Increasing biomass in Amazonian forest plots

Abstract

A previous study by Phillips et al. of changes in the biomass of permanent sample plots in Amazonian forests was used to infer the presence of a regional carbon sink. However, these results generated a vigorous debate about sampling and methodological issues. Therefore we present a new analysis of biomass change in old-growth Amazonian forest plots using updated inventory data. We find that across 59 sites, the above-ground dry biomass in trees that are more than 10 cm in diameter (AGB) has increased since plot establishment by 1.22 ± 0.43 Mg per hectare per year (ha Ϫ1 yr Ϫ1 , where 1 ha = 10 4 m 2 ), or 0.98 ± 0.38 Mg ha Ϫ1 yr Ϫ1 if individual plot values are weighted by the number of hectare years of monitoring. This significant increase is neither confounded by spatial or temporal variation in wood specific gravity, nor dependent on the allometric equation used to estimate AGB. The conclusion is also robust to uncertainty about diameter measurements for problematic trees: for 34 plots in western Amazon forests a significant increase in AGB is found even with a conservative assumption of zero growth for all trees where diameter measurements were made using optical methods and/or growth rates needed to be estimated following fieldwork. Overall, our results suggest a slightly greater rate of net stand-level change than was reported by Phillips et al. Considering the spatial and temporal scale of sampling and associated studies showing increases in forest growth and stem turnover, the results presented here suggest that the total biomass of these plots has on average increased and that there has been a regional-scale carbon sink in old-growth Amazonian forests during the previous two decades.

Widespread Amazon forest tree mortality from a single cross‐basin squall line event

“…Assuming a similar proportion of disturbed area that was observed over the Manaus area (0.2% of forested area (Text S3)) over the total forested area affected by the squall line (4.5 × 10 6 km 2 ( Figure S7b)) across the Amazon, we estimated a total potential damage of 542 ± 121 million trees across the basin by the squall (Text S3). This represents a loss of 0.14 Pg C, and equivalent to 23% of the estimated mean annual carbon accumulation (0.6 Pg C) [Baker et al, 2004] of Amazon forests.…”

Storage and Turnover of Organic Matter in Soil

“…Most coupled climate carbon-cycle models predict that terrestrial ecosystem productivity increases in the first half of this century due to CO 2 fertilization and moderate increases in temperature, but has moderate declines after that due to more severe changes in climate (Sitch 2003;Gerten 2004;Friedlingstein 2006;Fischlin et al 2007). For example, the productivity of intact Amazonian forests has been increasing over recent decades, variously explained by episodic disturbance and recovery dynamics, changing species distribution, CO 2 fertilization, modest warming, reduced tropical cloud cover, and increased radiation (Nemani 2003;Baker 2004;Chambers and Silver 2004;Lewis 2004;Malhi and Phillips 2004;Boisvenue and Running 2006). These C gains are predicted to be transient, however, due to losses associated with escalating heating and drying trends (Malhi and Phillips 2004).…”

Tree Diversity Changes over a Decade (2003-2013) in Four Inland Tropical Dry Evergreen Forest Sites on the Coromandel Coast of India

“…As in all other ecosystems, tropical forests too face a wide range of disturbances of variable duration, intensity and frequency. Long-term vegetation monitoring has been undertaken in various tropical forests around the world (Rees et al 2001;Laurance et al 2004;Weckel et al 2006;Marimon et al 2012;van den Berg et al 2012;Ge et al 2013), and an increasing number of studies have shown that forests have undergone dynamic widespread directional shifts in composition and structure (Enquist and Enquist 2011;Feeley et al 2011;Peng et al 2011;Fauset et al 2012;Kucbel et al 2012). Long-term monitoring of permanent forest plots provides data to assess aboveground standing biomass stock and C dynamics and assesses the response of the forest to the environmental drivers such as elevated temperature, CO 2 fertilization, increase in incoming solar radiation and nitrogen enrichment (Bhat and Ravindranath 2011).…”