and low-lying shrubs. They range from low to high intensity and often dictate the overall expansion of a fire.

• Crown fires are the most dangerous and intense, spreading through the top canopy of trees. They often begin as surface fires that “ladder” up into the trees, sustained by strong winds and high fuel loads.

This rest of this post falls into the following sections:

Section 1: Positive Impacts of Bush Fires

Section 2: Negative Impacts of Repeated Bush Fires

Section 3: Fire Protection and Management

Section 1: Positive Impacts of Bush Fires

Fire, as part of natural processes, has a positive role in the vegetation structure and composition, and helps recycle nutrients contained in old and dead trees.

Fires can have a positive impact on the environment when they:

• Remove old, woody and normally less palatable dry plant material and stimulate the growth of green grass which provides grazing for animals in the dry season. This natural rejuvenation ensures the health of the ecosystem, promoting biodiversity and supporting wildlife habitats;
• Cause many woody plants in savannas to produce multiple coppice shoots to replace those lost or damaged through fire;
• Control and reduce bush encroachment;
• Stimulate germination of some species of grasses and trees. (Some species cannot germinate without fire, for example, species in the genus Leucadendron are dependent on bush fires to either release seeds from their cones or to stimulate seeds to germinate. Serotinous species, which store their seeds in cones to protect them from being eaten, release these seeds en masse after a fire and the seeds then usually germinate without further help. Other species release their seeds when ripe and these are stored in the soil for many years until a fire occurs, when they in turn respond to a smoke cue. Some even germinate in response to both heat from the fire as well as smoke.)
• Reduce animal parasites such as ticks where a fire has swept through an area.

There is, however, concern that the increase of frequency and extent of burning due to human activities and the damage from these fires has grown to outweigh the benefits of fire on the ecosystem. Frequent burning has implications for carbon stocks and emissions, wildlife habitat, human health and life as well as livelihoods.

Section 2: Negative Impacts of Repeated Bush Fires (even in Fire-Adapted Ecosystems)

In Zimbabwe’s grasslands, savannas and woodlands, fire has always played a role in shaping the landscape. Natural fires sparked by lightning used to occur regularly at the end of the dry season. Today a much higher number of fires are started by humans, accidentally or deliberately, and this has changed the behaviour and impact of fire on our environment.

Fire can be a useful management tool when used carefully, such as controlled burns to remove accumulated dead grass or to open up habitats. However, uncontrolled bush fires, especially in Zimbabwe’s hot, dry seasons, can cause widespread harm that lasts for years or even decades.

Negative effects of repeated fires include:

Soil Damage and Erosion

Normally healthy soil is covered with a layer of leaf litter (dead leaves and grass that make a layer over the soil that is slowly decomposing into highly nutritious humus in the top layer of the soil which is supporting the microscopic life forms that break down nutrients and aerate the soil. Rainwater trickles easily through the leaf litter and the light, humus-rich layer into the soil.

When a bush fire rages through an area it consumes the leaf litter and bakes the humus that becomes a waxy layer that discourages water penetration. Smaller vegetation, such as grass and forbs, is removed and the soil is left bare and no longer held together by roots. In a fierce storm it is carried away in individual particles. This has highly negative environmental effects because the soil that is lost is the thin, fertile layer of topsoil where seeds germinate and water is absorbed. In short, without leaf litter and plant roots holding the soil:

• Rainwater runs off instead of soaking in,
• Soil is washed into rivers and dams,
• Nutrients are lost with the topsoil.

Fire & Belowground Mycorrhizal Dynamics in Miombo Woodlands

The impact of fire on woodland soils is often discussed purely in terms of physical erosion or ash chemistry. In Miombo ecosystems, however, soil is far more than a inert mineral bed – it is a living, interconnected biological system. The dominant trees of the Miombo do not survive on soil nutrients alone; they rely on a delicate belowground partnership with specialized fungi, visible on the surface as faint, moss-like patches. When intense fires sweep through, it is this fragile underground engine that suffers the most severe blow.

Belowground Vulnerability: Fire, Soil Crusts, and the Miombo Mycorrhizal Network

While the aboveground impact of fire on Miombo woodland—such as top-kill of saplings and canopy scorching—is easy to see, some of the most profound ecological damage occurs beneath the surface.

Unlike many surrounding savannas, Miombo woodland relies on a specialized subterranean architecture. Dominant canopy trees—primarily Brachystegia, Julbernardia, and Isoberlinia species—are obligate host trees for ectomycorrhizal fungi (EMF). These specialized fungal hyphae form vast, interconnected underground webs that sheath fine root tips, providing trees with essential nutrients (particularly phosphorus and nitrogen) from Zimbabwe’s old, highly weathered, and nutrient-poor soils.

The Moss-Like Surface: Biological Soil Crusts and Fungal Mats

On the soil surface, this fragile system becomes visible as delicate, moss-like patches. These are biological soil crusts—complex communities of bryophytes, lichens, micro-fungi, and cyanobacteria—intertwined with shallow fungal mats. This surface skin plays two vital roles:

1. Soil Stabilization: It binds sandy surface soils together, preventing severe water and wind erosion at the onset of the rainy season.
2. Moisture Retention & Nutrient Cycling: It traps moisture and creates a micro-habitat that facilitates early fungal colonization and seed germination.

The Impact of Hot, Late-Season Fires

When intense, hot fires burn during the late dry season (September to November), the thick layer of accumulated leaf litter is completely consumed, driving intense heat into the top of the soil profile. This surface heating has severe consequences for the woodland ecosystem:

• Fungal Network Destruction: Because active fine roots and hyphae concentrate in the organic surface layer where nutrients accumulate, intense heat cooks and sterilizes these upper soil zones. The delicate surface network is severed, cutting off nutrient transmission to host trees.
• Seedling Bottlenecks: Young Brachystegia and Julbernardia seedlings do not possess large nutrient reserves; they depend on rapidly linking into established mycorrhizal networks maintained by mature trees. Late-season fires destroy these shared fungal hubs, leaving emerging saplings unable to establish in nutrient-starved soil.
• Loss of Biocrust Integrity: When the biological crust is burnt away, the exposed bare soil crusts over smoothly, increasing rain runoff, reducing water infiltration, and accelerating erosion during early summer storms.

Management Implications: Cool Burns Protect Belowground Health

The sensitivity of the Miombo mycorrhizal network underscores why early-season management fires (cool burns in May–July) are critical. Cool, low-intensity fires leave a patchy mosaic of unburnt leaf litter, keeping soil temperatures low enough for fungal spore reservoirs and surface crusts to survive. Maintaining this belowground fungal network ensures that Miombo trees retain their nutrient pipeline, preventing the woodland from degrading into an open, grass-dominated fire cycle.

Effects on Water

After uncontrolled fires in the Gwayi-Tsilungwane area, for example, heavy rains washed ash and soil into streams, turning the water orange with suspended soil particles and clogging pans used by wildlife and communities alike.

Reduced infiltration of water into the ground results from an increase the layer of soil that repels water because it has been “baked” by the heat of a fire (see diagram above). This lack of water penetration impacts the recharging of ground water supplies. Decreased infiltration, therefore, leads ultimately to less water for livestock, irrigation, fish, wildlife and people

Surface water runoff increases after fires as rainwater tends to run rapidly across the surface, rather than penetrating the soil. This can happen over huge areas (like most of a river’s catchment area) causing soil loss and erosion. Soil erosion leads to the siltation of rivers and dams, thus reducing their water carrying capacity. This in its turn is likely to induce floods in low-lying areas.

Water quality suffers as a result. Fire also has a profound effect the quality of surface water resources as a result of increased post-fire sediment loads and excessive nutrient concentrations (nitrates and phosphates).

Zimbabwe’s dry climate means wildlife and communities alike depend on a small number of reliable water points in the dry season. Bush fires near rivers and pans increase sediment and ash in water, impacting water quality. Mud and ash, for example, washes into the Runde River system after bush fires, reducing water quality and affecting fish, hippos, crocodiles, and water birds. This causes stress on aquatic ecosystems and less clean water for wildlife and people.

Reduction of Plant Diversity

Loss of Mature Trees and Habitat Structure

Uncontrolled bush fires in hot, dry months can burn so intensely that they kill large, mature trees, not just grass and shrubs. A hot fire sweeping through a miombo woodland, for example, can set fire to tree canopies, trunks and eventually roots and once fire has taken hold of this wood it continues to smoulder for days until the whole tree is reduced to ash. Large trees that take decades to grow may die, leaving behind bare, open ground that takes many years to recover. In forests, a single fire can reduce woody plant richness by a third to two-thirds (depending on fire severity) and can have negative impacts on a huge number of different life forms that were depending on the vegetation.

Large trees form the backbone of Zimbabwe’s savannas and woodlands and are an essential part of the biodiversity of the region. Among other things they:

• Stabilise soils and influence water cycles;
• Provide shade for wildlife (and livestock);
• Offer nesting and roosting sites for birds;
• Support insects, reptiles and many small mammals with food and shelter.

The loss of these large trees causes loss of habitat complexity and the creatures that depend on it.

Uncontrolled, repeated fires reduce structural diversity within vegetation (young saplings growing amongst mature trees with many years of life in them and old trees reaching the end of their lives) as well as leading to a simplified ecosystem, often dominated by a few hardy species.

General Loss of Plant Diversity

• Fires give rise to an increased probability of further fires in subsequent years as dead trees topple to the ground, opening the forest to drying by sunlight, and building up the fuel load with an increase in fire-prone species.
• Repeated burns can lead to the extinction of some tree species and the replacement of vast areas of forest with grasslands.
• Fire typically results in the death of plants that are not particularly fire-tolerant and strongly promotes fire-tolerant species, e.g., trees that have thicker, insulating bark.
• Regeneration of new plants is perhaps the main obstacle for maintaining populations if seedlings and saplings face frequent and severe fire damage in savannas. (Given that fires occur several times in a decade, seedlings would need to acquire the ability to re-sprout rapidly.) Frequent and intense uncontrolled fires tend to favour hardy pioneer species — those that quickly sprout after disturbance — at the expense of slower-growing, diverse plant communities.

Natural ecosystems depend on a variety of grasses, herbs, shrubs and trees. When repeated bush fires eliminate the mid-layer of vegetation:

• Sensitive plant species decline,
• Flowers and forbs disappear, impacting pollinators,
• Grasslands become dominated by less nutritious or invasive grasses, for example, in parts of Matobo Hills Conservancy, repeated uncontrolled burns in late dry seasons have reduced the richness of perennial grass species, making the landscape less attractive and nutritious for grazers.

The result is lower biodiversity and reduced resilience to drought and climate change.

Increased Invasion by Non-Native Species

After intense bush fires, bare soil is vulnerable to invasion by exotic grasses and shrubs, species that often out-perform native species in disturbed environments.
Exotic grasses, for example, can:

• Suppress native plants
• Burn hotter and more often
• Reduce grazing quality

Areas invaded by Cenchrus ciliaris (buffel grass), for example, burn more frequently and hotter, forming a positive feedback loop that promotes further invasion and increases wildfire risk. Ecosystems altered in this way no longer support native wildlife as effectively.

Reduction of Animal Biodiversity

Fire can serve an important function in maintaining the health of certain ecosystems but on the whole fires are responsible for reducing biodiversity. The former Minister of Environment and Natural Resources, Francis Nhema, said “Veld fires do not only cause loss of life and property, but are also a major driver of biodiversity loss and habitat changes. A loss in biodiversity is associated with a loss of habitat and alteration of ecosystems like clean air, fresh water as well as ecological activities such as pollination, seed dispersal, greenhouse gas migration and decomposition of waste.”

Direct Harm to Wildlife

A single spark can set off a fire that moves faster than some animals can flee, particularly:

• Most arthropods 
• Slow-moving animals (tortoises, pangolins, hedgehogs)
• Young animals that are unable to travel far or fast.

Ground-nesting birds lose their nests. Burrowing animals and their young can be trapped by a fire. After uncontrolled bush fires in Gonarezhou National Park, local reports have noted reduced sightings of small mammals and ground-nesting birds, not because they permanently disappeared but because their burrows and nests were destroyed and they were forced into marginal areas with poorer forage. The result is lower survival rates for young animals and vulnerable species, altering population dynamics.

Destruction of Food Resources

Only very few species benefit from enhanced food supplies as a result of bush fires, e.g. birds such as marabou storks take advantage of fires to feast on the insects that are trying to escape the fire.

Uncontrolled bush fires destroy:

• Grassy forage for grazers
• Leaves, flowers and shoots eaten by browsers
• Fruits and seeds that many animals eat
• Insects that insectivores rely on.

Food shortages can weaken wildlife and reduce reproduction. Zimbabwe’s dry season builds up huge amounts of dead grass that will feed a hot wildfire consuming nearly everything in its path, leaving little for grazers like zebra, wildebeest, impala and other grazers until the rains finally arrive and new growth begins. In the Save Valley Conservancy, for example, a widespread wildfire consumed hundreds of square kilometres of grass just weeks before the onset of rains. Grazers were forced to migrate long distances, increasing competition, stress and mortality and making predator–prey encounters more intense.

Increased Human–Wildlife Conflict

Food shortages can also force animals into human-dominated areas, increasing conflict. When food and water are scarce after bush fires, animals such as elephant and buffalo move closer to farms and villages in search of food. The loss of forest food products such as Uapaca kirkiana fruits during the dry season has resulted in animals such as monkeys and baboons migrating to other areas or invading agricultural crops and destroying young plantations in some parts of Zimbabwe. Zimbabwe’s agricultural communities are already under pressure from drought and livestock needs. For example, Increasing crop damage by invading animals prompts retaliation on the part of the villagers. These higher levels of conflict are costly for wildlife and humans alike.

Long-term indirect effects on animal biodiversity

Uncontrolled bush fires cause stress and loss of habitat, territories, shelter and food. Repeated fires can result in the loss of key organisms in forest ecosystems, for example, fruit-eating birds, pollinators, decomposers, amphibians and reptiles and in its turn, this results in overall decline in these species. Fires also destroy leaf litter and its associated insect community, further reducing food availability for omnivores and carnivores.

Impacts on air quality

Uncontrolled bush fires contribute considerably to the concentrations of greenhouse gases such as nitrous oxide and carbon dioxide in the atmosphere and is the second largest source of greenhouse gases from human activities after the burning of fossil fuel.

The resulting air pollution from veld fires is also a source of public health risks and psychological distress as it alters the natural concentrations of atmospheric gases.

Socio-economic impacts on human livelihoods and food security

Veld fires destroy plantations, crops and pastures (as well as homes and equipment). In Zimbabwe veld fires are a significant threat to national economic recovery plans as they are destroying not only pastures necessary for livestock but also destroying vast plantations. Food security is compromised by bush fires which end up engulfing wheat and maize crops and also destroying wild food sources.

Most rural populations rely heavily on resources derived from forest and woodlands e.g., mazhanje (Uapaca kirkiana) fruit). The economic cost of these fires is substantial, and the biggest economic losses are felt by the local communities who depend on the forest for services and goods, for recreation and for spiritual activities.

Acute social impacts such as trauma are common among victims who, for example, have secured short-term loans to finance their farm operations and have now lost everything. At a household level, loss of shelter through veld fires has often left families traumatized as well as without food supplies and proper water and sanitation facilities and this may result in loss of livelihoods, divorces, and complete disintegration of the family unit.

 Long-Term Ecosystem Instability

Repeated uncontrolled fires can push ecosystems beyond natural recovery thresholds. Zimbabwe’s ecosystems evolved to accommodate occasional moderate, patchy outbreaks of fire, not massive, uncontrolled conflagrations. Too many fires can:

• Reduce soil carbon
• Decrease microbe and insect communities
• Interrupt nutrient cycling
• Greatly reduce biodiversity

Throughout Zimbabwe repeated uncontrolled bush fires have shifted vegetation toward unproductive shrublands, with fewer grasses and lower wildlife productivity. The overall result is less resilient ecosystems that are slower to recover after droughts or floods.

Section 3: Fire Protection and Management

Each year in Zimbabwe approximately a million hectares of forest and grassland are subject to veld fires. (Look at the 2011 map of the incidences of bush fires in Zimbabwe.)

Causes of bushfires

Documented veld fire causes, as recorded by the Environmental Management Authority (EMA), include reckless disposal of cigarette stubs, lighting fires by roadsides while waiting for early morning buses, deliberate lighting of fires, children playing with matches and improper household ash disposal. The causes can be divided into Deliberate and Accidental.

Deliberate

• Early burning or back burning to reduce the fuel load and the negative impact of wild fires and for the creation of fire breaks
• In the smallholder farming areas of Zimbabwe, farmers who have limited resources and equipment to clear and prepare land with mechanical equipment frequently use fire for land preparation. These land clearing fires often spread beyond the intended area of burn, and turn into bush fires.
• Land use strategies such as ranching use fires to remove invasive species and moribund grasses that are unpalatable to livestock and game and to encourage fresh growth. This practice of burning pasturelands is common in Zimbabwe and elsewhere in the tropics
• Smoking out bees during harvesting of wild honey
• Burning is still used as a hunting tool in Zimbabwe to flush out game. The hunting season often coincides with the dry season, when fuel load is high and dry, conditions which enhance the initiation and spread of veld fires.

Accidental

• Careless disposal of cigarettes
• Careless disposal of hot ash from household domestic fires in the rural areas
• Sparks from locomotives along some of the major railway lines such as the Bulawayo-Victoria Falls railway line,
• Lightning or spontaneous combustion during very hot dry summers
• Crews of long-distance haulage trucks often take breaks from driving and light fires to prepare food that are then not put out before departure. Other road users are also responsible for lighting of fires whilst waiting for night-time or early morning buses. (A report by EMA in 2011 showed that 60% of all fires started within 500 m from major roads.)

Prevention or control of bush fires

Each year in Zimbabwe approximately a million hectares of forest and grassland are subject to veld fires. The Environmental Management Authority is trying to combat this problem in various communities. It is very difficult, if not impossible, to prevent veld fires altogether. The emphasis should be on management practices such as early burning that reduces the negative impacts of devastating hot burns and enhance the positive effects of veld fires with the least possible negative impact on people and the environment. For this reason, EMA has been working with communities in fire prevention projects such as fireguard construction, hay bailing and training firefighting teams.

EMA’s measures to reduce uncontrolled fires

• According to EMA, the fire season runs from July to October and fires are prevalent during this time because of the dry weather conditions and the huge quantities of flammable material lying in the bush. During this period, there is legislation in place (Statutory Instrument 7 of 2007, Environmental Management (Environmental Impact Assessment and Ecosystems Protection) as read with Environmental Management Act (CAP 20:27) ) which forbids the starting of fires outside residential and commercial premises during the period from 31st July to 31st October of each year. In case of a fire outbreak, any person within the vicinity must extinguish the fire even if they are not the owner of the land or property.
• EMA recommends the construction of fireguards or firebreaks. These are clean strips of land where there is nothing that can burn, to stop a fire from spreading. Firebreaks are important because they halt a fire by removing the fuel load on which it feeds. It can also be useful as a ready source of sand or soil to put out a fire that is raging.
• EMA stipulates that a fire break should be at least 9m wide on boundaries of properties and internal fire breaks should be at least 4.5m wide.
• Firebreaks can be constructed by ploughing using ox-drawn ploughs or tractors, disking, hoeing. They can also be made with shovels, rakes and spades used to remove dry grass and twigs that can burn easily.
• Fire breaks should be inspected regularly to make sure that they are free of combustible material.
• EMA is helping communities be aware of the circumstances in which there is a particularly high risk of a fire breaking out, for example: – In the dry season -When conditions are particularly hot- When conditions are windy- Where is a lot of potential fuel (e.g. dry leaves, wood, dead plants and long, dry grass).

Conclusion

Fire, like grazing, rainfall and herbivory, is not an enemy of savanna systems but one of their defining forces. Problems arise not from fire itself, but from fire used without purpose, timing or understanding. When applied thoughtfully—matched to season, fuel load and management objective—fire can rejuvenate grasslands, suppress bush encroachment, improve habitat diversity and support both wildlife and livestock production.

Effective fire management therefore requires moving beyond blanket prescriptions of “no burning” or “burn every year.” Instead, it calls for flexibility, observation and learning from the land. Different landscapes, rainfall patterns and management goals demand different fire regimes. Early dry-season burns, late dry-season fires, patch-mosaic burning and fire exclusion all have their place when used deliberately and sparingly.

Ultimately, fire should be viewed as a tool—powerful, neutral, and unforgiving of misuse. In skilled hands it can restore balance and resilience to savanna ecosystems; in careless ones it can cause lasting damage. The challenge for land managers, conservationists and guides alike is to retain fire in the management toolbox, while applying it with humility, ecological insight and respect for the complex systems it shapes.

SOURCES

Dube, Ernest, “Environmental challenges posed by veld fires in fragile regions: The case of the Bulilima and Mangwe districts in southern Zimbabwe”, Jamba: Journal of Disaster Risk Studies, Feb. 2016. (https://www.researchgate.net/publication/284912780)

EMA, Are Veld fires a Threat to the Environment?, https://ema.co.zw/wp-content/uploads/2022/12/VELD-FIRES-A-THREAT-TO-THE-ENVIRONMENT.pdf

Nyamadzawo, G., Gwenzi, W., Kanda, A. et al. “Understanding the causes, socio-economic and environmental impacts, and management of veld fires in tropical Zimbabwe”. Fire Sci Rev 2, 2 (2013). https://doi.org/10.1186/2193-0414-2-2

UNDP, Preventing veldfires in the Zambezi Valley, April, 2023, https://www.undp.org/zimbabwe/stories/preventing-veldfires-zambezi-valley

ZIMFACT, What do we know about Zimbabwe’s veld Fire Problem?, https://zimfact.org/fact-sheet-what-do-we-know-about-zimbabwes-veld-fire-problem