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Author: Noormets, A.;
Source: In: Noormets, A. Phenology of ecosystem processes. Springer: NYC, New York. ix-xiii.
Publication Series: Book
Description: The effect of warming temperatures on biological processes has been well documented (Badeck et al. 2004; Parmesan and Yohe 2003), and is evidenced by changes in the timing of discernible life cycle events, like leaf-out and flowering of plants, and migration and reproduction of animals. It is implicit that these life cycle events are representative indicators of a change in some underlying process. Ever more sophisticated general circulation and ecosystem productivity models have narrowed the boundaries of uncertainty sufficiently to bring attention to the effect of the seasonal timing of ecosystem processes, notably carbon and water exchange. It is becoming increasingly evident that both interannual and regional variation have a strong phenological component (Baldocchi 2008). The associated changes in surface energy balance and partitioning (Wilson and Baldocchi 2000) both affect and are driven by vegetation phenology (Alessandri et al. 2007; Baldocchi 2008; Morisette et al. 2008). Quantifying the seasonality of these processes is required for constraining ecosystem productivity models (Kramer et al. 2002), refining remote sensing (RS) estimates of ecosystem properties (Morisette et al. 2008) and narrowing the uncertainty bounds on global biogeochemical models (Olesen et al. 2007). While the vegetation-index-based assessments (e.g. Goetz et al. 2005) broadly corroborate ground-based observations of long-term trends of lengthening growing season (Menzel 2000, 2003; Menzel et al. 2005), the patterns of interannual variation in land surface reflectance and vegetation processes do not always coincide (Badeck et al. 2004; Fisher et al. 2007). We hypothesize that the power of RS monitoring of vegetation processes would be improved if the calibration of the reflectance data was done against the process of interest (as opposed to validating a RS gross productivity product against a degree-day model of bud-break, for example). This is all the more important when considering that even ground-based observations may yield conflicting results when data collected with different methods is compared, because they may entail different (and sometimes implicit) assumptions (Parmesan 2007). Furthermore, process-based approach is required because even closely related processes do not have the same environmental drivers and same sensitivities to them. For example, the onset of ecosystem respiration is generally delayed in relation to gross productivity in temperate deciduous and boreal conifer forests (Falge et al. 2002). While continuous in nature, the driving factors of these processes vary seasonally (Davidson and Holbrook, current volume; Carbone and meeting into this book. It has been a rewarding experience. I am grateful to the Southern Global Change Program of US Forest Service for support and accommodation throughout the preparation of this volume.
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Noormets, A. 2009. Preface. In: Noormets, A. Phenology of ecosystem processes. Springer: NYC, New York. ix-xiii.
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