library(multcomp)

(met     <-  c(rnorm(16,6,2),rnorm(16,5,2),rnorm(32,4,2)))
(site    <-  c(rep("L", 16), rep("M", 16), rep("H", 32)))
(vtype   <-  c(rep(letters[1:4], 16), rep(letters[1:4], 16), rep(letters[1:4], 32)))

dat  <-  data.frame(site, vtype, met)

# using aov and TukeyHSD
aov.000  <-  aov(met ~ site * vtype, data=dat)
summary(aov.000)
TukeyHSD(aov.000)

# using Anova, and multcomp
lm.000     <-  lm(met ~ site * vtype, data=dat)
summary(lm.000)
library(car)
Anova.000  <-  Anova(lm.000, data=dat)

dat$int  <-  with(dat, interaction(site, vtype, sep = "x"))
lm.000   <-  lm(met ~ int, data = dat)
summary(lm.000)
summary(glht.000 <- glht(lm.000, linfct = mcp(int = "Tukey")))