Cascading Thresholds

1. Cascading Thresholds • Subsistence-related changes • Warming to fire to permafrost loss to wetland drying to subsistence change • Warming to fire to altered moose/caribou habitat/access to subsistence change • Cultural assimilation to declining subsistence • Declining subsistence to decreased well-being to migration to cities • Economics-related changes • Global oil shortage to rising village oil prices to migration • Warming to low river level to no barge deliveries to rising fuel costs to migration • Warming to drought to spruce budworm to dry firewood to biofuels to jobs • Warming to permafrost thaw to infrastructure costs to school/airport loss • Rising fire suppression costs to fire co-management to resource manag. plan • Rising fuel costs to smaller hunting radius to altered animal distrib to altered veg

2. Current experimental design/data collection and ties to future experimental design • Future experimental design • New experiments • Fate of datasets – three main decisions • Whether to maintain a data collection • Whether to maintain all replicates • Whether to maintain sampling frequency

3. Potential considerations and criteria for deciding future data collection efforts (i.e., future of present data collection efforts). • Considerations to maintain a data collection: • Data supportive of other research • Data are central to broader BNZ research objectives • Detected or potential to detect important change in ecosystem/community structure • Cost and labor relative to importance/value of data • Considerations to maintain replicates • Detected or potential to detect important divergent patterns over time • Do existing data sufficiently quantify spatial variation to the point where replication can be pared-down? • Considerations to maintain sampling frequency • Shorter term dynamics are relevant ecologically and to BNZ goals

4. Integration and Synthesis – New Experiment • How will potential changes in ecosystem structure alter material fluxes across the landscape • Potential Changes: • Permafrost thaw & thermokarst • Change in alder abundance • Others… • Response variables: • Carbon and nitrogen fluxes • Energy exchange • Successional trajectories • Others… • Experimental design (or start of design): • Watershed approach to monitor hydrologic and gaseous fluxes • Alder removal • Soil warming • Other manipulations???

5. Experimental Approaches to Threshold Change Problem: Threshold changes usually require strong drivers that may be difficult to replicate with experiments Examples: Ecosystem warming experiments that minimally warm the soil Fire experiments that burn at moderate or low severity

7. Soil Organic Matter The roles of substrate and environment Davidson and Janssens. 2006. Nature 440:165-173 Davidson and Janssenns, 2006 and Janssens. 2006. Nature 440:165-173

8. Sensitivities to Climate, succession,regime shifts How are SOM stocks and turnover changing? Goal is to establish: • Causal links • Substrate controls • Environmental controls Soil Organic Matter • Interactive effects • Substrate X DEnvironment • Feedbacks to Ecosystem

9. Soil Organic Matter • Synthesis activities: • site scale models for lter 1, lter 2, lter wet, cpcrw • Litterbag and substrate models • New long-term experiments • Litterbag and incubation, anchored in 5 yr C stock harvests: • Locations via substrate X enviroment • Historic evaluation of archives, data for substrate,environment

10. sig.@ 95% = selected for model (negative) = selected for model (positive) A. A. A. 2nd half winter snow B.Aug rain B. Jul Aug rain sig.@ 95% 2 years prior to ring formation 1 year prior to ring formation year of ring formation r2 = .46 C. Nov Dec snow (neg) Juday and Alix - IPEV/UAF

11. Compensatory effect of adding moisture Below median temperature r2 = .77 Range of sensitivity? Deleterious effect of withdrawing moisture Above median temperature cool/moist hot/dry Upper threshold? Lower threshold? Juday and Alix - IPEV/UAF

12. Future directions for vegetation dynamics: Scaling in time and space

13. Snow cover 12, 13 5, 6, 7 I III 10, 11 V 16 1, 2, 3, 4 8, 9 Climate warming A   Physiology Structure      composition, vegetation shifts enzymes, stomates 14 15 CO2, SH B II Physiological feedbacks: (1) higher decomposition CO2 (2) reduced transpiration SH (3) drought stress: CO2 (4) PF melting: CH4 (5) longer production period: CO2 (6) NPP response to N min: CO2 (7) NPP response to T: CO2 IV Disturbance fire, insects C E Land Use Permafrost warming, thawing logging, drainage, reindeer herding Response time D Structural feedbacks: (8) shrub expansion:  (9) treeline advance: , CO2 (10) forest degradation but CO2, SH (11) light to dark taiga:  but CO2, SH (12) more deciduous forest: , SH (13) fire / treeline retreat:  fast (seconds to months) intermediate (months to years) slow (years to decades) Biotic control Physical feedbacks Mediating processes Physical feedbacks: (14) increased, then reduced heat sinkGH,SH (15) watershed drainage SH (16) earlier snowmelt • Mechanisms: • : albedo GH: ground heat flux • SH: sensible heat flux • CO2, CH4: atmospheric concentration From McGuire, Chapin, Walsh, and Wirth. 2006. Integrated regional changes in arctic climate feedbacks: Implications for the global climate system. Annual Review of Environment and Resources 31:61-91.