Phenology, growth, and allocation in global terrestrial productivity

Authors: Jackson, RB, MJ Lechowicz, X Li, HA Mooney

We discuss the roles of phenology, growth, and allocation for terrestrial plant productivity. Data for trees are emphasized because the most detailed phenological information is available for forest systems and because forests contain most of terrestrial carbon in plants globally. We begin by providing a short history of the importance of phenology, growth, and allocation for productivity, including theoretical frameworks of Monsi and Kikuzawa. We then discuss various models of phenology and tree growth. Both the timing of shoot growth initiation and the length of the growing season are important, as illustrated with Anic¹s long-term measurements of 40 European tree species. Recent models combined with eddy covariance and satellite analyses indicate that a 5-10 day lengthening of the growing season can increase net productivity for forest systems by as much as one-third. Such a lengthening of the growing season is clearly possible if projections of global warming are correct. We also discuss the coupling of shoot and root growth. Recent analyses emphasize the importance of belowground productivity for global NPP, with fine roots alone likely responsible for one-third of terrestrial NPP. We end by highlighting two areas where progress should be especially fruitful in the next decade: 1) the combined use of remotely sensed data and global models to estimate global productivity, and 2) techniques for improving estimates of belowground productivity.