[R] spatial corStruct in lme

[Lyndon Brooks]

Hi,

I'm fitting a relatively simple growth model to some forest plot data. Two 
species of trees were planted in different mixtures in 10 (nearly-adjacent) 
plots and measured on four occasions over 10 years. The model is 
constructed in terms of the diameter increments (per year; DI) in the 3 
intervals, in which DI is modelled as a function of mid-interval D and DSQ. 
The details of the fixed part of the model are not so important here, but 
four pertinent variables are distance-dependent competition indices: 
C_spp1fromspp1, C_12, C_21, C_22.

The random structure is: random = ~ 1 | PLOT/TREE.

More complex random structures aren't required, there's no obvious 
heterogeneity, and the serial correlations (corSymm) are trivial.

I've been trying to fit a spatial correlation structure using the X, Y 
coordinates of each tree. I've obviously missed a point or so here.

It seems to me that such a structure could be fit for all trees (both 
species) on their average growth over the 3 intervals, by interval, or by 
species by interval.

For now, it would be step forward to get any of these working.

Apart from me learning how to do it, the import of this is that, if the 
CI's are doing what I hope they might, there should be little residual 
spatial correlation.

Thanks,

Lyndon.