[R-sig-eco] adonis and betadisper interpretation

[Hedi]

Hi,

I have some trouble with interpretation of R functions: adonis and 
betadisper. I am interesting in understanding if the communities differ 
according to land use treatment (3 treatments) and time (6,12,18,24 and 
30 months). I know that adonis works on the centroids for the groupings 
and betadisper on variance, the spread of the observations about the 
grouping means/centroids. The problem is both "betadisper" and "adonis" 
say that the factor "time" is significant. So can I say that my 
communities are still different according to time?
Actually what is the biological interpretation of the centroid of a 
community and the dispersion of a community?

Thanks