Shoo, Luke P., and Valdez Ramirez, Vanessa (2010) Global potential net primary production predicted from vegetation class, precipitation, and temperature: comment. Ecology, 91 (3). pp. 921-923.

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Abstract

[Extract] Terrestrial vegetation acts as a reservoir for significant amounts of carbon and is involved in annual processing of carbon through photosynthesis and respiration (Clark 2007). Empirical study of contemporary patterns of terrestrial net primary production (NPP) is therefore critical for understanding how the global carbon budget will be affected by ongoing climate change (Clark et al. 2003). Field-based measurements of NPP are necessary to calibrate process-based models and remote sensed surrogates of productivity (Chen et al. 2004, Nightingale et al. 2008) as well as to build algorithms that link NPP to climate at global scales (Lieth 1975, Schuur 2003).

In a recent analysis, Del Grosso et al. (2008) present an updated model of the global relationship between NPP and climate. The Del Grosso et al. (2008) model was considered to be an improvement on previous algorithms in two main respects. First, the model allowed for separate fitting of climate–NPP relationships for tree- and non-tree-dominated systems. For a given level of precipitation, non-tree-dominated systems were shown to exhibit significantly lower NPP than tree-dominated systems so it would seem sensible to parameterize equations for the two systems separately. Second, the new model drew upon a greatly expanded data set of NPP compiled as part of the Ecosystem Model–Data Intercomparison (EMDI) project (Olson et al. 2001) supported by the National Center for Ecological Analysis and Synthesis (NCEAS) in Santa Barbara, California, USA. The worldwide synthesis of data is expected to improve coverage, representation and replication of data from vegetation types, climates, and soils used to parameterize models. Here we raise some concerns about the methodological approach used to derive the “improved” models and their application in the retrospective reconstruction of past global trends in NPP in response to 20th-century climate change.

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