52 FOREST REPORT 2005
2.4 Forest damage
In the hot, dry summer of 2003 leaves of broad- leaf trees in large parts of the Swiss Central Pla- teau already turned yellow and brown at the end of July and some broadleaf trees and conifers with- ered.
The spruce bark beetle (or eight-spined spruce bark beetle) infested a record–breaking 2 million cubic metres of standing spruce. For the first time in 40 years there was a great increase in the popu- lation of silver fir bark beetles.
Non-indigenous insects and fungi are invading the Swiss natural habitat more and more often.
Among them are comparatively harmless organ- isms such as the horse chestnut leaf miner, but also extremely dangerous ones, for example, the sycamore black canker.
In the past 24 years there was only one year in which there were more forest fires in Switzerland than in 2003. The largest fire destroyed 350 hec- tares of forest near Leuk in Canton Valais.
Drought damage
Climatic events and organisms areconstantlyinfluencing forest ecology, which is especially no- ticeablewhen thereare negative impacts higher than the usual level. In WSL’s forest protection survey these eventsare listed un- der forest damage.Thereare,for example,descriptions of theway insects and fungus diseases de- velop andifand howgameani- malsdamage the forest.
Inpast years it was the sum- mer of 2003 that was especially extraordinary. It set a record in climatichistorybecause of its un- usual heat and dryness:fromJune toAugust the mercuryclimbed to average temperatures that were more than two degrees higher than the temperatures in thepre- viouslyhottest summers of1947 and 1994. For this reason the leaves ofbroadleaf trees in large areas of the Swiss Central Pla- teau already turned brown and yellowat the endofJuly.Nordid the conifers remain untouched:
in the spruce polewood forests there were dry cracks in some tree trunks.Trees growing on es- peciallydrysites–onknolls,ex- posed edges of the forests or in soil that can retain only a little water – were hit hardest. Trees on such sites sometimeswithered and died. Multi-layered stands werealsoaffected,andnumerous silver firs,especially young trees up to oneandahalf metres high, died there. In general theyoung trees planted one to two years earlier suffered the most.
The effect of the heat and lack of rain variedin the differ- ent regionsaccording toasurvey of the167district forestryoffices and technical forest management offices.Hardest hit were the for- est along the Jura and in the westernandcentralareas of the SwissCentralPlateau.In some of theseareasprematurechange of leafcolour andsubsequent leaf- fall were considered to be espe-
53 2 HEALTH AND VITALITY
cially serious. Conifers in these regionsalsodiedmore frequent- lyeven though theywere not in- festedwithbarkbeetles.
Bark beetles
After“Lothar”, the storm of the century,inDecember1999 spruce bark beetles (Ips typographus) multiplied tremendously. In 2001 theyinfested1.3millioncu- bicmetres of living spruce trees andin the followingyearalmost 1.2millioncubic metresaswell.
So the infestation reached alev- el neverpreviouslyrecorded.The hot,drysummer of2003further aggravated the situation.The first generation of emerging beetles found idealbreedingconditions in the drought-stressed spruce.
Theymultiplied so rapidly that, in late summerandinautumn,a secondsprucebarkbeetle genera- tionwas formedandevena third generation appeared in some parts.Altogether in2003 thebee- tles infested a record-breaking 2millioncubic metres of stand- ing spruce wood, amounting to about 650 000 trees.
The number of trees infest- edwithbeetles(beetle trees)still standing has markedlyincreased in recent years. The reasons for this are,firstly, that parts of the forests are no longer managed, and the federal government and thecantons havedevelopednew forest protection strategies. Sec- ondly, so many trees are infest- ed that in some regions forest workerscannot clear themaway quicklyenough.So,since“Loth- ar”,about 700 000 cubicmetres of sprucekilledbysprucebarkbee- tles have remainedin the forest.
This has hadanegative effect on thepresent situation,because the beetles proliferate especially at siteswhere manybeetle-infest- ed trees from the previous year have not been immediately re- moved. So spruce bark beetles are still hardatworkin thosear- easwhere“Lothar”did the most damage,and,asalreadyseen in 2002, are increasingly infesting variouspine species inalpinear- eas. The dwarf mountain pine
The effect of the heat and lack of rain varied in the different regions according to a survey. Hardest hit were the forest along the Jura and in the western and central areas of the Swiss Central Plateau.
2.4.1
Leaf discolouration in broadleaf trees
Premature leaf colour changebasedon datafrom theforestry districts. Districts where discolourationoccurredonly locally are not marked.
Change in leaf colour
•
•high– very hight
•
•weak–moderate
2.4.2
Beetle traps
Checkingabeetle trap.
54 FOREST REPORT 2005 (Pinus mugo),for example,isbe-
ing severelydecimated.
In addition to the eight- spined spruce bark beetle (Pit- yogenes chalcographus) and six-spined spruce bark beetle (Pityokteines curvidens), which often infest the same spruce trees together in lower regions,in2003 other bark beetles species bene- fitedfrom thewarmclimate.The population of the silver fir bark beetle (Pityokteines curvidens) exploded with numbers sud- denlyincreasing greatlyinquite largeareas for the first time since the endof the1940s.In mildlo- cations evena thirdgeneration of beetles wasproduced.This bark beetle species infestedmainlysil- ver firs,which grow onbottom- land soil,killingalarge number of treesamounting to more than 100 000 cubic metres. The silver fir bark beetles seem to prefer trees that have been weakened by drought to storm-damaged wood because, althougha great deal of pine timber wascleared away late or left lying after the storms “Vivian” and “Lothar”, there were then no widespread beetle outbreaks.
Non-indigenous organisms
As a result of global commerce and increasing mobility, non-in- digenous organisms are being brought into local natural habi- tats. Among the more harmless immigrants is the horsechestnut leaf miner (Cameraria ohridel- la),foundin Switzerlandfor the first in 1988. Since then it has spread rapidly and today caus- es noticeable leaf discoloration on horsechestnut trees in every largerSwiss town.In theChiasso area egg masses of the oak lace bug(Corythucha arcuata),an in- sect that originated in America, were foundon the leaves of ses- sile oaks (Quercus petraea) in 2003.Also in2003another non- indigenous insect found itsway into the forest. Hydrangeascale (Pulvinariahydrangeae)was first found in canton Zurich on the sycamore, Norwegian maple, and small-leaved linden. Black rot (Ceratocystis fimbriata f.sp.
platani), which was discovered inTicino in1983andin2001for the first time north of the Alps, namely,in Geneva,is extremely dangerous.Blackrot isaregular treekillerand treesattackedbyit die off.Thepathogen involvedis afungusconsideredinEurope to beaquarantine organism. Like- wise in thiscategoryis the fungus Phytophthora ramorum, which infected a decorative shrub of the genus Viburnum in a nurs- ery.This organism iscurrentlyre- sponsible for the mass mortality of oaksandother trees inCalifor- nia.It is not clear howdangerous this organismcouldbe for trees in Europe aswell. According to recent studies the beech could become infected too.
2.4.3
Beetle-infested timber and beetle infestation spots
Development of beetle-infested timberinmillions of cubic metresand number of beetle infestationspots.
Beetle–infested timber [Million m3] No. of beetle infestation spots
■Beetle-infested timber left standing:data first collected in 1999, estimated for 2003
■Forced use:in winter (October - March) beetle-infested timber felled:no data for 1984, estimated for 2003
■Forced use:in summer (April-September) beetle-infested timber felled
■Beetle infestation spots:number of infestation spots with more than 10 spruce trees
20 000 18 000 16 000 14 000 12 000 10 000 8 000 6 000 4 000 2 000 0 2,0
1,8 1,6 1,4 1,2 1,0 0,8 0,6 0,4 0,2
0,0 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03
55 2 HEALTH AND VITALITY
The average number of forest fires is usually about 100 fires per year.
Fire fighters normally contain most of the fires to an area of less than a hectare. Such fires seldom spread out of control.
Forest fires
The extreme heat and drought in spring and summer2003 meant that the danger of forest fires rose.Thedangerwasacute from March to August, apart from a few single short intervals. The cantons reported189 forest fires in thisperiod.In the last quarter of last century there were more fires, namely 216,only in 1990.
Theaverage for many years has been about 100 fires per year.
The flames destroyed a total of 564hectares,40% more than the long-term average of 405 hec- tares.This largeareaisalmost en- tirelydue to the large fire inLeuk (seebelow).The rest of the fires in 2003 were 3 hectares on av- erage,i.e. relativelysmall,affect- inga total of214hectares,which iswaybelow the long-termaver- age. Fire fighters could contain 88% of the fires toanareaof less thanahectare.
Sometimes, however, the fires spread out of control. On 13August,for example,350 hec- tares of forest went upin flames near Leuk in Canton Valais.
Larger firesalso raged in south- ern Switzerland. In two com- munities inTicino, Lodrinoand Someo, 55 and 58 hectares, re- spectively, were destroyed by fire. In Piz di Renten near San-
ta Mariain theCalancaValleyof theGrisonsafire smoulderedfor more than two months. 39 hec- tares of charred forest were the aftermath.
There were various caus- es for the fires.In 51cases fires were ignited through careless- ness.Another50 times firebroke out after lightning had struck.
Arsonists struck15 times.Other known causes were sparks from chimneys and the brake shoes of trains, contact with overhead electrical wires, and forest and farmwork.In36cases it was not possible to establish thecause of the fire.
2.4.4
Forest fires
Numberand areas of forest fires,as well as the average areaper fire.
Forest fires [No.]and area[in ha] Average area[in ha]per fire
■Forest fire areas
in hectares ■Number of forest fires ––Average area per fire 2000
1800 1600 1400 1200 1000 800 600 400 200
0 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 9697 98 99 00 01 02 03 25 20 15 10 5 0
FURTHERINFORMATION Swiss Federal Research Institute WSL 8903 Birmensdorf
Research Dept. FOREST Section Forest and environmental protection Phytosanitärer Beobachtungs- und Meldedienst PBMD
(0) 44 / 739 23 88 Forest fires:
Swiss Agency for the Environment, Forests and Landscape SAEFL 3003 Bern
Section Forest conservation and biodiversity
3003 Bern (0) 31/ 324 77 78
