36 FOREST REPORT 2005
1.4 Carbon stocks
Swiss trees and forest plants contain about 120 tons of carbon per hectare. These are the highest carbon stocks per area in Europe.
The part of the forest with the greatest storage capacity for carbon is the forest floor . Humus con- tains between 110 and 150 tons of carbon per hec- tare.
Since more wood is grown in Swiss forests than is used, the forest’s carbon stocks are also increas- ing. However, forests can only assimilate a small proportion of all the carbon dioxide emissions.
Forests and carbon dioxide
The greenhouse gasesin the at- mosphere, including carbon di- oxide, have increased by more thana thirdsince the nineteenth century. This has led to chang- esinclimate,whichis one of the reasonswhy the emission of these gases must be reduced. At the same time, it would be possible to remove and bind the carbon dioxidein theairby reforestation or through specific forest man- agement strategies since plants removecarbondioxide from the airandstore the released carbon (C) in their biomass. However, when these plants decompose orareburnt, thecarbon dioxide is released back into the atmos- phere again. Therefore, in the long –term, the binding of car- bondioxidein the forest is offset by its release.
Swiss forests contain four to five timesas much carbonin theirplant matterandin the for- 1.4.1
Distribution of carbon
Quantityofcarbon(C)per hectarein Swiss forests.
Below ground:
■Roots 29 tC/ha
■Dead wood 3.6 tC/ha
■Litter 13 t C/ha
■Soil 115 tC/ha Aboveground:
■Leaves 3.5 tC/ha
■Branches 20 t C/ha
■Stem wood 64 tC/ha
37 1 RESOURCES
est flooras theatmosphereabove Switzerland does. Slightly more than halfisin the forest soil; the rest is storedinplant matter.
The calculation of the car- bon bound in forest biomass is basedon figures relating to grow- ing stock(>1.2Growing stock), estimates of the biomass in the stems, branches, leaves and roots, and information on the density and the carbon content of wood.The greatest degree of uncertainty in this extrapolation comes from thebelow-groundbi- omass,whichisdifficult tocalcu- late.The roots storeabout aquar- ter of thecarbon.
These calculations have shown that Swiss forests bind about 130million tons ofcarbon
in their biomass, which means
that they bind anaverage of 120 tons ofcarbonper hectare.Thisis about three timesas muchas the Europeanaverageand60%more than the rest of central Europe.
The highcarbon stocks ofSwiss forests reflect both the favour- ableconditions for forest growth and thelargeamount of growing stockwithalowlevelof use.
The forestswith the highest carbon stocksare tobe foundin the Swiss Central Plateau since they have thebest growingcon- ditions. Those with the lowest values are on the southern side of theAlps.The forests thereare relatively young and only grow slowly.
1.4.2
Carbon stocks in biomass
Distributionofcarbon stocks in theabove- and
below-ground biomass in thedifferent forestry regions.
[t C/ha]
■Above- groundbio- mass
■Below- groundbio- mass
Jura Central Pre-Alps Alps Southern
Plateau Switzerland
150 120 90 60 30 0
1.4.3
Carbon stocks in the Swiss forest
Estimatedquantities ofcarbon(in millions of tons)in the forestcompared with in theatmosphere over Switzerland.
[inmillion tC]
■Upper estimate
■Lower estimate
CH-Atmosphere Forest living biomass Forest floor 200
160 120 80 40 0
Swiss forests contain four to five times as much carbon in their plant
matter and in the forest floor as the atmosphere above Switzerland does.
38 FOREST REPORT 2005
Carbon stocks in the forest floor
Soilsare thelargest carbon store in our ecologicalsystems.InSwit- zerland,forest soilsbind, togeth- er with the litter, an average of 110 to 150 tons ofcarbonper hec- tare,whichis slightly more than the plant biomass.These values are comparable to the carbon stocks of othercentralEuropean countries.
The forestsin southernSwit- zerland do not bindmuchcarbon in their plant biomass but have thelargest carbon stocksin their forest floors.Thisis thought tobe aresult of the highconcentrations of iron and aluminium oxide, which hinder thedecomposition of the humus through micro- organisms .
Soils are the largest carbon store in our ecological systems. In Switzer- land, forest soils together with the litter bind an average of 110 to 150 tons of carbon per hectare, which is slightly more than the plant bio- mass.
1.4.5
Carbon stocks in the forest floor
Quantities ofcarbon(in tons per hectare)in theforest floor in thedifferent forestry regions.
[t C/ha]
■Litter
■Mineral soil
Jura Central P. Pre-Alps Alps Southern Switzerland 180
150 120 90 60
30 0
1.4.4
Forest floor in autumn
Theforest floor is thelargestcarbon store containing more carbon than theabove-ground biomass.
39 1 RESOURCES
Carbon sink
Whetheraforest actsasa carbon sinkdoes not dependonitscar- bon stocks but on its develop- ment. This is because it is only possible for a forest to absorb morecarbondioxide from theat- mosphere thanit emitsaslongas enough forest grows. Data from both the 1985and1995 national forestry inventories can be used to estimate howmuchcarbondi- oxidewasboundby Swiss forests during thisperiod.The growing stock grew by about 30 million m3. If this is calculated as car- bon, it amounts toabout 0.8 to 1.0million tonsa year.
If we look, however, at the entirelifecycle ofaforest, thenit isalwayscarbondioxide neutral.
Whenplants grow, they incorpo- ratecarbondioxideinto theirbio- mass.When,however, they rot or burn, thecarbonis released and set freeinto the atmosphere, so that the sink effect of the forest hasa timelimit.Swiss forestscan currently only act ascarbondiox- ide sinksbecause they are under- used and expanding (>Indica- tors 1.1and1.2).Stormscan turn the sink intoasource ofcarbon dioxide overnight. For example, at the end of 1999 “Lothar” de- stroyed reserves containing four million tons of carbon within a fewhours.In viewof such events, expertsare cautiousabout mak- ing estimates, but assumeanan- nualcarbondioxide sinkcapaci- ty ofbetween0.1and1.0million tons ofcarbon.Thisis equivalent to 1 to 7% of the current emis- sions.Swiss forests therefore only
bind a very small proportion of the greenhouse emissions.
FURTHERINFORMATION Swiss FederalResearchInstituteWSL 8903 Birmensdorf
ResearchDept. FOREST Section Soil ecology (0)44/ 739 22 65
Swiss Agencyfor theEnvironment Forests andLandscape SAEFL 3003 Bern
Forest Agency
SectionForest utilization and timber industry
(0) 31/ 32477 78
1.4.6
Carbon binding in the Swiss forests
Absorptioncapacityof theSwiss forest in millions of tons of carbon(1t CO2-C=3,67 t CO2). Theforestcan bindonly a small proportionof thegreenhousegas emissions.
[inmillion tons CO2-C equivalent per year]
Forest C-binding:
approx. 0.1-1 mil- lion tCO2-C equiv- alent per year
Maximumallow- able according toKyoto Pro- tocol
Greenhousegas emissions over Switzerland
■N2O
■CH4
■CO2 15
12 9 6 3 0
