TROPICAL PEAT ACCUMULATION AND DECAY IN RELATION TO MANAGEMENT

Transcription

1 TROPICAL PEAT ACCUMULATION AND DECAY IN RELATION TO MANAGEMENT Michael A. Brady Workshop on Integrated Management and Rehabilitation of Peatlands 6-7 February 2004, Kuala Lumpur

2 Contents PROCESS MODELS OF PEAT ACCUMULATION AND DECAY TROPICAL PEAT ACCUMULATION EXPANDED PEAT MODEL RESULTS OF SUMATRA STUDY IMPLICATIONS FOR MANAGEMENT

3 PROCESS MODELS OF PEAT FIXATION AND DECAY Simplest quantitative model of peat accumulation x p = ( 1 e kt ) k x - accumulated mass of peat p - rate of addition of plant dry mass k - decay rate t - age of peat at a given depth

4 PROCESS MODELS OF PEAT FIXATION AND DECAY Decay rates in the catotelm and acrotelm layers of temperate peatlands differ 1-10% 2-layer concept to expand the basic peat model x = x ( t ) + x ( ) total A C C x total - total mass of peat x A - mass of the acrotelm layer with a characteristic time t that matter stays in the aerobic zone x C - steady state mass in the anaerobic zone

5 Simulated catotelm accumulation (dashed line) and decay (solid lines) over time in raised peat deposits in East Sumatra Catotelm thickness (m) Accumulated catotelm mass (kg m -2 ) asymptotic limit PI12 PI9 PI6/SE6 PS Time (years)

6 DOES THE MODEL EXPLAIN VARIATION IN TROPICAL PEAT ACCUMULATION? Padang Island 12 m peat Sugihan East 6 m peat 3 m peat Padang-Sugihan SUMATRA

7 TROPICAL FORESTED PEAT ACCUMULATION VS OTHERS accumulation rates faster average ground temperatures much higher peat originates largely from trees changes in forest composition, physiognomy and structure hydrological conditions little understood

8 RESULTS OF SUMATRA STUDY Autogenic controls (plant composition, structure, peat texture) and allogenic controls (climate, geology, hydrology) change across gradient of increasing peat depth

9 70 1) Aboveground litter on peat 2) Intact small roots in peat 3) Root fragments and chaff in peat 4) Matrix of hemic peat Woody nature of forested peatlands leads to variation in organic components of acrotelm peat kg m Study areas: Peat depth: PS3 SE6 PI6 PI9 PI12 3 m 6 m 6 m 9 m 12 m

10 Decay characteristics of aboveground litter change with increasing peat depth Study area and site 3 m deposit 6 m deposit 12 m deposit Litter variable PS3 SE6 PI6 PI9 PI12 Litter dry mass (kg m -2 ) Litterfall dry mass (kg m -2 a -1 ) Decay (kl): Mean residence time in litter layer (years) Mean residence time in litter bags (years)

11 Decay characteristics of peat from the top and base of the acrotelm layer change with increasing peat depth Peat respiration (mg CO 2 g d Acrotelm top (0-20 cm) PS3 SE6 PI6 PI9 PI12 Acrotelm base (20-40 cm) PS3 SE6 PI6 PI9 PI12 Study site 100% 50%

12 SUMMARY OF RESULTS Medium sites - slower rates of peat decay appeared more important for peat accumulation than faster rates of OM inputs (allogenic influence) Deep sites - rapid inputs of OM from roots appeared more important for OM accumulation that low rates of litter decay (autogenic influence)

13 SUMMARY OF RESULTS Sphagnum model not distinguish changes in OM input mass and resource quality Must be expanded aboveground and belowground inputs shifting plant composition and structure in tropical peatlands

14 EXPANDED MODEL OF PEAT ACCUMULATION Additions of mixed organic matter occur throughout profile of forested peat Expanded model compartments: 1. layer of aboveground litter 2. top layer of acrotelm peat 3. basal layer of acrotelm peat 4. top layer of catotelm peat 5. basal layer of catotelm peat

15 PI p = 0.00, k = p = 0.94, k = p = 0.56, k = p = 0.47, k = p = 0.51, k = Reconstruction of dry mass accumulation starting from the 14C age of the acrotelm base to the present time, does not adequately reflect present conditions Dry mass accumulation from acrotelm base (kg m -2 ) (>927) PI SE (>560) (>555) p = 0.00, k = p = 0.08, k = p = 0.08, k = p = 0.24, k = p = 0.69, k = 0.45 p = 0.00, k = p = 0.05, k = p = 0.05, k = p = 0.13, k = p = 0.73, k = PS3 p = 0.00, k = p = 0.04, k = p = 0.04, k = p = 0.22, k = p = 1.19, k = Litter (>260) Top acrotelm Base acrotelm New catotelm Old catotelm Years before present

16 PI p = 0.00, k = p = 0.57, k = p = 0.56, k = p = 0.47, k = p = 0.51, k = (>927) Age-corrected reconstruction of dry mass accumulation showing all sites aggrading slowly Dry mass accumulation from acrotelm base (kg m -2 ) PI6 (>560) 0 SE (>555) p = 0.00, k = p = 0.20, k = p = 0.08, k = p = 0.65, k = p = 0.69, k = 0.37 p = 0.00, k = p = 0.18, k = p = 0.05, k = p = 0.66, k = p = 0.73, k = PS3 (>260) p = 0.00, k = p = 0.14, k = p = 0.04, k = p = 0.85, k = p = 1.19, k = Litter 125 Top acrotelm 100 Base acrotelm 75 New catotelm Old catotelm Years before present

17 CONCLUSION 1 Autogenic controls (plant composition, structure, peat texture) more important than allogenic controls (climate, geology, hydrology) across gradient of increasing peat depth

18 CONCLUSION 2 The 3 model variables were affected differently across the gradient of increasing peat depth: Age not associated with increasing peat depth OM inputs varied due to vegetation composition (resource quality) and structural changes (fine roots) Decay varied due to shift in controls from moisture to resource quality

19 CONCLUSION 3 Age-corrected model simulation of the study areas suggests that: Medium peat deposits continue to accumulate peat at surface Deep peat deposit has reached steady state where watertable not rising further because root mat or potential maximum reached

20 IMPLICATIONS FOR CONSERVATION AND MANAGEMENT Peat forests where root mats have declined or disappeared by natural or artificial causes will remain in equilibrium or subside, but will not expand Net accumulations of peat will likely occur where high water levels and thick root mats still exist, and possibly in altered areas where these conditions are re-established

21 IMPLICATIONS FOR CONSERVATION AND MANAGEMENT Better understanding of peat accumulation allows us to identify which peat deposits can be developed and those that should be preserved Deposits in which peat is actively accumulating or in steady state may be given higher conservation status than those that are degrading Model of tropical peat accumulation reveals other management strategies in addition to water table control - the main management tool currently used

22 MANAGEMENT FACTORS 1. Vegetation Composition: Increases in the decomposability of organic matter puts (labile organic matter, high N and P, low lignin) from vegetation due to species changes 2. Belowground Biomass Allocation: Decreases in allocation of belowground biomass production due to species changes and increased nutrient release and availability 3. Microclimate: Increases in moisture losses by convection and evapotranspiration due to forest canopy removal 4. Peat Water Levels: Lowering of water levels through drainage 5. Peat Surface Topography: Increasing peat micro-relief, which promotes more rapid lateral drainage 6. Terrestrial and Aquatic Inputs to Peat: increased inputs of nutrient laden sediments and water from water bodies originally separated from the peat formation 7. Atmospheric Inputs to Peat: increased inputs of nutrients from atmospheric deposition from urban/industrial sources

23 MANAGEMENT FACTORS: Belowground Biomass Allocation Need to conserve forest species known to allocate large amounts of biomass belowground Little understanding of basic silviculture and morphological plasticity of most peat forest species Difficult to determine appropriate species in the absence of field trials under swampy conditions (Tristania, Calophyllum, Campnosperma) Peat forest conditions simulated in settlement and agricultural areas by maximizing tree cover and selection of species for high belowground biomass allocation and low quality litter

24 FURTHER STUDIES REQUIRED TO ENHANCE MANAGEMENT Direct evapotranspiration measurements to assess the effects of vegetation on peat moisture Long-term monitoring of peat elevation changes, waterlevel fluctuations and seasonal climate Monitoring studies to measure the below-surface interflow of water and nutrients through peat Multi-annual aboveground and belowground litter collections to confirm high rates of root production

25 THANK YOU