Here's an idea.  Throw out year.  If you have two visits to a plot per year, then fit visit 1 through 8 as a single repeated measure.  You can then look at 'year' effects by combining adjacent visits in an LSMESTIMATE statement.   And if the visits are not equally spaced in time, consider fitting a spline to both the fixed effect and as a random effect (see example 45.15 Comparing Multiple B Splines and Example 45.6 Radial Smoothing of Repeated Measures Data.   Steve Denham ... View more