Growing season and spatial variations of carbon fluxes of Arctic and boreal ecosystems in Alaska (USA)

Abstract

To better understand the spatial and temporal dynamics of CO2 exchange between Arctic ecosystems and the atmosphere, we synthesized CO2 flux data, measured in eight Arctic tundra and five boreal ecosystems across Alaska (USA) and identified growing season and spatial variations of the fluxes and environmental controlling factors. For the period examined, all of the boreal and seven of the eight Arctic tundra ecosystems acted as CO2 sinks during the growing season. Seasonal patterns of the CO2 fluxes were mostly determined by air temperature, except ecosystem respiration (RE) of tundra. For the tundra ecosystems, the spatial variation of gross primary productivity (GPP) and net CO2 sink strength were explained by growing season length, whereas RE increased with growing degree days. For boreal ecosystems, the spatial variation of net CO2 sink strength was mostly determined by recovery of GPP from fire disturbance. Satellite-derived leaf area index (LAI) was a better index to explain the spatial variations of GPP and NEE of the ecosystems in Alaska than were the normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI). Multiple regression models using growing degree days, growing season length, and satellite-derived LAI explained much of the spatial variation in GPP and net CO2 exchange among the tundra and boreal ecosystems. The high sensitivity of the sink strength to growing season length indicated that the tundra ecosystem could increase CO2 sink strength under expected future warming, whereas ecosystem compositions associated with fire disturbance could play a major role in carbon release from boreal ecosystems.

Assessing the spatial variability in peak season CO<sub>2</sub> exchange characteristics across the Arctic tundra using a light response curve parameterization

“…2, Table 2) of the assimilation parameters, suggesting that direct measurements of leaf area could be useful in estimating photosynthesis from tundra ecosystems. Satellite-derived LAI has also been shown to significantly explain photosynthesis in the Alaskan Arctic (Ueyama et al, 2013). Remotely sensed NDVI was not quite as powerful in explaining plant growth; NDVI explained 59-67 % of the variance in assimilation parameters (Fig.…”

“…The frequency of CO 2 flux signal measurements ranged from 5 to 20 Hz depending on the site. Varying data collection frequency between 5 and 10 Hz did not significantly affect resulting fluxes in Kytalyk (van der Molen et al, 2007). With the exception of Samoylov Island, with 1-hourly averaged flux data, all sites have averaged flux data into 30 minute averages.…”

Long-Term Release of Carbon Dioxide from Arctic Tundra Ecosystems in Alaska

“…R0 and Q10 were estimated each day using a 29-day moving window and least squares method (Ueyama et al, 2013). GPP is then calculated as GPP = NEE -ER.…”

Spatial and seasonal variations of CO2flux and photosynthetic and respiratory parameters of larch forests in East Asia

“…This implies that the larch forest requires more heat accumulation to start photosynthesis in colder regions, and this may be owing to the permafrost. Ueyama et al (2013) also reported that the MODIS LAI is the best vegetation index to explain the spatial variation of GPP in Arctic and boreal ecosystems in Alaska, and they suggested that the inclusion of the understory leaves in the MODIS LAI estimation was the probable reason for the better performance to explain the intersite variation of photosynthetic capacity in Alaska, where the understory vegetation plays an important role in the total ecosystem photosynthesis, than other vegetation indices such as the normalized difference vegetation index (NDVI) or enhanced vegetation index (EVI), which are corrected for the canopy background signal. Transfer functions from NDVI and EVI to LAI were different in different vegetation types (Street et al 2007), and this would be another possible reason.…”