CO₂ balance of boreal, temperate, and tropical forests derived from a global database

Abstract

Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome-specific carbon budgets; to re-examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO 2 balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 1C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO 2 balance required the introduction of substantial biome-specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non-CO 2 carbon fluxes are not presently being adequately accounted for. Nomenclauture:DOC 5 dissolved organic carbon; fNPP 5 foliage component of NPP; GPP 5 gross primary production (GPP40 denotes photosynthetic uptake); mNPP 5 missing component of NPP;NBP 5 net biome production (NBP40 denotes biome uptake); NECB 5 net ecosystem carbon balance (NECB40 denotes ecosystem uptake); NEE 5 net ecosystem exchange (NEE40 denotes ecosystem uptake); NEP 5 net ecosystem production (NEP40 denotes ecosystem uptake); NPP 5 net primary production (NPP40 denotes ecosystem uptake); R a 5 autotrophic respiration (R a 40 denotes respiratory losses); R e 5 ecosystem respiration (R e 40 denotes respiratory losses); R h 5 heterotrophic respiration (R h 40 denotes respiratory losses); rNPP 5 root component of NPP;R s 5 soil respiration (R s 40 denotes respiratory losses); VOC 5 volatile organic compounds; wNPP 5 wood component of NPP

Covariation between gross primary production and ecosystem respiration across space and the underlying mechanisms: A global synthesis

“…In this study, we initially found that the spatial variations in GPP and RE are commonly controlled by MAT, MAP, and EVI (Table 3). The controls of temperature and precipitation on the spatial variations in GPP and RE are similarly reported in China , Asian Hirata et al, 2008), European, and American regions Luyssaert et al, 2007;Reichstein et al, 2007b). Furthermore, we found that GPP and RE responded to the common climatic and vegetation factors in a parallel way across The framework illustrates that GPP and RE show similar responses to the spatial variations in environmental conditions (such as MAT and MAP) (panel.a1) and ecosystem traits (EVI) (panel.b1).…”

“…GPP represents the gross CO 2 uptake through photosynthesis by all plants at the ecosystem level (Chapin et al, 2002;Luyssaert et al, 2007). RE is the gross CO 2 release from the ecosystem through both autotrophic respiration (R a ), which provides energy for the growth and maintenance of foliage, wood, and roots (Chapin et al, 2002;Waring et al, 1998), and heterotrophic respiration (R h ), which derives from the process of decomposition through microbial activities (Luyssaert et al, 2007). Understanding the variations in GPP and RE and their relationships is helpful for better understanding the terrestrial carbon cycle and predicting the global carbon budget.…”

Anthropogenic perturbation of the carbon fluxes from land to ocean

“…Current soil respiration estimates neglect the C released to inland waters. A downward revision of the estimate of soil heterotrophic respiration to account for the soil C channelled to inland freshwater systems would nevertheless remain within the uncertainty of this flux 32 .…”

Biomass turnover time in terrestrial ecosystems halved by land use

“…We followed the same procedure as with the NPPpot assessment, using three global biome maps 31,42,43 . We used various databases for potential carbon stocks in vegetation 4,16,[60][61][62][63] Table 5 shows potential vegetation units and the potential carbon stock values assigned, and Supplementary Tables 8-12 show results from forest site-data studies that explicitly discern natural from managed forests 32,33 . A comparison of these data reveals that the data we use are well in line with the site-specific studies 36,37 .…”