Urmila Mallick's Qualifying Exam

Urmila Mallick will stand for the Qualifying Examination for acceptance into candidacy for the Ph.D. degree on Tuesday, January 27 at 1:00 PM in Kroon GO1. All faculty (only faculty) are welcome and invited to attend. A copy of Urmila’s dissertation prospectus and qualifying exam questions and answers and can be obtained from the Doctoral Program Office (contact: elisabeth.barsa@yale.edu).

Committee members:
• Profs. Os Schmitz and Mark Bradford (Co-Chairs)
• Prof. Amanda Sabalusky (Univ. Florida)

Provide written answers to the following questions. Return your answers and a copy of your PhD dissertation prospectus to your committee and to the YSE Doctoral program by 5:00 pm January 16, 2026.

1. Southern Africa is a diverse region, including countries such as South Africa, Botswana and Namibia. Please research and detail the following related to its soil carbon stocks and concentrations:

a) What data sources exist - public, private, GIS, peer-reviewed, etc. - that provide reliable data on the soil carbon stocks and concentrations across this region. Please list the sources and document the level of detail they provide, such as depth profiles, whether stocks and concentrations are total, organic and/or inorganic, whether they also report variables needed to calculate stocks like coarse fraction and bulk density, and whether they also report covariates that help to explain spatial patterns in the stocks and concentrations, such as mineralogy and texture.

b) State and explain your level of confidence in the soil carbon and related data associated with each of these sources and, if necessary, details if your confidence for any specific source varies for the different variables hey present. For example, some variables may be directly measured but with methods that are more/less appropriate, and other variables may be sourced/ aggregated from outside the database/ source.

c) Once you have completed a) and b), please use those data and covariates that you have collected to describe patterns in soil carbon stocks and concentrations across the region, making sure to state your level of confidence in these patterns in relation to the data sources available to you.

d) Lastly, using all the work you have done for a) - c), please provide a narrative (and relevant display items) that details what we can know about which controls on soil carbon in Southern Africa are most important for describing spatial patterns (across geographies, at hyperlocal scales (e.g. meters to 10s of meters), and by depth). Next, please explain the utility of that knowledge for understanding how we expect soil carbon, within the region, to respond in time (next 5 to 50 years) to changes in spatial and/or temporal controls, highlighting both what we can be confident in and where the evidence needs are greatest for us to meaningfully advance our understanding of controls on soil carbon for the Southern Africa region.


2. Long-term soil carbon storage comes about via: (i) physical protection when organic carbon becomes embedded in stable soil aggregates; and (ii) chemical transformation of soil organic carbon into inorganic forms that when bonded with soil minerals produce highly stable carbonates.

a) Identify the different mechanisms by which large vertebrate herbivores could intervene to mediate these two soil processes.

b) Explain in detail how the mechanisms identified in a) shape soil physical properties and chemical reactions that create long-term carbon stores.

c) Explain how spatial variation in soil biophysical properties and microclimate could interact with animal mediating effects to determine the rates and amounts of soil carbon storage. Also, hypothesize what the relative importance is of large vertebrate herbivores vs biophysical properties and climate in driving long-term soil carbon storage in different contexts determined by spatial variation.

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