Academic Reading — Test 6

Reading passage

To the casual observer, a bushfire sweeping through an Australian forest appears to be a scene of pure destruction. Yet for the eucalypts that dominate much of the continent's woodland, fire is not an enemy but a long-standing partner. Over millions of years, these trees have evolved an intimate relationship with flame, and many species now depend upon periodic burning to complete their life cycle. Far from being passive victims, eucalypts have developed a remarkable set of adaptations that allow them not merely to survive fire but to exploit it, often emerging from a blaze in a far stronger competitive position than the plants around them. The most visible of these adaptations is the capacity to regrow from buds that lie protected beneath the bark. Unlike most trees, in which the growth buds sit on the outer surface of the trunk and branches, many eucalypts carry dormant buds buried deep within the wood, shielded by an insulating layer of bark. These are known as epicormic buds. When fire scorches away the canopy, the heat triggers these hidden buds into action, and within weeks a blackened trunk may be clothed in fresh green shoots. This ability to resprout means that a tree which appears entirely dead can recover its full crown in a single growing season, a feat that few other large plants can match. Reproduction, too, is closely tied to fire. Many eucalypts store their seeds in tough, woody capsules that remain sealed on the branches for months or even years. The intense heat of a passing fire dries out these capsules and causes them to split open, releasing a shower of seed onto the ground below. Crucially, this release is timed to coincide with conditions that favour the young plants. The fire clears away competing undergrowth and returns nutrients to the soil in the form of ash, so that the seeds fall onto a bed that is open, sunlit and freshly fertilised. In effect, the parent tree withholds its seed until the moment when its offspring have the best possible chance of survival. The bark of the eucalypt plays a further protective role. In many species it is thick and fibrous, acting as a barrier that shields the living tissue beneath from the worst of the heat. Some eucalypts shed long ribbons of bark, which accumulate at the base of the trunk and on the forest floor. While this loose material undeniably adds to the fuel available to a fire, it also encourages flames to move quickly through an area rather than lingering, so that the heat passes before it can penetrate to the vulnerable core of the tree. This characteristic has led some researchers to suggest, controversially, that certain eucalypts may actively promote fire as a means of disadvantaging their competitors. This last idea points to a wider truth about the relationship between eucalypts and fire: it is one in which the tree does not simply endure the flames but, in a sense, cultivates them. The oils contained in eucalypt leaves are highly flammable, and the litter that the trees drop is slow to decay, building up over time into a thick and combustible layer. A forest dominated by eucalypts is therefore a forest predisposed to burn. Because the eucalypts recover so rapidly while many rival species do not, each fire tends to reinforce their dominance, locking the landscape into a cycle in which fire and eucalypt sustain one another. Human management of these forests has had to reckon with this deep dependency. For much of the twentieth century, the prevailing policy was to suppress fire wherever possible, in the belief that all burning was harmful. Experience has since shown that this approach can be counterproductive. When fire is excluded for long periods, dead material accumulates unchecked, and the eventual blaze, when it comes, burns with an intensity far greater than the forest would naturally experience. Such severe fires can kill even well-adapted eucalypts and destroy the seed stored in their canopies. Today, many land managers deliberately set controlled, low-intensity fires, known as prescribed burns, during cooler seasons. These reduce the build-up of fuel and mimic the gentler fires under which the forests evolved. The practice is not without risk, and a prescribed burn can occasionally escape its intended boundaries, but it reflects a growing recognition that, for the eucalypt forest, fire is not something to be eliminated but something to be managed wisely.