title: Does climate directly influence NPP globally?
abstract: The need for rigorous analyses of climate impacts has never been more crucial. Current textbooks state that climate directly influences ecosystem annual net primary productivity (NPP), emphasizing the urgent need to monitor the impacts of climate change. A recent paper challenged this consensus, arguing, based on an analysis of NPP for 1247 woody plant communities across global climate gradients, that temperature and precipitation have negligible direct effects on NPP and only perhaps have indirect effects by constraining total stand biomass (Mtot ) and stand age (a). The authors of that study concluded that the length of the growing season (lgs ) might have a minor influence on NPP, an effect they considered not to be directly related to climate. In this article, we describe flaws that affected that study's conclusions and present novel analyses to disentangle the effects of stand variables and climate in determining NPP. We re-analyzed the same database to partition the direct and indirect effects of climate on NPP, using three approaches: maximum-likelihood model selection, independent-effects analysis, and structural equation modeling. These new analyses showed that about half of the global variation in NPP could be explained by Mtot combined with climate variables and supported strong and direct influences of climate independently of Mtot , both for NPP and for net biomass change averaged across the known lifetime of the stands (ABC = average biomass change). We show that lgs is an important climate variable, intrinsically correlated with, and contributing to mean annual temperature and precipitation (Tann and Pann ), all important climatic drivers of NPP. Our analyses provide guidance for statistical and mechanistic analyses of climate drivers of ecosystem processes for predictive modeling and provide novel evidence supporting the strong, direct role of climate in determining vegetation productivity at the global scale.
authors.affiliation: SYSU-Alberta Joint Lab for Biodiversity Conservation, State Key Laboratory of Biocontrol and School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China.
authors.forename: Chengjin
authors.initials: C
authors.lastname: Chu
authors.affiliation: Department of Ecology and Evolution, University of California Los Angeles, Los Angeles, CA, 90095, USA.
authors.forename: Megan
authors.initials: M
authors.lastname: Bartlett
authors.affiliation: Ministry of Education Key Laboratory of Western China's Environmental Systems, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Youshi
authors.initials: Y
authors.lastname: Wang
authors.affiliation: SYSU-Alberta Joint Lab for Biodiversity Conservation, State Key Laboratory of Biocontrol and School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China.|Department of Renewable Resources, University of Alberta, Edmonton, AB, T6G 2H1, Canada.
authors.forename: Fangliang
authors.initials: F
authors.lastname: He
authors.affiliation: Department of Plant and Environmental Sciences, University of Copenhagen, Frederiksberg, DK-1871, Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Weiner
authors.affiliation: CNRS, ENFA; UMR5174 EDB (Laboratoire Evolution et Diversité Biologique), Université Paul Sabatier, Toulouse, France.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Chave
authors.affiliation: Department of Ecology and Evolution, University of California Los Angeles, Los Angeles, CA, 90095, USA.
authors.forename: Lawren
authors.initials: L
authors.lastname: Sack
mesh_terms: D018533:Biomass; D002980:Climate; D017753:Ecosystem; D008962:Models, Theoretical; D063245:Plant Development; D010944:Plants / Q000378:metabolism*; D011891:Rain; D012621:Seasons; D013696:Temperature
keywords: carbon; climate change; net primary productivity; production; rainfall