The burial of aboveground woody debris an important source of soil carbon. Jogeir N. Stokland

Transcription

1 The burial of aboveground woody debris an important source of soil carbon Jogeir N. Stokland Helsinki 7 th -8 th April 2014

2 Remaining mass (%) Common view of wood decomposition stage 1 stage 2 stage 3 40 stage stage 5 Assumptions: - complete above-ground decomposition - constant decomposition rate, climate and wood attribute dependent Time since death (years)

3 Buried wood is common (but not everywhere) m 3 /ha m 3 /ha m 3 /ha m 3 /ha m 3 /ha m 3 /ha m 3 /ha 935 m 3 /ha Buried dead wood in moss-covered organic soil, east Canada; up to 515 years old (Moroni et al. 2010) Green Brown broadleaved Red conif., wildfire Source: Moroni, M. T. et al. (ms) Buried wood: a common yet poorly documented form of coarse woody debris

4 Partly overgrown wood in Norway Downed logs, exposed (< 50 % covered by ground vegetation) Downed logs, partly overgrown (> 50 % covered by ground vegetation)

5 % partly overgrown logs Overgrown dead wood in Norway 80 Recently dead Alpine North boreal Mid boreal South boreal Hemi boreal Nemoral Little decayed Medium decayed Very decayed Almost decomposed Hemi boreal broadleaved South boreal Mid boreal North boreal (n = 2087 logs) (n = 2014 logs) (n = 1128 logs) (n = 1291 logs) Study area: SE Norway 150 sample sites 6250 downed logs 1) Burial absent in dry nemoral forest, but common in boreal forest. 2) increasing decay class (and correlating ground contact) increase probability of burial

6 % partly overgrown logs Overgrown wood and swamp forests Hemi boreal broadleaved South boreal Mid boreal North boreal Hypothesis: paludified (peat-covered) forest ground facilitate wood burial Cfr. Dynesius, M., Gibb, H., Hjältén, J Surface covering of downed logs: drivers of a neglected process in dead-wood ecology. PLoS ONE, 5(10): e Rich swamp forest Spruce swamp forest Pine swamp forest (Source: TemaNord 2003:514)

7 Carbon content and decomposition of buried wood

8 % partly overgrown logs Carbon content of buried wood nemoral broadleaved boreal 99 % 80 % of C released above-ground Hemi boreal broadleaved South boreal Mid boreal North boreal (n = 2087 logs) (n = 2014 logs) (n = 1128 logs) (n = 1291 logs) 1 Recently dead 2 Little decayed 3 Medium decayed 4 Very decayed 5 Almost decomposed 20 % of C from above-ground wood is buried

9 Long-term preservation, organic soils Wood buried years ago Eckstein et al (Dendrochronologia 27: )

10 Long-term preservation, organic soils Cross section of subfossil pine stems (a) 220-year old tree with regular narrow rings typical for the eastern bog areas (b) irregular growth pattern with formation of reaction wood in all directions, indicating unstable, wet soil conditions; (c) eccentric stem disks, characteristic for base of bent stems; (d) regular growth pattern with strong decrease in ring width (age trend) characteristic for growth on mineral soil; Eckstein et al (Dendrochronologia 27: )

11 Long-term preservation, landslide Buried 2-8 million years ago

12 Wetness enhances soil carbon content Mineral soils in Norway predicted from Yasso 07 and observed Precipitation Precipitation < 700 mm mm > 1200 mm Soil drainage Similar comparisons of predicted and observed soil carbon content suggest that mineral soil has increasingly higher carbon content with poorer soil drainage.

13 Conclusions 1. Buried wood is a (very) common phenomenon in boreal forests 2. Several factors facilitate burial (climatic zones/paludification, forest type, ground vegetation, ) 3. Burial slows down decomposition (lower temperature, wetness/anoxic conditions) 4. Estimates needed: a) frequency of burial b) decomposition rates