Working progress on Google Docs:

Ecotones are areas of abrupt physical and biological transition, usually between two ecosystems, having a set of characteristics uniquely defined by space and time scales and by the strength of interactions between adjacent ecosystems. They often host particularly rich and sometimes unique biodiversity.   Although this definition is widely used and agreed on, further differentiation is necessary between ecotones and simple boundaries, as well as from ecosystems, in order to justify retention of the concept:

-The interactions between ecosystems result in mechanisms that do not exist within the component ecosystems but in the ecotone alone. 
-The fundamental principles of energy, material and species dynamics are valid for both ecotones and ecosystems, but ecotones are characterized by discontinuities and by the variability of flows, in amounts as well as directions. 
-Ecosystem dynamics are stabilized by feedback mechanisms; ecotones are basically unstable, depending on the interactions between the component ecosystems.