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4-6 th Feb 2008, Weintal Resort, Tanunda, Australia.

Seasonal Changes of Soil and Ecosystem Respiration in a Young Forest J Hunt, T McSeveny and F Kelliher. 4-6 th Feb 2008, Weintal Resort, Tanunda, Australia. Carbon storage. New Zealand is a signatory to the Kyoto Protocol Required to create inventory of its GHG sources and sinks

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4-6 th Feb 2008, Weintal Resort, Tanunda, Australia.

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  1. Seasonal Changes of Soil and Ecosystem Respiration in a Young ForestJ Hunt, T McSeveny and F Kelliher 4-6th Feb 2008, Weintal Resort, Tanunda, Australia.

  2. Carbon storage • New Zealand is a signatory to the Kyoto Protocol • Required to create inventory of its GHG sources and sinks • Reduce GHG emissions to a fixed amount • NZ GHG emissions are increasing • Increased fuel use • Increased reliance on coal power stations • Increase in methane emitters • Reduction in pine plantations • Effort going into carbon storage in marginal lands, esp. re-afforestation with kanuka)

  3. The forest • Kanuka (Kunzia ericoides, Myrtaceae) • Short lived (60-100 yrs) • Fast growth habit, light demanding • Secondary invader, reclaims old pasture • Exotic grass/herb understory • 7m tall trees, 3 500 ha-1 • First forest on site, 35 yrs old • 49 tC ha-1,equivalent to a net gain of 1.4 tC ha-1 y-1

  4. Island in the middle of the braided Rakaia River Forest occupies 800 m x 2000 m 50 km SW of Christchurch (43 ºS) 60 masl Soils 100 yrs old NW foehn + katabatic winds Site Location X

  5. Instrumentation • Solar powered, closed-path, eddy covariance • Profiling system • Background met. • Soil moisture and temperature • Monthly soil surface respiration and biomass measurements

  6. Seasonal understory biomass • Tree leaf biomass was ~ 200 g m-2 • Unimodal change in total understory biomass • Change in live:dead ratio between spring and autumn

  7. Seasonal ecosystem respiration • Summer drought reduced ecosystem respiration by up to 7-fold • Spring and autumn respiration have similar response to temperature

  8. Ecosystem respiration under well watered conditions • At same temperature, autumn respiration 13% lower then in spring • Suggests change in carbon substrate supply or quality

  9. Response of ecosystem respiration to changes in soil VWC • Fit R10 to all data to remove temperature effect • If VWC < 12% then linear response of R10 to increasing soil moisture

  10. Comparison between soil surface and ecosystem respiration • Soil and ecosystem respiration bimodal • Ratio of Rs/Re remained stable until rewetting in April • After rewetting 3-fold increase in Rs • Sustained increase in Rs for 2 months

  11. Conclusions • Response of ecosystem respiration to temperature greater in spring than autumn • Due to increased substrate availability with active growth and greater biomass • When VWC > 12%, temperature and substrate availability were main drivers of ecosystem respiration • Rs/Re varied from 50-90%, not caused by differences in soil-canopy temperatures • Dynamic forest understorey can influence magnitude and seasonal maxima of ecosystem respiration

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