Reasons why fire suppression may not have affected the fire cycle

Several people (Weir et al. 1995, Johnson et al. 1995, 1998) have explored reasons why fire suppression may not have affected the fire cycle. In general, they feel that in closed-canopied forests, like the boreal, as little as 3% of the lightning caused fires account for up to 95% of the area burned (Stocks & Street 1993, Johnson & Wowchuck 1993). Most fires remain small, but a few occur under conditions that allow them to increase rapidly in size. It is this small proportion of large lightning caused fires which has the most influence on the area burned and the fire cycle.

In years with a large area burned, fires in these closed-canopied forests characteristically have high intensities, high rates of spread and high duff consumption. In these years, extreme fire behaviour is preceded by a persistent anomalous high pressure system which produces prolonged periods of above normal temperatures and below normal precipitation (Newark 1975, Harrington & Flannigan 1987), and leads to the severe drying of both medium and heavy fuels. Under these extreme conditions, fire behaviour exhibits little difference between aspect, elevation and vegetation type (Anderson 1968, Alexander et al. 1983, Nimchuck 1983, Janz & Nimchuck 1983, Street 1985, Flannigan & Harrington 1988, Fryer & Johnson 1988). In years with only a small area burned, differences in aspect, slope, elevation and vegetation composition can have a significant effect on the fire behaviour (Alexander & McAlpine 1987, Johnson et al 1998), however, the area burned in these years is insignificant.

The extreme fire behaviour associated with persistent high pressure systems results in large areas burned. It has been argued that during these years, it is unlikely that fire suppression can significantly influence the total area burned because under these conditions fire management agencies are quickly overwhelmed (Weir et al. 1995)

     7. Переведите письменно текст, расположив абзацы в логической последовательности:

1. The planned burn provides information that cannot be obtained by studying an accidental or escaped fire. The experiment is being conducted in an area in which researchers have taken many measurements prior to the burning - inventories of thousands of trees to catalogue their species, size, and number, surveys of seedlings, measurements of fuel on the forest floor, censuses of mammals, amphibians, and birds, and monthly measurements of canopy closure at 400 points within each square kilometer of forest. After the burn, a census will be taken of the trees to see how many have survived or how they may be reacting or recovering from the burn; and canopy density will be measured immediately after the fire and at monthly intervals, to monitor the impact of the fire and rate of recovery. Temperature and humidity will be monitored at multiple spots in each forest pre- and post-burn, to detect changes in the microclimate of the forest; and soil moisture will be measured at set points in the parcels at regular intervals, to see how the changes in canopy may effect the water available in the soil. According to Nepstad, "This experiment allows us to measure the impacts of recurring fire on the forest by comparing the trees, the animals, the leaf canopy, and the soil before vs. after the fire.”

2. This is the second phase of this work, the world's largest tropical fire experiment. One square kilometer was already burned in August 2004. This year, from mid-August to early September, one half square kilometer of last year’s burned area will be burned for a second time, and two square kilometers of virgin forest will be burned for the first of several times, to simulate the repeated impacts of escaped agricultural fires that burn through the understory of frontier forests every dry season. These areas are already slated for destruction to expand soy fields.

3. Fires are set in the litter of the forest floor using kerosene drip torches along parallel 1000m-long transects every 50 meters through the square-kilometer parcels, and allowed to spread through the forest naturally. Firebreaks are cleared along perimeter trails and roads in preparation for the event, and swept clear of debris immediately prior to igniting the fires, to contain the fire within the experimental parcel. In the first round of burning last year, the fire was quite low, creeping along the ground burning leaves and small branches that had accumulated on the forest floor. But in spite of the low stature of this first fire, many trees died through 'girdling' of their trunks - the fire lingered close to their thin bark long enough to damage the delicate cambium beneath, permanently cutting off the flow of sap between the roots and the leaves. While most trees in this ecosystem never evolved thick bark to protect themselves from fire, some appear more vulnerable to fire than others, and others that appear to have died soon bounce back by resprouting from their roots. In these repeated fires, scientists will learn just how resilient some of these species are. It is quite clear, however, that the composition of the forest will be altered following a fire, and researchers will monitor the impact on forest composition as well as the effect this change has on animal populations and behavior.

4. The goal of this research is to better understand what is the impact of fire on the transition forests, which lies between the tall dense rainforests at the core of the Amazon and the “Cerrado” savannas of central Brazil. According to Daniel Nepstad, a senior scientist with the Center, "By studying the characteristics of fires in this transitional forest on the edge of the Amazon rainforest, Center researchers hope to learn how these accidental fires may affect the vigor, health, biodiversity, and animal habitat in these forests, and in the end, to learn whether recurring fire may threaten the very existence of the forest." Repeated burning of transition forests in the Amazon could cause their eventual replacement by fire-prone scrub vegetation through a process call "savannization."

5. Woods Hole Research Center Plans Controlled Burn In Amazon Rainforest. Fire is an important agent of transformation in the Amazon landscape. Every year, low intensity fires burn thousands of square miles of Amazon forest. To study the effects of these fires on the forest, and the forests' ability to recover from repeated burning, Woods Hole Research Center scientists will burn two and a half square kilometers of forest in the transition forest of northern Mato Grosso state, at Fazenda Tanguro in Querencia, from late August into early September.