Duringthe last years, disturbances in the forest have received increasing attention,especially after the devastating storms of December 1999 and its unprecedentedconsequences. Nearly every summer the media reports about large wildfires,especially in the Mediterranean area and North America. Possible consequences ofa changing climate on the frequency and impact of disturbances are also topic ofdebate. On the other hand, in numerous European countries there is a trendtowards more nature oriented forest management, in which natural processes,including disturbances, have their place.
Disturbances such as storms and fireform an integral part of the forest ecosystem. They have always occurred inforests, either in natural or managed forests. Information, however, on theevents of disturbances are very scattered and incomplete, although first recordsof disturbances do date back to several hundreds of years, even as far as 1449(Schelhaas et al. 2001). Forest fires have received most attention in the recentpast, and most European countries have collected comprehensive statistics onforest fires. The FAO has been compiling these national statistics already sincethe early 1980s. Information on other disturbances is scattered throughoutliterature in European countries, many of which is in the national language andtherefore not very easily accessible. Alterra (Wageningen, The Netherlands) andthe European Forest Institute (Joensuu, Finland) have co-operated in order toidentify and compile this information as far as possible. The result of thiswork is a database on forest disturbance events in Europe including nearly30,000 records. The entries range from small biotic damages to large scalewindthrows and devastating forest fires.
In the compilation process, animportant source of information were the International Forest Fire News (IFFN)Country Notes, very often containing detailed and extensive time series onforest fires. With the help of these time series, it was possible to compile aEuropean wide time series on forest fires that extends further back than the FAOseries. This article presents some results of the analysis of the databasecontents on forest fires at a European scale. An estimate is made on thedevelopment of the burnt area in the classes forest land and forest andother wooded land over the period 1961-2000, as well as an estimate on thenumber of fires over the period 1971-2000.
This study focuses on Europeexcluding the Newly Independent States, including in total 31 countries.For all countries the burnt area was extracted from the database for the classesforest land, and forest and other wooded land. The same was done forthe number of fires. Since it is often not clearly stated if data refer toforest land or forest and other wooded land, the resulting figureshad to be analysed on its consistency. In some cases the same figures werereported, but in one source as being based on forest land and in anothersource on forest and other wooded land. From overlaps in time series forindividual countries, these errors could be corrected.
Not for all countries a full timeseries was available, therefore it was necessary to estimate missing values. Foreach country the average ratio was calculated between the burnt area of the twoclasses over the years where data was available. For years where only one of thetwo classes provided data, an estimation was performed to produce the value ofthe missing class using this ratio and the known value.
For all 31 European countries,averages were calculated over all known years for the burnt area on ‘forestland, on ‘forest and other wooded land’ and the number of forest fires. Theseaverages were aggregated to get a mean value for Europe for each of the requiredparameters. The contribution of each country to these mean values was thencalculated for all countries subject to this study.
If for a particular year one or morecountries lacked data for a required parameter, the total of the known valueswas calculated, as well as the average contribution of the correspondingcountries in the European total. From these average contributions the totalvalue for Europe could be estimated.
Example: Missing data on the forestfire area for a certain year in Spain.
Thetotal forest fire area for all other European countries adds to 240,000 ha, andthe average share of Spain in the European total is 20%. Therefore, the totalforest fire area in Europe is estimated to be 240,000 / 0.8 = 300,000 ha forthat year.
Over the period 1971-2000, theannual number of forest fires has increased visibly, from 40,000 on average in1971-1980 to 95,000 on average in 1991-2000 (Figure 1, Table 1). Especially inthe 1990s the increase is quite obvious. Several factors can play a role in thistrend. Firstly, the detection methods and the quality of the databases haveimproved considerably, most likely resulting in the detection and reporting ofmore fires. Secondly, due to aggressive and effective fire suppression policies,fires are extinguished earlier, which may lead to more but smaller fires. Thisdevelopment is reflected in Figure 4, which shows a decrease of the average firesize over time.
Otherfactors are also important, but more difficult to assess. This accountsespecially for various socio-economic factors, since most of the fires originatefrom human causes. One example is the increase of the recreational use offorests in the recent past that may contribute to an increase of forest fires.
The annual burnt area both onforest land and forest and other wooded land appears rather stablein the 1960s, after which it increases during the 1970s. This increase stops atthe end of 1970s and in the second half of the 1990s the annual area burnt showssigns of a decrease. The inter-annual variability is quite high and is mostvisible in the period 1975-2000 with a number of peak years clearly visible(Figure 2 and 3). The observed increase in inter-annual variability could be dueto more incomplete data coverage, less effective detection methods and reportingsystems before 1975. What are the exact causes of the increase is quitedifficult to identify. Certainly to be mentioned are socio-economic factors,e.g. (1) the decreased use of firewood, leading to higher fuel loads in theforest, (2) depopulation of the countryside, resulting in larger areas of closedforest and (3) the influence of climate change. Also forest management itselfplays a role, e.g. by establishing large monoculture plantations.
In the period 1991-2000, the averageannual burnt area of forest land amounts to 227,000 ha, which is about0.13% of the total forest area of the countries under consideration, using datafrom the Temporal and Boreal Forest Resource Assessment 2000 (UN-ECE/FAO, 2000).The average annual burnt area on forest and other wooded land in the sameperiod is about 0.23% of the total area of that class. These figures also varyconsiderably among countries and years as in the data from the DFDE database.
Mediterraneancountries account to most of the fires. On average 94% of the annual burntforest area occurs in the Mediterranean region, which is approx. 0.3% offorest land in the time span 1991-2000. The average annual area burnt onforest and other wooded land is higher for the same period (approx.0.47%). The most affected country is Portugal. An average of 1.25% forestland is annually affected by fires and 2.73% of forest and other wooded land.
Figure 1. The total reported and estimated number of forest fires in Europe 1970-1999.
Table 1. Averages of estimated number of fires and the estimated fire area for the two classes forest land and forest and other wooded land for Europe (excluding NIS countries) for 10 year intervals.
Number of fires (thousands) Area of fire on forest land (thousand ha) Area of fire on forest and other wooded land (thousand ha) Average fire size on forest and other wooded land (ha) 1961-1970 114 202 1971-1980 40 228 434 10.7 1981-1990 54 281 631 11.7 1991-1998 83 220 486 5.8 1971-1998 57 245 519 9.0
Figure 3. The total reported and estimated area of fires on forest and other wooded land in Europe 1961-1999.
Figure 4. The average burnt area/fire on forest and other wooded land 1970-1998.
Sources often do not clearly statewhich land category the reported data refer to, and in cases they may even bereported apparently to the wrong class. By implementing comparisons of differentsources these errors could mostly be corrected for. Often differences were foundin data concerning the same year and class. Partly these differences accountedto the use of different definitions or the use of different classes (e.g. onlystate owned forest land). In the majority of cases differences between sourcescould not be explained, indicating that the reliability of the data remainsuncertain. This became apparent when analysing data from different sources as atime series. For some countries, the ratio between burnt area on forestland and forest and other wooded land changed considerably betweendifferent time spans, indicating e.g. a possible change in definitions ormethodology. Also the methods of fire detection have improved during theinvestigated time period, making the resulting databases more reliable in recentdecades.
The method that is used forupscaling from the country level to European is quite rough, and it assumes thatthe area and number of fires in a particular year are correlated among thecountries. To a certain extent this is true as neighbouring countries often facethe similar weather conditions. This however holds only to a certain extent,since country specific factors may influence the fire frequency and intensity.Combined with the uncertainty within the data, one should be careful ininterpreting the results. Despite these restrictions the collected data onforest fires certainly provides a satisfactory picture of the trends in forestfires over the last decades.
A database has been constructed fromthe data that was collected during 1999 and 2000. Using these data it waspossible to construct a European wide overview of the number and area of forestfires. Although the uncertainty in the data most likely increased whileanalysing data back to the 1960s, as does as the uncertainty connected with themethod used, a trend is visible. It indicates an increase in the number of firesand the annual burnt area, especially in the 1970s and partly the 1980s. Theaverage size of the fires is apparently decreasing, which might be due toincreased fire fighting efforts. The fire situation is most severe in theMediterranean area, accounting for about 74% of all forest fires and more than90% of the annual burnt forest area in the 31 investigated European countries.
The analysis performed in this studyshows only one aspect of possibilities of the Database on Forest Disturbances inEurope (DFDE). The DFDE is currently still expanding, both with recent data andhistorical data. Also more detailed forest fire records are collected fromindividual countries or regions, thereby increasing the possibilities for moredetailed analyses.
Contributionsfrom IFFN readers are very welcome!
Schelhaas, M.J., Varis, S., Schuck,A., 2001. Database on Forest Disturbances in Europe (DFDE), European ForestInstitute, Joensuu, Finland. http://www.efi.fi/projects/dfde/
UN-ECE/FAO,2000. Forest Resources of Europe, CIS, North America,Australia, Japan and New Zealand. Main report. Geneva Timber and Forest StudyPapers, No. 17. United Nations, New York and Geneva. 445 p.