Jonathan Seaquist

Ecosystem phenology plays an important role in carbon exchange processes and can be derived from continuous records of carbon dioxide (CO2) exchange data. In this study we examined the potential use of phenological indices for characterizing cumulative annual CO2 exchange in four contrasting northern peatland ecosystems. We used the approach of Jonsson and Eklundh (2004) to derive a set of phenological indices based on the daily time series of gross primary production (GPP), ecosystem respiration (R-e), and net ecosystem production (NEP) measured in the four peatland sites. The main objectives of this study were (a) to examine the variation in phenological indices across sites and (b) to determine the relationships among phenological indices, environmental conditions, and cumulative annual CO2 exchange. The phenological index used to define the "start of the growing season" showed good potential for differentiation among sites based on their average annual site GPP. Sites with earlier growing seasons had the highest average annual site GPP. The "peak CO2 exchange rate" phenological index performed best in reflecting variations among sites and for estimating annual values of GPP, R-e, and NEP (Pearson correlation coefficients ranged between 0.77 and 0.99, p<0.05 for all.). The phenological indices and annual GPP, R-e, and NEP were sensitive to winter (January-March) and summer (July-September) temperature and precipitation, but correlations, though significant, were weak.