Adonis for significance of clusteredness from hclust (vegan package)

Hello:

I have created a dendrograms using hierarchical cluster analysis with the
vegan package (function: hclust).

By visually observing the dendrogram, I have determined that there are 3
main clusters if I "cut" the tree at the height 0.25  (please see the
dendrogram from the code).
I then created a new dataset, which is essentially the same as the
original, but I have added the categorical variable Group to represent
these 3 main clusters.
ST0 is group a, AP0 and AP100 is group b, and AP200 AP300 ST100 ST200 ST
300 is group c.
I want to now if they are significantly different from each other.  I
understand, from the output pasted below, that I can accept that there is a
significant effect of Group.  Is this the only thing I can say from
Permanova?  What would be the code for a follow up test to look at
pair-wise significant differences?
Thanks very much.

Call:
adonis(formula = species ~ Group, data = environ, permutations = 999)

Permutation: free
Number of permutations: 999

Terms added sequentially (first to last)

           Df SumsOfSqs  MeanSqs F.Model      R2 Pr(>F)
Group      2   0.40244 0.201219   4.969 0.66528  0.007 **
Residuals  5   0.20248 0.040495         0.33472
Total      7   0.60492                  1.00000
---
Signif. codes:  0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1