Yadvinder Malhi
University of Oxford, Environmental Change Institute, Faculty Member
- Professor of Ecosystem Scienceedit
Abstract Previous studies of changes in the biomass of permanent sample plots in Amazonian forests have been used to infer the presence of a regional carbon sink. However, these results have generated a vigorous debate about sampling and... more
Abstract Previous studies of changes in the biomass of permanent sample plots in Amazonian forests have been used to infer the presence of a regional carbon sink. However, these results have generated a vigorous debate about sampling and methodological issues. Therefore, here, we present a re-analysis of biomass change in old-growth, Amazonian forest plots, to address these concerns using updated inventory data.
Abstract Long-term studies using the RAINFOR network of forest plots have generated significant insights into the spatial and temporal dynamics of forest carbon cycling in Amazonia. In this work, we map and explore the landscape context... more
Abstract Long-term studies using the RAINFOR network of forest plots have generated significant insights into the spatial and temporal dynamics of forest carbon cycling in Amazonia. In this work, we map and explore the landscape context of several major RAINFOR plot clusters using Landsat ETM+ satellite data.
Abstract Warmer and drier climates over Eastern Amazonia have been predicted as a component of climate change during the next 50–100 years. It remains unclear what effect such changes will have on forest–atmosphere exchange of carbon... more
Abstract Warmer and drier climates over Eastern Amazonia have been predicted as a component of climate change during the next 50–100 years. It remains unclear what effect such changes will have on forest–atmosphere exchange of carbon dioxide (CO 2) and water, but the cumulative effect is anticipated to produce climatic feedback at both regional and global scales.
The production of aboveground soft tissue represents an important share of total net primary production in tropical rain forests. Here we draw from a large number of published and unpublished datasets (n= 81 sites) to assess the... more
The production of aboveground soft tissue represents an important share of total net primary production in tropical rain forests. Here we draw from a large number of published and unpublished datasets (n= 81 sites) to assess the determinants of litterfall variation across South American tropical forests. We show that across old-growth tropical rainforests, litterfall averages 8.61±1.91 Mgha− 1 yr− 1 (mean±standard deviation, in dry mass units).
Xylem density is a physical property of wood that varies between individuals, species and environments. It reflects the physiological strategies of trees that lead to growth, survival and reproduction. Measurements of branch xylem... more
Xylem density is a physical property of wood that varies between individuals, species and environments. It reflects the physiological strategies of trees that lead to growth, survival and reproduction. Measurements of branch xylem density, ρx, were made for 1653 trees representing 598 species, sampled from 87 sites across the Amazon basin.
Abstract We report results from a large-scale nutrient fertilization experiment along a “megadiverse”(154 unique species were included in the study) 3,000-m elevation transect in the Peruvian Andes and adjacent lowland Amazonia. Our... more
Abstract We report results from a large-scale nutrient fertilization experiment along a “megadiverse”(154 unique species were included in the study) 3,000-m elevation transect in the Peruvian Andes and adjacent lowland Amazonia. Our objectives were to test if nitrogen (N) and phosphorus (P) limitation shift along this elevation gradient, and to determine how an alleviation of nutrient limitation would manifest in ecosystem changes.
Abstract FLUXNET is a global network of micrometeorological flux measurement sites that measure the exchanges of carbon dioxide, water vapor, and energy between the biosphere and atmosphere. At present over 140 sites are operating on a... more
Abstract FLUXNET is a global network of micrometeorological flux measurement sites that measure the exchanges of carbon dioxide, water vapor, and energy between the biosphere and atmosphere. At present over 140 sites are operating on a long-term and continuous basis. Vegetation under study includes temperate conifer and broadleaved (deciduous and evergreen) forests, tropical and boreal forests, crops, grasslands, chaparral, wetlands, and tundra.
In this study, we concentrate on modelling gross primary productivity using two simple approaches to simulate canopy photosynthesis:" big leaf" and" sun/shade" models. Two approaches for calibration are used: scaling up of canopy... more
In this study, we concentrate on modelling gross primary productivity using two simple approaches to simulate canopy photosynthesis:" big leaf" and" sun/shade" models. Two approaches for calibration are used: scaling up of canopy photosynthetic parameters from the leaf to the canopy level and fitting canopy biochemistry to eddy covariance fluxes. Validation of the models is achieved by using eddy covariance data from the LBA site C14.
The tropical forests of Amazonia constitute one of the most important ecosystems of the Earth. They account for 45% of the world's tropical forest, storing about one fifth of the carbon residing in terrestrial vegetation and annually... more
The tropical forests of Amazonia constitute one of the most important ecosystems of the Earth. They account for 45% of the world's tropical forest, storing about one fifth of the carbon residing in terrestrial vegetation and annually processing about three times as much carbon through photosynthesis and respiration as humans release to the atmosphere through fossil fuel combustion. Amazonia also accounts for a large portion of global land surface evapotranspiration, and a significant fraction of the world's known species.
Abstract The medium seasonal variation daily of the radiation balance, flow of sensitive heat and flow of latent heat were analyzed, being considered the periods of April to December of 1999 and January to December of 2000, obtained of a... more
Abstract The medium seasonal variation daily of the radiation balance, flow of sensitive heat and flow of latent heat were analyzed, being considered the periods of April to December of 1999 and January to December of 2000, obtained of a metallic tower of 54 m of height in the National Forest of Caxiuanã, to 1042'30" S of latitude and 510 31'45" W of longitude. The results presented behavior similar to the obtained by other authors, detaching the important paper of the vegetation in the reduction of the incident solar radiation in the surface.
ABSTRACT Forest biomes are major reserves for terrestrial carbon, and major components of global primary productivity. The carbon balance of forests is determined by a number of component processes of carbon acquisition and carbon loss,... more
ABSTRACT Forest biomes are major reserves for terrestrial carbon, and major components of global primary productivity. The carbon balance of forests is determined by a number of component processes of carbon acquisition and carbon loss, and a small shift in the magnitude of these processes would have a large impact on the global carbon cycle.
Abstract. This communication reports a first attempt to assess the capability of MODIS NDVI, Enhanced Vegetation Index (EVI) and Normalized Difference Water Index (NDWI) from 2002 to 2005 time-series to detect the effects of the 2005... more
Abstract. This communication reports a first attempt to assess the capability of MODIS NDVI, Enhanced Vegetation Index (EVI) and Normalized Difference Water Index (NDWI) from 2002 to 2005 time-series to detect the effects of the 2005 drought on dense tropical forest canopies in Amazonia. The preliminary results reported in this communication suggest that the NDVI and NDWI have not responded to the rainfall anomaly in 2005 directly in a month basis.
Ecological orthodoxy suggests that old-growth forests should be close to dynamic equilibrium, but this view has been challenged by recent findings that neotropical forests are accumulating carbon and biomass, possibly in response to the... more
Ecological orthodoxy suggests that old-growth forests should be close to dynamic equilibrium, but this view has been challenged by recent findings that neotropical forests are accumulating carbon and biomass, possibly in response to the increasing atmospheric concentrations of carbon dioxide. However, it is unclear whether the recent increase in tree biomass has been accompanied by a shift in community composition.
ABSTRACT IPE-1 is part of a wide experimental programme to study the weather and climate of the central region of Brazil. The data collection campaign was carried out in the South Mato Grosso Pantanal in the experimental site in the farm... more
ABSTRACT IPE-1 is part of a wide experimental programme to study the weather and climate of the central region of Brazil. The data collection campaign was carried out in the South Mato Grosso Pantanal in the experimental site in the farm São Bento (19o33'S and 53o8'W), 1.5 km far from the Pantanal studies base of UFMS in Passo do Lontra, Corumbá, MS. One of the goals of the project is to study the turbulent exchanges above Pantanal in both seasons, wet and dry, particularly the turbulent fluxes and its variability.
Abstract. This paper shows the impact of fires in dense forests during the 2005 Amazonian drought. We used rainfall data from the Tropical Rainfall Monitoring Mission (TRMM) and burn scars were mapped using fraction images derived from... more
Abstract. This paper shows the impact of fires in dense forests during the 2005 Amazonian drought. We used rainfall data from the Tropical Rainfall Monitoring Mission (TRMM) and burn scars were mapped using fraction images derived from MODIS MOD09 product. We found that Acre State was the most affected by the drought and its effects on dense forests.
Global awareness of the significance of the role that tropical forests play in the global carbon cycle has never been greater, but much uncertainty still exists as to the exact magnitude of this role. Here I review and attempt to... more
Global awareness of the significance of the role that tropical forests play in the global carbon cycle has never been greater, but much uncertainty still exists as to the exact magnitude of this role. Here I review and attempt to synthesise the latest evidence of both the carbon source from tropical forest conversion, and the carbon sink in tropical vegetation.
Soil CO2 efflux is a large component of total respiration in many ecosystems. It is important to understand the environmental controls on soil CO2 efflux, in order to evaluate potential responses of ecosystems to climate change. This... more
Soil CO2 efflux is a large component of total respiration in many ecosystems. It is important to understand the environmental controls on soil CO2 efflux, in order to evaluate potential responses of ecosystems to climate change. This study investigated the relationship between total soil CO2 efflux and soil temperature, soil moisture and solar radiation on an interannual basis for a plot of temperate deciduous ancient semi-natural woodland at Wytham Woods in central southern England.
This study explored biotic and abiotic causes for spatio-temporal variation in soil respiration from surface litter, roots, and soil organic matter over one year at four rain forest sites with different vegetation structures and soil... more
This study explored biotic and abiotic causes for spatio-temporal variation in soil respiration from surface litter, roots, and soil organic matter over one year at four rain forest sites with different vegetation structures and soil types in the eastern Amazon, Brazil. Estimated mean annual soil respiration varied between 13–17 t C ha− 1 yr− 1, which was partitioned into 0–2 t C ha− 1 yr− 1 from litter, 6–9 t C ha− 1 yr− 1 from roots, and 5–6 t C ha− 1 yr− 1 from soil organic matter.
Abstract The rate of above-ground woody biomass production, WP, in some western Amazon forests exceeds those in the east by a factor of 2 or more. Underlying causes may include climate, soil nutrient limitations and species composition.... more
Abstract The rate of above-ground woody biomass production, WP, in some western Amazon forests exceeds those in the east by a factor of 2 or more. Underlying causes may include climate, soil nutrient limitations and species composition. In this modelling paper, we explore the implications of allowing key nutrients such as N and P to constrain the photosynthesis of Amazon forests, and also we examine the relationship between modelled rates of photosynthesis and the observed gradients in W P.
Abstract In this work the wavelet analysis has been applied to temperature and vertical wind velocity data. It provides an objective method to determine the time scales associated with nocturnal coherent structures above and within the... more
Abstract In this work the wavelet analysis has been applied to temperature and vertical wind velocity data. It provides an objective method to determine the time scales associated with nocturnal coherent structures above and within the Amazon rain forest canopy. The results show that the time scales corresponding to coherent structures of temperature were always greater than those associated with vertical velocity.
Summary• We present the results from a litter translocation experiment along a 2800-m elevation gradient in Peruvian tropical forests.
Leaf isoprene emission rates (Fiso) were studied in 2-year old trees of live oak (Quercus virginiana Mill.) during two drying–rewatering cycles. During the first drying–rewatering cycle, photosynthesis (A) and stomatal conductance (gs)... more
Leaf isoprene emission rates (Fiso) were studied in 2-year old trees of live oak (Quercus virginiana Mill.) during two drying–rewatering cycles. During the first drying–rewatering cycle, photosynthesis (A) and stomatal conductance (gs) decreased by 92%(±7%) and 91%(±8%), respectively, while Fiso remained essentially constant for 8 days of treatment. After 12 days under severe drought conditions, Fiso was reduced by 64%(±6%). Similar values were found during the second drying–rewatering cycle.
The carbon stores and dynamics of tropical forests are the subject of major international scientific and policy attention. Research associated with the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) has generated... more
The carbon stores and dynamics of tropical forests are the subject of major international scientific and policy attention. Research associated with the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) has generated substantial advances in our understanding of the cycling of carbon at selected forest sites in Brazilian Amazonia and generated new insights into how these processes may vary across the wider Amazonian region. Here we report on aspects of this new understanding.