Whether threshold-driven (SDIDT) systems are also necessary for self-organized criticality, and not merely sufficient, is an open question in the Tier-1 SOC literature, not a settled result

self-organized-criticalitycomplex-systemsthresholdsdidtforest-fire-modelnecessary-sufficientopen-questionsource-discipline

Watkins et al. (2015, Sec. 7.3, "Must SOC and SDIDT always be the same?") treats the relationship between threshold-driven "slowly driven, interaction-dominated threshold" (SDIDT) systems and true self-organized criticality (SOC) as unresolved, presenting three possible relationships between the two categories (their Fig. 3) rather than asserting one. On the "not sufficient" side they cite a concrete counterexample: the Forest Fire Model is SDIDT-shaped but "lack[s] scaling (Pruessner and Jensen, 2002a)" — demonstrated proof that threshold/SDIDT ingredients alone do not guarantee SOC. But whether SDIDT — and by extension threshold-driven interaction — is also necessary for SOC is explicitly left open: "It may well be, however, that conditions 4-6 are not complete," and completing "the list of sufficient conditions without making them too narrow" is called "one of the most important questions in SOC," not a solved one.

This complements claim-soc-tier1-literature-places-threshold-among-sufficient-not-necessary-conditions: that note establishes where the literature currently puts thresholds (sufficient, not necessary); this one establishes that the further claim — that they are also necessary, which the vault's inherited "necessary but not sufficient" phrasing implicitly asserted — is an active research question in 2015, not a settled fact. "Not sufficient" is well-supported by a named counterexample; "necessary" is argued for but explicitly flagged by the review's own authors as unresolved — a materially different epistemic status than a flat verdict.