Nearly all of Sweden lies within the boreal and hemiboreal zone, with most of the terrain covered by a fairly flammable vegetation of coniferous trees, ericaceous dwarf-shrubs and pleurocarpous mosses. Yet fire is not considered a serious problem today and the area burnt annually is minute in comparison with most other boreal regions. In fact, authorities did not even bother to collect fire statistics after 1975. For the last couple of years, statistics are again collected on a routine basis. These have not been reported in detail yet, but the total burnt area has been less than 5000 ha out of a total forested area of 22 million ha. There was also a special survey for the summer of 1994, which was unusually dry and hot. That summer 3500 ha burned in 2200 fires. Most fires were thus very small; only 37 were larger than 10 ha. This indicates a relatively benign situation and several factors may contribute. To begin with, high winds are rare during dry summer periods. Of the fires in 1994, only 11% started during days with noon wind speeds higher than 5 m per second and only a handful started during days with winds higher than 10 m per second. Also, the road network in the forest is very dense, which makes access for people and equipment rapid. In the southern half of the country the average distance in the forest to a navigable road is below 400 m and in the northern half of the country around 500 m. These roads have been put in primarily for timber hauling, but they most certainly also serve to reduce losses due to forest fires.
Most fires are caused by people, directly or indirectly. In 1994, arson was assumed to have caused 6% of the fires, smokers 2%, carelessness with fire (camp fires, refuse burning etc) 13% and various accidents 14%. An additional 30% of the fires were presumably human caused although the exact agent was unknown. That year lightning accounted for 35% of the fires, which is a very high figure in comparison with statistics from the period 1945-1975. It is probable that the summer of 1994 was unusually conducive to lightning ignitions. Most of these fires occurred in July, at the height of a long drought.
Historical analyses using fire-scarred trees have shown that the situation was drastically different in earlier times. As late as in the mid 1800s, on average more than 1% of the forested area in northern Sweden burned per year. Probably the situation was much the same further south, although less is known from there. The annually burnt area dropped steeply over the last decades of the 19th century and during the last 100 years there has not been any really large fire-years. The slump in area burnt coincide with the expansion of modern forestry. It is assumed that the rural people gradually abandoned old fire practices (such as burning for improving grazing conditions in the forest) and started to attack lightning ignitions aggressively as well. The contribution of man to the fire regime of the old days is not fully clear, but it most certainly varied from region to region and over time. The interior of northern Sweden was settled by farmers (mainly depending on cattle) only since the late 1600s. There is evidence that prior to this, fires were relatively few but some of them covered many thousand of hectares. With an increased number of settlements, the number of fires increased but their size went down. Therefore, the resulting area burned did not increase as much as might be expected. Instead, the most substantial change in the fire regime came with forestry towards the late 1800s, as outlined above.
Today there is a consensus among environmentalists and forestry people that the present fire situation is historically unprecedented and possibly unhealthy for biodiversity in the long run. Therefore some measures have been taken to increase the amount of fire in the landscape. Many forest companies have resumed the old tradition of burning felled areas. This is then used as an alternative to mechanical soil scarification. Still the area treated with fire is small (probably less than 2000 hectares during the last year) but it is increasing. On these areas there is often a residual stand which may serve to seed the area afterwards and increase the structural complexity of the future stand (dead wood, old living trees). There have also been some efforts to use fire in the management of forest reserves, although very little has been accomplished so far.
Forest Fire Prevention and Suppression
Since many years, Sweden has employed a modified version of an East-German fire danger rating system (WBKZ). It produces a single cumulative index and is operated by the Swedish Meteorological and Hydrological Institute. The country is divided into ca. 20 sections and, within each of these, WBKZ values from several weather stations are weighed to produce a single figure (1-5) illustrating the perceived fire danger. In case of a high index, or if otherwise called for, local authorities issue a ban to all open burning activities. This includes grass burning, camp fires and prescribed fires in the forest as well. It is up to the local fire chief, however, to make exemptions. This is nearly always needed in the case of prescribed fires, since the fire danger index is regularly at a high level when conditions are right for burning.
Many people have been sceptical towards the WBKZ ratings and during the last few years the Canadian forest fire danger rating system has been tested and will probably be in operation within a year.
During periods with high danger ratings, an aerial fire detection system in operated. Light private airplanes with a pilot and an observer/navigator are flown along fixed routes once (or sometimes twice) a day. The crew is not paid for this work, but the state pays for the airplane and the pilot gets free flying hours.
All suppression of fires is handled by the communes (townships) through their fire brigades (rescue service). There is no separate organization that especially handles forest fires. The state has little direct control over the communes and how fire suppression is organized. Communes (including cities) differ in population from 3000 to 700,000. The big communes have fire brigades that are operated by full-time professional firefighters. In the smaller communes, firefighters work part-time and are called in when needed.
The equipment used on forest fire operations is essentially the same as that used for fires in buildings. Very often fires can be suppressed using the water supply carried in the fire engines arriving at the site. When the distance from the road is too large, lightweight pumps and hose are carried into the forest. Usually some water source such as a tarn, lake or stream can be found within a few hundred meters from the fire. In later years there has been an increased use of helicopters, particularly if access is difficult or if the fire gets big. These are requested by the person in command of the fire. Most often they are from private air companies, but sometimes also naval or army helicopters are called in.
The costs for suppressing a forest are taken up to a certain amount by the communes, which depends on its population size (actually the amount of taxes supplied). Additional costs are reimbursed by the state. This system has created some problems for intentional burning operations in the last year. Some fire chiefs have been reluctant to grant permission for prescribed burning due to the risk of draining the communal resources, should the fire escape. Here there is a potential conflict which need to be solved if burning for biodiversity is to become successful. Another problem is the lack of experienced persons that can undertake burning operations. Forest companies today manage the forest with very few people and hardly any of these have much experience in fire management. Here there is a clear need for training courses. A five-day course involving both theory and practical training was held at Umeå by the Swedish University of Agricultural Sciences last summer and it will probably be run again in a year or two.
Research on forest fire has been conducted since the early 1900s. The first questions concerned the influence of fire on forest regeneration and soil productivity. Hardly anything was done on fire behaviour or risk assessment, probably because fires were no longer a significant threat. Fire history was done sporadically from the 1930s, but more systematically since the 1970s. Today, research is motivated largely by the concern for forest biodiversity, but some of the old questions are being dealt with again: what is the role of fire for the maintenance of site productivity in the long run? There have also been some research trying to connect fire history, fire behaviour and fire effects, with the aim to understanding the role of fire in earlier times at the landscape level.
Fig.1. Low-intensity surface fire in a Swedish boreal forest: Experimental burning by the Department of Forest Vegetation Ecology, Swedish University of Agricultural Sciences. Photo: Anders Granström
(will be added later)
From: Anders Granström Address:
Department of Forest Vegetation Ecology
Swedish University of Agricultural Sciences
S – 901 83 Umeå