Alexander R Cobb

Alexander R Cobb
Singapore-MIT Alliance for Research and Technology | SMART · Center for Environmental Sensing and Modeling

PhD

About

58
Publications
29,260
Reads
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1,770
Citations
Introduction
I work primarily on the hydrology and morphology of tropical peatlands, based on a combination of theory, remote sensing, and field measurements.
Additional affiliations
February 2009 - present
Singapore-MIT Alliance for Research and Technology
Position
  • Principal Investigator
November 2007 - December 2008
Harvard University
Position
  • PostDoc Position
Description
  • Plant biomechanics research
February 2007 - December 2008
University of Massachusetts Amherst
Position
  • PostDoc Position
Description
  • Plant biomechanics research
Education
July 2000 - June 2006
Harvard University
Field of study
  • Organismic and Evolutionary Biology
September 1998 - June 2000
Harvard University
Field of study
  • Organismic and Evolutionary Biology
September 1994 - June 1998

Publications

Publications (58)
Article
When organic peat soils are sufficiently dry, they become flammable. In Southeast Asian peatlands, widespread deforestation and associated drainage create dry conditions that, when coupled with El Niño-driven drought, result in catastrophic fire events that release large amounts of carbon and deadly smoke to the atmosphere. While the effects of ant...
Preprint
Full-text available
*Note well: This is a preprint that has not yet been peer-reviewed.* We used neural networks (trained on data from the NASA SMAP satellite) to model soil moisture in peatlands of Sumatra, Borneo and Peninsular Malaysia as a function of climate, degradation, and location. The neural networks were forced with regional climate model projections for 19...
Article
Full-text available
Tropical peatlands in Southeast Asia are a significant carbon sink, but are under major threat of fire resulting in significant carbon emissions. This study focused on the residual ash method, which has not been applied before for a tropical peatland, to determine the amount of carbon lost due to fire along two transects. To evaluate the method in...
Article
Full-text available
Tropical peatlands are among the most carbon-dense ecosystems on Earth, and their water storage dynamics strongly control these carbon stocks. The hydrological functioning of tropical peatlands differs from that of northern peatlands, which has not yet been accounted for in global land surface models (LSMs). Here, we integrated tropical peat-specific...
Article
Full-text available
Peatlands contain a significant fraction of global soil carbon, but how these reservoirs will respond to the changing climate is still relatively unknown. A global picture of the variations in peat organic matter chemistry will aid our ability to gauge peatland soil response to climate. The goal of this research is to test the hypotheses that 1) pe...
Poster
Full-text available
We evaluate retrieval of ground elevations and canopy metrics derived from GEDI waveform data, as well as single-photon data from the Advanced Topographic Laser Altimeter System (ATLAS) instrument on the Ice, Cloud and land Elevation Satellite-2 (ICESat-2) observatory, with reference to an airborne laser scanning dataset covering an area of over 10...
Preprint
Full-text available
Tropical peatlands are among the most carbon-dense ecosystems on Earth, and their water storage dynamics strongly control these carbon stocks. The hydrological functioning of tropical peatlands differs from that of northern peatlands, which has not yet been accounted for in global land surface models (LSMs). Here, we integrated tropical peat-specif...
Article
About half of the world’s tropical peatlands occur in Southeast (SE) Asia, where they serve as a major carbon (C) sink. Nearly 80% of natural peatlands in this region have been deforested and drained, with the majority under plantations and agriculture. This conversion increases peat oxidation which contributes to rapid C loss to the atmosphere as...
Article
Full-text available
Drainage canals associated with logging and agriculture dry out organic soils in tropical peatlands, thereby threatening the viability of long‐term carbon stores due to increased emissions from decomposition, fire, and fluvial transport. In Southeast Asian peatlands, which have experienced decades of land use change, the exact extent and spatial di...
Article
Full-text available
Peatlands represent large terrestrial carbon banks. Given that most peat accumulates in boreal regions, where low temperatures and water saturation preserve organic matter, the existence of peat in (sub)tropical regions remains enigmatic. Here we examined peat and plant chemistry across a latitudinal transect from the Arctic to the tropics. Near-su...
Article
Full-text available
Sedge-mediated gas transport to the atmosphere has been recognized as a significant CH4 pathway in northern peatlands; however, in the Tropics, this pathway remains unquantified. In Southeast Asia, degraded tropical peatlands covered with sedges and ferns have increased to almost 10% of the total peatland area due to an increased drainage and fires...
Article
Full-text available
Tropical peatlands store over 75 gigatons of carbon as organic matter that is protected from decomposition and fire by waterlogging if left undrained. Over millennia, this organic matter builds up between channels or rivers into gently mounded shapes called peat domes. Measurements of peat accumulation and water flow suggest that tropical peat dome...
Article
The Badas peat dome located in the Belait district is one of the biggest peat domes in Brunei. Over the years, this area has seen a noticeable loss of peatland due to fires and infrastructure development. In this paper, the anthropogenic effects on the Badas peat dome were studied for three survey areas using seismic refraction surveys, core analys...
Article
Full-text available
Peatlands cover many low-lying areas in the tropics. Tropical peatlands are intriguing systems because of their tight coupling between hydrology and carbon storage: they accumulate carbon over thousands of years because of waterlogging, and they remain waterlogged after growing into domed shapes because peat restricts drainage. This feedback betwee...
Article
Full-text available
Fires that emit massive amounts of CO2 and particulate matter now burn with regularity in Southeast Asian tropical peatlands. Natural peatlands in Southeast Asia are waterlogged for most of the year and experience little or no fire, but networks of canals constructed for agriculture have drained vast areas of these peatlands, making the soil vulner...
Poster
Full-text available
Anaerobic oxidation of methane (AOM) is a significant but poorly constrained biological sink in the global carbon cycle. While several studies estimate AOM is responsible for consuming ~80-90% produced in marine sediments, its role in curbing the CH4 atmospheric flux in terrestrial freshwater systems, particularly the deep continental biosphere, is...
Article
Full-text available
Emission of CO2 from tropical peatlands is an important component of the global carbon budget. Over days to months, these fluxes are largely controlled by water table depth. However, the diurnal cycle is less well understood, in part, because most measurements have been collected daily at midday. We used an automated chamber system to make hourly m...
Article
Full-text available
Peatlands represent large terrestrial carbon banks. Given that most peat accumulates in boreal regions, where low temperatures and water saturation preserve organic matter, the existence of peat in (sub)tropical regions remains enigmatic. Here we examined peat and plant chemistry across a latitudinal transect from the Arctic to the tropics. Near-su...
Article
Vessel length is an important functional trait for plant hydraulics, because it determines the ratio of flow resistances posed by lumen and pit membranes and hence controls xylem hydraulic efficiency. The most commonly applied methods to estimate vessel lengths are based on the injection of silicon or paint into cut-off stem segments. The number of...
Article
Full-text available
Tropical peatlands now emit hundreds of megatons of carbon dioxide per year because of human disruption of the feedbacks that link peat accumulation and groundwater hydrology. However, no quantitative theory has existed for how patterns of carbon storage and release accompanying growth and subsidence of tropical peatlands are affected by climate an...
Article
Full-text available
The first International Peat Congress (IPC) held in the tropics - in Kuching (Malaysia) - brought together over 1000 international peatland scientists and industrial partners from across the world (“International Peat Congress with over 1000 participants!,” 2016). The congress covered all aspects of peatland ecosystems and their management, with a...
Article
Vessels with simple perforation plates, found in the majority of angiosperms, are considered the evolutionarily most advanced conduits, least impeding the xylem sap flow. Nevertheless, when measured, their hydraulic resistivity (R, i.e., inverse value of hydraulic conductivity) is significantly higher than resistivity predicted using Hagen–Poiseuil...
Article
Full-text available
The first International Peat Congress (IPC) held in the tropics - in Kuching (Malaysia) - brought together over 1000 international peatland scientists and industrial partners from across the world ("International Peat Congress with over 1000 participants!," 2016). The congress covered all aspects of peatland ecosystems and their management, with a...
Article
Peatlands of Southeast Asia store large pools of carbon but the mechanisms of peat accumulation in tropical forests remain to be resolved. Patch dynamics and forest disturbance have seldom been considered as drivers that can amplify and dampen rates of peat accumulation. Here we used a modified piston corer, non-invasive geophysical measurements, a...
Article
Turfgrass covers a large fraction of the urbanized landscape, but the carbon exchange of urban lawns is poorly understood. We used eddy covariance and flux chambers in a grassland field manipulative experiment to quantify the carbon mass balance in a Singapore tropical turfgrass. We also assessed how management and variations in environmental facto...
Article
Solid and dissolved organic matter (DOM) compositions were investigated in a pristine and a deforested tropical peat forest in Brunei Darussalam. A combination of elemental (%C, %N, C/N), isotopic (δ15N, δ13C, Δ14C), molecular (lignin phenol biomarkers) and optical (Specific UV Absorbance at 280 nm (SUVA280), fluorescence index (FI)) analyses were...
Article
Full-text available
Tropical peat swamp forests in their natural state are important reservoir of biodiversity, carbon and water. However, they are rapidly vanishing due to agricultural conversion (mainly to oil palms), logging, drainage and fire. Peat swamp forests constitute an important contribution to global and regional biodiversity, providing an habitat to rare...
Article
Full-text available
This paper describes an off-grid (stand-alone) PV system for powering an eddy flux station on tropical grassland in Kranji (1°25’N, 103°43’E), Singapore. Eddy covariance flux systems are used to quantify exchanges of CO2, H2O and energy between the atmosphere and land. Our system includes gas analyzers for CO2 and H2O, and sensors for rainfall, win...
Article
Full-text available
Urban green spaces are appreciated for their amenity value, with increasing interest in the ecosystem services they could provide (e.g. climate amelioration and increasingly as possible sites for carbon sequestration). In Singapore, turfgrass occupies approximately 20% of the total land area and is readily found on both planned and residual spaces....
Article
1. Xylem hydraulic properties play an essential role in supporting growth and photosynthesis and influence sensitivity to environmental conditions such as drought and freezing. Consequently, stem hydraulic conductance can be used as a comparative measure of overall hydraulic adaptation across species and to assess the impact of environmental variat...
Article
Full-text available
This study compares the organic chemistry of peat beneath one of last remaining pristine tropical peat forests in Southeast Asia with a neighbouring peat dome that has been deforested, but not intentionally drained, in the Belait district of Brunei Darussalam, Borneo. We characterized the solid and dissolved organic matter collected from the two do...
Article
The hydrology of tropical peat forests is tied closely to decomposition processes in the soil and thus to the role of these forests as sinks of atmospheric carbon. We present results from an ongoing study on the hydrology and carbon cycle of a tropical peat forest in Brunei Darussalam. Data from rain gauges and well piezometers are combined with me...
Article
Full-text available
The dynamics of epiphytic bryophyte communities following natural and human disturbance have rarely been quantified. We describe the response of bryophyte communities on bigleaf maple trees (Acer macrophyllum Pursh) in Olympia, Washington, following their experimental removal. Approximately 8% of the exposed area was recolonized by bryophytes 1 yea...
Article
Full-text available
The soils of tropical peat forests store large amounts of carbon, which is susceptible to release by oxidation when these soils are drained. Therefore, fluctuations in water table depth are an important control on carbon sequestration and release in tropical peat soils. We present throughfall and water table observations using tipping bucket rain g...
Article
Full-text available
We are now reaching the stage at which specific genetic factors with known physiological effects can be tied directly and quantitatively to variation in phenology. With such a mechanistic understanding, scientists can better predict phenological responses to novel seasonal climates. Using the widespread model species Arabidopsis thaliana, we explor...
Article
Full-text available
Cellulose synthase-interactive protein 1 (CSI1) was identified in a two-hybrid screen for proteins that interact with cellulose synthase (CESA) isoforms involved in primary plant cell wall synthesis. CSI1 encodes a 2,150-amino acid protein that contains 10 predicted Armadillo repeats and a C2 domain. Mutations in CSI1 cause defective cell elongatio...
Article
Full-text available
Twining plants use their helical stems to clasp supports and to generate a squeezing force, providing stability against gravity. To elucidate the mechanism that allows force generation, we measured the squeezing forces exerted by the twiner Dioscorea bulbifera while following its growth using time-lapse photography. We show that the development of...
Article
Bordered pits are cavities in the lignified cell walls of xylem conduits (vessels and tracheids) that are essential components in the water-transport system of higher plants. The pit membrane, which lies in the center of each pit, allows water to pass between xylem conduits but limits the spread of embolism and vascular pathogens in the xylem. Aver...
Article
Freeze-thaw cycles pose a major physiological challenge for all temperate perennial plants, but monocotyledonous vines face a still greater risk because their few large vessels are especially susceptible to embolism and are not replaced by secondary growth. The genus Smilax is particularly remarkable because it is widespread in the tropics but incl...
Article
The hydraulic resistance of pit membranes was measured directly in earlywood vessels of Fraxinus americana and Ulmus americana. The area-specific resistance of pit membranes (r(mem)) was higher than modeled or measured values obtained previously for hardwood species, with r(mem) of 5.24 × 10(3) MPa·s·m(-1) for Fraxinus and 2.56 × 10(3) MPa·s·m(-1)...
Article
Full-text available
The dynamics of epiphytic bryophyte communities following natural and human disturbance have rarely been quantified. We describe the response of bryophyte communities on bigleaf maple trees (Acer macrophyllum Pursh) in Olympia, Washington, following their experimental removal. Approximately 8% of the exposed area was recolonized by bryophytes 1 yea...
Article
Full-text available
Although the significance of canopy plant communities to ecosystem function is well documented, the process by which such communities become established in trees remains poorly known. Colonization of tree surfaces by canopy-dwelling plants often begins with the establishment of bryophytes, so the conditions that affect the dispersal of bryophytes i...
Article
Full-text available
Thesis (Ph.D., Dept. of Organismic and Evolutionary Biology)--Harvard University, 2006. Thesis advisor: N.M. Holbrook. Includes bibliographical references (p. 147-163).

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Project (1)
Project
This project seeks to characterize and understand the morphology of peatlands. We examine how the changing morphology of peatlands is constrained by ecosystem and hydrologic processes, and conversely how peatland morphology can be used to make inferences about these processes.