What are the white dots on the tree in this photo?
I'm not 100% sure, but I think they look like scale insects (Coccoidea). In particular it looks at bit like a hermaphrodite cottony cushion scale insect (Icerya purchasi)...



The white fluffy thing underneath the insects is the ootheca (egg case). The mature insect migrates to the main trunk of its host tree and attaches to the bark. It then secretes the cottony sack between itself and the bark. Hundreds of eggs are laid into the case, which eventually hatches and the nymphs disperse to the tips of branches where they feed on leaves. As they get older they gradually move first to twigs, then to branches and finally back to the main trunk to breed again.