Long Description of Figure 1:

Two graphs showing change in potential productivity -- the first graph, A, shows the a decline in potential productivity for a soil variable - the line of no change is set at 0% change; the second graph, B, shows the same amount of decline of productivity as in A, but the line of no change is extended 15% above and below 0% before a change in a soil variable is considered to be a change that is significant enough to be considered as a monitoring variable (negative theshold standard is -15%).