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Background:The forests of western Amazonia are known to be more dynamic that the better-studied forests of eastern Amazonia, but there has been no comprehensive description of the carbon cycle of a western Amazonian forest. Aims:We present the carbon budget of two forest plots in Tambopata in south-eastern Peru, western Amazonia. In particular, we present, for the first time, the seasonal variation in the detailed carbon budget of a tropical forest. Methods:We measured the major components of net primary production (NPP) and total autotrophic respiration over 3–6 years. Results:The NPP for the two plots was 15.1 ± 0.8 and 14.2 ± 1.0 Mg C ha−1year−1, the gross primary productivity (GPP) was 35.5 ± 3.6 and 34.5 ± 3.5 Mg C ha−1year−1, and the carbon use efficiency (CUE) was 0.42 ± 0.05 and 0.41 ± 0.05. NPP and CUE showed a large degree of seasonality. Conclusions:The two plots were similar in carbon cycling characteristics despite the different soils, the most notable difference being high allocation of NPP to canopy and low allocation to fine roots in the Holocene floodplain plot. The timing of the minima in the wet–dry transition suggests they are driven by phenological rhythms rather than being driven directly by water stress. When compared with results from forests on infertile forests in humid lowland eastern Amazonia, the plots have slightly higher GPP, but similar patterns of CUE and carbon allocation. [ABSTRACT FROM PUBLISHER]

Background:Tropical montane cloud forests (TMCF) are unique ecosystems with high biodiversity and large carbon reservoirs. To date there have been limited descriptions of the carbon cycle of TMCF. Aims:We present results on the production, allocation and cycling of carbon for two mid-elevation (1500–1750 m) tropical montane cloud forest plots in San Pedro, Kosñipata Valley, Peru. Methods:We repeatedly recorded the components of net primary productivity (NPP) using biometric measurements, and autotrophic (Ra) and heterotrophic (Rh) respiration, using gas exchange measurements. From these we estimated gross primary productivity (GPP) and carbon use efficiency (CUE) at the plot level. Results:The plot at 1500 m was found very productive, with our results comparable with the most productive lowland Amazonian forests. The plot at 1750 m had significantly lower productivity, possibly because of greater cloud immersion. Both plots had similar patterns ofNPPallocation, a substantial seasonality inNPPcomponents and little seasonality inRa. Conclusions:These two plots lie within the ecotone between lower and upper montane forests, near the level of the cloud base. Climate change is likely to increase elevation of the cloud base, resulting in shifts in forest functioning. Longer-term surveillance of the carbon cycle at these sites would yield valuable insights into the response of TMCFs to a shifting cloud base. [ABSTRACT FROM PUBLISHER]

Background:Dead biomass, including woody debris (WD), is an important component of the carbon cycle in tropical forests. Aims:This study analyses WD (>2 cm) and other above-ground fluxes in mature tropical forest plots along an elevational gradient (210–3025 m above sea level) in southern Peru. Methods:This work was based on inventories of fine and coarse WD (FWD and CWD, respectively), above-ground biomass, and field-based and experimental respiration measurements. Results:Total WD stocks ranged from 6.26 Mg C ha−1at 3025 m to 11.48 Mg C ha−1at 2720 m. WD respiration was significantly correlated with moisture content (P< 0.001;R2= 0.25), temperature (P< 0.001;R2= 0.12) and wood density (P< 0.001;R2= 0.16). Controlled experiments showed that both water content and temperature increased respiration rates of individual WD samples. The full breadth of the temperature sensitivity coefficient, orQ10, estimates, ranging from 1.14–2.13, was low compared to other studies. In addition, temperature sensitivity of WD respiration was greater for higher elevations. Conclusions:Carbon stocks, mortality and turnover of above-ground biomass varied widely and were not significantly related with elevation or slope. This study demonstrates that some forests may be a carbon source due to legacies of disturbance and increasing temperatures, which may cause additional, short-term carbon efflux from WD. Predictions of tropical forest carbon cycles under future climate should incorporate WD dynamics and related feedback. [ABSTRACT FROM PUBLISHER]

Background:The forests of north-west Amazonia are characterised by the highest levels of tree diversity in the world, high rainfall and relatively fertile soils. Aims:Here we present a comprehensive description of the carbon cycle of two 1 ha forests plots in Allpahuayo, near Iquitos, Peru, one on an occasionally inundated alisol/gleysol landscape, the other on an arenosol (sandy soil). Methods:Data on the components of net primary productivity (NPP) and autotrophic respiration were collected over the period 2009–2011, and summed to estimate gross primary productivity (GPP) and carbon use efficiency (CUE). Results:Overall, these forests showed high values of GPP (39.05 ± 4.59 and 41.88 ± 4.60 Mg C ha−1year−1). Despite the lack of a dry season, the forests showed distinct seasonality in tree growth, litterfall, flowering and fine root productivity. This showed that tropical forests with little seasonality in water supply can still exhibit distinct seasonality in NPP and carbon use, apparently synchronised to the solar radiation cycle. We found remarkably little difference in productivity between the alisol/gleysol plot and the arenosol plot. Conclusions:The GPP was higher than those reported for forests in Brazilian Amazonia on more infertile soils. The CUE was also higher, which may be related to the high forest dynamism and natural disturbance rate. These two factors combined to result in amongst the highest NPP values reported for Amazonia. [ABSTRACT FROM PUBLISHER]

Background:The dry transitional forests of the southern Amazonia have received little attention from a carbon cycling and ecosystem function perspective, yet they represent ecosystems that may be impacted by global climate change in the future. Aims:To compare the full carbon cycle for two 1-ha forest plots that straddle the ecotone between humid forest and dry forest in Amazonia, ca. 100 km from Santa Cruz, Bolivia. Methods:2.5 years of measurements of the components of net primary production (NPP) and autotrophic respiration were collected. Results:Total NPP was 15.5 ± 0.89 Mg C ha−1year−1at the humid site and 11.27 ± 0.68 Mg C ha−1year−1at the dry site; a total Gross Primary Production (GPP) of 34.14 ± 2.92 Mg C ha−1year−1and 26.88 ± 2.70 Mg C ha−1year−1at the two sites. Carbon use efficiency for both sites was higher than reported for other Amazonian forests (0.45 ± 0.05 and 0.42 ± 0.05). Conclusions:Drier soil conditions selected for the dry deciduous tree species which had higher leaf photosynthesis and total GPP. NPP allocation patterns were similar at the two sites, suggesting that in terms of carbon allocation, the dry forests of the southern Amazonia behave as a scaled-down version of wetter humid forests. [ABSTRACT FROM PUBLISHER]