Boundary Issues: Direct Effects: Direct effects are those readily identifiable as part of a
process or production chain. They are mostly under the control of the chain elements, but problems
occur when accounting for co-products from system expansion (i.e. substitution). It is obvious that
different co-product accounting methods can have significant effects, and the magnitude can be
different for different chains. For example, results might be influenced by questions such as: (1) how
far should one drill down; (2) should agricultural inputs, fertilizer manufacture, or even sulfuric acid
manufacture be taken into account; and (3) what time scale should be considered for crop rotation?
Boundary Issues: Indirect Effects: Indirect effects are more speculative, subject to assumptions
and scenarios, and mostly outside the direct control of the chain elements. An example is land use
impact.