Loading...
Karam Sheban's Qualifying Exam
Private Location (sign in to display)
View MapDetails
Committee members:
• Prof. Mark Bradford (Chair)
• Prof. Marlyse Duguid
• Prof. Alex McAlvey (NYBG)
Please provide written and graphical or tabular answers to Questions 1 and 2.
Submit your answers (and a final draft of your dissertation prospectus if you have not yet done so) together in a single Word or PDF document to your committee by 5 pm Sunday May 25th. Your written exams run Monday May 12th to Sunday May 25th2025.
(1) Temperate silvopasture
Silvopasture is defined by the USDA as the “integration of trees and grazing livestock operations on the same land.” They go onto to state that, “These systems are intensively managed for both forest products and forage, providing both short- and long-term income sources.” They further state that silvopastural systems are created by the introduction of trees into pastures, or of forage into woodlands/ plantations.
Focusing on temperate silvopasture:
• Do you agree with the above definitions? If you would modify the definitions, please explain why.
• In what types of temperate systems (specify the geographic/ climatic boundaries) should silvopasture be effective based on process (i.e. mechanistic) knowledge? Is there a reason to consider “forage into woodlands” vs. “trees in pastures” vs. “forage into plantations” differently when answering this question?
• In what types of temperate systems is silvopasture effective based on empirical data? In addressing this question, please consider and rate (low to high) the confidence we can have in the empirical data, based on the quality of the available empirical evidence (where quality might refer to study design, measurement approaches, data analysis, etc.).
• Where are the primary gaps in process and empirical evidence for understanding the effectiveness of temperate silvopasture as an intervention?
In addressing the above bullets, answer based on at least three response variables, with two of them being effectiveness for (a) net carbon storage (i.e. climate mitigation through avoided emissions and atmospheric CO2 removals) and (b) forage quantity and quality, under regular climate and under stressors such as drought or heavy rainfall. Please also discuss a third response variable of your choosing that relates to forest products.
In your answers, please be sure to include:
(1) A set of search terms and search tools that you used to find key papers related to your project.
(2) A flow diagram of causal pathways that shows how the “management intervention” causally relates to the outcome (i.e. a directed acyclic graph / structural causal model). In addition to mediating causal pathways, identify other causes that should be measured because you expect them to have a strong impact on the outcome and/or to interact with the intervention, thereby introducing context dependency into the outcome. Describe timescales of impact/ responses.
(3) A written summary that explains and evaluates your confidence – based on process knowledge and empirical data – in each of the pathways shown in the causal diagram.
(4) Discussion of how your confidence in the effectiveness of silvopasture as an intervention is shaped by both the internal and external validity of the available evidence.
(2) Forest Farming and NCS
In a forthcoming Comment in the journal Nature Climate Change, you make the case that forest farming should not be left off the U.S. agroforestry agenda when it comes to considering agroforestry as a natural climate solution (NCS). What direct evidence is there that forest farming does function as an effective NCS? Given the large number of practices that might be defined as forest farming, are there practices and ecoclimatic conditions where forest farming should be a particularly effective NCS, and where it might be a poor NCS choice? In addressing this overall question, please pay particular attention to the evidence that is available and describe in detail what the counterfactuals are and evaluate the confidence we should have in the assumptions that they rest upon.
In addressing the above question, our deliberate intention is to leave your options to answer more open ended. However, we recommend that inclusion of the following will increase the rigor of your analysis:
(1) A causal diagram so that we can clearly understand how you visualize the pathways from forest farming to climate mitigation. Annotating the diagram to highlight where our assumptions are stronger/weaker, and our knowledge higher/lower, would help identify evidence needs and strengths.
(2) Some attention as to how you would test forest farming as a natural climate solution. For example, what confounding variables would you want measured and how would you prioritize those to maximize information gained; and what range of study designs (both experimental and observational) might be most useful and why?