A Large and Persistent Carbon Sink in the World's Forests

U.S. Department of Agriculture Forest Service, Newtown Square, PA 19073, USA.
Science (Impact Factor: 33.61). 08/2011; 333(6045):988-93. DOI: 10.1126/science.1201609
Source: PubMed


The terrestrial carbon sink has been large in recent decades, but its size and location remain uncertain. Using forest inventory
data and long-term ecosystem carbon studies, we estimate a total forest sink of 2.4 ± 0.4 petagrams of carbon per year (Pg
C year–1) globally for 1990 to 2007. We also estimate a source of 1.3 ± 0.7 Pg C year–1 from tropical land-use change, consisting of a gross tropical deforestation emission of 2.9 ± 0.5 Pg C year–1 partially compensated by a carbon sink in tropical forest regrowth of 1.6 ± 0.5 Pg C year–1. Together, the fluxes comprise a net global forest sink of 1.1 ± 0.8 Pg C year–1, with tropical estimates having the largest uncertainties. Our total forest sink estimate is equivalent in magnitude to the
terrestrial sink deduced from fossil fuel emissions and land-use change sources minus ocean and atmospheric sinks.

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    • "e l s e v i e r . c o m / l o c a t e / f o r e c o stock (Pan et al., 2011). In the southern boreal forest, mean annual temperatures have risen %1.5 °C since 1940 (Bale et al., 2002; Battisti et al., 2005; Netherer and Schopf, 2010) and are expected to increase an additional 3–7 °C in winter and 3–11 °C in summer by 2100 (Kling et al., 2003). "
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    ABSTRACT: Global climate change has the potential to dramatically alter multiple ecosystem processes, including herbivory. The development rates of both plants and insects are highly sensitive to temperature. Although considerable work has examined the effects of temperature on spring phenologies of plants and insects individually, few studies have examined how anticipated warming will influence their phenological synchrony. We applied elevated temperatures of 1.7 and 3.4 °C in a controlled chamberless outdoor experiment in northeastern Minnesota, USA to examine the relative responses in onset of egg eclosion by forest tent caterpillar (Malacosoma disstria Hübner) and budbreak of two of its major host trees (trembling aspen, Populus tremuloides Michaux, and paper birch, Betula papyrifera Marshall). We superimposed four insect population sources and two overwintering regimes onto these treatments, and computed degree-day models. Timing of egg hatch varied among population source, overwintering location, and spring temperature regime. As expected, the development rates of plants and insects advanced under warmer conditions relative to ambient controls. However, budbreak advanced more than egg hatch. The degree of phenological synchrony between M. disstria and each host plant was differentially altered in response to warming. The interval by which birch budbreak preceded egg hatch nearly doubled from ambient to +1.7 °C. In the case of aspen, the sequence changed from egg hatch preceding, to following, budbreak at +3.4 °C. Additionally, under temperature regimes simulating future conditions, some insect populations currently south of our study sites became more synchronous with the manipulated hosts than did currently coexisting insect populations. These findings reveal how climate warming can alter insect-host plant interactions, through changes in phenological synchrony, possibly driving host shifts among tree species and genotypes. They also suggest how herbivore variability, both among populations and within individual egg masses, may provide opportunities for adaptation, especially in species that are highly mobile and polyphagous.
    Full-text · Article · Feb 2016 · Forest Ecology and Management
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    • "Forest disturbances alter the balance between ecosystem carbon (C) uptake and loss, and are primary determinants of the terrestrial C balance (Bond-Lamberty et al., 2007; Gough et al., 2007; Amiro et al., 2010; Pan et al., 2011). Tree mortality from disturbance may affect ecosystem C balance in two ways: by reducing the amount of C fixed via canopy photosynthesis (or gross primary production, GPP), and by altering the quantity of C lost through ecosystem respiration (R E ), particularly as detritus-fueled microbial respiration increases (Liu et al., 2006; Harmon et al., 2011). "
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    ABSTRACT: Forested landscapes are shaped by disturbances varying in severity and source. Moderate disturbance from weather, pathogens, insects, and age-related senescence that kills only a subset of canopy trees may increase standing woody debris and alter the contribution of coarse woody debris (CWD) to total ecosystem respiration (RE). However, woody debris carbon (C) dynamics are rarely examined following moderate disturbances that increase standing dead wood pools. We used an experimental manipulation of moderate disturbance in an upper Great Lakes forest to: (1) examine multi-year changes in CWD mass through a moderate disturbance; (2) quantify in situ CWD respiration during different stages of decay for downed and standing woody debris and; (3) estimate the annual contribution of CWD respiration to the ecosystem C balance through comparison with RE and net ecosystem production (NEP). Six years following disturbance, we found that the standing dead wood mass of 24.5MgCha-1 was an order of magnitude greater than downed woody debris mass and a large source of ecosystem C flux. Instantaneous in situ respiration rates from standing and minimally decayed downed woody debris were not significantly different from one another. Separate estimates of ecosystem CWD respiration of 1.1-2.1MgCha-1yr-1 six years following disturbance were comparable in magnitude to NEP and 12.5-23.8% of RE, representing a substantial increase relative to pre-disturbance levels. Ecosystem respiration and NEP were stable following moderate disturbance even though ecosystem CWD respiration increased substantially, suggesting a reduction in the respiratory C contribution from other sources. We conclude that standing and downed CWD can be essential components of the ecosystem C balance following moderate severity disturbance.
    Full-text · Article · Feb 2016 · Forest Ecology and Management
    • "Forests in general and forest soils in particular play a vital role in carbon balance. The global soil carbon pool has been estimated to contain more than 3.3 times the atmospheric carbon pool and 4.5 times the biotic pool (Lal, 2004). Forest soils also account for 54% of stored carbon in old-growth forests (Luyssaert et al., 2008). Pan et al. (2011quantified global forest carbon sinks and estimated the total stock to be 861 Pg, of which 383 Pg (45%) is in soil (to a depth of 1 m), 363 Pg (42%) in above and belowground biomass, 73 Pg (8%) in deadwood and 43 Pg (5%) in litter. One-third of the world's soil carbon is stored in the tropics (Lemma et al., 2006). In forest ecosystems, b"
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    ABSTRACT: African tropical forests are thought to play an important role in global carbon sequestration. However, the increasing rate of deforestation and the impact of changes in land use require a critical and updated look at what is happening. This work emphasizes the role of bulk density as a main driver in carbon (C) and nitrogen (N) stock in four land-use categories: natural forest, tree plantations, crop land and degraded soil. The study was conducted in the Central Highlands of Ethiopia, where deforestation and human pressure on native forests are exacerbated and erosion has caused extensive soil loss. The methodological approach consisted of evaluating the confounding effect of bulk density and then estimating C and N stocks based on a fixed-mass method rather than the usual fixed-depth method, in order to compare differences across land use categories. Wehypothesized that elevation gradient would play a determining role in C and N concentrations and stocks in native forest, whereas tree species would be the main factor in plantations. C and N concentrations and bulk densities in mineral soil were analyzed as repeated measures in an irregular vertical space ranging from 0–10 cm, 10–30 cm, 30–50 cm and 50–100 cm, using a linear mixed model approach. Single observations from the forest floor were analyzed by a general linear model. Results indicated that soil depth is a more important factor than elevation gradient in native forests, though C and N concentrations and stocks diminished near human settlements. Native forest stored on average 84.4%, 26.4% and 33.7% more carbon and 82.4%, 51.8% and 27.1% more nitrogen than bare soil, crop land and plantations, respectively. Conversion of crop and degraded land to plantations ameliorated soil degradation conditions, but species selection didnot affect carbon and nitrogen stocks.
    No preview · Article · Jan 2016 · Geoderma
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