The impact of timber harvesting on the size, amount, and decay ...

<strong>The</strong> <strong>impact</strong> <strong>of</strong> <strong>timber</strong> <strong>harvesting</strong>on the size, amount, and decaystatus <strong>of</strong> large coarse woody debrisin the jarrah (Eucalyptus marginata)forestK.R. Whitford, K. Faunt 1 , M. SwinburnDepartment <strong>of</strong> Environment & ConservationWestern Australia2 Present affiliation: Drugs Policy & Services Branch, Department <strong>of</strong> Human Services, Melbourne Victoria

Location and Forest type• Jarrah (Eucalyptus marginata)– dry sclerophyll, mixed age forest• Medium sized tree,– slow growing (high quality forest -1.2 m 3 /ha/yr) ,– tolerates competition• Mediterranean climate– 650 to 1300 mm annual rainfall– Hot/dry summers and frequent fire• Varied <strong>harvesting</strong> history– No <strong>harvesting</strong> <strong>of</strong> old-growth– Shelterwood, gap, thinning– Commercial <strong>harvesting</strong> for firewood and charcoalproduction since 1990 (~ 10 tonnes/ha, including green)• CWD dependant species –– 85 species <strong>of</strong> macr<strong>of</strong>ungi associated with dead woodmany specifically colonize large logs,– Invertebrates, cryptogams (FORESTCHECK)– various herpet<strong>of</strong>auna, Carpet Python, Marbled Gecko,Southwestern Crevice Skink– Hollow using mammals - Chuditch, Numbat, Mardo,Western Pygmy Possum

Study sitesSites Harvesting history FiresPlot Forest block Number<strong>of</strong> timesharvestedYears harvested Numbersince19371 Ross 1 1 1960's 62 Scott 2 1920's, 70's 73 Windsor 1 1920's or 40's 94 Ross 2 1 1920's 65 Samson 2 < 1920, 50's 96 Chandler 1 3 < 1920, 40's, 70's 97 Chandler 2 2 < 1920, 40's 38 Torrens 0 Never harvested 59 Bombala 0 Never harvested 710 Surface 0 Never harvested 911 Tumlo 0 Never harvested 1112 Ross 3 0 Never harvested 11Means Previously harvested 1.7 < 1920 to 1970's 7.0Never harvested 0 Never harvested 8.6All sites - 7.7

Log (CWD) numbers and diameters• Similar shaped distributions• More logs on harvested sites SitesAll sites 121Never harvested 92Previously harvested"natural" logs 109sawn logs 32Number <strong>of</strong> logs(logs/ha)all logs 141

Log lengths• Similar shaped distributions• Greater total length <strong>of</strong> logs onharvest sitesLog lengthSites(m/ha)All sites 654Never harvested 482Previously harvested"natural" logssawn logsall logs 777

Log volumes• 27% <strong>of</strong> the total volume <strong>of</strong> CWD on previously harvested sites (30 m 3 /ha)originated from historical <strong>harvesting</strong> (i.e. sawn logs).• Large difference in total log volumeSitesLog volumes(m 3 /ha)Never harvested 80Previously harvested"natural" logs 80sawn logs 30Total 110

Log Decay classLogCharacteristic1 2 3 4 5 6 7 8 9 10Bark intact trace absent absent absent absent absent absent absent absentSapwoodShape <strong>of</strong>unburnt crosssectionLog contactwith thegroundhard, andbrownhard, greyto lightbrowngrey, surfacecan't bescuffed <strong>of</strong>fwith bootgrey, surfacescuffed byboot, butends hard tobreak <strong>of</strong>fsurface <strong>of</strong>sapwood iscrumblysapwoodeasily brokenaway by handsapwoodmissing onparts <strong>of</strong> logsapwoodgonesapwoodgoneround round round round 95% <strong>of</strong> round 90% 75% 50% < 25% 10%Log free<strong>of</strong> groundLog free <strong>of</strong>groundFissures absent crackspossibleLog in contactwith groundcracksLog in contactwith groundcrackspresent, slightfissuring, 1-2cm deep, 8 -10 cm apartMoss absent absent absent some mosspossibleHeartwoodstrengthBranchesRegenerationat stumphard hard Jarrah hardMarri may bestarting tocollapseMinorbranchesintactNone,baregroundMinorbranchesintactSome litter,smallweedsMajorbranches stillintact if notburnt awaySome litter,small weedsJarrah hard,MarricollapsingMajor branchstubs or noneLitter cover,small acaciasLog in contactwith groundfor full length2 cm deepabout 10 cmapartLog in contactwith groundfor full lengthSitting ingroundSitting inground3 - 4 cm deep 5 - 7 cm deepfurrows in logsurfacepresent present present May beabsentJarrah hardbut decay ispresent, MarricollapsingMajor branchstubs or noneLitter cover,bracken orlarger plantsheartwoodcan bebroken awayby handheartwoodeasily brokenaway andcrumbled byhandheartwoodeasily kickedawaymerging withgroundDeep furrowsin log surfaceMay beabsentheartwoodrotten andeasily kickedawaysapwoodgoneOnly traceevidence <strong>of</strong>log remainsMay beabsentnone none none none noneLitter cover,bracken orlarger plantsLitter cover,bracken orlarger plantsSimilar tosurroundingground coverSimilar tosurroundingground coverClass 1 2 3 4 5 6 7 8 9 10heartwoodrotten andeasily kickedawaySimilar tosurroundingground cover

Log Decay and log age• Large jarrah logs can persiston the ground for 70 to 80years. Few jarrah logs persistbeyond 100 years.• At Log Decay class 9 the woodis highly combustible and ifignited will completely burnaway.• Log combustibility increasesafter about 50 years on theground.Logs/ha2520151050Never Harvested - Two plots10 20 30 40 50 60 70 80 90Log Decay age class (years)

Log Decomposition classLogLog decomposition classcharacteristics1 2 3 4 5Bark intact intact trace absent absentTwigs

Impacts <strong>of</strong> previous <strong>harvesting</strong>Log numbersLog volume (m 3 /ha)454035302520151050Previously harvested - log volumesDOB = 20 to 30 cm, 43 logs/haDOB = 30 to 59 cm, 66 logs/haDOB > 59 cm, 25 logs/ha1, 10 years 2, 20 to 30 years 3, 40 to 50 years 4, 60 years 5, 70 to 100yearsDecomposition class, and approximate log ageLog Log volume volumeLog volume (m 3 /ha)454035302520151050Never harvested - log volumeDOB = 20 to 30 cm, 41 logs/haDOB = 30 to 59 cm, 40 logs/haDOB > 59 cm, 14 logs/ha1, 10 years 2, 20 to 30 years 3, 40 to 50 years 4, 60 years 5, 70 to 100yearsDecomposition class, and approximate log age

Current harvest <strong>of</strong> CWD80.6 m 3 /haHarvested29.4 m 3 /ha~ 3.7 to 6.1 m 3 /ha9.4 m 3 /haTotal <strong>of</strong> 110 m 3 /ha <strong>of</strong> logs(CWD with DOB>20cm)

Tree fall ratesDiameterFall rateStemsTreesclass(cm)% perdecadeper hafalling per100 yearsper hectare1.2Number <strong>of</strong> trees falling per 100 years per hectare25 51.935 26.945 15.455 1.2 9.2 1.1065 2.1 5.4 1.1375 2.1 3.4 0.71Number <strong>of</strong> trees falling1.00.80.60.40.285 2.1 1.9 0.4095 1.6 1.1 0.18105 3.1 0.7 0.22115 4.9 0.3 0.15125 3 0.2 0.06135 2.9 0.1 0.03145 2.4 0.2 0.05155 4.1All stems 116.7>59 cm 2.7 22.5 3.00.055 65 75 85 95 105 115 125 135 145Diameter class• Large standing jarrah (> 59 cm diameter) have lowrates <strong>of</strong> fall.• Approximately 3 trees per ha will fall in 100 years (>59 cm diameter).• <strong>The</strong>se large diameter logs contribute a large volumeto the forest floor.

Hollows• Few logs have hollows• 408 hollows in 275 logs from 1451 logs• Never harvested 47.4 ± 23.7 hollows/ha• Previously harvested 24.4 ± 3.8 hollows/ha• Only 46 hollows potentially suited to Chuditch,Numbat, or Mardo• Never harvested 6.0 ± 3.2 hollows/ha• Previously harvested 1.9 ± 0.7 hollows/ha• Twice as many hollows on never harvestedsites (ns) and three times as many usablehollows (ns).• Harvesting does not increases the availability<strong>of</strong> log hollows – may decrease it• Logs with hollows are more likely to occur inlarge diameter logs• Logs with hollows are in all decompositionclasses but are more likely to occur inDecomposition classes 3, 4, and 512Number <strong>of</strong> logs with usablehollows108642046 usable hollows found in 1451 logs25 35 45 55 65 75 85 95 105 115 125 135Log diameter class

Conclusions• Harvesting– Large amounts <strong>of</strong> CWD (110m 3 /ha).– Current harvest <strong>of</strong> CWD is relatively small– Possible future deficit in the large diameter highly decayed material• Research – Deficit in large decayed material– Is this <strong>impact</strong> a concern ?– What species will be <strong>impact</strong>ed– Volume required• Research – Log Decay, log age and fire– Effect <strong>of</strong> log diameter on Log Decay age.– Combustibility and Log Decay, and fire frequency and decay rate.• Research – Hollows– Log hollows suited to fauna are very rare– Far more common on never harvested. Why?– Where are the potentially usable hollows,• Management– Monitor CWD volumes, and assess decay using 9 stage Log Decay assessment– Are our log habitat retention prescriptions targeting the right logs?

Acknowledgements• Alcoa World Alumina, Australia• Barrack Silicon• Forest Products Commission staff• Rob Hill, Gunnar Hornum, Pam Laird, DavePickett