Scott Goetz Changes in Productivity with Climate Change at High Latitudes: the role of Disturbance

J. Hansen et al., PNAS 103: (2006) Average T in versus base, °C

Major Arctic Feedbacks to the Climate System From Arctic Climate Impact Assessment

Fires have become more frequent & extensive.. Temperature and Fire Trends in North American High Latitudes Burned area Air Temp. ∆T a

Soil Organic Carbon is Concentrated in High Latitudes Source: USDA, graphic by Steve Allison (UCI) “The Carbon Bomb”

Carbon Stock in Russian Forests Houghton et al. (2007) ERL

Fire Disturbance in the Boreal Forest photos: Jim Randerson

High fire severity Low fire severity Mature conifer Mixed deciduous/conifer Conifer Low density mature conifer ↑ drainage ↑ active layer Warmer soil ↓ drainage ↓ active layer Cooler soil ↑ Albedo ↓ NPP ↓ Albedo ↑ NPP Resprouting shrubs Forbs and grasses ↓ Albedo ↓ NPP ↓ Biomass ↑ SOC ↑ Albedo ↑ NPP ↑ Biomass ↓ SOC accumulation ↑ Albedo ↓ NPP ↓ Biomass ↓ SOC accumulation ↓ Albedo ↑ NPP ↑ Biomass ↑ SOC accumulation High density mature conifer Time Conditions Predictions Goetz et al. ERL 2007 {Mack, Johnstone, Kasischke} Fire Severity Implications for Trajectories of Regrowth Productivity & Albedo

Soja et al RSE Fires & Burned Area Maps

Large Fire Database (Stocks) Burned Area Maps Large Fire Database (Brian Stocks, CFS) Vegetation index

Satellite Monitoring of Forest Regrowth following Fire Anomalies: Burned –vs– Unburned Areas burned unburned difference fire event → Growing Season (JJA, bi-monthly) Goetz et al. RSE 2006

Unburned Areas Photosynthesis Trends Goetz et al. PNAS 2005 Trend Tundra m ha (%) Unburned Forest Negative 2.7 ( 4%)25.8 (22%) Near Zero45.1 (62%)87.9 (74%) Positive24.5 (34%) 5.1 ( 4%)

Trends In Photosynthetic Activity Trend (-Feedback) -Trend (+Feedback) Goetz et al. ERL 2007

Weakening of Mid to High Latitude Carbon Sinks Observed weakening of the growth rate of terrestrial carbon sinks in these regions. Angert et al. 2005, PNAS; Buermann et al. 2007, PNAS; Ciais et al. 2005, Science; Bunn & Goetz 2006 Earth Int. Summer Summer /05 NDVI Anomaly [Normalized Difference Vegetation Index] Myneni et al Science, Slayback & Tucker et al., Zhou et al. [others].

Why do trends in Tundra differ from those of Forest? Responses to Climate Using gridded climate data (CCM) Tundra responds primarily to maximum summer temperature Forest responses are more complicated Mostly key on previous year’s conditions Spring minimum temperatures (+) & precipitation (+) Summer max temperature (-) Bunn & Goetz, 2005, GRL

Links between High Latitude Productivity and “Drought” Zhang, Kimball et al., JGRb in press Bunn, Goetz, Kimball et al. Eos 2007 Net Productivity Dryness of Air (VPD)

D’Arrigo et al Alaskan Tree Ring Indices Temperature correlation Precip correlation

D’Arrigo et al Extra-tropical Temperatures and Tree Ring Indices

Changes in Shrub Growth at High Latitudes Alaska North Slope photos courtesy of Ken Tape, UAF

Summer net C exchange measured by a mobile eddy covariance tower compared with a reference stationary tower located in tundra Transitions to shrub tundra and forest are likely to lead to greater summer C storage. Carbon fluxes at Council, Alaska courtesy of C. Thompson

Changes in vegetation distribution of Arctic Ecosystems will have substantial effects on summer water and energy exchanges between the land surface and the atmosphere (e.g. Thompson et al. 2005, Chapin et al. 2005, Randerson et al. 2006) Summer Albedo Strong correlations between above-ground biomass and albedo, latent & sensible heat fluxes, and net radiation. Above-ground biomass (g m -2 ) Tundra Low shrub Tall shrub Woodland Forest

Anaktuvuk River Fire in Tundra, North Slope of Alaska 2007 ~70 km long and ~13-20 km wide, total >1000 km 2