Search

Tropical forests exchange large amounts of water and energy with the atmosphere and are important in controlling regional and global climate; however, climate and evaportranspiration (E) vary significantly across multiple time scales. To better understand temporal patterns in E and climate, we measured the energy balance and meteorology of a semi-deciduous forest in the rainforest-savanna ecotone of northern Mato Grosso, Brazil, over a 7-year period and analyzed regional climate patterns over a 16-year period. Spectral analysis revealed that E and local climate exhibited consistent cycles over annual, seasonal, and weekly time scales. Annual and seasonal cycles were also apparent in the regional monthly rainfall and humidity time series, and a cycle on the order of 3-5.5 years was also apparent in the regional air temperature time series, which is coincident with the average return interval of El Niño. Annual rates of E were significantly affected by the 2002 El Niño. Prior to this event, annual E was on average 1,011 mm/year and accounted for 52% of the annual rainfall, while after, annual E was 931 mm/year and accounted for 42% of the annual rainfall. Our data also suggest that E declined significantly over the 7-year study period while air temperature significantly increased, which was coincident with a long-term, regional warming and drying trend. These results suggest that drought and warming induced by El Niño and/or climate change cause declines in E for semi-deciduous forests of the southeast Amazon Basin.

Estimates of net primary (NPP) and ecosystem production (NEP) are needed for tropical savanna, which is structurally diverse but understudied compared to tropical rainforest. We used eddy covariance and inventory methods to estimate carbon (C) fluxes for an upland mixed grassland and a seasonally flooded forest to determine the correspondence between these methods and assess the contribution of C cycling components to the total NPP. Both techniques provided similar estimates of net ecosystem CO2 exchange (−3.0 ‒ 2.3 MgC ha−1 y−1 for eddy covariance vs. −2.0 ‒ 4.3 MgC ha−1 y−1 for inventory), gross primary production (7.5–16.3 MgC ha−1 y−1 for eddy covariance vs. 8.7–18.4 MgC ha−1 y−1 for inventory), and total NPP (0.9–7.5 MgC ha−1 y−1 for eddy covariance vs. 2.0–9.5 MgC ha−1 y−1 for inventory). Belowground NPP accounted for 49%–53% of the total NPP for both ecosystems, followed by aboveground litter (26%–27%) and wood (16%–17%) production. Increases in water availability increased the potential for C storage, but the mechanism was different in the savanna types. Compared to other savanna ecosystems, the mixed grassland had a lower productivity and C use efficiency (CUE = NPP/GPP = 0.28), while the Cerrado forest had a high CUE (0.58) and similar C flux rates to other tropical savanna forests. The agreement in the C cycle estimates derived from the eddy covariance and inventory methods increases our confidence in the productivity estimates for these tropical savanna ecosystems. Plain Language Summary: Estimates of net primary and ecosystem production are needed for tropical savannas, which are highly diverse but understudied compared to tropical forests. Several methods have been used to measure primary and ecosystem production; however, these approaches have errors and uncertainties. We used available methods to estimate the productivity of a grass‐dominated savanna in the southern Amazon Basin and a seasonally flooded forest in the northern Pantanal to assess the correspondence in the productivity estimated from these methods and evaluate the contribution of above and belowground processes to the overall ecosystem productivity. Productivity estimates derived from the different techniques were similar. Belowground processes accounted for 49%–53% of the productivity followed by leaf (26%–27%) and wood (16%–17%) production. Increases in water availability increased the productivity for both savanna types, but for different reasons. An increase in soil moisture caused an increase productivity in the mixed grassland but a decline in carbon losses from the seasonally flooded forest. Compared to other savanna ecosystems, the mixed grassland had lower productivity while the forest had high productivity. While our measurements are spatially and temporally limited, the broad agreement in the different methods increases our confidence in the productivity estimates for these tropical savanna ecosystems. Key Points: Estimates of C cycling from inventory and eddy covariance methods were similar for two floristically different tropical savannas of BrazilBelowground NPP was 49%–53% of the total NPP for both ecosystems, followed by aboveground litter (26%–27%) and wood (16%–17%) productionThe grass dominated savanna had a low C use efficiency (CUE = NPP/GPP = 0.28) while the Cerrado forest had a CUE = 0.58 [ABSTRACT FROM AUTHOR]

Temporal variations in land-atmosphere water vapor exchange are more pronounced in seasonal environments, especially grass-dominated savannas (known as campo sujo Cerrado ) of the southern and eastern Amazon Basin. Recent work in campo sujo indicates that rates of canopy conductance ( g c ) were directly and indirectly affected by a variety of meteorological variables, which limited our understanding of how seasonal variation in meteorology affected rates of g c . Thus, our overall objective here is to determine how individual meteorological variables affect seasonal variations in g c . Estimates of g c were derived using the inverted Penman–Monteith equation from hourly eddy-covariance measurements of evapotranspiration made between March 2011 and December 2013. We employed the so-called Jarvis-type model to estimate g c , which allows us to specify the functional role of each variable on g c , to evaluate how variations in meteorology affect rates of Cerrado g c . The model was parameterized using eddy covariance data from 2012 and tested with data collected in 2011 and 2013. Using orthogonal regression and the Willmott index of agreement, we found that the model estimates compared well to those derived from eddy covariance, especially in 2011. Sensitivity analyses revealed that g c was sensitive to warming and drying, particularly during the dry season when drought stress from low soil moisture availability was already limiting g c . Warming and drying in response to climate change is expected to increase dry season duration, and dry season intensification may already be occurring in central and southern Mato Grosso. Given the high degree of surface-atmosphere coupling for this ecosystem, and the fact that g c is an important link between canopy-scale C and water cycling, our data suggest that dry season intensification may further limit CO 2 and H 2 O vapor exchange during the dry season. [ABSTRACT FROM AUTHOR]

Deforestation and climate change have the capacity to alter rainfall regimes, water availability, and surface-atmosphere flux of water and energy of tropical forests, especially in ecotonal, semi-deciduous tropical forests of the southern Amazon Basin, which have experienced rapid regional warming and deforestation over the last three decades. To reduce uncertainty regarding current and future energy and water flux, micrometeorological measurements of latent ( Qe) and sensible heat flux ( Qh) and canopy conductance ( Gc) were combined with measurements of sap flux density ( Fd) and maximum leaf conductance ( gsmax) to characterize the seasonal controls on mass (H2O) and energy exchange of an ecotonal, semi-deciduous forest in northern Mato Grosso, Brazil over the 2005-2006 annual cycle. Average diel patterns and daily rates of energy flux and conductance declined during the dry season; however, the decline in Fd and Qe was smaller and/or more gradual than Gc and gsmax. Weekly averages of transpiration calculated from sap flow measurements during the dry-wet season transition period were positively correlated (r2 = 0.47; p < 0.05; n = 11) with estimates of leaf area index (LAI) derived from the Modis-Aqua satellite platform while estimates of evapotranspiration ET derived from eddy covariance were not, presumably because these estimates also include an evaporation component. Overall, our results suggest that access to deep water reserves can support high rates of Fd and Qe during the dry season, but because of high evaporative demand, declines in plant water potential lead to a corresponding decline in Gc. Furthermore, seasonal variations in LAI, that are likely to be controlled in part by plant water status and phenology, constrain tree and stand transpiration. Thus the consistency of Qe over the annual cycle appears to be the result of trade-offs between water availability (rainfall, soil moisture, water potential), canopy structural properties (LAI), and meteorological conditions including vapor pressure deficit and net radiation. [ABSTRACT FROM AUTHOR]

Describes a scaling approach applied for measuring the net carbon dioxide flux to provide an estimate of the net exchange during the 1994-1996 annual cycle for the Kuparuk Basin. Use of carbon flux data as input for the calculation of gross primary production; Indications that were received from basin-wide estimates of net carbon dioxide about the level of different categories of tundra; Comparison between estimates of carbon dioxide exchange received by direct measurement and scaling method.

Presents a study of the acclimation of ecosystem carbon dioxide exchange in the Alaskan Arctic region in response to decadal climate warming. Thoughts on the effect of continued warming of the ecosystem; Methods; Impact that the warming has on such things as the changes in nutrient cycling, physiological acclimation, and population and community reorganization; Results; Conclusions.

The article focuses on a study related to physiological models for the measurement of carbon dioxide flux in arctic Tundra Landscape. Topics discussed include requirement of arctic ecosystem carbon dioxide in exchange soil carbon, impact of climatic changes on arctic ecosystem, and use of gross primary production (GPP), whole-ecosystem respiration (R) and air temperature for photosynthetic photon flux density.

• Tree RGR was measured in Brazilian upland and flooded savanna using dendrometers. • Measurements were made during an intense El Niño-La Niña cycle. • Community RGR was affected by rainfall, dry season length, and temperature. • Growth responses to climate variation were species specific. • Varying responses to climate change will alter species composition and productivity. Tropical forest trees are sensitive to climate variations, especially during anomalously warm and dry years that occur during El Niño. However, species growth responses are poorly understood. We measured annual stem growth of 27 different tree species from upland and seasonally flooded forests and woodlands in the Cuiaba Basin and Northern Pantanal of Mato Grosso, Brazil. Stem growth increment was measured using plastic, spring-loaded dendrometer bands installed on 344 trees. Measurements were made between 2015 and 2019, which encompassed the 2015–16 El Niño that was one of the warmest and driest on record. Relative stem growth rates (RGR) at both sites increased with higher rainfall and declined with an increase in maximum temperature, but the RGR of trees in the Cuiaba Basin also declined as the length of the dry season increased. RGR, and the response of RGR to climate variation, varied substantially across species. Some species only exhibited a significant RGR response to variations in rainfall, maximum temperature, or dry season length, other species responded to more than one climate variable, and a subset were insensitive to the variation in all three climate variables studied. Rainfall appeared to be a stronger control on RGR in the predominately upland Cuiaba Basin (87% of species exhibited a significant RGR response to rainfall in the Cuiaba Basin vs. 39% in the Pantanal) while temperature was a stronger control on RGR in the seasonally flooded Pantanal (67% of species exhibited a significant RGR response to temperature in the Pantanal vs. 53% in the Cuiaba Basin). While our study period was short, and measurements were done on a small subset of available species, our data indicate that variations in climate affect the growth of tropical forest and woodland tree species differently. These species-specific responses have the potential to alter community diversity and productivity as climate change ensues. [ABSTRACT FROM AUTHOR]

Tropical forests and savanna (cerrado) are important carbon (C) sinks; however, few data exist for seasonally flooded forests. We quantified the annual rates of aboveground net primary production (ANPP) over a five-year period for two forests, an upland mixed forest and a seasonally flooded cerrado forest, located in the northern Pantanal region of Brazil. We hypothesized that rates of ANPP would be higher for the mixed forest than the cerrado forest because seasonal flooding can limit rates of tree growth. ANPP was calculated as the sum of the annual litter production measured from litterfall traps and the stem growth increment measured from dendrometers and tree density. ANPP varied between 3.8–5.5 MgC ha−1 y−1 for the flooded forest and 1.6–4.6 MgC ha−1 y−1 for the upland forest. Litter production accounted for 57% of the ANPP, and the difference in ANPP between the upland and flooded forests was due to consistently higher litter production in the flooded forest. Annual variations in ANPP were not correlated with annual precipitation, presumably because the hydrology of these sites is driven more by the flood stage of the Cuiaba River than by local precipitation. However, consistent declines in forest floor litter mass occurred at both sites, suggesting that C storage may be responding to some unknown disturbance that occurred prior to our sampling campaign. Seasonal variation in rainfall exerted an important control on litter production dynamics, with leaf litter production increasing during the dry season and stem and reproductive litter production increasing during the wet season. While there are few studies of seasonally flooded tropical forests, our data suggest that the seasonally flooded and upland forests of the northern Pantanal can act as appreciable aboveground C sinks. [ABSTRACT FROM AUTHOR]

Climate change has the capacity to alter water availability and the litter production of tropical forests, which will alter rates of carbon (C) cycling and storage. We conducted a short-term field experiment in two hydrologically diverse forests in the Brazilian Pantanal to assess the initial response of litter decomposition and soil respiration (Rsoil) to variations in litter pool size. Total annual Rsoil and decomposition significantly declined with litter removal and increased with litter addition, but the rate of litter decomposition was highest for plots where litter was removed. Rsoil was positively related to soil organic matter content and the rate of litter decomposition, but not soil moisture or temperature, suggesting that the litter treatment effects on decomposition and Rsoil were due to changes in C availability and not litter effects on the soil environment (i.e., temperature and moisture). Rsoil was not significantly different between the forests studied here even though they had large differences in hydrology; however, litter decomposition was significantly higher in seasonally flooded forest, especially when augmented with litter. These results suggest that alterations in litter production from land use and/or climate change will alter short-term rates of decomposition and Rsoil for these and other floodplain forests of the Pantanal and Amazon Basin. [ABSTRACT FROM AUTHOR]

• CO 2 flux was measured with eddy covariance in a seasonally flooded pasture. • The pasture was a large C emitter, emitting 337 g CO 2 C m−2 y−1 to the atmosphere. • The pasture was a C sink when soil was anaerobic but a source when soil was aerobic. • Low productive pastures in the Pantanal may be important sources of atmospheric CO 2. • Management and altered hydrology of Pantanal pastures can reduce net CO 2 uptake. The Pantanal is the largest seasonal wetland in the world with a landscape that consists of a mosaic of permanent aquatic habitats, and floodable and non-floodable savannas, pastures and forests. Drought events are expected to occur more frequently in the Pantanal biome under future climate conditions, but the effects of land management and hydrological extremes on pastures have been poorly studied at spatial scales relevant to local livestock. In this study, we measured CO 2 C fluxes using eddy covariance over a hydrological year on pastures within a cattle farm in the Brazilian Pantanal that experienced seasonal flooding. Our measurements show that seasonally flooded pastures were large emitters of CO 2 C, contributing 337 g CO 2 C m−2 year−1 to the atmosphere. During flooding, when the soils were anaerobic, and soil O 2 was close to zero, the flooded pasture was a net sink of -18 g CO 2 C m−2, while during the aerobic phase (soil O 2 > 15%) the pasture was a significant CO 2 source to the atmosphere (301 g CO 2 C m−2). Transitions to and from anaerobic conditions corresponded to 54 g CO 2 C m−2. Our results indicate that the seasonally flooded cattle pastures in the Brazilian Pantanal may be an important regional source of CO 2 C for the atmosphere. Better management, and use of drought resistant grasses, may be a way to improve soil C stocks and limit emissions, especially as global climate change is anticipated to increase heating and drying for the Pantanal biome. [ABSTRACT FROM AUTHOR]