Quote from Jim Worrall on 2022 August 31, 18:36

I’ve gotten involved in writing a chapter mostly focusing on decline diseases.  This is a challenge because there are a lot of ideas out there on what a decline disease is, and whether we even need such a disease category.  On top of that, the concept of decline disease inevitably gets confused with other uses of the word 'decline' in forest biology, despite the fact that these meanings are clearly distinct.

• "Decline" as a symptom,  the long-term decrease in growth and loss of vigor of a tree.  Note that this is a symptom, based on one or more trees.  In this sense, decline may be caused by many things, including decline diseases.
• "Decline" as a long-term decrease in population, dominance, or area occupied by a species.  This is not a symptom and is not based on individual trees.  An example is successional processes.  This term was long used for the decrease of aspen dominance in the West.  This 'decline' was associated with decrease in fire, which provides a regeneration opportunity for aspen, and high populations of ungulates like cows and elk, which consume aspen regeneration.  I don't think anyone would consider that a decline disease.

So, a major step first is to come up with a practical, operational definition of decline disease.  Hopefully one that would not be interpreted very differently by people.  I think what we have now is pretty good, but to be honest I'm not crazy in love with it.  In its essence, it is diseases that fit Sinclair’s (and Manion’s) 3-factor concept, but also those in which the predisposing/inciting factor may be the same, but occurs uncommonly AND must be repeated or chronic to lead to decline. 

 

I hope we can find a unified definition that is both compatible with a good part of the literature and with which most pathologists can agree.  I'd be interested to hear other concepts of decline disease.