Influence of spring and autumn phenological transitions on forest ecosystem productivity

Abstract

We use eddy covariance measurements of net ecosystem productivity (NEP) from 21 FLUXNET sites (153 site-years of data) to investigate relationships between phenology and productivity (in terms of both NEP and gross ecosystem photosynthesis, GEP) in temperate and boreal forests. Results are used to evaluate the plausibility of four different conceptual models. Phenological indicators were derived from the eddy covariance time series, and from remote sensing and models. We examine spatial patterns (across sites) and temporal patterns (across years); an important conclusion is that it is likely that neither of these accurately represents how productivity will respond to future phenological shifts resulting from ongoing climate change. In spring and autumn, increased GEP resulting from an 'extra' day tends to be offset by concurrent, but smaller, increases in ecosystem respiration, and thus the effect on NEP is still positive. Spring productivity anomalies 3227This journal is q 2010 The Royal Society on May 11, 2018 http://rstb.royalsocietypublishing.org/ Downloaded from appear to have carry-over effects that translate to productivity anomalies in the following autumn, but it is not clear that these result directly from phenological anomalies. Finally, the productivity of evergreen needleleaf forests is less sensitive to phenology than is productivity of deciduous broadleaf forests. This has implications for how climate change may drive shifts in competition within mixedspecies stands.

Geographical pattern in first bloom variability and its relation to temperature sensitivity in the USA and China

“…The phenological change relating to the start and end of the growing season can affect the vegetation productivity and carbon cycle (Keenan et al 2014;Richardson et al 2010Richardson et al , 2013. Also, the shift in plant phenophases would result in mismatches between plants and pollinators, predators and prey, and pests and hosts (DeLucia et al 2012;Donnelly et al 2011;Hegland et al 2008).…”

Toward a synthetic understanding of the role of phenology in ecology and evolution

“…Phenology determines the time period over which photosynthesis can occur, and the increase in primary productivity resulting from this temporal effect can exceed the direct effect of temperature on photosynthetic rate (Piao et al 2007). In this issue, Richardson et al (2010) investigate how this phenological effect on ecosystem productivity varies across temperate forest types and between spring and autumn seasons, showing that an extended growing season can increase net productivity despite increased carbon loss at high temperatures.…”

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

“…We used relative rather than absolute (e.g., LAI = 1.0 m 2 m À2 or GEP = 2 g C m À2 day À1 ) measures to account for differences in magnitude of both leaf area and CO 2 fluxes across sites (see also Richardson et al, 2010 for a similar approach; alternative methods have been proposed elsewhere, e.g., Gu et al, 2003).…”

“…GDD is growing degree days; T is temperature; C is carbon; PFT is plant functional type (2003) tion, for both deciduous and evergreen sites, we included a series of diagnostic phenological metrics extracted from the measured and modeled time series of NEE and GEP. Transition dates and thresholds were estimated from smoothing splines fit to measured and modeled data at the daily time step, as illustrated in Richardson et al (2010). The phenological transition dates we estimated from the data were as follows:…”

“…Phenology influences both spatial and temporal (at seasonal-to-interannual time scales) variability in ecosystem productivity (Baldocchi et al, 2001;Churkina et al, 2005;Richardson et al, 2009aRichardson et al, , 2010Dragoni et al, 2011), and it is of fundamental importance for ecosystem carbon cycling, terrestrial carbon sequestration, and mitigation of anthropogenic CO 2 emissions. Furthermore, phenology affects the following: hydrology (Hogg et al, 2000), as leaf-out is accompanied by an increase in evapotranspiration and reduced throughfall; nutrient cycling processes (Cooke & Weih, 2005), as senescence results in fresh litter inputs to the soil; and atmospheric and climate system feedbacks (Schwartz, 1992), as the amount and condition of foliage present affects albedo, surface energy balance, and surface roughness (Moore et al, 1996;Sakai et al, 1997;Peñ uelas et al, 2009).…”