Dear Sir/Ma, I am a young forest biometrician that adopted the method that consider how correlation within plot and between stand can be handled. Actually i am working on modelling height-diameter relationship under different canopy layer using mixed model approach. METHODOLOGY:> Height and diameter measurement of tree under different canopy layer was taken at stand level. >stand attributes such as quadratic mean diameter(Dq),mean height(Hm),dominant height(Ho),dominant diameter(Do),Basal area of the largest tree(BAL) were included in the selected models. >I considered Dq,Hm,Ho,Do and BAL as the fixed component,and canopy layers as the random component.The canopy layer are tagged suppressed(4),intermediate(3),Co-dominant(2) and dominant(4) >How do i analyse the fixed and random effect of this models.The models and example of data to be analysed are attached.I will be grateful for any suggestions and the command to run this analysis on R.