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

1.Current experimental design/data collection and ties to future experimental design 2.Future experimental design 3.New experiments Fate of datasets – three main decisions 1.Whether to maintain a data collection 2.Whether to maintain all replicates 3.Whether to maintain sampling frequency

Potential considerations and criteria for deciding future data collection efforts (i.e., future of present data collection efforts). I. 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 II. 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? III. Considerations to maintain sampling frequency Shorter term dynamics are relevant ecologically and to BNZ goals

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???

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

Davidson and Janssens Nature 440: Davidson and Janssenns, 2006 and Janssens Nature 440: Soil Organic Matter The roles of substrate and environment

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

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 Soil Organic Matter

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

Juday and Alix - IPEV/UAF Compensatory effect of adding moisture Deleterious effect of withdrawing moisture Above median temperature Below median temperature cool/moist hot/dry r 2 =.77 Lowerthreshold? Upperthreshold? Range of sensitivity?

Future directions for vegetation dynamics: Scaling in time and space

From McGuire, Chapin, Walsh, and Wirth Integrated regional changes in arctic climate feedbacks: Implications for the global climate system. Annual Review of Environment and Resources 31: Physiology Climate warming Structure Land Use composition, vegetation shifts Disturbance CO 2, SH  Permafrost warming, thawing Physical feedbacks Biotic control Mediating processes       Snow cover 1, 2, 3, 4 5, 6, 7 8, 9 10, 11 12, 13 A B C enzymes, stomates fire, insects logging, drainage, reindeer herding D E I II IV III V  fast (seconds to months) intermediate (months to years) slow (years to decades) Response time Mechanisms:  : albedo GH: ground heat flux SH: sensible heat flux CO 2, CH 4 : atmospheric concentration 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  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:   Physical feedbacks: (14) increased, then reduced heat sink GH ,SH  (15) watershed drainage SH  (16) earlier snowmelt  