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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Available from: Pekka Kauppi, Sep 30, 2015
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    • "Forest soils also account for 54% of stored carbon in old-growth forests (Luyssaert et al., 2008). Pan et al. (2011) quantified 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). "
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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.
    Geoderma 01/2016; 261:70-79. DOI:10.1016/j.geoderma.2015.06.022 · 2.77 Impact Factor
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    • "Tropical deforestation and degradation are a large source of carbon (C) emissions into the atmosphere, contributing some 7–15% to the total anthropogenic C emissions since the early 2000s (Harris et al., 2012; Pan et al., 2011). This carbon loss from the terrestrial biosphere is thought to be approximately balanced by forest regrowth and by an increase in terrestrial ecosystem carbon storage ability through time related to global or regional forcings, such as CO 2 fertilization, temperature increase, or rainfall fluctuations (Lewis, Lloyd, Sitch, Mitchard, & Laurance, 2009; Pan et al., 2011). An effective strategy for mitigating anthropogenic CO 2 emissions is to implement national and international governance agreements that will help curb deforestation and forest degradation (Agrawal, Nepstad, & Chhatre, 2011). "
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    ABSTRACT: In recent years, LiDAR technology has provided accurate forest aboveground biomass (AGB) maps in several forest ecosystems, including tropical forests. However, its ability to accurately map forest AGB changes in high-biomass tropical forests has seldom been investigated. Here, we assess the ability of repeated LiDAR acquisitions to map AGB stocks and changes in an old-growth Neotropical forest of French Guiana. Using two similar aerial small-footprint LiDAR campaigns over a four year interval, spanning ca. 20 km2, and concomitant ground sampling, we constructed a model relating median canopy height and AGB at a 0.25-ha and 1-ha resolution. This model had an error of 14% at a 1-ha resolution (RSE=54.7 Mg ha-1) and of 23% at a 0.25-ha resolution (RSE=86.5 Mg ha-1). This uncertainty is comparable with values previously reported in other tropical forests and confirms that aerial LiDAR is an efficient technology for AGB mapping in high-biomass tropical forests. Our map predicts a mean AGB of 340 Mg ha-1 within the landscape. We also created an AGB change map, and compared it with ground-based AGB change estimates. The correlation was weak but significant only at the 0.25-ha resolution. One interpretation is that large natural tree-fall gaps that drive AGB changes in a naturally regenerating forest can be picked up at fine spatial scale but are veiled at coarser spatial resolution. Overall, both field-based and LiDAR-based estimates did not reveal a detectable increase in AGB stock over the study period, a trend observed in almost all forest types. Small footprint LiDAR is a powerful tool to dissect the fine-scale variability of AGB and to detect the main ecological controls underpinning forest biomass variability both in space and time.
    Remote Sensing of Environment 11/2015; 169:93-101. DOI:10.1016/j.rse.2015.08.001 · 6.39 Impact Factor
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    • "Forest areas are estimated to be 4.0 Â 10 7 km 2 , accounting for $31% of the world land area (FAOSTAT, 2011). Forests produce half of net primary production in the world (Groombridge and Jenkins, 2002), and play an important role in the global carbon cycle (Bonan, 2008; Fang et al., 2014b; Pan et al., 2011; Yu et al., 2014), water and heat fluxes (Pongratz et al., 2010), biodiversity, and soil and water conservation (Achard and Hansen, 2012). In history , about 40% of global forests have been converted to cropland, pasture, and other man-made land cover types, especially for the Mediterranean forests, and temperature deciduous and dry tropical forests, in response to increasing demand for food, energy, and economic interests (Achard and Hansen, 2012; Foley et al., 2005). "
    ISPRS Journal of Photogrammetry and Remote Sensing 11/2015; 109:1-16. DOI:10.1016/j.isprsjprs.2015.08.010 · 3.13 Impact Factor
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