Terrestrial biosphere models need better representation of vegetation phenology: results from the North American Carbon Program Site Synthesis

Abstract

Phenology, by controlling the seasonal activity of vegetation on the land surface, plays a fundamental role in regulating photosynthesis and other ecosystem processes, as well as competitive interactions and feedbacks to the climate system. We conducted an analysis to evaluate the representation of phenology, and the associated seasonality of ecosystem-scale CO 2 exchange, in 14 models participating in the North American Carbon Program Site Synthesis. Model predictions were evaluated using long-term measurements (emphasizing the period 2000-2006) from 10 forested sites within the AmeriFlux and Fluxnet-Canada networks. In deciduous forests, almost all models consistently predicted that the growing season started earlier, and ended later, than was actually observed; biases of 2 weeks or more were 566-584, doi: 10.1111/j.1365-2486.2011.02562.x This article is a U.S. government work, and is not subject to copyright in the United States.Global Change Biology (2012) 18,typical. For these sites, most models were also unable to explain more than a small fraction of the observed interannual variability in phenological transition dates. Finally, for deciduous forests, misrepresentation of the seasonal cycle resulted in over-prediction of gross ecosystem photosynthesis by +160 ± 145 g C m À2 yr À1 during the spring transition period and +75 ± 130 g C m À2 yr À1 during the autumn transition period (13% and 8% annual productivity, respectively) compensating for the tendency of most models to under-predict the magnitude of peak summertime photosynthetic rates. Models did a better job of predicting the seasonality of CO 2 exchange for evergreen forests. These results highlight the need for improved understanding of the environmental controls on vegetation phenology and incorporation of this knowledge into better phenological models. Existing models are unlikely to predict future responses of phenology to climate change accurately and therefore will misrepresent the seasonality and interannual variability of key biosphere-atmosphere feedbacks and interactions in coupled global climate models.

Temperate and boreal forest tree phenology: from organ-scale processes to terrestrial ecosystem models

“…This factor is key for an accurate representation of the interannual variability of the carbon balance (Delpierre et al 2012), the tree resistance to abiotic stresses, and the tree reproductive success. However, the seasonality of physiological processes is still poorly represented in TEMs, in which phenological schemes are confined to the simulation of leaf onset and leaf loss in the simplest manner (Table 1; see, also, Richardson et al 2012), and is still rarely used in species distribution models. Phenological models have primarily been developed for simulating the phenology of leaves and flowers, whereas the modeling of the phenologies of other organs (e.g., wood, fine roots, fruits/cones) is still in its infancy.…”

“…This discrepancy is likely, in part, attributed to the fact that the phenology of leaves is relatively more "apparent" 1 and, therefore, easier to monitor than the phenologies of other organs (e.g., wood and fine roots). In addition to the growing number of observational reports on leaf phenology, a number of studies published during the previous 20 years have been dedicated to the modeling of leaf phenology (Hänninen and Kramer 2007;Chuine et al 2013), resulting in the development of models that have been incorporated, with moderate success (see Richardson et al 2012), into terrestrial ecosystem models (TEMs). In contrast, as a consequence of the scarcity of papers documenting the phenology of non-leafy organs in forest trees, the underlying organ-specific phenological processes are often poorly represented in models.…”

Spatial and temporal variability of key bio-temperature indicators on the Qinghai-Tibetan Plateau for the period 1961-2013

“…These bio-temperature indicators are associated closely with plant growth and distribution; therefore, they are often adopted as thresholds in models designed to predict the future effects of climate change on ecosystems Sitch et al, 2003). Numerous models have been developed on the basis of bio-temperature indicators to predict plant phenology and crop production; such models have typically been demonstrated to be robust (Grigorieva et al, 2010;Fu et al, 2012;Richardson et al, 2012). Thus, changes in key bio-temperature metrics can be considered to indicate changes in the structure, function, and distribution of vegetation.…”

“…The total amount of temperature is known as the accumulated temperature or the growing degree-days (Richardson et al, 2012;Fernández-Long et al, 2013) and typically represents a plant's growing-season heat requirements. Owing to the differences in threshold temperatures among various vegetation types, the accumulated temperature must be quantified from variable starting points (ISEQXP CAS, 1988;Zheng et al, 2010;Fernández-Long et al, 2013).…”

Impact of estimated solar radiation on gross primary productivity simulation in subtropical plantation in southeast China

“…carbon dynamics via ecosystem models is necessary for investigating the driving forces and mechanism of carbon sequestration (Pommerening et al, 2011;Richardson et al, 2012). Global solar radiation (R s ) is an essential input variable to ecosystem models.…”