Influence of spring phenology on seasonal and annual carbon balance in two contrasting New England forests

Abstract

Spring phenology is thought to exert a major influence on the carbon (C) balance of temperate and boreal ecosystems. We investigated this hypothesis using four spring onset phenological indicators in conjunction with surface-atmosphere CO(2) exchange data from the conifer-dominated Howland Forest and deciduous-dominated Harvard Forest AmeriFlux sites. All phenological measures, including CO(2) source-sink transition dates, could be well predicted on the basis of a simple two-parameter spring warming model, indicating good potential for improving the representation of phenological transitions and their dynamic responsiveness to climate variability in land surface models. The date at which canopy-scale photosynthetic capacity reached a threshold value of 12 micromol m(-2) s(-1) was better correlated with spring and annual flux integrals than were either deciduous or coniferous bud burst dates. For all phenological indicators, earlier spring onset consistently, but not always significantly, resulted in higher gross primary productivity (GPP) and ecosystem respiration (RE) for both seasonal (spring months, April-June) and annual flux integrals. The increase in RE was less than that in GPP; depending on the phenological indicator used, a one-day advance in spring onset increased springtime net ecosystem productivity (NEP) by 2-4 g C m(-2) day(-1). In general, we could not detect significant differences between the two forest types in response to earlier spring, although the response to earlier spring was generally more pronounced for Harvard Forest than for Howland Forest, suggesting that future climate warming may favor deciduous species over coniferous species, at least in this region. The effect of earlier spring tended to be about twice as large when annual rather than springtime flux integrals were considered. This result is suggestive of both immediate and lagged effects of earlier spring onset on ecosystem C cycling, perhaps as a result of accelerated N cycling rates and cascading effects on N uptake, foliar N concentrations and photosynthetic capacity.

Tracking plant physiological properties from multi-angular tower-based remote sensing

“…2a). This result confirms the findings of previous studies (Richardson et al 2007(Richardson et al , 2009). However, minimum and maximum values of the phenological assessment (Fig.…”

Relationships between large-scale circulation patterns and carbon dioxide exchange by a deciduous forest

“…The large-scale circulation patterns have different effects on climate at the three sites due to their different geographic location (Table 1), and CO 2 exchange responds differentially with respect to latitude and climatic variations [e.g., Nemani et al, 2003;Gong and Ho, 2003;Notaro et al, 2006a;Hember and Lafleur, 2008;Grant et al, 2009;Wharton et al, 2009]. Another possible reason is that the three AmeriFlux research sites have different forest composition species, which affects the response of CO 2 exchange to the climate [e.g., Hadley et al, 2009;Richardson et al, 2009]. In this study, the annual NEE of deciduousdominated Harvard Forest and Morgan Monroe State Forest exhibits significant correlations with climate indices in fall, while conifer-dominated Howland Forest NEE is closely linked to climate indices in winter and spring.…”

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

“…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).…”