KANTOJEN KORJUUN VAIKUTUKSET MAAPERÄN RAVINNEDYNAMIIKKAAN JA RAKENTEESEEN

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1 KANTOJEN KORJUUN VAIKUTUKSET MAAPERÄN RAVINNEDYNAMIIKKAAN JA RAKENTEESEEN LILLI KAARAKKA MARJO PALVIAINEN, RIITTA HYVÖNEN, MIKAEL MARJANEN, HELJÄ-SISKO HELMISAARI INTRODUCTION STAND NUTRIENT DYNAMICS Nutrient cycle closed in an undisturbed system Translocation of nutrients Above ground biomass Bulk deposition N mineralization rate of inorganic N available for plants Litterfall Translocation Throughfall N limiting nutrient Forest floor biomass Stemflow 80 % of N in foliage, 60% C in living vegetation Soil available (exchangeable) elements Uptake Mineralization Below ground biomass Immobilization Weathering Soil (recalcitrant) elemental pool Logging residue C/N high C/N promotes immobilization Leaching 2

2 STAND NUTRIENT DYNAMICS FOREST SOILS IN FINLAND Organic soils 29 % (histosols) Upland, mineral soils podzols (50%), arenosol, cambisols, leptosols C content in boreal forest soils 28 % in the organic layer 68 % in the upper 1 m of mineral soil 4 % lower than 1 m depth (Tamminen and Starr 2006) Photo: Å. Nilsson 3 INTRODUCTION STUMP HARVESTING The intensity of the harvest operation determines the extent of disturbances on soil surface Stump All wood and bark of a tree below the stump crosssection 20,000 hectares harvested in 2010 UPM started pulling stumps in

3 INTRODUCTION STUMP HARVESTING AND SOIL DAMAGE Soil surface disturbance mounding 20 30% stump harvesting % Driving times increased Site sensitivity Lack of long-term trials 5 INTRODUCTION STUMP HARVESTING AND SOIL DAMAGE 6

4 WHY HARVEST STUMPS? Harvestable dry-mass 23 25% of the trunk mass High net recovery of biomass per ha additional revenue Reduces the risk of root rot (Heterobasidion sp., Armillaria sp.) Benefits site preparation, survival of planted seedlings Promotes natural regeneration 7 WHY NOT TO HARVEST STUMPS? Reduces amount of CWD, C and nutrient pools Habitat loss, biodiversity Future costs (productivity) Soil compaction Nutrient leaching and erosion (exposure of mineral soil) Many of the negative effects of stump removal on forest soil are interconnected and site-dependent 8

5 PH.D. PROJECT SOILCHANGESAND ECOSYSTEM RECOVERYFROMCHEMICALAND PHYSICAL LOAD Aim is to assess the effects of physical and chemical load on the longevity of soil changes Effects of stump harvesting soil nutrient, carbon and nitrogen dynamics, acidity and surface disturbance, and soil compaction 9 OBJECTIVES POTENTIAL IMPACTS OF A DISTURBANCE ON SOIL (I.E. HARVESTING) 1 SOIL PHYSICAL PROPERTIES exposure, erosion, compaction 2 SOIL CHEMICAL PROPERTIES loss of SOM, C, N and nutrients 3 SECONDARY EFFECTS biodiversity, regeneration, wood properties, landscape changes 10

6 OBJECTIVES The aim of this study was to determine how stump harvesting affects soil C and N pools, C and N mineralization soil surface disturbance Main hypotheses increased soil disturbance after stump harvest could potentially result in C and N losses through mineralization stump harvest causes larger surface disturbance compared to mounding 11 STUDY SITES Relatively fertile Norway spruce stands Logged in Harvested volume m 3 /ha Treatments: mounding or stump harvesting Logging residues collected in all stands 12

7 SAMPLING SOIL SAMPLING MOUND UNDISTURBED top humus 0-5 cm 5-10 cm cm humus 0-5 cm 5-10 cm cm PIT 0-5 cm 5-10 cm cm 13 SAMPLING SURFACE DISTURBANCE AND SOIL COMPACTION 14

8 LABORATORY WORK Incubation infrared gas analyzer CO2 measured in certain intervals N mineralization difference b/w start inorganic N and incubated inorganic N 15 RESULTS C pools (kg ha -1 ) Mounding = WTH, stump harvest = WTH + S Treatment effects manifested themselves in the surfaces layers 16

9 RESULTS C mineralization Respiration (μg CO 2 -C g -1 day -1 ) higher at all disturbance classes in the top most layers of the soil after stump harvesting 17 RESULTS N mineralization Undisturbed soil higher N mineralization (mg N kg C -1 day -1 ) post stump harvesting Mounds mineralization higher in the top layer after stump harvesting Pits/excavation holes higher N mineralization 18

10 RESULTS Surface disturbance and soil compaction Logged 2010 Logged 2007 Logged RESULTS Surface disturbance and soil compaction Stump harvest clearly increased soil surface disturbance over mounding The proportion of the undisturbed surfaces slightly increases over time at the stump harvested sites Stump harvest had caused soil compaction on the undisturbed surfaces 4 years after harvest 7 years after harvest 13 years after harvest 20

11 CN DYNAMICS POST STUMP HARVEST Disturbance and mixing Lower C/N in soil Decomposition increased C and N mineralization soil recalcitrant C pool affected? 21 CONCLUSIONS Post-stump harvest landscape large surfaces of exposed mineral soil, deep ruts caused by harvesting equipment, water deposition/run-off/erosion Soil compaction changes in the deeper layers? Changes in C fluxes temporal scale? CWD? Photos: HS, Helmisaari 22

12 Stump harvesting represents an increase in the intensity of forest management activities Highly likely to intensify the negative environmental effects of existing forestry practices Need for future studies, follow-up longer time periods Degree of uncertainty remains, large variation in soil C data Whole ecosystem and rotation C budget/pool SFM guidelines Photo: L. Kaarakka 23 STUMP HARVESTING = ROOT SYSTEM HARVESTING? SHARE OF ROOTS IS OVER 70% OF THE HARVESTED SPRUCE STUMPS (VAITTINEN 2008) Photo: M. Nurmi 24

13 DISCUSSION & CONCLUSIONS Forest management perspective WTH vs. stump harvesting vs. conventional harvesting carbon pool? nutrients (N, P, K)? soil acidification Stump harvesting with logging residue retention? immobilization of N by microbes and emerging vegetation Biodiversity CDW, saprohylix species 25 REPORTS AND GUIDELINES 26

14 RESEARCH GROUP / CO-OPERATION University of Helsinki Heljä-Sisko Helmisaari Marjo Palviainen Marjut Wallner Mikael Marjanen Erno Launonen SLU Riitta Hyvönen-Olsson Bengt Olsson Monika Strömgren Tryggve Persson FUNDING Maj and Tor Nessling Foundation 27